April Weber

April Weber

Thursday, 10 March 2011 17:16

Evaluation of the Work Environment

Hazard Surveillance and Survey Methods

Occupational surveillance involves active programmes to anticipate, observe, measure, evaluate and control exposures to potential health hazards in the workplace. Surveillance often involves a team of people that includes an occupational hygienist, occupational physician, occupational health nurse, safety officer, toxicologist and engineer. Depending upon the occupational environment and problem, three surveillance methods can be employed: medical, environmental and biological. Medical surveillance is used to detect the presence or absence of adverse health effects for an individual from occupational exposure to contaminants, by performing medical examinations and appropriate biological tests. Environmental surveillance is used to document potential exposure to contaminants for a group of employees, by measuring the concentration of contaminants in the air, in bulk samples of materials, and on surfaces. Biological surveillance is used to document the absorption of contaminants into the body and correlate with environmental contaminant levels, by measuring the concentration of hazardous substances or their metabolites in the blood, urine or exhaled breath of workers.

Medical Surveillance

Medical surveillance is performed because diseases can be caused or exacerbated by exposure to hazardous substances. It requires an active programme with professionals who are knowledgeable about occupational diseases, diagnoses and treatment. Medical surveillance programmes provide steps to protect, educate, monitor and, in some cases, compensate the employee. It can include pre-employment screening programmes, periodic medical examinations, specialized tests to detect early changes and impairment caused by hazardous substances, medical treatment and extensive record keeping. Pre-employment screening involves the evaluation of occupational and medical history questionnaires and results of physical examinations. Questionnaires provide information concerning past illnesses and chronic diseases (especially asthma, skin, lung and heart diseases) and past occupational exposures. There are ethical and legal implications of pre-employment screening programmes if they are used to determine employment eligibility. However, they are fundamentally important when used to (1) provide a record of previous employment and associated exposures, (2) establish a baseline of health for an employee and (3) test for hypersusceptibility. Medical examinations can include audiometric tests for hearing loss, vision tests, tests of organ function, evaluation of fitness for wearing respiratory protection equipment, and baseline urine and blood tests. Periodic medical examinations are essential for evaluating and detecting trends in the onset of adverse health effects and may include biological monitoring for specific contaminants and the use of other biomarkers.

Environmental and Biological Surveillance

Environmental and biological surveillance starts with an occupational hygiene survey of the work environment to identify potential hazards and contaminant sources, and determine the need for monitoring. For chemical agents, monitoring could involve air, bulk, surface and biological sampling. For physical agents, monitoring could include noise, temperature and radiation measurements. If monitoring is indicated, the occupational hygienist must develop a sampling strategy that includes which employees, processes, equipment or areas to sample, the number of samples, how long to sample, how often to sample, and the sampling method. Industrial hygiene surveys vary in complexity and focus depending upon the purpose of the investigation, type and size of establishment, and nature of the problem.

There are no rigid formulas for performing surveys; however, thorough preparation prior to the on-site inspection significantly increases effectiveness and efficiency. Investigations that are motivated by employee complaints and illnesses have an additional focus of identifying the cause of the health problems. Indoor air quality surveys focus on indoor as well as outdoor sources of contamination. Regardless of the occupational hazard, the overall approach to surveying and sampling workplaces is similar; therefore, this chapter will use chemical agents as a model for the methodology.

Routes of Exposure

The mere presence of occupational stresses in the workplace does not automatically imply that there is a significant potential for exposure; the agent must reach the worker. For chemicals, the liquid or vapour form of the agent must make contact with and/or be absorbed into the body to induce an adverse health effect. If the agent is isolated in an enclosure or captured by a local exhaust ventilation system, the exposure potential will be low, regardless of the chemical’s inherent toxicity.

The route of exposure can impact the type of monitoring performed as well as the hazard potential. For chemical and biological agents, workers are exposed through inhalation, skin contact, ingestion and injection; the most common routes of absorption in the occupational environment are through the respiratory tract and the skin. To assess inhalation, the occupational hygienist observes the potential for chemicals to become airborne as gases, vapours, dusts, fumes or mists.

Skin absorption of chemicals is important primarily when there is direct contact with the skin through splashing, spraying, wetting or immersion with fat-soluble hydrocarbons and other organic solvents. Immersion includes body contact with contaminated clothing, hand contact with contaminated gloves, and hand and arm contact with bulk liquids. For some substances, such as amines and phenols, skin absorption can be as rapid as absorption through the lungs for substances that are inhaled. For some contaminants such as pesticides and benzidine dyes, skin absorption is the primary route of absorption, and inhalation is a secondary route. Such chemicals can readily enter the body through the skin, increase body burden and cause systemic damage. When allergic reactions or repeated washing dries and cracks the skin, there is a dramatic increase in the number and type of chemicals that can be absorbed into the body. Ingestion, an uncommon route of absorption for gases and vapours, can be important for particulates, such as lead. Ingestion can occur from eating contaminated food, eating or smoking with contaminated hands, and coughing and then swallowing previously inhaled particulates.

Injection of materials directly into the bloodstream can occur from hypodermic needles inadvertently puncturing the skin of health care workers in hospitals, and from high-velocity projectiles released from high-pressure sources and directly contacting the skin. Airless paint sprayers and hydraulic systems have pressures high enough to puncture the skin and introduce substances directly into the body.

The Walk-Through Inspection

The purpose of the initial survey, called the walk-through inspection, is to systematically gather information to judge whether a potentially hazardous situation exists and whether monitoring is indicated. An occupational hygienist begins the walk-through survey with an opening meeting that can include representatives of management, employees, supervisors, occupational health nurses and union representatives. The occupational hygienist can powerfully impact the success of the survey and any subsequent monitoring initiatives by creating a team of people who communicate openly and honestly with one another and understand the goals and scope of the inspection. Workers must be involved and informed from the beginning to ensure that cooperation, not fear, dominates the investigation.

During the meeting, requests are made for process flow diagrams, plant layout drawings, past environmental inspection reports, production schedules, equipment maintenance schedules, documentation of personal protection programmes, and statistics concerning the number of employees, shifts and health complaints. All hazardous materials used and produced by an operation are identified and quantified. A chemical inventory of products, by-products, intermediates and impurities is assembled and all associated Material Safety Data Sheets are obtained. Equipment maintenance schedules, age and condition are documented because the use of older equipment may result in higher exposures due to the lack of controls.

After the meeting, the occupational hygienist performs a visual walk-through survey of the workplace, scrutinizing the operations and work practices, with the goal of identifying potential occupational stresses, ranking the potential for exposure, identifying the route of exposure and estimating the duration and frequency of exposure. Examples of occupational stresses are given in figure 1. The occupational hygienist uses the walk-through inspection to observe the workplace and have questions answered. Examples of observations and questions are given in figure 2.

Figure 1.  Occupational stresses. 


Figure 2.  Observations and questions to ask on a walk-through survey.


In addition to the questions shown in figure 5, questions should be asked that uncover what is not immediately obvious. Questions could address:

  1. non-routine tasks and schedules for maintenance and cleaning activities
  2. recent process changes and chemical substitutions
  3. recent physical changes in the work environment
  4. changes in job functions
  5. recent renovations and repairs.


Non-routine tasks can result in significant peak exposures to chemicals that are difficult to predict and measure during a typical workday. Process changes and chemical substitutions may alter the release of substances into the air and affect subsequent exposure. Changes in the physical layout of a work area can alter the effectiveness of an existing ventilation system. Changes in job functions can result in tasks performed by inexperienced workers and increased exposures. Renovations and repairs may introduce new materials and chemicals into the work environment which off-gas volatile organic chemicals or are irritants.

Indoor Air Quality Surveys

Indoor air quality surveys are distinct from traditional occupational hygiene surveys because they are typically encountered in non-industrial workplaces and may involve exposures to mixtures of trace quantities of chemicals, none of which alone appears capable of causing illness (Ness 1991). The goal of indoor air quality surveys is similar to occupational hygiene surveys in terms of identifying sources of contamination and determining the need for monitoring. However, indoor air quality surveys are always motivated by employee health complaints. In many cases, the employees have a variety of symptoms including headaches, throat irritation, lethargy, coughing, itching, nausea and non-specific hypersensitivity reactions that disappear when they go home. When health complaints do not disappear after the employees leave work, non-occupational exposures should be considered as well. Non-occupational exposures include hobbies, other jobs, urban air pollution, passive smoking and indoor exposures in the home. Indoor air quality surveys frequently use questionnaires to document employee symptoms and complaints and link them to job location or job function within the building. The areas with the highest incidence of symptoms are then targeted for further inspection.

Sources of indoor air contaminants that have been documented in indoor air quality surveys include:

  • inadequate ventilation (52%)
  • contamination from inside of the building (17%)
  • contamination from outside of the building (11%)
  • microbial contamination (5%)
  • contamination from the building materials (3%)
  • unknown causes (12%).


For indoor air quality investigations, the walk-through inspection is essentially a building and environmental inspection to determine potential sources of contamination both inside and outside of the building. Inside building sources include:

  1. building construction materials such as insulation, particleboard, adhesives and paints
  2. human occupants that can release chemicals from metabolic activities
  3. human activities such as smoking
  4. equipment such as copy machines
  5. ventilation systems that can be contaminated with micro-organisms.


Observations and questions that can be asked during the survey are listed in figure 3.

Figure 3. Observations and questions for an indoor air quality walk-through survey.


Sampling and Measurement Strategies

Occupational exposure limits

After the walk-through inspection is completed, the occupational hygienist must determine whether sampling is necessary; sampling should be performed only if the purpose is clear. The occupational hygienist must ask, “What will be made of the sampling results and what questions will the results answer?” It is relatively easy to sample and obtain numbers; it is far more difficult to interpret them.

Air and biological sampling data are usually compared to recommended or mandated occupational exposure limits (OELs). Occupational exposure limits have been developed in many countries for inhalation and biological exposure to chemical and physical agents. To date, out of a universe of over 60,000 commercially used chemicals, approximately 600 have been evaluated by a variety of organizations and countries. The philosophical bases for the limits are determined by the organizations that have developed them. The most widely used limits, called threshold limit values (TLVs), are those issued in the United States by the American Conference of Governmental Industrial Hygienists (ACGIH). Most of the OELs used by the Occupational Safety and Health Administration (OSHA) in the United States are based upon the TLVs. However, the National Institute for Occupational Safety and Health (NIOSH) of the US Department of Health and Human Services has suggested their own limits, called recommended exposure limits (RELs).

For airborne exposures, there are three types of TLVs: an eight-hour time-weighted-average exposure, TLV-TWA, to protect against chronic health effects; a fifteen-minute average short-term exposure limit, TLV-STEL, to protect against acute health effects; and an instantaneous ceiling value, TLV-C, to protect against asphyxiants or chemicals that are immediately irritating. Guidelines for biological exposure levels are called biological exposure indices (BEIs). These guidelines represent the concentration of chemicals in the body that would correspond to inhalation exposure of a healthy worker at a specific concentration in air. Outside of the United States as many as 50 countries or groups have established OELs, many of which are identical to the TLVs. In Britain, the limits are called the Health and Safety Executive Occupational Exposure Standards (OES), and in Germany OELs are called Maximum Workplace Concentrations (MAKs).

OELs have been set for airborne exposures to gases, vapours and particulates; they do not exist for airborne exposures to biological agents. Therefore, most investigations of bioaerosol exposure compare indoor with outdoor concentrations. If the indoor/outdoor profile and concentration of organisms is different, an exposure problem may exist. There are no OELs for skin and surface sampling, and each case must be evaluated separately. In the case of surface sampling, concentrations are usually compared with acceptable background concentrations that were measured in other studies or were determined in the current study. For skin sampling, acceptable concentrations are calculated based upon toxicity, rate of absorption, amount absorbed and total dose. In addition, biological monitoring of a worker may be used to investigate skin absorption.

Sampling strategy

An environmental and biological sampling strategy is an approach to obtaining exposure measurements that fulfils a purpose. A carefully designed and effective strategy is scientifically defensible, optimizes the number of samples obtained, is cost-effective and prioritizes needs. The goal of the sampling strategy guides decisions concerning what to sample (selection of chemical agents), where to sample (personal, area or source sample), whom to sample (which worker or group of workers), sample duration (real-time or integrated), how often to sample (how many days), how many samples, and how to sample (analytical method). Traditionally, sampling performed for regulatory purposes involves brief campaigns (one or two days) that concentrate on worst-case exposures. While this strategy requires a minimum expenditure of resources and time, it often captures the least amount of information and has little applicability to evaluating long-term occupational exposures. To evaluate chronic exposures so that they are useful for occupational physicians and epidemiological studies, sampling strategies must involve repeated sampling over time for large numbers of workers.


The goal of environmental and biological sampling strategies is either to evaluate individual employee exposures or to evaluate contaminant sources. Employee monitoring may be performed to:

  • evaluate individual exposures to chronic or acute toxicants
  • respond to employee complaints about health and odours
  • create a baseline of exposures for a long-term monitoring programme
  • determine whether exposures comply with governmental regulations
  • evaluate the effectiveness of engineering or process controls
  • evaluate acute exposures for emergency response
  • evaluate exposures at hazardous waste sites
  • evaluate the impact of work practices on exposure
  • evaluate exposures for individual job tasks
  • investigate chronic illnesses such as lead and mercury poisoning
  • investigate the relationship between occupational exposure and disease
  • carry out an epidemiological study.


Source and ambient air monitoring may be performed to:

  • establish a need for engineering controls such as local exhaust ventilation systems and enclosures
  • evaluate the impact of equipment or process modifications
  • evaluate the effectiveness of engineering or process controls
  • evaluate emissions from equipment or processes
  • evaluate compliance after remediation activities such as asbestos and lead removal
  • respond to indoor air, community illness and odour complaints
  • evaluate emissions from hazardous waste sites
  • investigate an emergency response
  • carry out an epidemiological study.


When monitoring employees, air sampling provides surrogate measures of dose resulting from inhalation exposure. Biological monitoring can provide the actual dose of a chemical resulting from all absorption routes including inhalation, ingestion, injection and skin. Thus, biological monitoring can more accurately reflect an individual’s total body burden and dose than air monitoring. When the relationship between airborne exposure and internal dose is known, biological monitoring can be used to evaluate past and present chronic exposures.

Goals of biological monitoring are listed in figure 4.

Figure 4. Goals of biological monitoring.


Biological monitoring has its limitations and should be performed only if it accomplishes goals that cannot be accomplished with air monitoring alone (Fiserova-Bergova 1987). It is invasive, requiring samples to be taken directly from workers. Blood samples generally provide the most useful biological medium to monitor; however, blood is taken only if non-invasive tests such as urine or exhaled breath are not applicable. For most industrial chemicals, data concerning the fate of chemicals absorbed by the body are incomplete or non-existent; therefore, only a limited number of analytical measurement methods are available, and many are not sensitive or specific.

Biological monitoring results may be highly variable between individuals exposed to the same airborne concentrations of chemicals; age, health, weight, nutritional status, drugs, smoking, alcohol consumption, medication and pregnancy can impact uptake, absorption, distribution, metabolism and elimination of chemicals.


What to sample

Most occupational environments have exposures to multiple contaminants. Chemical agents are evaluated both individually and as multiple simultaneous assaults on workers. Chemical agents can act independently within the body or interact in a way that increases the toxic effect. The question of what to measure and how to interpret the results depends upon the biological mechanism of action of the agents when they are within the body. Agents can be evaluated separately if they act independently on altogether different organ systems, such as an eye irritant and a neurotoxin. If they act on the same organ system, such as two respiratory irritants, their combined effect is important. If the toxic effect of the mixture is the sum of the separate effects of the individual components, it is termed additive. If the toxic effect of the mixture is greater than the sum of the effects of the separate agents, their combined effect is termed synergistic. Exposure to cigarette smoking and inhalation of asbestos fibres gives rise to a much greater risk of lung cancer than a simple additive effect.

Sampling all the chemical agents in a workplace would be both expensive and not necessarily defensible. The occupational hygienist must prioritize the laundry list of potential agents by hazard or risk to determine which agents receive the focus.

Factors involved in ranking chemicals include:

  • whether the agents interact independently, additively or synergistically
  • inherent toxicity of the chemical agent
  • quantities used and generated
  • number of people potentially exposed
  • anticipated duration and concentration of the exposure
  • confidence in the engineering controls
  • anticipated changes in the processes or controls
  • occupational exposure limits and guidelines.
Where to sample

To provide the best estimate of employee exposure, air samples are taken in the breathing zone of the worker (within a 30 cm radius of the head), and are called personal samples. To obtain breathing zone samples, the sampling device is placed directly on the worker for the duration of the sampling. If air samples are taken near the worker, outside of the breathing zone, they are called area samples. Area samples tend to underestimate personal exposures and do not provide good estimates of inhalation exposure. However, area samples are useful for evaluating contaminant sources and measuring ambient levels of contaminants. Area samples can be taken while walking through the workplace with a portable instrument, or with fixed sampling stations. Area sampling is routinely used at asbestos abatement sites for clearance sampling and for indoor air investigations.

Whom to sample

Ideally, to evaluate occupational exposure, each worker would be individually sampled for multiple days over the course of weeks or months. However, unless the workplace is small (<10 employees), it is usually not feasible to sample all the workers. To minimize the sampling burden in terms of equipment and cost, and increase the effectiveness of the sampling programme, a subset of employees from the workplace is sampled, and their monitoring results are used to represent exposures for the larger work force.

To select employees who are representative of the larger work force, one approach is to classify employees into groups with similar expected exposures, called homogeneous exposure groups (HEGs) (Corn 1985). After the HEGs are formed, a subset of workers is randomly selected from each group for sampling. Methods for determining the appropriate sample sizes assume a lognormal distribution of exposures, an estimated mean exposure, and a geometric standard deviation of 2.2 to 2.5. Prior sampling data might allow a smaller geometric standard deviation to be used. To classify employees into distinct HEGs, most occupational hygienists observe workers at their jobs and qualitatively predict exposures.

There are many approaches to forming HEGs; generally, workers may be classified by job task similarity or work area similarity. When both job and work area similarity are used, the method of classification is called zoning (see figure 5). Once airborne, chemical and biological agents can have complex and unpredictable spatial and temporal concentration patterns throughout the work environment. Therefore, proximity of the source relative to the employee may not be the best indicator of exposure similarity. Exposure measurements made on workers initially expected to have similar exposures may show that there is more variation between workers than predicted. In these cases, the exposure groups should be reconstructed into smaller sets of workers, and sampling should continue to verify that workers within each group actually have similar exposures (Rappaport 1995).

Figure 5.  Factors involved in creating HEGs using zoning.


Exposures can be estimated for all the employees, regardless of job title or risk, or it can be estimated only for employees who are assumed to have the highest exposures; this is called worst-case sampling. The selection of worst-case sampling employees may be based upon production, proximity to the source, past sampling data, inventory and chemical toxicity. The worst-case method is used for regulatory purposes and does not provide a measure of long-term mean exposure and day-to-day variability. Task-related sampling involves selecting workers with jobs that have similar tasks that occur on a less than daily basis.

There are many factors that enter into exposure and can affect the success of HEG classification, including the following:

  1. Employees rarely perform the same work even when they have the same job description, and rarely have the same exposures.
  2. Employee work practices can significantly alter exposure.
  3. Workers who are mobile throughout the work area may be unpredictably exposed to several contaminant sources throughout the day.
  4. Air movement in a workplace can unpredictably increase the exposures of workers who are located a considerable distance from a source.
  5. Exposures may be determined not by the job tasks but by the work environment.


Sample duration

The concentrations of chemical agents in air samples are either measured directly in the field, obtaining immediate results (real-time or grab), or are collected over time in the field on sampling media or in sampling bags and are measured in a laboratory (integrated) (Lynch 1995). The advantage of real-time sampling is that results are obtained quickly onsite, and can capture measurements of short-term acute exposures. However, real-time methods are limited because they are not available for all contaminants of concern and they may not be analytically sensitive or accurate enough to quantify the targeted contaminants. Real-time sampling may not be applicable when the occupational hygienist is interested in chronic exposures and requires time-weighted-average measurements to compare with OELs.

Real-time sampling is used for emergency evaluations, obtaining crude estimates of concentration, leak detection, ambient air and source monitoring, evaluating engineering controls, monitoring short-term exposures that are less than 15 minutes, monitoring episodic exposures, monitoring highly toxic chemicals (carbon monoxide), explosive mixtures and process monitoring. Real-time sampling methods can capture changing concentrations over time and provide immediate qualitative and quantitative information. Integrated air sampling is usually performed for personal monitoring, area sampling and for comparing concentrations to time-weighted-average OELs. The advantages of integrated sampling are that methods are available for a wide variety of contaminants; it can be used to identify unknowns; accuracy and specificity is high and limits of detection are usually very low. Integrated samples that are analysed in a laboratory must contain enough contaminant to meet minimum detectable analytical requirements; therefore, samples are collected over a predetermined time period.

In addition to analytical requirements of a sampling method, sample duration should be matched to the sampling purpose. For source sampling, duration is based upon the process or cycle time, or when there are anticipated peaks of concentrations. For peak sampling, samples should be collected at regular intervals throughout the day to minimize bias and identify unpredictable peaks. The sampling period should be short enough to identify peaks while also providing a reflection of the actual exposure period.

For personal sampling, duration is matched to the occupational exposure limit, task duration or anticipated biological effect. Real-time sampling methods are used for assessing acute exposures to irritants, asphyxiants, sensitizers and allergenic agents. Chlorine, carbon monoxide and hydrogen sulphide are examples of chemicals that can exert their effects quickly and at relatively low concentrations.

Chronic disease agents such as lead and mercury are usually sampled for a full shift (seven hours or more per sample), using integrated sampling methods. To evaluate full shift exposures, the occupational hygienist uses either a single sample or a series of consecutive samples that cover the entire shift. The sampling duration for exposures that occur for less than a full shift are usually associated with particular tasks or processes. Construction workers, indoor maintenance personnel and maintenance road crews are examples of jobs with exposures that are tied to tasks.

How many samples and how often to sample?

Concentrations of contaminants can vary minute to minute, day to day and season to season, and variability can occur between individuals and within an individual. Exposure variability affects both the number of samples and the accuracy of the results. Variations in exposure can arise from different work practices, changes in pollutant emissions, the volume of chemicals used, production quotas, ventilation, temperature changes, worker mobility and task assignments. Most sampling campaigns are performed for a couple of days in a year; therefore, the measurements obtained are not representative of exposure. The period over which samples are collected is very short compared with the unsampled period; the occupational hygienist must extrapolate from the sampled to the unsampled period. For long-term exposure monitoring, each worker selected from a HEG should be sampled multiple times over the course of weeks or months, and exposures should be characterized for all shifts. While the day shift may be the busiest, the night shift may have the least supervision and there may be lapses in work practices.

Measurement Techniques

Active and passive sampling

Contaminants are collected on sampling media either by actively pulling an air sample through the media, or by passively allowing the air to reach the media. Active sampling uses a battery-powered pump, and passive sampling uses diffusion or gravity to bring the contaminants to the sampling media. Gases, vapours, particulates and bioaerosols are all collected by active sampling methods; gases and vapours can also be collected by passive diffusion sampling.

For gases, vapours and most particulates, once the sample is collected the mass of the contaminant is measured, and concentration is calculated by dividing the mass by the volume of sampled air. For gases and vapours, concentration is expressed as parts per million (ppm) or mg/m3, and for particulates concentration is expressed as mg/m3 (Dinardi 1995).

In integrated sampling, air sampling pumps are critical components of the sampling system because concentration estimates require knowledge of the volume of sampled air. Pumps are selected based upon desired flowrate, ease of servicing and calibration, size, cost and suitability for hazardous environments. The primary selection criterion is flowrate: low-flow pumps (0.5 to 500 ml/min) are used for sampling gases and vapours; high-flow pumps (500 to 4,500 ml/min) are used for sampling particulates, bioaerosols and gases and vapours. To insure accurate sample volumes, pumps must be accurately calibrated. Calibration is performed using primary standards such as manual or electronic soap-bubble meters, which directly measure volume, or secondary methods such as wet test meters, dry gas meters and precision rotameters that are calibrated against primary methods.

Gases and vapours: sampling media

Gases and vapours are collected using porous solid sorbent tubes, impingers, passive monitors and bags. Sorbent tubes are hollow glass tubes that have been filled with a granular solid that enables adsorption of chemicals unchanged on its surface. Solid sorbents are specific for groups of compounds; commonly used sorbents include charcoal, silica gel and Tenax. Charcoal sorbent, an amorphous form of carbon, is electrically nonpolar, and preferentially adsorbs organic gases and vapours. Silica gel, an amorphous form of silica, is used to collect polar organic compounds, amines and some inorganic compounds. Because of its affinity for polar compounds, it will adsorb water vapour; therefore, at elevated humidity, water can displace the less polar chemicals of interest from the silica gel. Tenax, a porous polymer, is used for sampling very low concentrations of nonpolar volatile organic compounds.

The ability to accurately capture the contaminants in air and avoid contaminant loss depends upon the sampling rate, sampling volume, and the volatility and concentration of the airborne contaminant. Collection efficiency of solid sorbents can be adversely affected by increased temperature, humidity, flowrate, concentration, sorbent particle size and number of competing chemicals. As collection efficiency decreases chemicals will be lost during sampling and concentrations will be underestimated. To detect chemical loss, or breakthrough, solid sorbent tubes have two sections of granular material separated by a foam plug. The front section is used for sample collection and the back section is used to determine breakthrough. Breakthrough has occurred when at least 20 to 25% of the contaminant is present in the back section of the tube. Analysis of contaminants from solid sorbents requires extraction of the contaminant from the medium using a solvent. For each batch of sorbent tubes and chemicals collected, the laboratory must determine the desorption efficiency, the efficiency of removal of chemicals from the sorbent by the solvent. For charcoal and silica gel, the most commonly used solvent is carbon disulphide. For Tenax, the chemicals are extracted using thermal desorption directly into a gas chromatograph.

Impingers are usually glass bottles with an inlet tube that allows air to be drawn into the bottle through a solution that collects the gases and vapours by absorption either unchanged in solution or by a chemical reaction. Impingers are used less and less in workplace monitoring, especially for personal sampling, because they can break, and the liquid media can spill onto the employee. There are a variety of types of impingers, including gas wash bottles, spiral absorbers, glass bead columns, midget impingers and fritted bubblers. All impingers can be used to collect area samples; the most commonly used impinger, the midget impinger, can be used for personal sampling as well.

Passive, or diffusion monitors are small, have no moving parts and are available for both organic and inorganic contaminants. Most organic monitors use activated charcoal as the collection medium. In theory, any compound that can be sampled by a charcoal sorbent tube and pump can be sampled using a passive monitor. Each monitor has a uniquely designed geometry to give an effective sampling rate. Sampling starts when the monitor cover is removed and ends when the cover is replaced. Most diffusion monitors are accurate for eight-hour time-weighted-average exposures and are not appropriate for short-term exposures.

Sampling bags can be used to collect integrated samples of gases and vapours. They have permeability and adsorptive properties that enable storage for a day with minimal loss. Bags are made of Teflon (polytetrafluoroethylene) and Tedlar (polyvinylfluoride).

Sampling media: particulate materials

Occupational sampling for particulate materials, or aerosols, is currently in a state of flux; traditional sampling methods will eventually be replaced by particle size selective (PSS) sampling methods. Traditional sampling methods will be discussed first, followed by PSS methods.

The most commonly used media for collecting aerosols are fibre or membrane filters; aerosol removal from the air stream occurs by collision and attachment of the particles to the surface of the filters. The choice of filter medium depends upon the physical and chemical properties of the aerosols to be sampled, the type of sampler and the type of analysis. When selecting filters, they must be evaluated for collection efficiency, pressure drop, hygroscopicity, background contamination, strength and pore size, which can range from 0.01 to 10 μm. Membrane filters are manufactured in a variety of pore sizes and are usually made from cellulose ester, polyvinylchloride or polytetrafluoroethylene. Particle collection occurs at the surface of the filter; therefore, membrane filters are usually used in applications where microscopy will be performed. Mixed cellulose ester filters can be easily dissolved with acid and are usually used for collection of metals for analysis by atomic absorption. Nucleopore filters (polycarbonate) are very strong and thermally stable, and are used for sampling and analysing asbestos fibres using transmission electron microscopy. Fibre filters are usually made of fibreglass and are used to sample aerosols such as pesticides and lead.

For occupational exposures to aerosols, a known volume of air can be sampled through the filters, the total increase in mass (gravimetric analysis) can be measured (mg/m3 air), the total number of particles can be counted (fibres/cc) or the aerosols can be identified (chemical analysis). For mass calculations, the total dust that enters the sampler or only the respirable fraction can be measured. For total dust, the increase in mass represents exposure from deposition in all parts of the respiratory tract. Total dust samplers are subject to error due to high winds passing across the sampler and improper orientation of the sampler. High winds, and filters facing upright, can result in collection of extra particles and overestimation of exposure.

For respirable dust sampling, the increase in mass represents exposure from deposition in the gas exchange (alveolar) region of the respiratory tract. To collect only the respirable fraction, a preclassifier called a cyclone is used to alter the distribution of airborne dust presented to the filter. Aerosols are drawn into the cyclone, accelerated and whirled, causing the heavier particles to be thrown out to the edge of the air stream and dropped to a removal section at the bottom of the cyclone. The respirable particles that are less than 10 μm remain in the air stream and are drawn up and collected on the filter for subsequent gravimetric analysis.

Sampling errors encountered when performing total and respirable dust sampling result in measurements that do not accurately reflect exposure or relate to adverse health effects. Therefore, PSS has been proposed to redefine the relationship between particle size, adverse health impact and sampling method. In PSS sampling, the measurement of particles is related to the sizes that are associated with specific health effects. The International Organization for Standardization (ISO) and the ACGIH have proposed three particulate mass fractions: inhalable particulate mass (IPM), thoracic particulate mass (TPM) and respirable particulate mass (RPM). IPM refers to particles that can be expected to enter through the nose and mouth, and would replace the traditional total mass fraction. TPM refers to particles that can penetrate the upper respiratory system past the larynx. RPM refers to particles that are capable of depositing in the gas-exchange region of the lung, and would replace the current respirable mass fraction. The practical adoption of PSS sampling requires the development of new aerosol sampling methods and PSS-specific occupational exposure limits.

Sampling media: biological materials

There are few standardized methods for sampling biological material or bioaerosols. Although sampling methods are similar to those used for other airborne particulates, viability of most bioaerosols must be preserved to ensure laboratory culturability. Therefore, they are more difficult to collect, store and analyse. The strategy for sampling bioaerosols involves collection directly on semisolid nutrient agar or plating after collection in fluids, incubation for several days and identification and quantification of the cells that have grown. The mounds of cells that have multiplied on the agar can be counted as colony-forming units (CFU) for viable bacteria or fungi, and plaque-forming units (PFU) for active viruses. With the exception of spores, filters are not recommended for bioaerosol collection because dehydration causes cell damage.

Viable aerosolized micro-organisms are collected using all-glass impingers (AGI-30), slit samplers and inertial impactors. Impingers collect bioaerosols in liquid and the slit sampler collects bioaerosols on glass slides at high volumes and flowrates. The impactor is used with one to six stages, each containing a Petri dish, to allow for separation of particles by size.

Interpretation of sampling results must be done on a case-by-case basis because there are no occupational exposure limits. Evaluation criteria must be determined prior to sampling; for indoor air investigations, in particular, samples taken outside of the building are used as a background reference. A rule of thumb is that concentrations should be ten times background to suspect contamination. When using culture plating techniques, concentrations are probably underestimated because of losses of viability during sampling and incubation.

Skin and surface sampling

There are no standard methods for evaluating skin exposure to chemicals and predicting dose. Surface sampling is performed primarily to evaluate work practices and identify potential sources of skin absorption and ingestion. Two types of surface sampling methods are used to assess dermal and ingestion potential: direct methods, which involve sampling the skin of a worker, and indirect methods, which involve wipe sampling surfaces.

Direct skin sampling involves placing gauze pads on the skin to absorb chemicals, rinsing the skin with solvents to remove contaminants and using fluorescence to identify skin contamination. Gauze pads are placed on different parts of the body and are either left exposed or are placed under personal protective equipment. At the end of the workday the pads are removed and are analysed in the laboratory; the distribution of concentrations from different parts of the body are used to identify skin exposure areas. This method is inexpensive and easy to perform; however, the results are limited because gauze pads are not good physical models of the absorption and retention properties of skin, and measured concentrations are not necessarily representative of the entire body.

Skin rinses involve wiping the skin with solvents or placing hands in plastic bags filled with solvents to measure the concentration of chemicals on the surface. This method can underestimate dose because only the unabsorbed fraction of chemicals is collected.

Fluorescence monitoring is used to identify skin exposure for chemicals that naturally fluoresce, such as polynuclear aromatics, and to identify exposures for chemicals in which fluorescent compounds have been intentionally added. The skin is scanned with an ultraviolet light to visualize contamination. This visualization provides workers with evidence of the effect of work practices on exposure; research is underway to quantify the fluorescence intensity and relate it to dose.

Indirect wipe sampling methods involve the use of gauze, glass fibre filters or cellulose paper filters, to wipe the insides of gloves or respirators, or the tops of surfaces. Solvents may be added to increase collection efficiency. The gauze or filters are then analysed in the laboratory. To standardize the results and enable comparison between samples, a square template is used to sample a 100 cm2 area.

Biological media

Blood, urine and exhaled air samples are the most suitable specimens for routine biological monitoring, while hair, milk, saliva and nails are less frequently used. Biological monitoring is performed by collecting bulk blood and urine samples in the workplace and analysing them in the laboratory. Exhaled air samples are collected in Tedlar bags, specially designed glass pipettes or sorbent tubes, and are analysed in the field using direct-reading instruments, or in the laboratory. Blood, urine and exhaled air samples are primarily used to measure the unchanged parent compound (same chemical that is sampled in workplace air), its metabolite or a biochemical change (intermediate) that has been induced in the body. For example, the parent compound lead is measured in blood to evaluate lead exposure, the metabolite mandelic acid is measured in urine for both styrene and ethyl benzene, and carboxyhaemoglobin is the intermediate measured in blood for both carbon monoxide and methylene chloride exposure. For exposure monitoring, the concentration of an ideal determinant will be highly correlated with intensity of exposure. For medical monitoring, the concentration of an ideal determinant will be highly correlated with target organ concentration.

The timing of specimen collection can impact the usefulness of the measurements; samples should be collected at times which most accurately reflect exposure. Timing is related to the excretion biological half-life of a chemical, which reflects how quickly a chemical is eliminated from the body; this can vary from hours to years. Target organ concentrations of chemicals with short biological half-lives closely follow the environmental concentration; target organ concentrations of chemicals with long biological half-lives fluctuate very little in response to environmental exposures. For chemicals with short biological half-lives, less than three hours, a sample is taken immediately at the end of the workday, before concentrations rapidly decline, to reflect exposure on that day. Samples may be taken at any time for chemicals with long half-lives, such as polychlorinated biphenyls and lead.

Real-time monitors

Direct-reading instruments provide real-time quantification of contaminants; the sample is analysed within the equipment and does not require off-site laboratory analysis (Maslansky and Maslansky 1993). Compounds can be measured without first collecting them on separate media, then shipping, storing and analysing them. Concentration is read directly from a meter, display, strip chart recorder and data logger, or from a colour change. Direct-reading instruments are primarily used for gases and vapours; a few instruments are available for monitoring particulates. Instruments vary in cost, complexity, reliability, size, sensitivity and specificity. They include simple devices, such as colorimetric tubes, that use a colour change to indicate concentration; dedicated instruments that are specific for a chemical, such as carbon monoxide indicators, combustible gas indicators (explosimeters) and mercury vapour meters; and survey instruments, such as infrared spectrometers, that screen large groups of chemicals. Direct-reading instruments use a variety of physical and chemical methods to analyse gases and vapours, including conductivity, ionization, potentiometry, photometry, radioactive tracers and combustion.

Commonly used portable direct-reading instruments include battery-powered gas chromatographs, organic vapour analysers and infrared spectrometers. Gas chromatographs and organic vapour monitors are primarily used for environmental monitoring at hazardous waste sites and for community ambient air monitoring. Gas chromatographs with appropriate detectors are specific and sensitive, and can quantify chemicals at very low concentrations. Organic vapour analysers are usually used to measure classes of compounds. Portable infrared spectrometers are primarily used for occupational monitoring and leak detection because they are sensitive and specific for a wide range of compounds.

Small direct-reading personal monitors are available for a few common gases (chlorine, hydrogen cyanide, hydrogen sulphide, hydrazine, oxygen, phosgene, sulphur dioxide, nitrogen dioxide and carbon monoxide). They accumulate concentration measurements over the course of the day and can provide a direct readout of time-weighted-average concentration as well as provide a detailed contaminant profile for the day.

Colorimetric tubes (detector tubes) are simple to use, cheap and available for a wide variety of chemicals. They can be used to quickly identify classes of air contaminants and provide ballpark estimates of concentrations that can be used when determining pump flow rates and volumes. Colorimetric tubes are glass tubes filled with solid granular material which has been impregnated with a chemical agent that can react with a contaminant and create a colour change. After the two sealed ends of a tube are broken open, one end of the tube is placed in a hand pump. The recommended volume of contaminated air is sampled through the tube by using a specified number of pump strokes for a particular chemical. A colour change or stain is produced on the tube, usually within two minutes, and the length of the stain is proportional to concentration. Some colorimetric tubes have been adapted for long duration sampling, and are used with battery-powered pumps that can run for at least eight hours. The colour change produced represents a time-weighted-average concentration. Colorimetric tubes are good for both qualitative and quantitative analysis; however, their specificity and accuracy is limited. The accuracy of colorimetric tubes is not as high as that of laboratory methods or many other real-time instruments. There are hundreds of tubes, many of which have cross-sensitivities and can detect more than one chemical. This can result in interferences that modify the measured concentrations.

Direct-reading aerosol monitors cannot distinguish between contaminants, are usually used for counting or sizing particles, and are primarily used for screening, not to determine TWA or acute exposures. Real-time instruments use optical or electrical properties to determine total and respirable mass, particle count and particle size. Light-scattering aerosol monitors, or aerosol photometers, detect the light scattered by particles as they pass through a volume in the equipment. As the number of particles increases, the amount of scattered light increases and is proportional to mass. Light-scattering aerosol monitors cannot be used to distinguish between particle types; however, if they are used in a workplace where there are a limited number of dusts present, the mass can be attributed to a particular material. Fibrous aerosol monitors are used to measure the airborne concentration of particles such as asbestos. Fibres are aligned in an oscillating electric field and are illuminated with a helium neon laser; the resulting pulses of light are detected by a photomultiplier tube. Light-attenuating photometers measure the extinction of light by particles; the ratio of incident light to measured light is proportional to concentration.

Analytical Techniques

There are many available methods for analysing laboratory samples for contaminants. Some of the more commonly used techniques for quantifying gases and vapours in air include gas chromatography, mass spectrometry, atomic absorption, infrared and UV spectroscopy and polarography.

Gas chromatography is a technique used to separate and concentrate chemicals in mixtures for subsequent quantitative analysis. There are three main components to the system: the sample injection system, a column and a detector. A liquid or gaseous sample is injected using a syringe, into an air stream that carries the sample through a column where the components are separated. The column is packed with materials that interact differently with different chemicals, and slows down the movement of the chemicals. The differential interaction causes each chemical to travel through the column at a different rate. After separation, the chemicals go directly into a detector, such as a flame ionization detector (FID), photo-ionization detector (PID) or electron capture detector (ECD); a signal proportional to concentration is registered on a chart recorder. The FID is used for almost all organics including: aromatics, straight chain hydrocarbons, ketones and some chlorinated hydrocarbons. Concentration is measured by the increase in the number of ions produced as a volatile hydrocarbon is burned by a hydrogen flame. The PID is used for organics and some inorganics; it is especially useful for aromatic compounds such as benzene, and it can detect aliphatic, aromatic and halogenated hydrocarbons. Concentration is measured by the increase in the number of ions produced when the sample is bombarded by ultraviolet radiation. The ECD is primarily used for halogen-containing chemicals; it gives a minimal response to hydrocarbons, alcohols and ketones. Concentration is measured by the current flow between two electrodes caused by ionization of the gas by radioactivity.

The mass spectrophotometer is used to analyse complex mixtures of chemicals present in trace amounts. It is often coupled with a gas chromatograph for the separation and quantification of different contaminants.

Atomic absorption spectroscopy is primarily used for the quantification of metals such as mercury. Atomic absorption is the absorption of light of a particular wavelength by a free, ground-state atom; the quantity of light absorbed is related to concentration. The technique is highly specific, sensitive and fast, and is directly applicable to approximately 68 elements. Detection limits are in the sub-ppb to low-ppm range.

Infrared analysis is a powerful, sensitive, specific and versatile technique. It uses the absorption of infrared energy to measure many inorganic and organic chemicals; the amount of light absorbed is proportional to concentration. The absorption spectrum of a compound provides information enabling its identification and quantification.

UV absorption spectroscopy is used for analysis of aromatic hydrocarbons when interferences are known to be low. The amount of absorption of UV light is directly proportional to concentration.

Polarographic methods are based upon the electrolysis of a sample solution using an easily polarized electrode and a nonpolarizable electrode. They are used for qualitative and quantitative analysis of aldehydes, chlorinated hydrocarbons and metals.



Thursday, 10 March 2011 17:05

Recognition of Hazards

A workplace hazard can be defined as any condition that may adversely affect the well-being or health of exposed persons. Recognition of hazards in any occupational activity involves characterization of the workplace by identifying hazardous agents and groups of workers potentially exposed to these hazards. The hazards might be of chemical, biological or physical origin (see table 1). Some hazards in the work environment are easy to recognize—for example, irritants, which have an immediate irritating effect after skin exposure or inhalation. Others are not so easy to recognize—for example, chemicals which are accidentally formed and have no warning properties. Some agents like metals (e.g., lead, mercury, cadmium, manganese), which may cause injury after several years of exposure, might be easy to identify if you are aware of the risk. A toxic agent may not constitute a hazard at low concentrations or if no one is exposed. Basic to the recognition of hazards are identification of possible agents at the workplace, knowledge about health risks of these agents and awareness of possible exposure situations.

Table 1.  Hazards of chemical, biological and physical agents.

Type of hazard






Chemicals enter the body principally through inhalation, skin absorption or ingestion. The toxic effect might be acute, chronic or both.,



Corrosive chemicals actually cause tissue destruction at the site of contact. Skin, eyes and digestive system are the most commonly affected parts of the body.

Concentrated acids and alkalis, phosphorus


Irritants cause inflammation of tissues where they are deposited. Skin irritants may cause reactions like eczema or dermatitis. Severe respiratory irritants might cause shortness of breath, inflammatory responses and oedema.

Skin: acids, alkalis, solvents, oils Respiratory: aldehydes, alkaline dusts, ammonia, nitrogendioxide, phosgene, chlorine, bromine, ozone

Allergic reactions

Chemical allergens or sensitizers can cause skin or respiratory allergic reactions.

Skin: colophony (rosin), formaldehyde, metals like chromium or nickel, some organic dyes, epoxy hardeners, turpentine

Respiratory: isocyanates, fibre-reactive dyes, formaldehyde, many tropical wood dusts, nickel



Asphyxiants exert their effects by interfering with the oxygenation of the tissues. Simple asphyxiants are inert gases that dilute the available atmospheric oxygen below the level required to support life. Oxygen-deficient atmospheres may occur in tanks, holds of ships, silos or mines. Oxygen concentration in air should never be below 19.5% by volume. Chemical asphyxiants prevent oxygen transport and the normal oxygenation of blood or prevent normal oxygenation of tissues.

Simple asphyxiants: methane, ethane, hydrogen, helium

Chemical asphyxiants: carbon monoxide, nitrobenzene, hydrogencyanide, hydrogen sulphide



Known human carcinogens are chemicals that have been clearly demonstrated to cause cancer in humans. Probable human carcinogens are chemicals that have been clearly demonstrated to cause cancer in animals or the evidence is not definite in humans. Soot and coal tars were the first chemicals suspected to cause cancer.

Known: benzene (leukaemia); vinyl chloride (liver angio-sarcoma); 2-naphthylamine, benzidine (bladder cancer); asbestos (lung cancer, mesothelioma); hardwood dust (nasalor nasal sinus adenocarcinoma) Probable: formaldehyde, carbon tetrachloride, dichromates, beryllium




Reproductive toxicants interfere with reproductive or sexual functioning of an individual.

Manganese, carbon disulphide, monomethyl and ethyl ethers of ethylene glycol, mercury


Developmental toxicants are agents that may cause an adverse effect in offspring of exposed persons; for example, birth defects. Embryotoxic or foetotoxic chemicals can cause spontaneous abortions or miscarriages.

Organic mercury compounds, carbon monoxide, lead, thalidomide, solvents




Systemic poisons are agents that cause injury to particular organs or body systems.

Brain: solvents, lead, mercury, manganese

Peripheral nervous system: n-hexane, lead, arsenic, carbon disulphide

Blood-forming system: benzene, ethylene glycol ethers

Kidneys: cadmium, lead, mercury, chlorinated hydrocarbons

Lungs: silica, asbestos, coal dust (pneumoconiosis)








Biological hazards can be defined as organic dusts originating from different sources of biological origin such as virus, bacteria, fungi, proteins from animals or substances from plants such as degradation products of natural fibres. The aetiological agent might be derived from a viable organism or from contaminants or constitute a specific component in the dust. Biological hazards are grouped into infectious and non-infectious agents. Non-infectious hazards can be further divided into viable organisms, biogenic toxins and biogenic allergens.


Infectious hazards

Occupational diseases from infectious agents are relatively uncommon. Workers at risk include employees at hospitals, laboratory workers, farmers, slaughterhouse workers, veterinarians, zoo keepers and cooks. Susceptibility is very variable (e.g., persons treated with immunodepressing drugs will have a high sensitivity).

Hepatitis B, tuberculosis, anthrax, brucella, tetanus, chlamydia psittaci, salmonella

Viable organisms and biogenic toxins

Viable organisms include fungi, spores and mycotoxins; biogenic toxins include endotoxins, aflatoxin and bacteria. The products of bacterial and fungal metabolism are complex and numerous and affected by temperature, humidity and kind of substrate on which they grow. Chemically they might consist of proteins, lipoproteins or mucopolysaccharides. Examples are Gram positive and Gram negative bacteria and moulds. Workers at risk include cotton mill workers, hemp and flax workers, sewage and sludge treatment workers, grain silo workers.

Byssinosis, “grain fever”, Legionnaire’s disease

Biogenic allergens

Biogenic allergens include fungi, animal-derived proteins, terpenes, storage mites and enzymes. A considerable part of the biogenic allergens in agriculture comes from proteins from animal skin, hair from furs and protein from the faecal material and urine. Allergens might be found in many industrial environments, such as fermentation processes, drug production, bakeries, paper production, wood processing (saw mills, production, manufacturing) as well as in bio-technology (enzyme and vaccine production, tissue culture) and spice production. In sensitized persons, exposure to the allergic agents may induce allergic symptoms such as allergic rhinitis, conjunctivitis or asthma. Allergic alveolitis is characterized by acute respiratory symptoms like cough, chills, fever, headache and pain in the muscles, which might lead to chronic lung fibrosis.

Occupational asthma: wool, furs, wheat grain, flour, red cedar, garlic powder

Allergic alveolitis: farmer’s disease, bagassosis, “bird fancier’s disease”, humidifier fever, sequoiosis






Noise is considered as any unwanted sound that may adversely affect the health and well-being of individuals or populations. Aspects of noise hazards include total energy of the sound, frequency distribution, duration of exposure and impulsive noise. Hearing acuity is generally affected first with a loss or dip at 4000 Hz followed by losses in the frequency range from 2000 to 6000 Hz. Noise might result in acute effects like communication problems, decreased concentration, sleepiness and as a consequence interference with job performance. Exposure to high levels of noise (usually above 85 dBA) or impulsive noise (about 140 dBC) over a significant period of time may cause both temporary and chronic hearing loss. Permanent hearing loss is the most common occupational disease in compensation claims.

Foundries, woodworking, textile mills, metalworking


Vibration has several parameters in common with noise-frequency, amplitude, duration of exposure and whether it is continuous or intermittent. Method of operation and skilfulness of the operator seem to play an important role in the development of harmful effects of vibration. Manual work using powered tools is associated with symptoms of peripheral circulatory disturbance known as “Raynaud’s phenomenon” or “vibration-induced white fingers” (VWF). Vibrating tools may also affect the peripheral nervous system and the musculo-skeletal system with reduced grip strength, low back pain and degenerative back disorders.

Contract machines, mining loaders, fork-lift trucks, pneumatic tools, chain saws




The most important chronic effect of ionizing radiation is cancer, including leukaemia. Overexposure from comparatively low levels of radiation have been associated with dermatitis of the hand and effects on the haematological system. Processes or activities which might give excessive exposure to ionizing radiation are very restricted and regulated.

Nuclear reactors, medical and dental x-ray tubes, particle accelerators, radioisotopes




Non-ionizing radiation consists of ultraviolet radiation, visible radiation, infrared, lasers, electromagnetic fields (microwaves and radio frequency) and extreme low frequency radiation. IR radiation might cause cataracts. High-powered lasers may cause eye and skin damage. There is an increasing concern about exposure to low levels of electromagnetic fields as a cause of cancer and as a potential cause of adverse reproductive outcomes among women, especially from exposure to video display units. The question about a causal link to cancer is not yet answered. Recent reviews of available scientific knowledge generally conclude that there is no association between use of VDUs and adverse reproductive outcome.

Ultraviolet radiation: arc welding and cutting; UV curing of inks, glues, paints, etc.; disinfection; product control

Infrared radiation: furnaces, glassblowing

Lasers: communications, surgery, construction




Identification and Classification of Hazards

Before any occupational hygiene investigation is performed the purpose must be clearly defined. The purpose of an occupational hygiene investigation might be to identify possible hazards, to evaluate existing risks at the workplace, to prove compliance with regulatory requirements, to evaluate control measures or to assess exposure with regard to an epidemiological survey. This article is restricted to programmes aimed at identification and classification of hazards at the workplace. Many models or techniques have been developed to identify and evaluate hazards in the working environment. They differ in complexity, from simple checklists, preliminary industrial hygiene surveys, job-exposure matrices and hazard and operability studies to job exposure profiles and work surveillance programmes (Renes 1978; Gressel and Gideon 1991; Holzner, Hirsh and Perper 1993; Goldberg et al. 1993; Bouyer and Hémon 1993; Panett, Coggon and Acheson 1985; Tait 1992). No single technique is a clear choice for everyone, but all techniques have parts which are useful in any investigation. The usefulness of the models also depends on the purpose of the investigation, size of workplace, type of production and activity as well as complexity of operations.

Identification and classification of hazards can be divided into three basic elements: workplace characterization, exposure pattern and hazard evaluation.

Workplace characterization

A workplace might have from a few employees up to several thousands and have different activities (e.g., production plants, construction sites, office buildings, hospitals or farms). At a workplace different activities can be localized to special areas such as departments or sections. In an industrial process, different stages and operations can be identified as production is followed from raw materials to finished products.

Detailed information should be obtained about processes, operations or other activities of interest, to identify agents utilized, including raw materials, materials handled or added in the process, primary products, intermediates, final products, reaction products and by-products. Additives and catalysts in a process might also be of interest to identify. Raw material or added material which has been identified only by trade name must be evaluated by chemical composition. Information or safety data sheets should be available from manufacturer or supplier.

Some stages in a process might take place in a closed system without anyone exposed, except during maintenance work or process failure. These events should be recognized and precautions taken to prevent exposure to hazardous agents. Other processes take place in open systems, which are provided with or without local exhaust ventilation. A general description of the ventilation system should be provided, including local exhaust system.

When possible, hazards should be identified in the planning or design of new plants or processes, when changes can be made at an early stage and hazards might be anticipated and avoided. Conditions and procedures that may deviate from the intended design must be identified and evaluated in the process state. Recognition of hazards should also include emissions to the external environment and waste materials. Facility locations, operations, emission sources and agents should be grouped together in a systematic way to form recognizable units in the further analysis of potential exposure. In each unit, operations and agents should be grouped according to health effects of the agents and estimation of emitted amounts to the work environment.

Exposure patterns

The main exposure routes for chemical and biological agents are inhalation and dermal uptake or incidentally by ingestion. The exposure pattern depends on frequency of contact with the hazards, intensity of exposure and time of exposure. Working tasks have to be systematically examined. It is important not only to study work manuals but to look at what actually happens at the workplace. Workers might be directly exposed as a result of actually performing tasks, or be indirectly exposed because they are located in the same general area or location as the source of exposure. It might be necessary to start by focusing on working tasks with high potential to cause harm even if the exposure is of short duration. Non-routine and intermittent operations (e.g., maintenance, cleaning and changes in production cycles) have to be considered. Working tasks and situations might also vary throughout the year.

Within the same job title exposure or uptake might differ because some workers wear protective equipment and others do not. In large plants, recognition of hazards or a qualitative hazard evaluation very seldom can be performed for every single worker. Therefore workers with similar working tasks have to be classified in the same exposure group. Differences in working tasks, work techniques and work time will result in considerably different exposure and have to be considered. Persons working outdoors and those working without local exhaust ventilation have been shown to have a larger day-to-day variability than groups working indoors with local exhaust ventilation (Kromhout, Symanski and Rappaport 1993). Work processes, agents applied for that process/job or different tasks within a job title might be used, instead of the job title, to characterize groups with similar exposure. Within the groups, workers potentially exposed must be identified and classified according to hazardous agents, routes of exposure, health effects of the agents, frequency of contact with the hazards, intensity and time of exposure. Different exposure groups should be ranked according to hazardous agents and estimated exposure in order to determine workers at greatest risk.

Qualitative hazard evaluation

Possible health effects of chemical, biological and physical agents present at the workplace should be based on an evaluation of available epidemiological, toxicological, clinical and environmental research. Up-to-date information about health hazards for products or agents used at the workplace should be obtained from health and safety journals, databases on toxicity and health effects, and relevant scientific and technical literature.

Material Safety Data Sheets (MSDSs) should if necessary be updated. Data Sheets document percentages of hazardous ingredients together with the Chemical Abstracts Service chemical identifier, the CAS-number, and threshold limit value (TLV), if any. They also contain information about health hazards, protective equipment, preventive actions, manufacturer or supplier, and so on. Sometimes the ingredients reported are rather rudimentary and have to be supplemented with more detailed information.

Monitored data and records of measurements should be studied. Agents with TLVs provide general guidance in deciding whether the situation is acceptable or not, although there must be allowance for possible interactions when workers are exposed to several chemicals. Within and between different exposure groups, workers should be ranked according to health effects of agents present and estimated exposure (e.g., from slight health effects and low exposure to severe health effects and estimated high exposure). Those with the highest ranks deserve highest priority. Before any prevention activities start it might be necessary to perform an exposure monitoring programme. All results should be documented and easily attainable. A working scheme is illustrated in figure 1.

Figure 1. Elements of risk assessment


In occupational hygiene investigations the hazards to the outdoor environment (e.g., pollution and greenhouse effects as well as effects on the ozone layer) might also be considered.

Chemical, Biological and Physical Agents

Hazards might be of chemical, biological or physical origin. In this section and in table 1 a brief description of the various hazards will be given together with examples of environments or activities where they will be found (Casarett 1980; International Congress on Occupational Health 1985; Jacobs 1992; Leidel, Busch and Lynch 1977; Olishifski 1988; Rylander 1994). More detailed information will be found elsewhere in this Encyclopaedia.

Chemical agents

Chemicals can be grouped into gases, vapours, liquids and aerosols (dusts, fumes, mists).


Gases are substances that can be changed to liquid or solid state only by the combined effects of increased pressure and decreased temperature. Handling gases always implies risk of exposure unless they are processed in closed systems. Gases in containers or distribution pipes might accidentally leak. In processes with high temperatures (e.g., welding operations and exhaust from engines) gases will be formed.


Vapours are the gaseous form of substances that normally are in the liquid or solid state at room temperature and normal pressure. When a liquid evaporates it changes to a gas and mixes with the surrounding air. A vapour can be regarded as a gas, where the maximal concentration of a vapour depends on the temperature and the saturation pressure of the substance. Any process involving combustion will generate vapours or gases. Degreasing operations might be performed by vapour phase degreasing or soak cleaning with solvents. Work activities like charging and mixing liquids, painting, spraying, cleaning and dry cleaning might generate harmful vapours.


Liquids may consist of a pure substance or a solution of two or more substances (e.g., solvents, acids, alkalis). A liquid stored in an open container will partially evaporate into the gas phase. The concentration in the vapour phase at equilibrium depends on the vapour pressure of the substance, its concentration in the liquid phase, and the temperature. Operations or activities with liquids might give rise to splashes or other skin contact, besides harmful vapours.


Dusts consist of inorganic and organic particles, which can be classified as inhalable, thoracic or respirable, depending on particle size. Most organic dusts have a biological origin. Inorganic dusts will be generated in mechanical processes like grinding, sawing, cutting, crushing, screening or sieving. Dusts may be dispersed when dusty material is handled or whirled up by air movements from traffic. Handling dry materials or powder by weighing, filling, charging, transporting and packing will generate dust, as will activities like insulation and cleaning work.


Fumes are solid particles vaporized at high temperature and condensed to small particles. The vaporization is often accompanied by a chemical reaction such as oxidation. The single particles that make up a fume are extremely fine, usually less than 0.1 μm, and often aggregate in larger units. Examples are fumes from welding, plasma cutting and similar operations.


Mists are suspended liquid droplets generated by condensation from the gaseous state to the liquid state or by breaking up a liquid into a dispersed state by splashing, foaming or atomizing. Examples are oil mists from cutting and grinding operations, acid mists from electroplating, acid or alkali mists from pickling operations or paint spray mists from spraying operations.



Thursday, 10 March 2011 16:45

Goals, Definitions and General Information

Work is essential for life, development and personal fulfilment. Unfortunately, indispensable activities such as food production, extraction of raw materials, manufacturing of goods, energy production and services involve processes, operations and materials which can, to a greater or lesser extent, create hazards to the health of workers and those in nearby communities, as well as to the general environment.

However, the generation and release of harmful agents in the work environment can be prevented, through adequate hazard control interventions, which not only protect workers’ health but also limit the damage to the environment often associated with industrialization. If a harmful chemical is eliminated from a work process, it will neither affect the workers nor go beyond, to pollute the environment.

The profession that aims specifically at the prevention and control of hazards arising from work processes is occupational hygiene. The goals of occupational hygiene include the protection and promotion of workers’ health, the protection of the environment and contribution to a safe and sustainable development.

The need for occupational hygiene in the protection of workers’ health cannot be overemphasized. Even when feasible, the diagnosis and the cure of an occupational disease will not prevent further occurrences, if exposure to the aetiological agent does not cease. So long as the unhealthy work environment remains unchanged, its potential to impair health remains. Only the control of health hazards can break the vicious circle illustrated in figure 1.

Figure 1. Interactions between people and the environment


However, preventive action should start much earlier, not only before the manifestation of any health impairment but even before exposure actually occurs. The work environment should be under continuous surveillance so that hazardous agents and factors can be detected and removed, or controlled, before they cause any ill effects; this is the role of occupational hygiene.

Furthermore, occupational hygiene may also contribute to a safe and sustainable development, that is “to ensure that (development) meets the needs of the present without compromising the ability of the future generations to meet their own needs” (World Commission on Environment and Development 1987). Meeting the needs of the present world population without depleting or damaging the global resource base, and without causing adverse health and environmental consequences, requires knowledge and means to influence action (WHO 1992a); when related to work processes this is closely related to occupational hygiene practice.













Occupational health requires a multidisciplinary approach and involves fundamental disciplines, one of which is occupational hygiene, along with others which include occupational medicine and nursing, ergonomics and work psychology. A schematic representation of the scopes of action for occupational physicians and occupational hygienists is presented in figure 2.

Figure 2. Scopes of action for occupational physicians and occupational hygienists.


It is important that decision makers, managers and workers themselves, as well as all occupational health professionals, understand the essential role that occupational hygiene plays in the protection of workers’ health and of the environment, as well as the need for specialized professionals in this field. The close link between occupational and environmental health should also be kept in mind, since the prevention of pollution from industrial sources, through the adequate handling and disposal of hazardous effluents and waste, should be started at the workplace level. (See “Evaluation of the work environment”).





Concepts and Definitions

Occupational hygiene

Occupational hygiene is the science of the anticipation, recognition, evaluation and control of hazards arising in or from the workplace, and which could impair the health and well-being of workers, also taking into account the possible impact on the surrounding communities and the general environment.

Definitions of occupational hygiene may be presented in different ways; however, they all have essentially the same meaning and aim at the same fundamental goal of protecting and promoting the health and well-being of workers, as well as protecting the general environment, through preventive actions in the workplace.

Occupational hygiene is not yet universally recognized as a profession; however, in many countries, framework legislation is emerging that will lead to its establishment.

Occupational hygienist

 An occupational hygienist is a professional able to:

  • anticipate the health hazards that may result from work processes, operations and equipment, and accordingly advise on their planning and design
  • recognize and understand, in the work environment, the occurrence (real or potential) of chemical, physical and biological agents and other stresses, and their interactions with other factors, which may affect the health and well-being of workers
  • understand the possible routes of agent entry into the human body, and the effects that such agents and other factors may have on health
  • assess workers’ exposure to potentially harmful agents and factors and to evaluate the results
  •  evaluate work processes and methods, from the point of view of the possible generation and release/propagation of potentially harmful agents and other factors, with a view to eliminating exposures, or reducing them to acceptable levels
  • design, recommend for adoption, and evaluate the effectiveness of control strategies, alone or in collaboration with other professionals to ensure effective and economical control
  • participate in overall risk analysis and management of an agent, process or workplace, and contribute to the establishment of priorities for risk management
  • understand the legal framework for occupational hygiene practice in their own country
  • educate, train, inform and advise persons at all levels, in all aspects of hazard communication
  • work effectively in a multidisciplinary team involving other professionals
  • recognize agents and factors that may have environmental impact, and understand the need to integrate occupational hygiene practice with environmental protection.


It should be kept in mind that a profession consists not only of a body of knowledge, but also of a Code of Ethics; national occupational hygiene associations, as well as the International Occupational Hygiene Association (IOHA), have their own Codes of Ethics (WHO 1992b).  


Occupational hygiene technician

An occupational hygiene technician is “a person competent to carry out measurements of the work environment” but not “to make the interpretations, judgements, and recommendations required from an occupational hygienist”. The necessary level of competence may be obtained in a comprehensive or limited field (WHO 1992b).

International Occupational Hygiene Association (IOHA)

IOHA was formally established, during a meeting in Montreal, on June 2, 1987. At present IOHA has the participation of 19 national occupational hygiene associations, with over nineteen thousand members from seventeen countries.

The primary objective of IOHA is to promote and develop occupational hygiene throughout the world, at a high level of professional competence, through means that include the exchange of information among organizations and individuals, the further development of human resources and the promotion of a high standard of ethical practice. IOHA activities include scientific meetings and publication of a newsletter. Members of affiliated associations are automatically members of IOHA; it is also possible to join as an individual member, for those in countries where there is not yet a national association.


In addition to an accepted definition of occupational hygiene and of the role of the occupational hygienist, there is need for the establishment of certification schemes to ensure acceptable standards of occupational hygiene competence and practice. Certification refers to a formal scheme based on procedures for establishing and maintaining knowledge, skills and competence of professionals (Burdorf 1995).

IOHA has promoted a survey of existing national certification schemes (Burdorf 1995), together with recommendations for the promotion of international cooperation in assuring the quality of professional occupational hygienists, which include the following:

  • “the harmonization of standards on the competence and practice of professional occupational hygienists”
  • “the establishment of an international body of peers to review the quality of existing certification schemes”.


Other suggestions in this report include items such as: “reciprocity” and “cross-acceptance of national designations, ultimately aiming at an umbrella scheme with one internationally accepted designation”.

The Practice of Occupational Hygiene

The classical steps in occupational hygiene practice are:

  • the recognition of the possible health hazards in the work environment
  • the evaluation of hazards, which is the process of assessing exposure and reaching conclusions as to the level of risk to human health
  • prevention and control of hazards, which is the process of developing and implementing strategies to eliminate, or reduce to acceptable levels, the occurrence of harmful agents and factors in the workplace, while also accounting for environmental protection.


The ideal approach to hazard prevention is “anticipated and integrated preventive action”, which should include:

  • occupational health and environmental impact assessments, prior to the design and installation of any new workplace
  • selection of the safest, least hazardous and least polluting technology (“cleaner production”)
  • environmentally appropriate location
  • proper design, with adequate layout and appropriate control technology, including for the safe handling and disposal of the resulting effluents and waste
  • elaboration of guidelines and regulations for training on the correct operation of processes, including on safe work practices, maintenance and emergency procedures.


The importance of anticipating and preventing all types of environmental pollution cannot be overemphasized. There is, fortunately, an increasing tendency to consider new technologies from the point of view of the possible negative impacts and their prevention, from the design and installation of the process to the handling of the resulting effluents and waste, in the so-called cradle-to-grave approach. Environmental disasters, which have occurred in both developed and developing countries, could have been avoided by the application of appropriate control strategies and emergency procedures in the workplace.

Economic aspects should be viewed in broader terms than the usual initial cost consideration; more expensive options that offer good health and environmental protection may prove to be more economical in the long run. The protection of workers’ health and of the environment must start much earlier than it usually does. Technical information and advice on occupational and environmental hygiene should always be available to those designing new processes, machinery, equipment and workplaces. Unfortunately such information is often made available much too late, when the only solution is costly and difficult retrofitting, or worse, when consequences have already been disastrous.

Recognition of hazards

Recognition of hazards is a fundamental step in the practice of occupational hygiene, indispensable for the adequate planning of hazard evaluation and control strategies, as well as for the establishment of priorities for action. For the adequate design of control measures, it is also necessary to physically characterize contaminant sources and contaminant propagation paths.

The recognition of hazards leads to the determination of:

  • which agents may be present and under which circumstances
  • the nature and possible extent of associated adverse effects on health and well-being.


The identification of hazardous agents, their sources and the conditions of exposure requires extensive knowledge and careful study of work processes and operations, raw materials and chemicals used or generated, final products and eventual by-products, as well as of possibilities for the accidental formation of chemicals, decomposition of materials, combustion of fuels or the presence of impurities. The recognition of the nature and potential magnitude of the biological effects that such agents may cause if overexposure occurs, requires knowledge on and access to toxicological information. International sources of information in this respect include International Programme on Chemical Safety (IPCS), International Agency for Research on Cancer (IARC) and International Register of Potentially Toxic Chemicals, United Nations Environment Programme (UNEP-IRPTC).

Agents which pose health hazards in the work environment include airborne contaminants; non-airborne chemicals; physical agents, such as heat and noise; biological agents; ergonomic factors, such as inadequate lifting procedures and working postures; and psychosocial stresses.

Occupational hygiene evaluations

Occupational hygiene evaluations are carried out to assess workers’ exposure, as well as to provide information for the design, or to test the efficiency, of control measures.

Evaluation of workers’ exposure to occupational hazards, such as airborne contaminants, physical and biological agents, is covered elsewhere in this chapter. Nevertheless, some general considerations are provided here for a better understanding of the field of occupational hygiene.

It is important to keep in mind that hazard evaluation is not an end in itself, but must be considered as part of a much broader procedure that starts with the realization that a certain agent, capable of causing health impairment, may be present in the work environment, and concludes with the control of this agent so that it will be prevented from causing harm. Hazard evaluation paves the way to, but does not replace, hazard prevention.

Exposure assessment

Exposure assessment aims at determining how much of an agent workers have been exposed to, how often and for how long. Guidelines in this respect have been established both at the national and international level—for example, EN 689, prepared by the Comité Européen de Normalisation (European Committee for Standardization) (CEN 1994).

In the evaluation of exposure to airborne contaminants, the most usual procedure is the assessment of inhalation exposure, which requires the determination of the air concentration of the agent to which workers are exposed (or, in the case of airborne particles, the air concentration of the relevant fraction, e.g., the “respirable fraction”) and the duration of the exposure. However, if routes other than inhalation contribute appreciably to the uptake of a chemical, an erroneous judgement may be made by looking only at the inhalation exposure. In such cases, total exposure has to be assessed, and a very useful tool for this is biological monitoring.

The practice of occupational hygiene is concerned with three kinds of situations:

  • initial studies to assess workers’ exposure
  • follow-up monitoring/surveillance
  • exposure assessment for epidemiological studies.


A primary reason for determining whether there is overexposure to a hazardous agent in the work environment, is to decide whether interventions are required. This often, but not necessarily, means establishing whether there is compliance with an adopted standard, which is usually expressed in terms of an occupational exposure limit. The determination of the “worst exposure” situation may be enough to fulfil this purpose. Indeed, if exposures are expected to be either very high or very low in relation to accepted limit values, the accuracy and precision of quantitative evaluations can be lower than when the exposures are expected to be closer to the limit values. In fact, when hazards are obvious, it may be wiser to invest resources initially on controls and to carry out more precise environmental evaluations after controls have been implemented.

Follow-up evaluations are often necessary, particularly if the need existed to install or improve control measures or if changes in the processes or materials utilized were foreseen. In these cases, quantitative evaluations have an important surveillance role in:

  • evaluating the adequacy, testing the efficiency or disclosing possible failures in the control systems
  • detecting whether alterations in the processes, such as operating temperature, or in the raw materials, have altered the exposure situation.


Whenever an occupational hygiene survey is carried out in connection with an epidemiological study in order to obtain quantitative data on relationships between exposure and health effects, the exposure must be characterized with a high level of accuracy and precision. In this case, all exposure levels must be adequately characterized, since it would not be enough, for example, to characterize only the worst case exposure situation. It would be ideal, although difficult in practice, to always keep precise and accurate exposure assessment records since there may be a future need to have historical exposure data.

In order to ensure that evaluation data is representative of workers’ exposure, and that resources are not wasted, an adequate sampling strategy, accounting for all possible sources of variability, must be designed and followed. Sampling strategies, as well as measurement techniques, are covered in “Evaluation of the work environment”.

Interpretation of results

The degree of uncertainty in the estimation of an exposure parameter, for example, the true average concentration of an airborne contaminant, is determined through statistical treatment of the results from measurements (e.g., sampling and analysis). The level of confidence on the results will depend on the coefficient of variation of the “measuring system” and on the number of measurements. Once there is an acceptable confidence, the next step is to consider the health implications of the exposure: what does it mean for the health of the exposed workers: now? in the near future? in their working life? will there be an impact on future generations?

The evaluation process is only completed when results from measurements are interpreted in view of data (sometimes referred to as “risk assessment data”) derived from experimental toxicology, epidemiological and clinical studies and, in certain cases, clinical trials. It should be clarified that the term risk assessment has been used in connection with two types of assessments—the assessment of the nature and extent of risk resulting from exposure to chemicals or other agents, in general, and the assessment of risk for a particular worker or group of workers, in a specific workplace situation.

In the practice of occupational hygiene, exposure assessment results are often compared with adopted occupational exposure limits which are intended to provide guidance for hazard evaluation and for setting target levels for control. Exposure in excess of these limits requires immediate remedial action by the improvement of existing control measures or implementation of new ones. In fact, preventive interventions should be made at the “action level”, which varies with the country (e.g., one-half or one-fifth of the occupational exposure limit). A low action level is the best assurance of avoiding future problems.

Comparison of exposure assessment results with occupational exposure limits is a simplification, since, among other limitations, many factors which influence the uptake of chemicals (e.g., individual susceptibilities, physical activity and body build) are not accounted for by this procedure. Furthermore, in most workplaces there is simultaneous exposure to many agents; hence a very important issue is that of combined exposures and agent interactions, because the health consequences of exposure to a certain agent alone may differ considerably from the consequences of exposure to this same agent in combination with others, particularly if there is synergism or potentiation of effects.

Measurements for control

Measurements with the purpose of investigating the presence of agents and the patterns of exposure parameters in the work environment can be extremely useful for the planning and design of control measures and work practices. The objectives of such measurements include:

  • source identification and characterization
  • spotting of critical points in closed systems or enclosures (e.g., leaks)
  • determination of propagation paths in the work environment
  • comparison of different control interventions
  • verification that respirable dust has settled together with the coarse visible dust, when using water sprays
  • checking that contaminated air is not coming from an adjacent area.


Direct-reading instruments are extremely useful for control purposes, particularly those which can be used for continuous sampling and reflect what is happening in real time, thus disclosing exposure situations which might not otherwise be detected and which need to be controlled. Examples of such instruments include: photo-ionization detectors, infrared analysers, aerosol meters and detector tubes. When sampling to obtain a picture of the behaviour of contaminants, from the source throughout the work environment, accuracy and precision are not as critical as they would be for exposure assessment.

Recent developments in this type of measurement for control purposes include visualization techniques, one of which is the Picture Mix Exposure—PIMEX (Rosen 1993). This method combines a video image of the worker with a scale showing airborne contaminant concentrations, which are continuously measured, at the breathing zone, with a real-time monitoring instrument, thus making it possible to visualize how the concentration varies while the task is performed. This provides an excellent tool for comparing the relative efficacy of different control measures, such as ventilation and work practices, thus contributing to better design.

Measurements are also needed to assess the efficiency of control measures. In this case, source sampling or area sampling are convenient, alone or in addition to personal sampling, for the assessment of workers’ exposure. In order to assure validity, the locations for “before” and “after” sampling (or measurements) and the techniques used should be the same, or equivalent, in sensitivity, accuracy and precision.

Hazard prevention and control

The primary goal of occupational hygiene is the implementation of appropriate hazard prevention and control measures in the work environment. Standards and regulations, if not enforced, are meaningless for the protection of workers’ health, and enforcement usually requires both monitoring and control strategies. The absence of legally established standards should not be an obstacle to the implementation of the necessary measures to prevent harmful exposures or control them to the lowest level feasible. When serious hazards are obvious, control should be recommended, even before quantitative evaluations are carried out. It may sometimes be necessary to change the classical concept of “recognition-evaluation-control” to “recognition-control-evaluation”, or even to “recognition-control”, if capabilities for evaluation of hazards do not exist. Some examples of hazards in obvious need of action without the necessity of prior environmental sampling are electroplating carried out in an unventilated, small room, or using a jackhammer or sand-blasting equipment with no environmental controls or protective equipment. For such recognized health hazards, the immediate need is control, not quantitative evaluation.

Preventive action should in some way interrupt the chain by which the hazardous agent—a chemical, dust, a source of energy—is transmitted from the source to the worker. There are three major groups of control measures: engineering controls, work practices and personal measures.

The most efficient hazard prevention approach is the application of engineering control measures which prevent occupational exposures by managing the work environment, thus decreasing the need for initiatives on the part of workers or potentially exposed persons. Engineering measures usually require some process modifications or mechanical structures, and involve technical measures that eliminate or reduce the use, generation or release of hazardous agents at their source, or, when source elimination is not possible, engineering measures should be designed to prevent or reduce the spread of hazardous agents into the work environment by:

  • containing them
  • removing them immediately beyond the source
  • interfering with their propagation
  • reducing their concentration or intensity.


Control interventions which involve some modification of the source are the best approach because the harmful agent can be eliminated or reduced in concentration or intensity. Source reduction measures include substitution of materials, substitution/modification of processes or equipment and better maintenance of equipment.

When source modifications are not feasible, or are not sufficient to attain the desired level of control, then the release and dissemination of hazardous agents in the work environment should be prevented by interrupting their transmission path through measures such as isolation (e.g., closed systems, enclosures), local exhaust ventilation, barriers and shields, isolation of workers.

Other measures aiming at reducing exposures in the work environment include adequate workplace design, dilution or displacement ventilation, good housekeeping and adequate storage. Labelling and warning signs can assist workers in safe work practices. Monitoring and alarm systems may be required in a control programme. Monitors for carbon monoxide around furnaces, for hydrogen sulphide in sewage work, and for oxygen deficiency in closed spaces are some examples.

Work practices are an important part of control—for example, jobs in which a worker’s work posture can affect exposure, such as whether a worker bends over his or her work. The position of the worker may affect the conditions of exposure (e.g., breathing zone in relation to contaminant source, possibility of skin absorption).

Lastly, occupational exposure can be avoided or reduced by placing a protective barrier on the worker, at the critical entry point for the harmful agent in question (mouth, nose, skin, ear)—that is, the use of personal protective devices. It should be pointed out that all other possibilities of control should be explored before considering the use of personal protective equipment, as this is the least satisfactory means for routine control of exposures, particularly to airborne contaminants.

Other personal preventive measures include education and training, personal hygiene and limitation of exposure time.

Continuous evaluations, through environmental monitoring and health surveillance, should be part of any hazard prevention and control strategy.

Appropriate control technology for the work environment must also encompass measures for the prevention of environmental pollution (air, water, soil), including adequate management of hazardous waste.

Although most of the control principles hereby mentioned apply to airborne contaminants, many are also applicable to other types of hazards. For example, a process can be modified to produce less air contaminants or to produce less noise or less heat. An isolating barrier can isolate workers from a source of noise, heat or radiation.

Far too often prevention dwells on the most widely known measures, such as local exhaust ventilation and personal protective equipment, without proper consideration of other valuable control options, such as alternative cleaner technologies, substitution of materials, modification of processes, and good work practices. It often happens that work processes are regarded as unchangeable when, in reality, changes can be made which effectively prevent or at least reduce the associated hazards.

Hazard prevention and control in the work environment requires knowledge and ingenuity. Effective control does not necessarily require very costly and complicated measures. In many cases, hazard control can be achieved through appropriate technology, which can be as simple as a piece of impervious material between the naked shoulder of a dock worker and a bag of toxic material that can be absorbed through the skin. It can also consist of simple improvements such as placing a movable barrier between an ultraviolet source and a worker, or training workers in safe work practices.

Aspects to be considered when selecting appropriate control strategies and technology, include the type of hazardous agent (nature, physical state, health effects, routes of entry into the body), type of source(s), magnitude and conditions of exposure, characteristics of the workplace and relative location of workstations.

The required skills and resources for the correct design, implementation, operation, evaluation and maintenance of control systems must be ensured. Systems such as local exhaust ventilation must be evaluated after installation and routinely checked thereafter. Only regular monitoring and maintenance can ensure continued efficiency, since even well-designed systems may lose their initial performance if neglected.

Control measures should be integrated into hazard prevention and control programmes, with clear objectives and efficient management, involving multidisciplinary teams made up of occupational hygienists and other occupational health and safety staff, production engineers, management and workers. Programmes must also include aspects such as hazard communication, education and training covering safe work practices and emergency procedures.

Health promotion aspects should also be included, since the workplace is an ideal setting for promoting healthy life-styles in general and for alerting as to the dangers of hazardous non-occupational exposures caused, for example, by shooting without adequate protection, or smoking.

The Links among Occupational Hygiene, Risk Assessment and Risk Management

Risk assessment

Risk assessment is a methodology that aims at characterizing the types of health effects expected as a result of a certain exposure to a given agent, as well as providing estimates on the probability of occurrence of these health effects, at different levels of exposure. It is also used to characterize specific risk situations. It involves hazard identification, the establishment of exposure-effect relationships, and exposure assessment, leading to risk characterization.

The first step refers to the identification of an agent—for example, a chemical—as causing a harmful health effect (e.g., cancer or systemic poisoning). The second step establishes how much exposure causes how much of a given effect in how many of the exposed persons. This knowledge is essential for the interpretation of exposure assessment data.

Exposure assessment is part of risk assessment, both when obtaining data to characterize a risk situation and when obtaining data for the establishment of exposure-effect relationships from epidemiological studies. In the latter case, the exposure that led to a certain occupational or environmentally caused effect has to be accurately characterized to ensure the validity of the correlation.

Although risk assessment is fundamental to many decisions which are taken in the practice of occupational hygiene, it has limited effect in protecting workers’ health, unless translated into actual preventive action in the workplace.

Risk assessment is a dynamic process, as new knowledge often discloses harmful effects of substances until then considered relatively harmless; therefore the occupational hygienist must have, at all times, access to up-to-date toxicological information. Another implication is that exposures should always be controlled to the lowest feasible level.

Figure 3 is presented as an illustration of different elements of risk assessment.

Figure 3. Elements of risk assessment.


Risk management in the work environment

It is not always feasible to eliminate all agents that pose occupational health risks because some are inherent to work processes that are indispensable or desirable; however, risks can and must be managed.

Risk assessment provides a basis for risk management. However, while risk assessment is a scientific procedure, risk management is more pragmatic, involving decisions and actions that aim at preventing, or reducing to acceptable levels, the occurrence of agents which may pose hazards to the health of workers, surrounding communities and the environment, also accounting for the socio-economic and public health context.

Risk management takes place at different levels; decisions and actions taken at the national level pave the way for the practice of risk management at the workplace level.

Risk management at the workplace level requires information and knowledge on:

  • health hazards and their magnitude, identified and rated according to risk assessment findings
  • legal requirements and standards
  • technological feasibility, in terms of the available and applicable control technology
  • economic aspects, such as the costs to design, implement, operate and maintain control systems, and cost-benefit analysis (control costs versus financial benefits incurred by controlling occupational and environment hazards)
  • human resources (available and required)
  • socio-economic and public health context


to serve as a basis for decisions which include:

  • establishment of a target for control
  • selection of adequate control strategies and technologies
  • establishment of priorities for action in view of the risk situation, as well as of the existing socio-economic and public health context (particularly important in developing countries)


and which should lead to actions such as:

  • identification/search of financial and human resources (if not yet available)
  • design of specific control measures, which should be appropriate for the protection of workers’ health and of the environment, as well as safeguarding as much as possible the natural resource base
  • implementation of control measures, including provisions for adequate operation, maintenance and emergency procedures
  • establishment of a hazard prevention and control programme with adequate management and including routine surveillance.


Traditionally, the profession responsible for most of these decisions and actions in the workplace is occupational hygiene.

One key decision in risk management, that of acceptable risk (what effect can be accepted, in what percentage of the working population, if any at all?), is usually, but not always, taken at the national policy-making level and followed by the adoption of occupational exposure limits and the promulgation of occupational health regulations and standards. This leads to the establishment of targets for control, usually at the workplace level by the occupational hygienist, who should have knowledge of the legal requirements. However, it may happen that decisions on acceptable risk have to be taken by the occupational hygienist at the workplace level—for example, in situations when standards are not available or do not cover all potential exposures.

All these decisions and actions must be integrated into a realistic plan, which requires multidisciplinary and multisectorial coordination and collaboration. Although risk management involves pragmatic approaches, its efficiency should be scientifically evaluated. Unfortunately risk management actions are, in most cases, a compromise between what should be done to avoid any risk and the best which can be done in practice, in view of financial and other limitations.

Risk management concerning the work environment and the general environment should be well coordinated; not only are there overlapping areas, but, in most situations, the success of one is interlinked with the success of the other.

Occupational Hygiene Programmes and Services

Political will and decision making at the national level will, directly or indirectly, influence the establishment of occupational hygiene programmes or services, either at the governmental or private level. It is beyond the scope of this article to provide detailed models for all types of occupational hygiene programmes and services; however, there are general principles that are applicable to many situations and may contribute to their efficient implementation and operation.

A comprehensive occupational hygiene service should have the capability to carry out adequate preliminary surveys, sampling, measurements and analysis for hazard evaluation and for control purposes, and to recommend control measures, if not to design them.

Key elements of a comprehensive occupational hygiene programme or service are human and financial resources, facilities, equipment and information systems, well organized and coordinated through careful planning, under efficient management, and also involving quality assurance and continuous programme evaluation. Successful occupational hygiene programmes require a policy basis and commitment from top management. The procurement of financial resources is beyond the scope of this article.

Human resources

Adequate human resources constitute the main asset of any programme and should be ensured as a priority. All staff should have clear job descriptions and responsibilities. If needed, provisions for training and education should be made. The basic requirements for occupational hygiene programmes include:

  • occupational hygienists—in addition to general knowledge on the recognition, evaluation and control of occupational hazards, occupational hygienists may be specialized in specific areas, such as analytical chemistry or industrial ventilation; the ideal situation is to have a team of well-trained professionals in the comprehensive practice of occupational hygiene and in all required areas of expertise
  • laboratory personnel, chemists (depending on the extent of analytical work)
  • technicians and assistants, for field surveys and for laboratories, as well as for instrument maintenance and repairs
  • information specialists and administrative support.


One important aspect is professional competence, which must not only be achieved but also maintained. Continuous education, in or outside the programme or service, should cover, for example, legislation updates, new advances and techniques, and gaps in knowledge. Participation in conferences, symposia and workshops also contribute to the maintenance of competence.

Health and safety for staff

Health and safety should be ensured for all staff in field surveys, laboratories and offices. Occupational hygienists may be exposed to serious hazards and should wear the required personal protective equipment. Depending on the type of work, immunization may be required. If rural work is involved, depending on the region, provisions such as antidote for snake bites should be made. Laboratory safety is a specialized field discussed elsewhere in this Encyclopaedia.

Occupational hazards in offices should not be overlooked—for example, work with visual display units and sources of indoor pollution such as laser printers, photocopying machines and air-conditioning systems. Ergonomic and psychosocial factors should also be considered.


These include offices and meeting room(s), laboratories and equipment, information systems and library. Facilities should be well designed, accounting for future needs, as later moves and adaptations are usually more costly and time consuming.

Occupational hygiene laboratories and equipment

Occupational hygiene laboratories should have in principle the capability to carry out qualitative and quantitative assessment of exposure to airborne contaminants (chemicals and dusts), physical agents (noise, heat stress, radiation, illumination) and biological agents. In the case of most biological agents, qualitative assessments are enough to recommend controls, thus eliminating the need for the usually difficult quantitative evaluations.

Although some direct-reading instruments for airborne contaminants may have limitations for exposure assessment purposes, these are extremely useful for the recognition of hazards and identification of their sources, the determination of peaks in concentration, the gathering of data for control measures, and for checking on controls such as ventilation systems. In connection with the latter, instruments to check air velocity and static pressure are also needed.

One of the possible structures would comprise the following units:

  • field equipment (sampling, direct-reading)
  • analytical laboratory
  • particles laboratory
  • physical agents (noise, thermal environment, illumination and radiation)
  • workshop for maintenance and repairs of instrumentation.


Whenever selecting occupational hygiene equipment, in addition to performance characteristics, practical aspects have to be considered in view of the expected conditions of use—for example, available infrastructure, climate, location. These aspects include portability, required source of energy, calibration and maintenance requirements, and availability of the required expendable supplies.

Equipment should be purchased only if and when:

  • there is a real need
  • skills for the adequate operation, maintenance and repairs are available
  • the complete procedure has been developed, since it is of no use, for example, to purchase sampling pumps without a laboratory to analyse the samples (or an agreement with an outside laboratory).


Calibration of all types of occupational hygiene measuring and sampling as well as analytical equipment should be an integral part of any procedure, and the required equipment should be available.

Maintenance and repairs are essential to prevent equipment from staying idle for long periods of time, and should be ensured by manufacturers, either by direct assistance or by providing training of staff.

If a completely new programme is being developed, only basic equipment should be initially purchased, more items being added as the needs are established and operational capabilities ensured. However, even before equipment and laboratories are available and operational, much can be achieved by inspecting workplaces to qualitatively assess health hazards, and by recommending control measures for recognized hazards. Lack of capability to carry out quantitative exposure assessments should never justify inaction concerning obviously hazardous exposures. This is particularly true for situations where workplace hazards are uncontrolled and heavy exposures are common.


This includes library (books, periodicals and other publications), databases (e.g. on CD-ROM) and communications.

Whenever possible, personal computers and CD-ROM readers should be provided, as well as connections to the INTERNET. There are ever-increasing possibilities for on-line networked public information servers (World Wide Web and GOPHER sites), which provide access to a wealth of information sources relevant to workers’ health, therefore fully justifying investment in computers and communications. Such systems should include e-mail, which opens new horizons for communications and discussions, either individually or as groups, thus facilitating and promoting exchange of information throughout the world.


Timely and careful planning for the implementation, management and periodic evaluation of a programme is essential to ensure that the objectives and goals are achieved, while making the best use of the available resources.

Initially, the following information should be obtained and analysed:

  • nature and magnitude of prevailing hazards, in order to establish priorities
  • legal requirements (legislation, standards)
  • available resources
  • infrastructure and support services.


The planning and organization processes include:

  • establishment of the purpose of the programme or service, definition of objectives and the scope of the activities, in view of the expected demand and the available resources
  • allocation of resources
  • definition of the organizational structure
  • profile of the required human resources and plans for their development (if needed)
  • clear assignment of responsibilities to units, teams and individuals
  • design/adaptation of the facilities
  • selection of equipment
  • operational requirements
  • establishment of mechanisms for communication within and outside the service
  • timetable.


Operational costs should not be underestimated, since lack of resources may seriously hinder the continuity of a programme. Requirements which cannot be overlooked include:

  • purchase of expendable supplies (including items such as filters, detector tubes, charcoal tubes, reagents), spare parts for equipment, etc.
  • maintenance and repairs of equipment
  • transportation (vehicles, fuel, maintenance) and travel
  • information update.


Resources must be optimized through careful study of all elements which should be considered as integral parts of a comprehensive service. A well-balanced allocation of resources to the different units (field measurements, sampling, analytical laboratories, etc.) and all the components (facilities and equipment, personnel, operational aspects) is essential for a successful programme. Moreover, allocation of resources should allow for flexibility, because occupational hygiene services may have to undergo adaptations in order to respond to the real needs, which should be periodically assessed.

Communication, sharing and collaboration are key words for successful teamwork and enhanced individual capabilities. Effective mechanisms for communication, within and outside the programme, are needed to ensure the required multidisciplinary approach for the protection and promotion of workers’ health. There should be close interaction with other occupational health professionals, particularly occupational physicians and nurses, ergonomists and work psychologists, as well as safety professionals. At the workplace level, this should include workers, production personnel and managers.

The implementation of successful programmes is a gradual process. Therefore, at the planning stage, a realistic timetable should be prepared, according to well-established priorities and in view of the available resources.


Management involves decision-making as to the goals to be achieved and actions required to efficiently achieve these goals, with participation of all concerned, as well as foreseeing and avoiding, or recognizing and solving, the problems which may create obstacles to the completion of the required tasks. It should be kept in mind that scientific knowledge is no assurance of the managerial competence required to run an efficient programme.

The importance of implementing and enforcing correct procedures and quality assurance cannot be overemphasized, since there is much difference between work done and work well done. Moreover, the real objectives, not the intermediate steps, should serve as a yardstick; the efficiency of an occupational hygiene programme should be measured not by the number of surveys carried out, but rather by the number of surveys that led to actual action to protect workers’ health.

Good management should be able to distinguish between what is impressive and what is important; very detailed surveys involving sampling and analysis, yielding very accurate and precise results, may be very impressive, but what is really important are the decisions and actions that will be taken afterwards.

Quality assurance

The concept of quality assurance, involving quality control and proficiency testing, refers primarily to activities which involve measurements. Although these concepts have been more often considered in connection with analytical laboratories, their scope has to be extended to also encompass sampling and measurements.

Whenever sampling and analysis are required, the complete procedure should be considered as one, from the point of view of quality. Since no chain is stronger than the weakest link, it is a waste of resources to use, for the different steps of a same evaluation procedure, instruments and techniques of unequal levels of quality. The accuracy and precision of a very good analytical balance cannot compensate for a pump sampling at a wrong flowrate.

The performance of laboratories has to be checked so that the sources of errors can be identified and corrected. There is need for a systematic approach in order to keep the numerous details involved under control. It is important to establish quality assurance programmes for occupational hygiene laboratories, and this refers both to internal quality control and to external quality assessments (often called “proficiency testing”).

Concerning sampling, or measurements with direct-reading instruments (including for measurement of physical agents), quality involves adequate and correct:

  • preliminary studies including the identification of possible hazards and the factors required for the design of the strategy
  • design of the sampling (or measurement) strategy
  • selection and utilization of methodologies and equipment for sampling or measurements, accounting both for the purpose of the investigation and for quality requirements
  • performance of the procedures, including time monitoring
  • handling, transport and storage of samples (if the case).


Concerning the analytical laboratory, quality involves adequate and correct:

  • design and installation of the facilities
  • selection and utilization of validated analytical methods (or, if necessary, validation of analytical methods)
  • selection and installation of instrumentation
  • adequate supplies (reagents, reference samples, etc.).


For both, it is indispensable to have:

  • clear protocols, procedures and written instructions
  • routine calibration and maintenance of the equipment
  • training and motivation of the staff to adequately perform the required procedures
  • adequate management
  • internal quality control
  • external quality assessment or proficiency testing (if applicable).


Furthermore, it is essential to have a correct treatment of the obtained data and interpretation of results, as well as accurate reporting and record keeping.

Laboratory accreditation, defined by CEN (EN 45001) as “formal recognition that a testing laboratory is competent to carry out specific tests or specific types of tests” is a very important control tool and should be promoted. It should cover both the sampling and the analytical procedures.

Programme evaluation

The concept of quality must be applied to all steps of occupational hygiene practice, from the recognition of hazards to the implementation of hazard prevention and control programmes. With this in mind, occupational hygiene programmes and services must be periodically and critically evaluated, aiming at continuous improvement.

Concluding Remarks

Occupational hygiene is essential for the protection of workers’ health and the environment. Its practice involves many steps, which are interlinked and which have no meaning by themselves but must be integrated into a comprehensive approach.



All new buildings and civil engineering structures go through the same cycle of conception or design, groundworks, building or erection (including the roof of a building), finishing and provision of utilities and final commissioning before being brought into use. In the course of years, those once new buildings or structures require maintenance including re-painting and cleaning; they are likely to be renovated by being updated or changed or repaired to correct damage by weather or accident; and finally they will need to be demolished to make way for a more modern facility or because their use is no longer required. This is true of houses; it is also true of large, complex structures like power stations and bridges. Each stage in the life of a building or civil engineering structure presents hazards, some of which are common to all work in construction (like the risk from falls) or unique to the particular type of project (such as the risk from collapse of excavations during preparation of foundations in either building or civil engineering).

For each type of project (and, indeed, each stage within a project) it is possible to forecast what will be the principal hazards to the safety of construction workers. The risk from falls is common to all construction projects, even those at ground level. This is supported by the evidence of accident data which show that up to half of fatal accidents to construction workers involve falls.

New Facilities

Conception (design)

Physical hazards to those engaged in design of new facilities normally arise from visits by professional staff to carry out surveys. Visits by unaccompanied staff to unknown or abandoned sites may expose them to risks from dangerous access, unguarded openings and excavations and, in a building, to electrical wiring and equipment in a dangerous condition. If the survey requires entry into rooms or excavations that have been closed for some time, there is the risk of being overcome by carbon dioxide or reduced oxygen levels. All hazards are increased if visits are made to an unlit site after dark or if the lone visitor has no means of communicating with others and summoning aid. As a general rule, professional staff should not be required to visit sites where they will be on their own. They should not visit after dark unless the site is well lit. They should not enter enclosed spaces unless these have been tested and shown to be safe. Lastly, they should be in communication with their base or have an effective means of getting help.

Conception or design proper should play an important part in influencing safety when contractors are actually working onsite. Designers, be they architects or civil engineers, should be expected to be more than mere producers of drawings. In creating their design, they should, by reason of their training and experience, have some idea how contractors are likely to have to work in putting the design into effect. Their competence should be such that they are able to identify to contractors the hazards that will arise from those methods of working. Designers should try to “design out” hazards arising from their design, making the structure more “buildable” as regards health and safety and, where possible, substituting safer materials in the specifications. They should improve access for maintenance at the design stage and reduce the need for maintenance workers to be put at risk by incorporating features or materials that will require less frequent attention during the life of the building.

In general, designers are able to design out hazards only to a limited extent; there will usually be significant residual risks that the contractors will have to take into account when devising their own safe systems of work. Designers should provide contractors with information on these hazards so that the latter are able to take both the hazards and necessary safety procedures into account, firstly when tendering for the job, and secondly when developing their systems of work to do the job safely.

The importance of specifying materials with better health and safety properties tends to be underestimated when considering safety by design. Designers and specifiers should consider whether materials are available with better toxic or structural properties or that can be used or maintained more safely. This requires designers to think about the materials that will be used and to decide whether following previous practice will adequately protect construction workers. Often cost is the determining factor in choice of materials. However, clients and designers should realize that while materials with better toxic or structural properties may have a higher initial cost, they often yield much bigger savings over the life of the building because construction and maintenance workers require less expensive access or protective equipment.


Usually the first job to be done on the site after site surveys and laying out of the site once the contract has been awarded (assuming there is no need for demolition or site clearance) is groundworks for the foundations. In the case of domestic housing, the footings are unlikely to require excavations greater than half a metre and may be dug by hand. For blocks of flats, commercial and industrial buildings and some civil engineering, the foundations may need to be several metres below ground level. This will require the digging of trenches in which work will have to carried out to lay or erect the foundations. Trenches deeper than 1 m are likely to be dug using machines such as excavators. Excavations are also dug to permit laying of cables and pipes. Contractors often use special-purpose excavators capable of digging deep but narrow excavations. If workers have to enter these excavations, the hazards are essentially the same as those encountered in excavations for foundations. However, there is usually more scope in cable and pipe excavations or trenches to adopt methods of working that do not require workers to enter the excavation.

Work in excavations deeper then 1 m needs especially careful planning and supervision. The hazard is the risk of being struck by earth and debris as the ground collapses along the side of the excavation. Ground is notoriously unpredictable; what looks firm can be caused to slip by rain, frost or vibration from other construction activities nearby. What looks like firm, stiff clay dries out and cracks when exposed to the air or will soften and slip after rain. A cubic metre of earth weighs more than 1 tonne; a worker struck by only a small fall of ground risks broken limbs, crushed internal organs and suffocation. Because of the vital importance to safety of selecting a suitable method of support for the sides of the excavation, before work starts, the ground should be surveyed by a person experienced in safe excavation work to establish the type and condition of the ground, especially the presence of water.

Support for trench sides

Double-sided support. It is not safe to rely on cutting or “battering” back the sides of the excavation to a safe angle. If the ground is wet sand or silt, the safe angle of batter would be as low as 5 to 10 above horizontal, and there is generally not enough room onsite for such a wide excavation. The most common method of providing safety for work in excavations is to support both sides of the trench through shoring. With double-sided support, the loads from the ground on one side are resisted by similar loads acting through struts between the opposing sides. Timber of good quality must be used to provide vertical elements of the support system, known as poling boards. Poling boards are driven into the ground as soon as excavation begins; the boards are edge to edge, and thus provide a timber wall. This is done on each side of the excavation. As the excavation is dug deeper, the poling boards are driven into the ground ahead of the excavation. When the excavation is a metre deep, a row of horizontal boards (known as walings or wales) is placed against the poling boards and then held in position by timber or metal struts wedged between the opposing walings at regular intervals. As digging proceeds, the poling boards are driven further into the ground with their walings and struts, and it will be necessary to create a second row of walings and struts if the excavation is deeper than 1.2 m. Indeed, an excavation of 6 m could require up to four rows of walings.

The standard timber methods of support are unsuitable if the excavation is deeper than 6 m or the ground is water bearing. In these situations, other types of support for the sides of excavations are required, such as vertical steel trench sheets, closely spaced with horizontal timber walings and metal adjustable struts, or full-scale steel sheet piling. Both methods have the advantage that the trench sheets or sheet piles can be driven by machine before excavation proper starts. Also, trench sheets and sheet piles can be withdrawn at the end of the job and re-used. Support systems for excavations deeper than 6 m or in water-bearing ground should be custom designed; standard solutions will not be adequate.

Single-sided support. An excavation that is rectangular in shape and too large for the support methods described above to be practicable may have one or more of its sides supported by a row of poling boards or trench sheets. These are themselves supported first by one or more rows of horizontal walings which are themselves then held in place by angled rakes back to a strong anchorage or support point.

Other systems. It is possible to use manufactured steel boxes of adjustable width that may be lowered into excavations and within which work can be carried out safely. It is also possible to use proprietary waling frame systems, whereby a horizontal frame is lowered into the excavation between the poling boards or trench sheets; the waling frame is forced apart and applies pressure to keep the poling boards upright by the action of hydraulic struts across the frame which can be pumped from a position of safety outside the excavation.

Training and supervision. Whatever method of support is adopted, the work should be carried out by trained workers under supervision of an experienced person. The excavation and its supports should be inspected each day and after each occasion that they have been damaged or displaced (e.g., after a heavy rain). The only assumption one is entitled to make regarding safety and work in excavations is that all ground is liable to fail and therefore no work should ever be carried out with workers in an unsupported excavation deeper than 1 m. See also the article “Trenching” in this chapter.


Erection of the main part of the building or civil engineering structure (the superstructure) takes place after completion of the foundation. This part of the project usually requires work at heights above ground. The biggest single cause of fatal and major injury accidents is falls from heights or on the same level.

Ladder work

Even if the job is simply building a house, the number of workers involved, the amount of building materials to be handled and, in later stages, the heights at which work will have to be carried out all require more than simple ladders for access and safe places of work.

There are limitations on the sort of work that can be done safely from ladders. Work more than 10 m above ground is usually beyond the safe reach of ladders; lengthy ladders themselves become dangerous to handle. There are limitations on the reach of workers on ladders as well as on the amount of equipment and materials they can safely carry; the physical strain of standing on ladder rungs limits the time they can spend on such work. Ladders are useful for carrying out short-duration, light-weight work within safe reach of the ladder; typically, inspection and repair and painting of small areas of the building’s surface. Ladders also provide access in scaffolds, in excavations and in structures where more permanent access has not yet been provided.

It will be necessary to use temporary working platforms, the most common of which is scaffolding. If the job is a multi-storey block of flats, office building or structure like a bridge, then scaffolding of varying degrees of complexity will be required, depending on the scale of the job.


Scaffolds consist of easily assembled frameworks of steel or timber on which working platforms may be placed. Scaffolds may be fixed or mobile. Fixed scaffolds—that is, those erected alongside a building or structure—are either independent or putlog. The independent scaffold has uprights or standards along both sides of its platforms and is capable of remaining upright without support from the building. The putlog scaffold has standards along the outer edges of its working platforms, but the inner side is supported by the building itself, with parts of the scaffold frame, the putlogs, having flattened ends that are placed between courses of brickwork to gain support. Even the independent scaffold needs to be rigidly “tied” or secured to the structure at regular intervals if there are working platforms above 6 m or if the scaffold is sheeted for weather protection, thus increasing wind-loadings.

Working platforms on scaffolds consist of good-quality timber boards laid so that they are level and both ends are properly supported; intervening supports will be necessary if the timber is liable to sag due to loading by people or materials. Platforms should never be less than 600 mm in width if used for access and working or 800 mm if used also for materials. Where there is a risk of falling more than 2 m, the outer edge and ends of a working platform should be protected by a rigid guard rail, secured to the standards at a height of between 0.91 and 1.15 m above the platform. To prevent materials falling off the platform, a toe board rising at least 150 mm above the platform should be provided along its outer edge, again secured to the standards. If guard rails and toe-boards have to be removed to permit passage of materials, they should be replaced as soon as possible.

Scaffold standards should be upright and properly supported at their bases on base plates, and if necessary on timber. Access within fixed scaffolds from one working platform level to another is usually by means of ladders. These should be properly maintained, secured at top and bottom and extend at least 1.05 m above the platform.

The principal hazards in the use of scaffolds—falls of person or materials—usually arise from shortcomings either in the way the scaffold is first erected (e.g., a piece such as a guard rail is missing) or in the way it is misused (e.g., by being overloaded) or adapted during the course of the job for some purpose that is unsuitable (e.g., sheeting for weather protection is added without adequate ties to the building). Timber boards for scaffold platforms become displaced or break; ladders are not secured at top and bottom. The list of things that can go wrong if scaffolds are not erected by experienced persons under proper supervision is almost limitless. Scaffolders are themselves particularly at risk from falls during erection and dismantling of scaffolds, because they are often obliged to work at heights, in exposed positions without proper working platforms (see figure 1).

Figure 1.  Assembling scaffolding at a Geneva, Switzerland, construction site without adequate protection.


Tower scaffolds. Tower scaffolds are either fixed or mobile, with a working platform on top and an access ladder inside the tower frame. The mobile tower scaffold is on wheels. Such towers easily become unstable and should be subject to height limitations; for the fixed tower scaffold the height should not be more than 3.5 times the shortest base dimension; for mobile, the ratio is reduced to 3 times. The stability of tower scaffolds should be increased by use of outriggers. Workers should not be permitted on the top of mobile tower scaffolds while the scaffold is being moved or without the wheels being locked.

The principal hazard with tower scaffolds is overturning, throwing people off the platform; this may be due to the tower being too tall for its base, failure to use outriggers or lock wheels or unsuitable use of the scaffold, perhaps by overloading it.

Slung and suspended scaffolds. The other main category of scaffold is those that are slung or suspended. The slung scaffold is essentially a working platform hung by wire ropes or scaffold tubes from an overhead structure like a bridge. The suspended scaffold is again a working platform or cradle, suspended by wire ropes, but in this case it is capable of being raised and lowered. It is often provided for maintenance and painting contractors, sometimes as part of the equipment of the finished building.

In either case, the building or structure must be capable of supporting the slung or suspended platform, the suspension arrangements must be strong enough and the platform itself should be sufficiently robust to carry the intended load of people and materials with guard sides or rails to prevent them from falling out. For the suspended platform, there should be at least three turns of rope on the winch drums at the lowest position of the platform. Where there are no arrangements to prevent the suspended platform from falling in the event of failure of a rope, workers using the platform should wear a safety harness and rope attached to a secure anchorage point on the building. Persons using such platforms should be trained and experienced in their use.

The principal hazard with slung or suspended scaffolds is failure of the supporting arrangements, either of the structure itself or the ropes or tubes from which the platform is hung. This can arise from incorrect erection or installation of the slung or suspended scaffold or from overloading or other misuse. Failure of suspended scaffolds has resulted in multiple fatalities and can endanger the public.

All scaffolds and ladders should be inspected by a competent person at least weekly and before being used again after weather conditions that may have damaged them. Ladders which have cracked styles or broken rungs should not be used. Scaffolders who erect and dismantle scaffolds should be given specific training and experience to ensure their own safety and the safety of others who may use the scaffolds. Scaffolds are often provided by one, perhaps the main, contractor for use by all contractors. In this situation, tradespeople may modify or displace parts of scaffolds to make their own job easier, without restoring the scaffold afterwards or realizing the hazard they have created. It is important that the arrangements for coordination of health and safety across the site deal effectively with the action of one trade on the safety of another.

Powered access equipment

On some jobs, during both construction and maintenance, it may be more practicable to use powered access equipment than scaffolding in its various forms. Providing access to the underside of a factory roof undergoing recladding or access to the outside of a few windows in a building may be safer and cheaper than scaffolding out the whole structure. Powered access equipment comes in a variety of forms from manufacturers, for example, platforms that may be raised and lowered vertically by hydraulic action or the opening and closing of scissor jacks and hydraulically-powered articulated arms with a working platform or cage on the end of the arm, commonly called cherry pickers. Such equipment is generally mobile and can be moved to the place it is required and brought into use in a matter of moments. Safe use of powered access equipment requires that the job be within the specification for the machine as described by the manufacturer (i.e., the equipment must not overreach or be overloaded).

Powered access equipment requires a firm, level floor on which to operate; it may be necessary to put out outriggers to ensure that the machine does not tip over. Workers on the working platform should have access to operating controls. Workers should be trained in safe use of such equipment. Properly operated and maintained, powered access equipment can provide safe access where it may be virtually impossible to provide scaffolding, for example, during the early stages of erection of a steel frame or to provide access for steel erectors to the connecting points between columns and beams.

Steel erection

The superstructure of both buildings and civil engineering structures often involves erection of substantial steel frames, sometimes of great height. While responsibility for ensuring safe access for steel erectors who assemble these frames rests principally with the management of steel erection contractors, their difficult job can be made easier by the designers of the steel work. Designers should ensure that patterns of bolt holes are simple and facilitate easy insertion of bolts; the pattern of joints and bolt holes should be as uniform as possible throughout the frame; rests or perches should be provided on columns at joints with beams, so that the ends of beams may rest still while steel erectors are inserting bolts. As far as possible, the design should ensure that access stairs form part of the early frame so that steel erectors have to rely less on ladders and beams for access.

Also, the design should provide for holes to be drilled in suitable places in the columns during fabrication and before the steel is delivered to site, which will permit securing of taut wire ropes, to which steel erectors wearing safety harnesses may secure their running lines. The aim should be to get floor plates in place in steel frames as soon as possible, to reduce the amount of time that steel erectors have to rely on safety lines and harnesses or ladders. If the steel frame has to remain open and without floors while erection continues to higher levels, then safety nets should be slung below the various working levels. As far as possible, the design of the steel frame and the working practices of the steel erectors should minimize the extent to which workers have to “walk steel”.


While raising the walls is an important and hazardous stage in erecting a building, putting the roof in place is equally important and presents special hazards. Roofs are either flat or pitched. With flat roofs the principal hazard is of persons or materials falling either over the edge or down openings in the roof. Flat roofs are usually constructed either from wood or cast concrete, or slabs. Flat roofs must be sealed against entry of water, and various materials are used, including bitumen and felt. All materials required for the roof have to be raised to the required level, which may require goods hoists or cranes if the building is tall or the quantities of covering and sealant are substantial. Bitumen may have to be heated to assist spreading and sealing; this may involve taking on to the roof a gas cylinder and melting pot. Roof-workers and persons beneath can be burned by the heated bitumen and fires can be started involving the roof structure.

The hazard from falls can be prevented on flat roofs by erecting temporary edge protection in the form of guard rails of dimensions similar to the guard rails in scaffolds. If the building is still surrounded by external scaffolding, this can be extended up to roof level, to provide edge protection for roof-workers. Falls down openings in flat roofs can be prevented by covering them or, if they have to remain open, by erecting guard rails round them.

Pitched roofs are most commonly found on houses and smaller buildings. The pitch of the roof is achieved by erecting a wooden frame to which the outer covering of the roof, usually clay or concrete tiles, is attached. The pitch of the roof may exceed 45 above horizontal, but even a shallower pitch presents hazards when wet. To prevent roof-workers from falling while fixing battens, felt and tiles, roof ladders should be used. If the roof ladder cannot be secured or supported at its bottom end, it should have a properly designed ridge-iron that will hook over the ridge tiles. Where there is doubt about the strength of ridge tiles, the ladder should be secured by means of a rope from its top rung, over the ridge tiles and down to a strong anchorage point.

Fragile roofing materials are used on both pitched and curved or barrel roofs. Some roof lights are made of fragile materials. Typical materials include sheets of asbestos cement, plastic, treated chipboard and wood-wool. Because roof-workers frequently step through sheets they have just laid, safe access to where the sheets are to be laid, and a safe position from which to do it, are required. This is usually in the form of a series of roof ladders. Fragile roofing materials present an even greater hazard to maintenance workers, who may be unaware of their fragile nature. Designers and architects can improve the safety of roof-workers by not specifying fragile materials in the first place.

Laying of roofs, even flat roofs, can be dangerous in high winds or heavy rain. Materials such as sheets, normally safe to handle, become dangerous in such weather. Unsafe roof-work not only endangers roof-workers, but also presents hazards to the public beneath. Erection of new roofs is hazardous, but, if anything, maintenance of roofs is even more dangerous.


Renovation includes both maintenance of the structure and changes to it during its life. Maintenance (including cleaning and repainting of woodwork or other exterior surfaces, repointing of cement and repairs to walls and the roof) presents hazards from falling similar to those of erection of the structure because of the need to gain access to high parts of the structure. Indeed, the hazards may be greater because during smaller, short-duration maintenance jobs, there is a temptation to cut costs on provision of safe access equipment, for example, by trying to do from a ladder what can be safely done only from a scaffold. This is especially true of roof work, where replacement of a tile may take only minutes but there is still the possibility of a worker falling to his or her death.

Maintenance and cleaning

Designers, especially architects, can improve safety for maintenance and cleaning workers by taking into account in their designs and specifications the need for safe access to roofs, to plant rooms, to windows and to other exposed positions on the outside of the structure. Avoiding the need for access at all is the best solution, followed next by permanent safe access as part of the structure, perhaps stairs or a walkway with guard rails or a powered access platform permanently slung from the roof. The least satisfactory situation for maintenance personnel is where a scaffold similar to that used to erect the building is the only way to provide safe access. This will be less of a problem for major, longer duration renovation work, but on short-duration jobs, the cost of full scaffolding is such that there is a temptation to cut corners and use mobile powered access equipment or tower scaffolds where they are unsuitable or inadequate.

If renovation involves major re-cladding of the building or wholesale cleaning using high-pressure water jetting or chemicals, total scaffolding may be the only answer that will not only protect the workers but also allow the hanging of sheeting to protect the public nearby. Protection of workers involved in cleaning using high-pressure water jets includes impervious clothing, boots and gloves, and a face screen or goggles to protect the eyes. Cleaning involving chemicals such as acids will require similar but acid-resistant protective clothing. If abrasives are used to clean the structure a silica-free substance should be used. Since use of abrasives will give rise to dust that may be injurious, approved respiratory equipment should be worn by the workers. Repainting of windows in a tall office building or block of flats cannot be done safely from ladders, although this is usually possible on domestic housing. It will be necessary to provide either scaffolding or to hang suspended scaffolds such as cradles from the roof, ensuring that suspension points are adequate.

Maintenance and cleaning of civil engineering structures, like bridges, tall chimneys or masts may involve working at such heights or in such positions (e.g., above water) that prohibit the erection of a normal scaffold. As far as possible, work should be done from a fixed scaffold slung or cantilevered from the structure. Where this is not possible, work should be done from a properly suspended cradle. Modern bridges often have their own cradles as parts of the permanent structure; these should be checked fully before being used for a maintenance job. Civil engineering structures are often exposed to the weather, and work should not be permitted in high winds or heavy rain.

Window cleaning

Window cleaning presents its own hazards, especially where it is done from the ground on ladders, or with improvised arrangements for access on taller buildings. Window cleaning is not usually regarded as part of the construction process, and yet is a widespread operation that can endanger both the window cleaners and the public. Safety in window cleaning is, however, influenced by one part of the construction process-design. If architects fail to take into account the need for safe access, or alternatively to specify windows of a design that can be cleaned from inside, then the job of the window cleaning contractor will be much more hazardous. Whilst designing out the need for external window cleaning or installing proper access equipment as part of the original design may initially cost more, there should be considerable savings over the life of the building in maintenance costs and a reduction in hazards.


Refurbishment is an important and hazardous aspect of renovation. It takes place when for example, the essential structure of the building or bridge is left in place but other parts are repaired or replaced. Typically in domestic housing, refurbishment involves stripping out windows, possibly floors and stairs, along with wiring and plumbing, and replacing them with new and usually upgraded items. In a commercial office building, refurbishment involves windows and possibly floors, but also is likely to involve stripping out and replacing cladding to a framed building, installing new heating and ventilation equipment and lifts or total rewiring.

In civil engineering structures such as bridges, refurbishment may involve stripping the structure back to its basic frame, strengthening it, renewing parts and replacing the roadway and any cladding.

Refurbishment presents the usual hazards to construction workers: falling and falling materials. The hazard is made more difficult to control where the premises remain occupied during refurbishment, as is often the case in domestic premises such as blocks of flats, when alternative accommodations to house occupants are simply not available. In that situation the occupants, especially children, face the same hazards as construction workers. There may be hazards from power cables to portable tools such as saws and drills required during refurbishment. It is important that the work be carefully planned to minimize hazards to both workers and the public; the latter need to know what will be going on and when. Access to rooms, stairs or balconies where work is to be carried out should be prevented. Entrances to blocks of flats may have to be protected by fans to protect persons from falling materials. At the close of the working shift, ladders and scaffolds should be removed or closed off in a manner that does not allow children to get onto them and endanger themselves. Similarly, paints, gas cylinders and power tools should be removed or stored safely.

In occupied commercial buildings where services are being refurbished, it should not be possible for liftway doors to be opened. If refurbishment interferes with fire and emergency equipment, special arrangements need to be made to warn both occupants and workers if fire breaks out. Refurbishment of both domestic and commercial premises may require removal of asbestos-containing materials. This presents major health risks to the workers and the occupants when they return. Such asbestos removal should be carried out only by specially trained and equipped contractors. The area where asbestos is being removed will need to be sealed off from other parts of the building. Before the occupants return to areas from which asbestos has been stripped, the atmosphere in those rooms should be monitored and the results evaluated to ensure that asbestos fibre levels in air are below permissible levels.

Usually the safest way to carry out refurbishment is to totally exclude occupants and members of the public; however, this is sometimes simply not practicable.


Provision of utilities in buildings, such as electricity, gas, water and telecommunications, is usually carried out by specialist subcontractors. Principal hazards are falls due to poor access, dust and fumes from drilling and cutting and electric shock or fire from electrical and gas services. The hazards are the same in houses, only on a smaller scale. The job is easier for contractors if proper allowance has been made by the architect in designing the structure to accommodate the utilities. They require space for ducts and channels in walls and floors plus sufficient additional space for installers to operate effectively and safely. Similar considerations apply to maintenance of utilities after the building has been taken into use. Proper attention to the detailing of ducts, channels and openings in the initial design of the structure should mean that these are either cast or built into the structure. It will then not be necessary for construction workers to chase out channels and ducts or to open up holes using power tools, which create large quantities of harmful dust. If adequate space is provided for heating and air conditioning ducts and equipment, the job of the installers is both easier and safer because it is then possible to work from safe positions rather than, for example, standing on boards wedged across the inside of vertical ducts. If lighting and wiring have to be installed overhead in rooms with high ceilings, contractors may need scaffolding or tower scaffolds in addition to ladders.

Installation of utility services should be conform to recognized local standards. These should, for example, cover all safety aspects of electrical and gas installations so that contractors are in no doubt as to standards required for wiring, insulation, earthing (grounding), fusing, isolation and, for gas, protection for pipework, isolation, adequate ventilation and fitting of safety devices for flame failure and loss of pressure. Failure by contractors to deal adequately with these matters of detail in the installation or maintenance of utilities will create hazards for both their own workers and the occupants of the building.

Interior finishing

If the structure is of brick or concrete, the interior finish may require initial plastering to provide a surface which can be painted. Plastering is a traditional craft trade. The principal hazards are severe strain to the back and arms from handling bagged material and plaster boards and then the actual plastering process, especially when the plasterer is working overhead. After plastering, surfaces may be painted. The hazard here is from vapours given off by thinners or solvents and sometimes from the paint itself. If possible, water-based paints should be used. If solvent-based paints have to be used, the rooms should be well ventilated, if necessary by the use of fans. If materials used are toxic and adequate ventilation cannot be achieved, then respiratory and other personal protection should be worn.

Sometimes interior finishing may require the fixing of cladding or linings to the walls. If this involves use of cartridge guns to secure the panels to timber studding the hazard will principally arise from the way the gun is operated. Cartridge-driven nails can easily be fired through walls and partitions or can ricochet on striking something hard. Contractors need to plan this work carefully, if necessary excluding other persons from the vicinity.

Finishing may require tiles or slabs of various materials to be fixed to walls and floors. Cutting large quantities of ceramic tiles or stone slabs using powered cutters gives rise to great quantities of dust and should either be done wet or in an enclosed area. The principal hazard with tiles, including carpet tiles, arises from the need to stick them in position. Adhesives used are solvent based and give off vapours that are harmful, and in an enclosed space they can be flammable. Unfortunately, those laying tiles are kneeling down low over the point where vapours are given off. Water-based adhesives should be used. Where solvent-based adhesives have to be used, rooms should be well ventilated (fan assisted), the quantity of adhesives brought into the workroom should be kept to a minimum and drums should be decanted into smaller tins used by tilers outside the workroom.

If finishing requires installations of sound- or heat-insulation materials, as is often the case in blocks of flats and commercial buildings, these may be in the form of sheets or slabs that are cut, blocks that are laid and fixed together or to a surface by a cement or in a wet form that is sprayed. Hazards include exposure to dust that may both irritate and be harmful. Asbestos-containing materials should not be used. If artificial mineral fibres are used, respiratory protection and protective clothing should be worn to prevent skin irritation.

Fire hazards in interior finishing

Many of the finishing operations in a building involve use of materials that greatly increase the fire hazard. The basic structure may be relatively non-flammable steel, concrete and brick. However, the finishing trades introduce wood, possibly paper, paints and solvents.

At the same time that interior finishing is being performed work may be going on nearby using electric powered tools, or the electrical services may be being installed. Nearly always there is a source of ignition for flammable vapour and materials used in finishing. Many very costly fires have been ignited during finishing, putting workers at risk and usually damaging not only the finishing of the building but also its main structure. A building undergoing finishing is an enclosure in which possibly hundreds of workers are using flammable materials. The main contractor should ensure that proper arrangements are made to provide and protect means of escape, keep access routes clear from obstructions, reduce the quantity of flammable materials stored and in use inside the building, warn contractors of fire and, when necessary, evacuate the building.

Exterior finishing

Some of the materials used in internal finishing may also be used on the exterior, but exterior finishing is generally concerned with cladding, sealing and painting. The cement courses in brick and block work are generally “pointed” or finished as the bricks or blocks are laid and require no further attention. The exterior of walls may be cement that is to be painted or have an application of a layer of small stones, as in stucco or roughcast. Exterior finishing, like general construction work, is done outdoors and is subject to the effects of the weather. By far the greatest hazard is the risk of falling, often heightened by difficulties in handling components and materials. Use of paints, sealants and adhesives containing solvents is less of a problem than in internal finishing because natural ventilation prevents a build-up of harmful or flammable concentrations of vapour.

Again, designers can influence the safety of exterior finishing by specifying cladding panels that can be safely handled (i.e., not too heavy or large) and making arrangements so that cladding can be done from safe positions. The frames or floors of the building should be designed to incorporate features like lugs or recesses that permit easy landing of cladding panels, especially when placed in position by crane or hoist. Specification of materials such as plastics for window frames and fascias eliminates the need for painting and repainting and reduces subsequent maintenance. This benefits the safety of both construction workers and the occupants of house or flat.


Landscaping on a large scale may involve earth-moving similar to that involved in highway and canal works. It may require deep excavations to install drains; extensive areas may have to be slabbed or concreted; rocks may have to be moved. Finally, the client may wish to create the impression of a mature, well-established development, so that fully grown trees will be planted. All of this requires excavation, digging and loading. It often also requires considerable lifting capacity.

Landscape contractors are usually specialists who do not spend much of their time working as part of construction contracts. The main contractor should ensure that landscape contractors are brought to the site at an appropriate time (not necessarily towards the end of the contract). Major excavation and pipe laying may best be carried out early in the life of the project, when similar work is being done for the foundations of the building. Landscaping must not undermine or endanger the building or overload the structure by heaping earth on or against it and its outbuildings in a dangerous manner. If topsoil is to be removed and later placed back in position, sufficient space to heap it in a safe manner will have to be provided.

Landscaping may also be required at industrial premises and public utilities for safety and environmental reasons. Around a petrochemical plant it may be necessary to level off the ground or provide a particular direction of slope, possibly covering the ground with stone chips or concrete to prevent the growth of vegetation. On the other hand, if landscaping around industrial premises is intended to improve appearance or environmental reasons (e.g., to reduce noise or hide an unsightly plant), it may require embankments and erection of screens or planting of trees. Highways and railroad tracks today have to include features that will reduce noise if they are near urban areas or hide the operations if they are in environmentally sensitive areas. Landscaping is not just an afterthought, because as well as improving the appearance of the building or plant, it may, depending on the nature of the development, preserve the environment and improve safety generally. Therefore, it needs to be designed and planned as an integral part of the project.


Demolition is perhaps the most dangerous construction operation. It has all the hazards of working at heights and being struck by falling materials, but it is carried out in a structure that has been weakened either as part of the demolition, or as the result of storms, damage produced by flood, fire, explosions or simple wear and tear. The hazards during demolition are falls, being struck or buried in falling material or by the unintentional collapse of the structure, noise and dust. One of the practical problems with ensuring health and safety during demolition is that it can proceed very rapidly; with modern equipment a great deal can be demolished in a couple of days.

There are three principal ways of demolishing a structure: take it down piecemeal; knock it or push it down; or blast it down using explosives. Choice of method is dictated by the condition of the structure, its surroundings, the reasons for the demolition and cost. Use of explosives will usually not be possible when other buildings are close by. Demolition needs to be planned as carefully as any other construction process. The structure to be demolished should be thoroughly surveyed and any drawings obtained, so that as much information as possible on the nature of the structure, its method of construction and materials is available to the demolition contractor. Asbestos is commonly found in buildings and other structures that are to be demolished and requires contractors who are specialists in handling it.

Planning of the demolition process should ensure that the structure is not overloaded or unevenly loaded with debris and that there are suitable openings for chuting of debris for safe removal. If the structure is to be weakened by cutting parts of the frame (especially reinforced concrete or other highly stressed types of structure) or by removing parts of a building such as floors or internal walls, this must not so weaken the structure that it may collapse unexpectedly. Debris and scrap materials should be planned to fall in such a way that they can be removed or saved safely and appropriately; sometimes the cost of a demolition job depends on salvaging valuable scrap or components.

If the structure is to be demolished piecemeal (i.e., taken down bit by bit), without using remotely operated powered picks and cutters, workers will inevitably have to do the job using hand tools or hand-held powered tools. This means they may have to work at heights on exposed faces or above openings created to allow debris to fall. Accordingly, temporary scaffold working platforms will be necessary. The stability of such scaffolds should not be endangered by removal of parts of the structure or fall of debris. If stairs are no longer available for use by workers because the stairwell opening is being used to chute debris external ladders or scaffolds will be necessary.

Removal of points, spires or other tall features on the top of buildings is sometimes done most safely by workers operating from properly-designed buckets slung from the safety hook of a crane.

In piecemeal demolition, the safest method is to take the building down in a sequence opposite to the way it was put up. Debris should be removed regularly so that working places and access do not become obstructed.

If the structure is to be pushed or pulled over or knocked down, it is usually pre-weakened, with the attendant hazards. Pulling down is sometimes done by removing floors and internal walls, attaching wire ropes to strong points on the upper parts of the building and using an excavator or other heavy machine to pull on the wire rope. There is a real hazard from flying wire ropes if they break due to overload or failure of the anchorage point on the building. This technique is not suitable for very tall buildings. Pushing over, again after pre-weakening, involves use of heavy plant such as crawler-mounted grabs or pushers. The cabs of such equipment should be shielded to prevent drivers from being injured by falling debris. The site should not be allowed to become so obstructed by fallen debris as to create instability for machine used to pull or push the building down.


The most common form of demolition (and if done properly, in many ways the safest) is “balling” down, using a steel or concrete ball suspended from a hook on a crane with a jib strong enough to withstand the special strains imposed by balling. The jib is moved sideways and the ball swung against the wall to be demolished. The principal hazard is trapping the ball in the structure or debris, then trying to extricate it by raising the crane hook. This grossly overloads the crane, and either the crane cable or the jib may fail. It may be necessary for a worker to climb up to where the ball is wedged and free it. However, this should not be done if there is a risk of that part of the building collapsing on the worker. Another hazard associated with less skilled crane operators is balling too hard, so that unintended parts of the building are accidentally brought down.


Demolition using explosives can be done safely, but it must be carefully planned and carried out only by experienced workers under competent supervision. Unlike military explosives, the purpose of blasting to demolish a building is not to totally reduce the building to a heap of rubble. The safe way to do it is, after pre-weakening, to use no more explosive than will safely bring down the structure so that debris can be safely removed and scrap salvaged. Contractors carrying out blasting should survey the structure, obtain drawings and as much information as possible on its method of construction and materials. Only with this information is it possible to determine whether blasting is appropriate in the first place, where charges should be placed, how much explosive should be used, what steps may be necessary to prevent ejection of debris and what sort of separation zones will be required around the site to protect workers and the public. If there are a number of explosive charges, electrical shotfiring with detonators will usually be more practical, but electrical systems can develop faults, and on simpler jobs the use of detonator cord may be more practical and safer. Aspects of blasting that require careful preliminary planning are what is to be done if there is either a misfire or if the structure does not fall as planned and is left hanging in a dangerous state of instability. If the job is close to housing, highways or industrial developments, the people in the area should be warned; local police are usually involved in clearing the area and halting pedestrian and vehicular traffic.

Tall structures like television towers or cooling towers may be felled using explosives, providing they have been pre-weakened so that they fall safely.

Demolition workers are exposed to high noise levels because of noisy machinery and tools, falling debris or blasts from explosives. Hearing protection will usually be required. Dust is produced in large quantities as buildings are demolished. A preliminary survey should ascertain whether and where lead or asbestos are present; if possible, these should be removed before the start of the demolition. Even in the absence of such notable hazards, dust from demolition is often irritating if not actually injurious, and an approved dust mask should be worn if the work area cannot be kept wet to control the dust.

Demolition is both dirty and arduous, and a high level of welfare facilities should be provided, including toilets, washplaces, cloakrooms for both normal clothing and work clothes and a place to shelter and take meals.


Dismantling differs from demolition in that part of the structure or, more commonly, a large piece of machinery or equipment is disassembled and removed from site. For example, removal of part or the whole of a boiler from a power house in order to replace it, or replacement of a steel girder bridge span is dismantling rather than demolition. Workers involved in dismantling tend to do a great deal of oxyacetylene or gas cutting of steel work, either to remove parts of the structure or to weaken it. They may use explosives to knock over an item of equipment. They use heavy lifting machinery to remove large girders or pieces of machinery.

Generally, workers engaged in such activities face all the same hazards of falling, things falling on them, noise, dust and harmful substances that are met in demolition proper. Contractors who carry out dismantling require a sound knowledge of structures to ensure that they are taken apart in a sequence that does not cause a sudden and unexpected collapse of the main structure.

Overwater Work

Work over and alongside water as in bridge building and maintenance, in docks and sea and river defence work presents special hazards. The hazard may be increased if the water is flowing or tidal, as opposed to still; rapid water movement makes it more difficult to rescue those who fall in. Falling in water presents the hazard of drowning (in even quite shallow water if the person is injured in the fall as well as hypothermia if the water is cold and infection if it is polluted).

The first precaution is to prevent workers from falling by ensuring that there are proper walkways and workplaces with guard rails. These should not be allowed to become wet and slippery. If walkways are not possible, as perhaps in the earlier stages of steel erection, the workers should wear harnesses and ropes attached to secure anchorage points. These should be supplemented with safety nets slung beneath the work position. Ladders and grablines should be provided to assist fallen workers to climb out of the water, as, for example, at the edges of docks and sea defences. While workers are not on a properly boarded out platform with guard rails or are travelling to and from their worksite, they should wear buoyancy aids. Lifebuoys and rescue lines should be placed at regular intervals along the edge of the water.

Work in docks, river maintenance and sea defences often involves use of barges to carry piling rigs and excavators to remove dredged out spoil. Such barges are equivalent to working platforms and should have suitable guard rails, lifebuoys and rescue and grab lines. Safe access from the shore, dock or river side should be provided in the form of walkways or gangways with guard rails. This should be so arranged as to adjust safely with the changing levels of tidal water.

Rescue boats should be available, fitted with grablines and with lifebuoys and rescue lines on board. If the water is cold or flowing, the boats should be continuously staffed, and should be powered and ready to carry out a rescue mission immediately. If water is polluted with industrial effluent or sewage, arrangements should be made to transport those who fall into such water to a medical centre or hospital for immediate treatment. Water in urban areas may be contaminated with the urine of rats, which may infect open skin abrasions, causing Weil’s disease.

Work over water is often carried out in locations that are subject to strong winds, driving rain or icing conditions. These increase the risk of falls and heat loss. Severe weather may make it necessary to stop work, even in the middle of a shift; to avoid excessive heat loss it may be necessary to supplement normal wet or cold weather protective clothing with thermal underclothing.

Underwater Work


Diving is a specialized form of working underwater. The hazards faced by divers are drowning, decompression sickness (or the “bends”), hypothermia from the cold and becoming trapped below water. Diving may be required during construction or maintenance of docks, sea and river defences and at piers and abutments of bridges. It is often required in waters where visibility is poor or in locations where there is a risk of entanglement for the diver and his or her equipment. Diving may be carried out from dry land or from a boat. If the work requires only a single diver, then as a minimum a team of three will be required for safety. The team consists of the diver in the water, a fully equipped standby diver ready to enter the water immediately in the event of an emergency and a diving supervisor in charge. The diving supervisor should be at the safe position on land or in the boat from which the diving is to take place.

Diving at depths less than 50 m is usually carried out by divers wearing wet suits (i.e., suits that do not exclude water) and wearing self-contained underwater breathing apparatus with an open face mask (i.e., SCUBA diving gear). At depths greater than 50 m or in very cold water, it will be necessary for divers to wear suits that are heated by a supply of pumped warm water and closed diving masks, and equipment for breathing not compressed air but air plus a mixture of gases (i.e., mixed-gas diving). Divers must wear a suitable safety line and be able to communicate with the surface and in particular with their diving supervisor. The local emergency services should be advised by the diving contractor that diving is to take place.

Both divers and equipment require examination and testing. Divers should be trained to a recognized national or international standard, firstly and always for air diving and secondly for mixed-gas diving if this is to take place. They should be required to provide written evidence of successful completion of a diver training course. Divers should have an annual medical examination with a doctor experienced in hyperbaric medicine. Each diver should have a personal logbook in which a record of physicals and of his or her dives is kept. If a diver has been suspended from diving as a result of the physical, this also should be recorded in the logbook. A diver under suspension should not be allowed to dive or act as a standby diver. Divers should be asked by their diving supervisor if they are well, especially whether they have any respiratory illness, before being allowed to dive. Diving equipment, suits, belts, ropes, masks and cylinders and valves should be checked every day before use.

Satisfactory operation of cylinder and demand valves should be demonstrated by divers for their diving supervisor.

In the event of an accident or other reasons for the sudden ascent of a diver to the surface, he or she may experience the bends or be at risk of them and require to be recompressed. For this reason it is desirable that the whereabouts of a medical or other decompression chamber suitable for divers is located before diving starts. Those in charge of the chamber should be alerted to the fact that diving is taking place. Arrangements should be available for the rapid transport of divers requiring decompression.

Because of their training and equipment, plus all the backup required for safety, use of divers is very expensive, and yet the amount of time they are actually working on the riverbed may be limited. For these reasons there are temptations for diving contractors to use untrained or amateur divers or a diving team that is deficient in numbers and equipment. Only reputable diving contractors should be used for diving in construction, and particular care needs to be taken over the selection of divers who claim to have been trained in other countries where standards may be lower.


Caissons are rather like a large inverted saucepans whose rims sit on the bed of the harbour or river. Sometimes open caissons are used, which, as their name implies, have an open top. They are used on land to sink a shaft into soft ground. The bottom edge of the caisson is sharpened, workers excavate inside the caisson, and it sinks into the ground as soil is removed, thus creating the shaft. Similar open caissons are used in shallow water, but their depth may be extended by adding sections on top as the caisson sinks into the river or harbour bed. Open caissons rely on pumping to control the entry of water and soil into the base of the caisson. For deeper work still, a closed caisson will have to be used. Compressed air is pumped into it to displace the water, and workers are able to enter through an airlock, usually on top, and go down to work in air on that bed. Workers are able to work under water but are freed from the constraints of wearing diving equipment, and visibility is much better. The hazards in “pneumatic” caisson work are the bends and, as in all types of caisson including the simplest open caisson, drowning if water gets into the caisson through any structural failure or loss of air pressure. Because of the risk of entry of water, means of escape such as ladders up to the entry point should be available at all times in both open and pneumatic caissons.

Caissons should be inspected daily before they are used by someone competent and experienced in caisson work. Caissons may be raised and lowered as single units by heavy lifting equipment, or they may be constructed from components in the water. Construction of caissons should be under the supervision of a similarly competent person.

Tunnelling underwater

Tunnelling, when carried out in porous ground beneath water, may need to be done under compressed air. Driving tunnels for public transportation systems in city centres beneath rivers is a widespread practice, owing to lack of space above ground and environmental considerations. Compressed air working will be as limited as possible because of its danger and inefficiency.

Tunnels beneath water in porous ground will be lined with concrete or cast iron rings and grouted. But at the actual heading where the tunnel is being dug and in the short length where tunnel rings are being placed in position, there will not be a sufficiently water-tight surface for the work to proceed without some means of keeping out the water. Working under compressed air may still be used for the tunnel head and ring or segment placing part of the tunnel driving and lining process. Workers involved in driving the heading (i.e., on a TBM operating the rotating cutting head) or using hand tools, and those operating ring and segment placing equipment, will have to pass through an airlock. The rest of the now lined tunnel will not require to be compressed, and thus there will be easier transit of personnel and materials.

Tunnellers who have to work in compressed air face the same hazard of the bends as divers and caisson workers. The airlock giving access to the compressed-air workings should be supplemented by a second airlock through which workers pass at the end of the shift to be decompressed. If there is only a single airlock, this may create bottlenecks and also be dangerous. Hazards arise if workers are not decompressed sufficiently slowly at the end of their shift or if lack of airlock capacity holds up entry of vital equipment to the workings under pressure. Airlocks and decompression chambers should be under the supervision of a competent person experienced in compressed-air tunnelling and proper decompression.



Wednesday, 09 March 2011 20:47

Major Sectors

The term construction industry is used worldwide to cover what is a collection of industries with very different practices, brought together temporarily on the site of a building or civil engineering job. The scale of operations ranges from a single worker carrying out a job lasting minutes only (e.g., replacing a roof tile with equipment consisting of a hammer and nails and possibly a ladder) to vast building and civil engineering projects lasting many years that involve hundreds of different contractors, each with their own expertise, plant and equipment. However, despite the enormous variation in scale and complexity of operations, the major sectors of the construction industry have a great deal in common. There is always a client (known sometimes as the owner) and a contractor; except for the very smallest jobs, there will be a designer, either an architect or engineer, and if the project involves a range of skills, it will inevitably require additional contractors working as subcontractors to the main contractor (see also the article “Organizational factors affecting health and safety” in this chapter). While small-scale domestic or agricultural buildings may be built on the basis of an informal agreement between the client and builder, the vast majority of building and civil engineering work will be carried out under the terms of a formal contract between the client and contractor. This contract will set out details of the structure or other work that the contractor is to provide, the date by which it is to be built and the price. Contracts may contain a great deal besides the job, the time and the price, but those are the essentials.

The two broad categories of construction projects are building and civil engineering. Building applies to projects involving houses, offices, shops, factories, schools, hospitals, power and railway stations, churches and so on—all those kinds of structures that in everyday speech we describe as “buildings”. Civil engineering applies to all the other built structures in our environment, including roads, tunnels, bridges, railways, dams, canals and docks. There are structures that appear to fall into both categories; an airport involves extensive buildings as well as civil engineering in the creation of the airfield proper; a dock may involve warehouse buildings as well excavation of the dock and raising of the dock walls.

Whatever the type of structure, building and civil engineering both involve certain processes such as building or erection of the structure, its commissioning, maintenance, repair, alteration and ultimately its demolition. This cycle of processes occurs regardless of the type of structure.

Small Contractors and the Self-employed

While there are variations from country to country, construction is typically an industry of small employers. As many as 70 to 80% of contractors employ less than 20 workers. This is because many contractors start out as a single tradesperson working alone on small-scale jobs, probably domestic ones. As their business expands, such tradespeople start to employ a few workers themselves. The workload in construction is rarely consistent or predictable, as some jobs finish and others start up at different times. There is a need in the industry to be able to move groups of workers with particular skills from job to job as the work requires. Small contractors fulfil this role.

Alongside the small contractors there is a population of self-employed workers. Like agriculture, construction has a very high proportion of self-employed workers. These again are usually tradespeople, such as carpenters, painters, electricians, plumbers and bricklayers. They are able to find a place in either small-scale domestic work or as part of the workforce on bigger jobs. In the boom construction period of the late 1980s, there was an increase in workers claiming to be self-employed. This was partly because of tax incentives for the individuals concerned and use by contractors of so-called self-employed who were cheaper than employees. Contractors were not faced with the same level of social security costs, were not required to train self-employed persons and could get rid of them more easily at the end of jobs.

The presence in construction of so many small contractors and self-employed individuals tends to militate against effective management of health and safety for the job as a whole and, with such a transitory workforce, certainly makes it more difficult to provide proper safety training. Analysis of fatal accidents in the United Kingdom over a 3-year period showed that about half the fatal accidents happened to workers who had been onsite for a week or less. The first few days on any site are especially hazardous to construction workers because, however experienced they may be as tradespeople, each site is a unique experience.

Public and Private Sectors

Contractors may be part of the public sector (e.g., the works department of a city or district council) or they are part of the private sector. A considerable amount of maintenance used to be done by such public works departments, especially on housing, schools and roads. Recently there has been a move to encourage greater competition in such work, partly as a result of pressures for better value for money. This has led firstly to a reduction in the size of public works departments, even their total disappearance in some places, and to the introduction of mandatory competitive tendering. Jobs previously done by public works departments are now done by private-sector contractors under severe “lowest tender wins” conditions. In their need to cut costs, contractors may be tempted to reduce what are seen as overheads such as safety and training.

The distinction between public and private sectors may also apply to clients. Central and local government (along with transportation and public utilities if under the control of central or local government) may all be clients for construction. As such they would generally be thought to be in the public sector. Transportation and utilities run by corporations would usually be considered to be in the private sector. Whether a client is in the public sector sometimes influences attitudes towards inclusion of some items of safety or training in the cost of construction work. Recently public- and private-sector clients have been under similar constraints as regards competitive tendering.

Work across National Boundaries

An aspect of public-sector contracts of increasing importance is the need for tenders to be invited from beyond national boundaries. In the European Union, for example, large-scale contracts beyond a value set out in Directives, must be advertised within the Union so that contractors from all member countries may tender. The effect of this is to encourage contractors to work across national boundaries. They are then required to work in accordance with the local national health and safety laws. One of the aims of the European Union is to harmonize standards between member states in health and safety laws and their application. Major contractors working in parts of the world subject to similar regimes must therefore be familiar with health and safety standards in those countries where they carry out work.


In buildings, the designer is usually an architect, although on small-scale domestic housing, contractors sometime provide such design expertise as is necessary. If the building is large or complex, there may be architects dealing with design of the overall scheme as well as structural engineers concerned with design of, for example, the frame, and specialist engineers involved with design of the services. The architect for the building will ensure that sufficient space is provided in the right places in the structure to permit installation of plant and services. Specialist designers will be concerned to ensure that the plant and services are designed to operate to the required standard when installed in the structure in the places provided by the architect.

In civil engineering, the lead in design is more likely to be taken by a civil or structural engineer, although in high-profile jobs where visual impact may be an important factor, an architect may have an important role in the design team. In tunnelling, railways and highways, the lead in design is likely to be taken by structural or civil engineers.

The role of the developer is to seek to improve the utilization of land or buildings and profit from that improvement. Some developers simply sell the improved land or buildings and have no further interest; others may retain ownership of land or even buildings and reap a continuing interest in the form of rents that are greater than before the improvements.

The skill of the developer is to identify sites either as empty land or under-utilized and out-of-date buildings where application of construction skills will improve their value. The developer may use his or her own finances, but perhaps more often exercises further skills in identifying and bringing together other sources of finance. Developers are not a modern phenomenon; the expansion of cities over the last 200 years owes a great deal to developers. Developers may themselves be clients for the construction work, or they may simply act as agents for other parties who provide finance.

Types of Contract

In the traditional contract, the client arranges for a designer to prepare a full design and specifications. Contractors are then invited by the client to tender or bid for doing the job in accordance with the design. The role of the contractor is largely confined to construction proper. The contractor’s involvement in questions of design or specification is then mainly a matter of seeking such changes as will make it easier or more efficient to build—to improve “buildability”.

The other common arrangement in construction is the design and build contract. The client requires a building (perhaps an office block or shopping development) but has no firm ideas on detailed aspects of its design other than the size of site, number of persons to be accommodated or scale of activities to be carried out in it. The client then invites tenders from either designers or contractors to submit both design and construction proposals. Contractors working in design and build either have their own design organization or have close links with an external designer who will work for them on the job. Design and build may involve two stages in design: an initial stage where a designer prepares an outline scheme which is then put out to tender; and a second stage where the successful design and build contractor will then carry out further design on detailed aspects of the job.

Maintenance and emergency contracts cover a wide variety of arrangements between clients and contractors and represent a significant proportion of the work of the construction industry. They generally run for a fixed period, require the contractor to do certain types of work or to work on a “call-off” basis (i.e., work that the client calls the contractor in to do). Emergency contracts are widely used by public authorities who are responsible for providing a public service that ought not to be interrupted; government agencies, public utilities and transportation systems make wide use of them. Operators of factories, particularly those with continuous processes such as petrochemicals, also make wide use of emergency contracts to deal with problems in their facilities. Having entered such a contract, the contractor undertakes to make available suitable workers and plant to carry out the work, often at very short notice (e.g., in the case of emergency contracts). The advantage to the client is that he or she does not need to retain workers on payroll or have plant and equipment that may only occasionally be used to deal with maintenance and emergencies.

Pricing of maintenance and emergency contracts may be on the basis of a fixed sum per annum, or on the basis of time spent carrying out work, or some combination.

Perhaps the most common publicly known example of such contractors is maintenance of roads and emergency repairs to gas main or power supplies that have either failed or been accidentally damaged.

Whatever the form of contract, the same possibilities arise for clients and designers to influence the health and safety of contractors by decisions made in the early stage of the job. Design and build perhaps permits closer liaison between the designer and contractor on health and safety.


Price is always an element in a contract. It may simply be a single sum for the cost of doing the job, such as building a house. Even with a single lump sum, the client may have to pay part of the price in advance of the job starting, to enable the contractor to buy materials. The price may, however, be on a cost-plus basis, where the contractor is to recover his or her costs plus an agreed amount or percentage for profit. This arrangement tends to work to the disadvantage of the client, since there is no incentive for the contractor to keep costs down. The price may also have bonuses and penalties attached to it, so that the contractor will receive more money if, for example, the job is completed earlier than the agreed time. Whatever form the price takes for the job, it is usual for payments to be made in stages as the work progresses, either on completion of certain parts of the job by agreed dates or on the basis of some agreed method of measuring the work. At the end of construction proper, it is common for an agreed proportion of the price to be kept back by the clients until “snags” have been put right or the structure has been commissioned.

During the course of the job, the contractor may encounter problems that were not foreseen when the contract was made with the client. These might require changes to the design, the construction method or the materials. Usually such changes will create extra costs for the contractor, who then seeks to recover from the client on the basis that these items become agreed “variations” from the original contract. Sometimes recovery of the cost of variations can make the difference for the contractor between doing the job at a profit or loss.

The pricing of contracts can affect health and safety if inadequate provision is made in the contractor’s tender to cover the costs of providing safe access, lifting equipment and so on. This becomes even more difficult where, in an attempt to ensure that they obtain value for money from contractors, clients pursue a vigorous policy of competitive tendering. Governments and local authorities apply policies of competitive tendering to their own contracts, and indeed there may be laws requiring that contracts can be awarded only on the basis of competitive tendering. In such a climate, there is always a risk that the health and safety of construction workers will suffer. In cutting costs, clients may resist a reduction in the standard of construction materials and methods, but at the same time be totally unaware that in accepting the lowest tender, they have accepted working methods that are more likely to endanger construction workers. Even in a situation of competitive tendering, contractors submitting tenders should have to make clear to the client that their bid adequately covers the cost of health and safety involved in their proposals.

Developers can influence health and safety in construction in ways similar to clients, firstly by using contractors who are competent in health and safety and architects who take health and safety into account in their designs, and secondly in not automatically accepting the lowest tenders. Developers generally want to be associated only with successful developments, and one measure of success ought to be projects where there are no major health and safety problems during the construction process.

Building Standards and Planning

In the case of buildings, whether housing, commercial or industrial, projects are subject to planning laws that dictate where certain types of development may take place (e.g., that a factory may not be built among houses). Planning laws may be very specific about the appearance, materials and size of buildings. Typically areas identified as industrial zones are the only places where factory buildings may be erected.

Often there are also building regulations or similar standards that specify in precise detail many aspects of the design and specification of buildings—for example, the thickness of walls and timbers, depth of foundations, insulation characteristics, size of windows and rooms, layout of electrical wiring and earthing, layout of plumbing and pipework and many other issues. These standards have to be followed by clients, designers, specifiers and contractors. They limit their choices but at the same time ensure that buildings are built to an acceptable standard. Planning laws and building regulations thus affect the design of buildings and their cost.


Projects to build housing may consist of a single house or vast estates of individual houses or flats. The client may be each individual householder, who will then normally be responsible for maintenance of his or her own house. The contractor will usually remain responsible for correcting defects in construction for a period of months after building is finished. However, if the project is for many houses, the client may be a public body, either in local or national government, with responsibility for providing housing. There are also large private bodies like housing associations for whom numbers of houses may be built. Public or private bodies with responsibilities for providing housing generally rent the finished houses to occupants, retaining a greater or lesser degree of responsibility for maintenance also. Building projects involving blocks of flats usually have a client for the block as a whole, who then lets out individual flats under a leasing arrangement. In this situation the owner of the block has responsibility for carrying out maintenance but passes on the cost to the tenants. In some countries ownership of individual flats in a block can rest with the occupants of each flat. There has to be some arrangement, sometimes through an estate management contractor, whereby maintenance can be carried out and the necessary costs raised among the occupants.

Often houses are built on a speculative basis, by a developer. Specific clients or occupants of those houses may not have been identified at the outset but come on the scene after construction has begun and purchase or rent the property like any other article. Houses are usually fitted out with electrical, plumbing and drainage services and heating systems; a gas supply may also be laid on. Sometimes in an attempt to cut costs, houses are only partially finished, leaving it to the purchaser to install some of the fittings and to paint or decorate the building.

Commercial Buildings

Commercial buildings include offices, factories, schools, hospitals, shops—an almost endless list of different types of buildings. In most cases these buildings are constructed for a particular client. However, offices and shops are often built on a speculative basis like housing, with the hope of attracting buyers or tenants. Some clients require an office or shop to be totally fitted out to their requirements, but very often the contract is for the structure and main services, with the client making arrangements to fit out the premises using specialist contractors in office and shop fitting.

Hospitals and schools are built for clients who have a clear idea of precisely what they want, and the clients often provide design input into the project. Plant and equipment in hospitals may cost more than the structure and involve a great deal of design that has to satisfy stringent medical standards. National or local government may also play a part in the design of schools by laying down very detailed requirements on space standards and equipment as part of its wider role in education. National governments usually have very detailed standards as to what is acceptable in hospital buildings and plant. Fitting out of hospitals and similarly complex buildings is a form of construction work usually carried out by specialist subcontractors. Such contractors not only require knowledge of health and safety in construction in general, but also need expertise in ensuring that their operations do not adversely affect the hospital’s own activities.

Industrial Construction

Industrial building or construction involves use of the mass- production techniques of manufacturing industry to produce parts of buildings. The ultimate example is the house brick, but normally the expression is applied to building using concrete parts or units that are assembled onsite. Industrial construction expanded rapidly after the Second World War to meet the demand for cheap housing, and it is more commonly found in mass housing developments. Under factory conditions it is possible to mass produce cast units that are consistently accurate in a way that would be virtually impossible under normal site conditions.

Sometimes units for industrial construction are manufactured away from the construction site in factories that may supply a wide area; sometimes, where the individual development is itself very large, a factory is set up onsite to serve that sole site.

Units designed for industrial construction must be structurally strong enough to stand up to being moved, lifted and lowered; they must incorporate anchorage points, or slots to permit safe attachment of lifting tackle, and must also include appropriate lugs or recesses to permit the units to fit together both easily and strongly. Industrial construction demands plant for transporting and lifting units into position and space and arrangements to store units safely when delivered to site, so that units are not damaged and workers are not injured. This technique of building tends to produce visually unattractive buildings, but on a large scale it is cheap; a whole room can be assembled from six cast units with window and door openings in place.

Similar techniques are used to produce concrete units for civil engineering structures like elevated motorways and tunnel linings.

Turn-key Projects

Some clients for industrial or commercial buildings containing extensive complex plant wish simply to walk into a facility that will be up and running from their first day in the premises. Laboratories are sometimes constructed and fitted out on this basis. Such an arrangement is a “turn-key” project, and here the contractor will ensure that all aspects of plant and services are fully operational before handing the project over. The job may be done under a design and build contract so that, in effect, the turn-key contractor deals with everything from design to commissioning.

Civil Engineering and Heavy Construction

The civil engineering of which the public is most aware is work on highways. Some highway work is the creation of new roads on virgin land, but much of it is the extension and repair of existing highways. Contracts for highway work are usually for state or local government agencies, but sometimes roads remain under the control of contractors for some years after completion, during which time they are permitted to charge tolls. If civil engineering structures are being financed by government, then both the design and actual construction will be subject to a high degree of supervision by officials on behalf of government. Contracts for construction of highways are usually let to contractors on the basis of a contractor being responsible for a section of so many kilometres of the highway. There will be a main contractor for each section; but highway construction involves a number of skills, and aspects of the job such as steel work, concrete, shuttering and surfacing may be subcontracted by the main contractor to specialist firms. Highway construction is also sometimes carried out under management contract arrangements, where a civil engineering consultancy will provide management for the job, with all the work being done by subcontractors. Such a management contractor may also have been involved in design of the highway.

Construction of highways requires the creation of a surface whose gradients are suitable for the sort of traffic that will use it. In a generally level terrain, creation of the foundation of the highway may involve earthmoving—that is, shifting soil from cuttings to create embankments, building bridges across rivers and driving tunnels through mountainsides where it is not possible to go round the obstruction. Where labour costs are higher, such operations are carried out using mechanically powered plant such as excavators, scrapers, loaders and lorries. Where labour costs are lower, these processes may be carried out manually by large numbers of workers using hand tools. Whatever the actual methods adopted, highway construction requires high standards of route surveying and planning of the job.

Highway maintenance frequently requires roads to remain in use whilst repairs or improvements are carried out in part of the road. There is thus a hazardous interface between traffic movement and construction operations which makes good planning and management of the job even more important. There are often national standards for signage and coning off of roadworks and requirements as to the amount of separation there should be between construction and traffic, which may be difficult to achieve in a confined area. Control of traffic approaching roadworks is usually the responsibility of the local police, but requires careful liaison between them and the contractors. Highway maintenance creates traffic hold-ups, and accordingly contractors are put under pressure to finish jobs quickly; sometimes there are bonuses for finishing early and penalties for finishing late. Financial pressures must not undermine safety on what is very dangerous work.

Surfacing of highways may involve concrete, stone or tarmacadam. This requires a substantial logistical train to ensure that the required quantities of surfacing materials are in place in the right condition to ensure that surfacing proceeds without interruption. Tarmacadam requires special purpose spreading plant that keeps the surfacing material plastic while spreading it. Where the job is re-surfacing, plant will be required including picks and breakers so that the existing surface is broken up and removed. A final finish is usually applied to the surfaces of highways involving use of heavy powered rollers.

Creation of cuttings and tunnels may require use of explosives and then arrangements to shift the muck displaced by the blasting. The sides of cuttings may require permanent supports to prevent landslides or falls of ground onto the finished road.

Elevated highways often require structures similar to bridges, especially if the elevated section passes through an urban area when space is limited. Elevated highways are often constructed from cast reinforced concrete sections that are either cast in situ or cast in a fabrication area and then shifted to the required position onsite. The work will require large-capacity lifting machinery to lift cast sections, shuttering and reinforcing.

Temporary support arrangements or “falsework” to support sections of either elevated highways or bridges while they are being cast in position need to be designed to take into account the uneven loads imposed by concrete as it is poured. Design of falsework is as important as design of the structure proper.


Bridges in remote areas may be simple constructions from timber. More commonly today bridges are from reinforced concrete or steel. They may also be clad in brickwork or stone. If the bridge is to span a considerable gap, whether above water or not, its design will require specialist designers. Using today’s materials, the strength of the bridge span or arch is not achieved by mass material, which would be simply too heavy, but by skilful design. The main contractor for a bridge building job is usually a major general civil-engineering contractor with management expertise and plant. However, specialist subcontractors may deal with major aspects of the job like erection of steel work to form the span or casting or placing cast sections of the span in place. If the bridge is over water, one or both abutments that support the ends of the bridge may themselves have to be constructed in water, involving piling, coffer dams, mass concrete or stone work. A new bridge may be part of a new highway system, and approach roads may have to be built, themselves possibly elevated.

Good design is especially important in bridge building, so that the structure is strong enough to withstand the loads imposed on it in use and to ensure that it will not require maintenance or repair too frequently. The appearance of a bridge is often a very important factor, and again good design can balance the conflicting demands of sound engineering and aesthetics. Provision of safe means of access for maintenance of bridges needs to be taken into account during design.


Tunnels are a specialized form of civil engineering. They vary in size from the Channel Tunnel, with over 100 km of bores from 6 to 8 m in diameter, to mini-tunnels whose bores are too small for workers to enter and which are created by machines launched from access shafts and controlled from the surface. In urban areas, tunnels may be the only way to provide or improve transport routes or to provide water and drainage facilities. The proposed route of the tunnel requires as detailed a survey as possible to confirm the kind of ground that the tunnel workings will be in and whether there will be groundwater. The nature of the ground, the presence of groundwater and the end use of the tunnel all influence the choice of tunnelling method.

If the ground is consistent, like the chalk-clay beneath the English Channel, then machine digging may be possible. If high groundwater pressures are not encountered during pre- construction survey, then it is usually unnecessary for the workings to be pressurized to keep out the water. If working in compressed air cannot be avoided, this adds considerably to costs because airlocks have to be provided, workers need to be allowed time to decompress, and access to workings for plant and materials may be made more difficult. A large tunnel for a road or railway in consistent non-hard-rock ground might be dug using a full-face tunnel-boring machine (TBM). This is really a train of different machines linked together and moving forward on rails under its own power. The front face is a circular cutting head that rotates and feeds spoil back through the TBM. Behind the cutting head are various sections of the TBM that place the segments of tunnel lining rings in position around the surface of the tunnel, grout behind the lining rings and, in a very confined space, provide all the machinery to handle and place ring segments (each weighing some tonnes), remove spoil, bring grout and extra segments forward and house electric motors and hydraulic pumps to power the cutting head and segment-placing mechanisms.

A tunnel in non-hard-rock ground which is not consistent enough to use a TBM, may be dug using equipment such as roadheaders that bite into the face of the heading. Spoil falling from the roadheader onto the tunnel floor are to be collected by diggers and removed by lorry. This technique permits digging of tunnels that are not circular in section. The ground in which such a tunnel is dug will not usually have sufficient strength for it to remain unlined; without some form of lining there might be falls from roof and walls. The tunnel may be lined by liquid concrete sprayed onto a steel mesh held in position by rock bolts (the “New Austrian tunnelling method”) or by cast concrete.

If the tunnel is in hard rock, the heading will be dug by means of blasting, using explosives placed into shot holes drilled into the rock face. The trick here is to use the minimum of blast to achieve a fall of rock in the position and sizes required, thereby making it easier to remove the spoil. On bigger jobs, multiple drills mounted on tracked bases will be used along with diggers and loaders to remove spoil. Hard rock tunnels are often simply trimmed to provide an even surface, but are not then further lined. If the rock surface remains friable with a risk of pieces falling, then a lining will be applied, usually some form of sprayed or cast concrete.

Whatever the method of construction adopted for the tunnel, the effective supply of tunnelling materials and removal of spoil are vital to the successful progress of the job. Large tunnelling jobs may require extensive narrow-gauge construction rail systems to provide logistical support.


Dams invariably contain large quantities of earth or rock to provide mass to resist the pressure from water behind them; some dams are also covered in masonry or reinforced concrete. Depending on the length of the dam, its construction often requires earthmoving on the very largest scale. Dams tend to be built in remote locations dictated by the need to ensure that water is available at a position where it is technically possible to restrict the flow of the river. Thus temporary roads may have to be built before dam building may start in order to get plant, materials and personnel to the site. Workers on dam projects may be so far from home that full-scale living accommodations have to be provided along with the usual construction site facilities. It is necessary to divert the river away from the site of the workings, and a coffer dam and temporary riverbed may have be created.

A dam constructed simply from earth or rock that has been shifted will require large scale excavation, digging and scraping plant as well as lorries. If the dam wall is covered by masonry or cast concrete, it will be necessary to employ high or long-reach cranes capable of depositing masonry, shuttering, reinforcing and concrete in the right places. A continuous supply of good-quality concrete will be necessary, and a concrete-mixing plant will be necessary alongside the dam workings, with the concrete either handled in batches by crane or pumped to the job.

Canals and docks

Construction and repair of canals and docks contain some aspects of other jobs that have been described, such as roadworks, tunnels and bridges. It is particularly important in canal building for surveying to be to the highest standard before work begins, especially regarding levels and to ensure that material that has had to be dug out can economically be used elsewhere in the job. Indeed the early railway engineers owed a great deal to the experience of canal builders a century before. The canal will require a source for its water and will either tap into a natural source such as a river or lake or create an artificial one in the form of a reservoir. Digging of docks may start on dry land, but sooner or later has to link up to either a river, a canal, the sea or another dock.

Canal and dock building requires excavators and loaders to open up the ground. Spoil may be removed by lorry or water transport may be used. Docks are sometimes developed on ground that has a long history of industrial use. Industrial wastes may have escaped into such ground over many years, and spoil removed in digging or extending the docks will be heavily contaminated. Work in repairing a canal or dock is likely to have to be carried out while adjacent parts of the system are kept in use. The workings may have to rely on coffer dams for protection. Failure of a coffer dam during extension of Newport Docks in Wales in the early years of this century resulted in nearly 100 deaths.

Clients for canals and docks are likely to be public authorities. However, sometimes docks are constructed for corporations alongside their major production plants or for corporate clients to handle a particular type of incoming or outgoing goods (e.g., motor cars). Repair and renovation of canals is nowadays often for the leisure industry. Like dams, both canal and dock construction may be in very remote situations, requiring provision of facilities for workers beyond those of a normal construction site.


Construction of railroads or railways historically came after canals and before major highways. Clients in railway construction contracts may be rail operators themselves or governmental agencies, if the railways are financed by government. As with highways, design of a railroad that is economical and safe to build and operate depends on good surveying beforehand. In general, locomotives do not operate effectively on steep gradients, and therefore those designing layout of the track are concerned with avoiding changes in levels, going round or through obstacles rather than over them.

Designers of railroads are subject to two constraints unique to the industry: first, curves in the track layout must generally conform to very large radii (otherwise trains cannot negotiate them); second, all the structures connected with the railway—its bridge arches, tunnels and stations—must be capable of accommodating the envelope of the largest locomotives and rolling stock that will use the track. The envelope is the silhouette of the rolling stock plus clearance to allow safe passage through bridges, tunnels and so on.

Contractors involved in building and repair of railroads require the usual construction plant and effective logistical arrangements to ensure that rail track and ballast as well as construction materials are always available in what may be remote locations. Contractors may use the track they have just laid to run trains supplying the works. Contractors involved in maintenance of existing operational railways have to ensure that their work does not interfere with the operations of the railway and endanger workers or the public.


The rapid expansion of air transportation since the middle of the 20th century has resulted in one of the biggest and most complex forms of construction: the building and extension of airports.

Clients for airport construction are usually governments at the national or local level or agencies representing the government. Some airports are built for major cities. Airports are rarely for private clients such as business corporations.

Planning the work is sometimes made more difficult because of environmental constraints that have been placed on the project in relation to noise and pollution. Airports require a lot of space, and if they are located in more heavily populated areas, creation of the runways and space for terminal buildings and car parks may require reinstatement of derelict or otherwise difficult land. Building an airport involves levelling a large area, which may require earth moving and even land reclamation, and then construction of a wide variety of often very large buildings, including hangars, maintenance workshops, control towers and fuel storage facilities, as well as terminal buildings and parking.

If the airport is being built on soft ground, buildings may require piled foundations. Actual runways require good foundations; hardcore supporting the surface layers of concrete or tarmac needs to be heavily compacted. Plant used on airport construction is similar in scale and type to that used in major highway projects, except that it is concentrated within a limited area rather than over the many miles of a highway.

Airport maintenance is a particularly difficult type of work where resurfacing the runways has to be integrated with continuing operation of the airport. Usually the contractor is allowed an agreed number of hours during the night when he or she can work on a runway that is temporarily taken out of use. All the contractor’s plant, materials and workforce have to be marshalled off the runways, prepared to move immediately to the work site at the agreed start time. The contractor must finish his or her work and get off the runways again at the agreed time when flights may resume. Whilst working on the runway, the contractor must not impede or otherwise endanger aircraft movement on other runways.



Improving Occupational Health and Safety

Construction companies are increasingly adopting the quality management systems spelled out by the International Organization for Standardization (ISO), such as the ISO 9000 series and the subsequent regulations that have been based on it. Although no recommendations on occupational health and safety are specified in this set of standards, there are cogent reasons for including preventive measures when implementing a management system such as that required by the ISO 9000.

Occupational health and safety regulations are written and implemented and are continuously being adapted to technological progress as well as to new safety techniques and to advances in occupational medicine. All too often, however, they are not followed, either deliberately or out of ignorance. When this occurs, models for safety management, such as the ISO 9000 series, assist in integrating the structure and content of preventive measures into management. The advantages of such a comprehensive approach are obvious.

Integrated management means that occupational health and safety regulations are no longer looked at in isolation, but gain relevance from the corresponding sections of a quality management handbook, as well as in process and work instructions, thus creating a fully integrated system. This integral approach can improve the chances of greater attention to accident prevention measures in daily construction practice and, thereby, reduce the number of workplace accidents and injuries. Dissemination of a handbook that integrates occupational health and safety procedures into the processes it describes is crucial for this process.

New management methods are aimed at putting people closer to the centre of the processes. Co-workers are being more actively involved. Information, communication and cooperation are promoted across hierarchical barriers. The reduction of absences due to illness or workplace accidents enhances the implementation of the principles of quality management in construction.

With the development of new building methods and equipment, safety requirements increase steadily in number. The increasing concern with environmental protection makes the problem even more complex. Coping with the demands of modern prevention is difficult without appropriate regulations and a centrally directed articulation of the process and work instructions. Clear divisions of responsibility and effective coordination for the prevention plan should, therefore, be written into the quality management system.

Improving Competitiveness

Documentation of the existence of an occupational safety management system is increasingly required when contractors submit bids for work, and its effectiveness has become one of the criteria for awarding a contract.

The pressure of international competition could become even greater in the future. It seems prudent, therefore, to integrate preventive measures into the quality management system now, rather than waiting and being forced by increasing competitive pressure to do so later, when the pressure of time and the costs of personnel and financing will be much greater. Furthermore, a not inconsiderable benefit of an integrated prevention/quality management system is that having such a well-documented programme in place is likely to reduce the costs of coverage, not only for workers’ compensation, but also for product liability.

Company Management

Company management must be committed to the integration of occupational health and safety into the management system. Goals specifying the content and time-frame of this effort should be defined and included in the basic statement of company policy. The necessary resources should be made available and appropriate personnel assigned to accomplish the project goals. Specialized safety personnel are generally required in large and mid-sized construction companies. In smaller companies, the employer must take the responsibility for the preventive aspects of the quality management system.

A periodic company management review closes the circle. The collective experiences in utilizing the integrated prevention/ quality management system should be examined and assessed, and plans for revision and for subsequent review should be formulated by company management.

Assessing Results

Assessment of results of the occupational safety management system that has been instituted is the second step in the integration of preventive measures and quality management.

The dates, kinds, frequency, causes and costs of accidents should be compiled, analysed and shared with all those in the company with relevant responsibilities. Such an analysis enables the company to set priorities in formulating or modifying process and work instructions. It also makes clear the extent to which occupational health and safety experience affects all divisions and all processes in the construction company. For this reason, defining the interface between company processes and preventive aspects takes on great importance. During bid preparation, the resources in time and money needed for comprehensive preventive measures, such as those incurred in clearing debris, can be precisely calculated.

When purchasing construction materials, attention should be paid to the availability of substitutes for potentially dangerous materials. From the beginning of a project responsibility for occupational health and safety should be assigned for particular aspects and each phase of the construction project. The need and availability for special training in occupational health and safety as well as the relative risks of injury and disease should be compelling considerations in the adoption of particular construction processes. These conditions must be recognized early on so that appropriately qualified workers can be selected and the courses of instruction can be arranged in a timely manner.

The responsibilities and authorities of the personnel assigned to safety and how they fit into the daily work should be documented in writing and collated with the onsite task descriptions. The construction company’s occupational safety staff should appear shown in its organizational chart, which, along with a clear responsibility matrix and schematic flow-charts of processes, should appear in the quality management handbook.

An Example from Germany

In practice, there are four formal procedures and their combinations for integrating occupational health and safety into a quality management system that have been implemented in Germany:

  1. A quality management handbook and a separate occupational safety management handbook are developed. Each has its own procedures and work instructions. In extreme cases, this creates ineffective, insular organizational solutions, which require twice the amount of work and in practice do not accomplish the desired results.
  2. An additional section is inserted into the quality management handbook with the heading “Occupational health and safety”. All statements on occupational health and safety are organized in this section. This path is chosen by some construction companies. Positioning a health and safety problem in a separate section may well highlight the importance of prevention, but it entails the risk being ignored as a “fifth wheel” and serves more as an evidence of intent rather than a command for appropriate action.
  3. All aspects of occupational health and safety are worked directly into the quality management system. This is the most systematic implementation of the basic idea of integration. The integrated and flexible structuring of the presentation models of the German DIN EN ISO 9001-9003 permits such an inclusion.
  4. The Underground Construction Trade Organization (Berufs-genossenschaft) favours a modular integration. This concept is explained below.


Integration in Quality Management

Once the assessment is completed, at the latest, those responsible for the construction project should contact the quality management officers and decide on the steps for actually integrating occupational safety into the management system. Comprehensive preparatory work should facilitate setting common priorities during the work that promise the greatest preventive results.

The demands of prevention that come out of the assessment are first divided into those that can be categorized according to the processes specific to the company and those that should be considered separately since they are more widespread, more comprehensive or of such a special character that they demand separate consideration. The following question can be of assistance in this categorization: Where would the interested reader of the handbook (e.g., the “customer” or the worker) most likely look for the relevant preventive policy, the section of a chapter devoted to a process specific to the company, or in a special section on occupational health and safety? Thus, it appears, a specialized procedural instruction on transporting hazardous materials would make the most sense in almost all construction companies if it were included in section on handling, storing, packing, conserving and shipping.

Coordination and Implementation

After this formal categorization should come linguistic coordination to ensure easy readability (this means presentation in the appropriate language(s) and in terms easily understood by individuals with educational levels characteristic of the particular workforce). Finally, the final documents must be formally endorsed by the top management of the company. At this juncture, it would be useful to publicize the significance of the changed or newly-implemented procedures and work instructions in company bulletins, safety circles, memos and any other available media, and to promote their application.

General Audits

To assess the effectiveness of the instructions, appropriate questions may be prepared for inclusion into general audits. In this manner, the coherence of work processes and occupational health and safety considerations is made unmistakably clear to the worker. Experience has shown that workers may at first be surprised when an audit team on the construction site in their particular division routinely asks questions on accident prevention as a matter of course. The consequent increase in the attention paid to safety and health by the workforce confirms the value of the integration of prevention into the quality management programme.



Diversity of Projects and Work Activities

Many people outside the construction industry are unaware of the diversity and degree of specialization of work undertaken by the industry, though they see portions of it every day. In addition to traffic delays caused by encroachments on roads and street excavations, the public is frequently exposed to buildings being erected, subdivisions being constructed and, occasionally, to the demolition of structures. What is hidden away from view, in most cases, is the large amount of specialized work done either as part of a “new” construction project or as part of the ongoing repairs maintenance associated with almost anything constructed in the past.

The list of activities is very diverse, ranging from electrical, plumbing, heating and ventilating, painting, roofing and flooring work to very specialized work such as installing or repairing overhead doors, setting heavy machinery, applying fireproofing, refrigeration work and installing or testing communications systems.

The value of construction can be partially measured by the value of building permits. Table 1 shows the value of construction in Canada in 1993.

Table 1.  Value of construction projects in Canada, 1993 (based on value of building permits issued in 1993).

Type of project

Value ($ Cdn)

% of total

Residential buildings (houses, apartments)



Industrial buildings (factories, mining plants)



Commercial buildings (offices, stores, shops etc.)



Institutional buildings (schools, hospitals)



Other buildings (airports, bus stations, farm buildings, etc.)



Marine facilities (wharves,dredging)



Roads and highways



Water and sewage systems



Dams and irrigation



Electric power (thermal/nuclear/hydro)



Railway, telephone and telegraph



Gas and oil (refineries, pipelines)



Other engineering construction (bridges, tunnels, etc.)






Source: Statistics Canada 1993.

The health and safety aspects of the work depend in large measure on the nature of the project. Each type of project and each work activity presents different hazards and solutions. Often, the severity, scope or size of the problem is related to the size of the project as well.

Client-Contractor Relationships

Clients are the individuals, partnerships, corporations or public authorities for whom construction is carried out. The vast majority of construction is done under contractual arrangements between clients and contractors. A client may select a contractor based on past performance or through an agent such as an architect or engineer. In other cases, it may decide to offer the project through advertising and tendering. The methods used and the client’s own attitude to health and safety can have a profound effect on the project’s health and safety performance.

For example, if a client chooses to “pre-qualify” contractors to ensure that they meet certain criteria, then this process excludes inexperienced contractors, those who may not have had satisfactory performance and those without qualified personnel required for the project. While health and safety performance has not previously been one of the common qualifications sought or considered by clients, it is gaining in usage, primarily with large industrial clients and with government agencies that purchase construction services.

Some clients promote safety much more than others. In some cases, this is due to the risk of damage to their existing facilities when contractors are brought in to perform maintenance or to expand the client’s facilities. Petrochemical companies in particular make it clear that contractor safety performance is a key condition of the contract.

Conversely, those firms who choose to offer their project through an unqualified open bidding process to obtain the lowest price often end up with contractors that may be unqualified to perform the work or who take short cuts to save on time and materials. This can have an adverse effect on health and safety performance.

Contractor-Contractor Relationships

Many people who are not familiar with the nature of the contractual arrangements common in construction presume that one contractor performs all or at least the major part of most building construction. For example, if a new office tower, sports complex or other high-visibility project is being constructed, the general contractor usually erects signs and often company flags to indicate its presence and to create the impression that this is “its project”. Years ago, this impression may have been relatively accurate, since some general contractors actually undertook to perform substantial parts of the project with their own direct-hire forces. However, since the mid-1970s, many, if not most, general contractors have assumed more of a project management role on large projects, with the vast majority of the work contracted out to a network of subcontractors, each of which has special skills in a particular aspect of the project. (See table 2)

Table 2. Contractors/subcontractors on typical industrial/commercial/institutional projects

Project manager/general contractor
Excavating contractor
Formwork contractor
Reinforcing steel contractor
Structural steel contractor
Electrical contractor
Plumbing contractor
Drywall contractor
Painting contractor
Glazing contractor
Masonry contractor
Finish carpentry/cabinet work contractor
Flooring contractor
Heating/ventilation/air conditioning contractor
Roofing contractor
Landscaping contractor

As a result, the general contractor could actually have fewer staff onsite than any of several subcontractors on the project. In some cases the main contractor has no workforce directly involved in construction activities, but manages the work of subcontractors. On most major projects in the industrial, commercial and institutional (ICI) sector, there are several layers of subcontractors. Typically, the primary level of subcontractors have contracts with the general contractor. However, these subcontractors may contract part of their work out to other smaller or more specialized subcontractors.

The influence that this network of contractors may have on health and safety becomes fairly obvious when it is compared with a fixed worksite such as a factory or a mill. At a typical fixed-industry workplace, there is only one management entity, the employer. The employer has sole responsibility for the workplace, the lines of command and communication are simple and direct, and only one corporate philosophy applies. At a construction project, there may be ten or more employer entities (representing the general contractor and the usual subcontractors), and the lines of communication and authority tend to be more complex, indirect and often confused.

The attention given to health and safety by the person or company in charge can influence the health and safety performance of others. If the general contractor has attached a high degree of importance to health and safety, this can have a positive influence on the health and safety performance of the subcontractors on the project. The converse is also true.

Additionally, the overall health and safety performance of the site can be adversely affected by the performance of one subcontractor (e.g., if one subcontractor has poor housekeeping, leaving a mess behind as his or her forces move through the project, it can create problems for all of the other subcontractors onsite).

Regulatory efforts regarding health and safety are generally more difficult to introduce and administer in these multi-employer workplaces. It may be difficult to determine which employer has responsibility for which hazards or solutions, and any administrative controls which appear to be eminently workable in a single-employer workplace may need significant modification to be workable on a multi-employer construction project. For example, information regarding hazardous materials used on a construction project must be communicated to those who work with or near the materials, and workers must be adequately trained. At a fixed workplace with only one employer, all of the material and the information accompanying it is much more readily obtained, controlled and communicated, whereas on a construction project, any of the various subcontractors may be bringing in hazardous materials of which the general contractor has no knowledge. Additionally, workers employed by one subcontractor using a certain material may have been trained, but the crew working for another subcontractor in the same area but doing something entirely different may know nothing about the material and yet could be as much at risk as those using the material directly.

Another factor which emerges regarding contractor-contractor relationships relates to the bidding process. A subcontractor who bids too low may take short-cuts that compromise health and safety. In these cases, the general contractor must ensure that subcontractors adhere to the standards, specifications and statutes pertaining to health and safety. It is not uncommon on projects where everyone has bid very low to observe continuing health and safety problems coupled with excessive passing of responsibility, until regulatory authorities step in to impose a solution.

A further problem relates to the scheduling of work and the impact this can have on health and safety. With several different subcontractors on the site at one time, competing interests may create problems. Each contractor wants to get his or her work done as quickly as possible. When two or more contractors want to occupy the same space, or when one has to perform work overhead of another, problems can occur. This is typically a much more common problem in construction than in fixed industry, where the main competing interests tend to involve only operations versus maintenance.

Employer-Employee Relationships

The several employers on a particular project may have somewhat different relationships with their employees than those common at most fixed industrial workplaces. For example, unionized workers at a manufacturing facility tend to belong to one union. When the employer needs additional workers, it interviews and hires them and the new employees join the union. Where there are former unionized workers on layoff, they are re-hired generally on a seniority basis.

In the unionized part of the construction industry, a completely different system is used. Employers form collective associations which then enter into agreements with building and construction trade unions. The majority of the non-salaried direct-hire employees in the industry work through their union. When, for example, a contractor needs five additional carpenters at a project, he or she would call the local Carpenters’ Union and place a request for five carpenters to show up for work at the project on a certain day. The union would notify the five members at the top of the employment list that they are to report to the project to work for the particular firm. Depending on the provisions of the collective agreement between the employers and the union, the contractor may be able to “name hire” or select some of these workers. If there are no union members available to fill the employment call, the employer may be able to hire temporary workers who would join the union, or the union may bring in skilled workers from other locals to help fill the demand.

In non-unionized situations, employers use different processes to obtain additional staff. Prior employment lists, local employment centres, word of mouth and advertising in local newspapers are the principal methods used.

It is not uncommon for workers to be employed by several different employers in the course of a year. The employment duration varies with the nature of the project and the amount of work to be done. This places a large administrative load on the construction contractors compared with their fixed-industry counterparts (e.g., recordkeeping for income taxes, workers’ compensation, unemployment insurance, union dues, pensions, licensing and other regulatory or contractual issues).

This situation presents some unique challenges compared to the typical fixed-industry workplace. Training and qualifications must not only be standardized but portable from one job or sector to another. These important issues affect the construction industry much more profoundly than fixed industries. Construction employers expect workers to come to the project with certain skills and capabilities. In most trades, this is accomplished by a comprehensive apprenticeship programme. If a contractor places a call for five carpenters, he or she expects to see five qualified carpenters at the project on the day they are needed. If health and safety regulations require special training, the employer needs to be able to access a pool of workers with this training, since the training may not be readily available at the time the work is scheduled to start. An example of this is the Certified Worker Programme required at larger construction projects in Ontario, Canada, which involves having joint health and safety committees. Since this training is not currently part of the apprenticeship programme, alternative training systems had to be put in place to create a pool of trained workers.

With growing emphasis on specialized training or at least confirmation of skill level, training programmes conducted in conjunction with the building and construction trades unions will likely grow in importance, number and variety.

Inter-union Relationships

The structure of organized labour mirrors the way in which contractors have specialized within the industry. On a typical construction project, five or more trades may be represented onsite at any one time. This involves many of the same problems posed by multiple employers. Not only are there competing interests to deal with, but lines of authority and communication are more complex and sometimes blurred when compared with a single-employer, single-union workplace. This influences many aspects of health and safety. For example, which worker from which union will represent all workers on the project if there is a regulatory requirement for a health and safety representative? Who gets trained in what and by whom?

In the case of rehabilitation and reinstatement of injured workers, the options for skilled construction workers are much more limited than those of their fixed-industry counterparts. For example, an injured worker at a factory may be able to return to some other job at that workplace without crossing important jurisdictional boundaries between one union and another, because there is typically only one union in the factory. In construction, each trade has fairly clearly defined jurisdiction over the types of work its members can perform. This greatly limits the options for injured workers who may not be able to perform their normal pre-injury job functions but could none the less perform some other related work at that workplace.

Occasionally, jurisdictional disputes arise over which union should perform certain types of work which have health and safety implications. Examples include scaffold erection, boom truck operation, asbestos removal and rigging. Regulations in these areas need to consider jurisdictional concerns, especially with respect to licensing and training.

The Dynamic Nature of Construction

Construction workplaces are in many respects quite different from fixed industry. Not only are they different, they tend to be constantly changing. Unlike a factory which operates at a given location day after day, with the same equipment, the same workers, the same processes and generally the same conditions, construction projects evolve and change from day to day. Walls are erected, new workers from different trades arrive, materials change, employers change as they complete their portions of the work, and most projects are affected to some degree just by the changes in the weather.

When one project is completed, workers and employers move on to other projects to start all over again. This indicates the dynamic nature of the industry. Some employers work in several different cities, provinces, states or even countries. Similarly, many skilled construction workers move with the work. These factors influence many aspects of health and safety, including workers’ compensation, health and safety regulations, performance measurement and training.


The construction industry is presented with some very different conditions from those in fixed industry. These conditions must be considered when control strategies are being contemplated and may help to explain why things are done differently in the construction industry. Solutions developed with the input from both construction labour and construction management, who know these conditions and how to deal effectively with them, offer the best chance for improving health and safety performance.



Implementation of the EC directive Minimum Regulations for Health and Safety on Temporary and Mobile Building Sites typifies the legal regulations emanating from the Netherlands and from the European Union. Their aim is to improve working conditions, to combat disability and to reduce sickness absenteeism. In the Netherlands, these regulations for the construction industry are expressed in the Arbouw Resolution, Chapter 2, Section 5.

As is often the case, the legislation seems to be following the social changes that began in 1986, when organizations of employers and employees joined to establish the Arbouw Foundation to provide services for construction companies in civil engineering and utility construction, earth works, roadbuilding and water construction and the completion sectors of the industry. Thus, the new regulations are scarcely a problem for the responsible companies already committed to implement health and safety considerations. The fact that these principles are often very difficult to put into practice, however, has led to non-observance and unfair competition and, consequently, the need for legal regulations.

Legal Regulations

The legal regulations focus on preventive measures before the construction project is started and while it is in progress. This will yield the greatest long-term benefit.

The Health and Safety Act stipulates that evaluations of risks must address not only those arising from materials, preparations, tools, equipment and so on, but also those involving special groups of workers (e.g., pregnant women, young and elderly workers and those with disabilities).

Employers are obliged to have written risk evaluations and inventories produced by certified experts, who may be employees or external contractors. The document must include recommendations for eliminating or limiting the risks and must also stipulate phases of the work when qualified specialists will be required. Some construction companies have developed their own approach to the evaluation, the General Business Investigation and Risk Inventory and Evaluation (ABRIE), which has become the prototype for the industry.

The Health and Safety Act obliges employers to offer a periodic health examination to their employees. The purpose is to identify health problems that may make certain jobs especially hazardous for some workers unless certain precautions are taken. This requirement echoes the various collective labour agreements in the construction industry which for years have required employers to provide employees with comprehensive occupational health care, including periodic medical examinations. The Arbouw Foundation has contracted with the Federation of Occupational Health and Safety Care Centres for the provision of these services. Over the years, a wealth of valuable information has been accumulated which has contributed to enhancement of the quality of the risk inventories and evaluations.

Absenteeism Policy

The Health and Safety Act also requires employers to have an absenteeism policy which includes a stipulation that experts in this field be retained to monitor and counsel disabled employees.

Joint Responsibility

Many health and safety risks can be traced to inadequacies in the building and organization choices or to poor planning of the work when setting up a project. To obviate this, the employers, employees and the government agreed in 1989 on a working conditions covenant. Among other things, it specified cooperation between clients and contractors and between contractors and subcontractors. This has resulted in a code of conduct which serves as a model for the implementation of the European directive on temporary and mobile building sites.

As part of the covenant, Arbouw formulated limits for exposure to hazardous substances and materials, along with guidelines for the application in various construction operations.

Under the leadership of Arbouw, the FNV Building Workers and Wood Workers Union, the FNV Industry Union and the Mineral Wool Association, Benelux, agreed to a contract that called for the development of glass wool and mineral wool products with less dust emission, development of the safest possible production methods for glass wool and mineral wool, formulation and promotion of working methods for the safest use of these products and performance of the research necessary to establish safe exposure limits to them. The exposure limit for respirable fibres was set at 2/cm3 although a limit of 1/cm3 was regarded as feasible. They also agreed to eliminate the use of raw and secondary materials that are health risks, using as criteria the exposure limits formulated by Arbouw. Performance under this agreement will be monitored until it expires on 1 January 1999.

Construction Process Quality

The implementation of the EC directive does not stand in isolation but is an integral part of company health and safety policies, along with quality and environmental policies. Health and safety policy is critical part of the quality policy of the companies. The laws and regulations will be enforceable only if the employers and employees of the construction industry have played a role in their development. The government has dictated the development of a model health and safety plan that is practicable and can be enforced to prevent unfair competition from companies that ignore or subvert it.



Wednesday, 09 March 2011 20:12

Preventive Health Services in Construction

The construction industry forms 5 to 15% of the national economy of most countries and is usually one of the three industries having the highest rate of work-related injury risks. The following chronic occupational health risks are pervasive (Commission of the European Communities 1993):

  • Musculoskeletal disorders, occupational hearing loss, dermatitis and lung disorders are the most common occupational diseases.
  • An increased risk of respiratory tract carcinomas and mesothelioma caused by asbestos exposure has been observed in all countries where occupational mortality and morbidity statistics are available.
  • Disorders resulting from improper nutrition, smoking or use of alcohol and drugs are associated especially with migrant workers, a substantial portion of construction employment in many countries.


Preventive health services for construction workers should be planned with these risks as priorities.

Types of Occupational Health Services

Occupational health services for construction workers consist of three main models:

  1. specialized services for construction workers
  2. occupational health care for construction workers rendered by providers of broad-based occupational health services
  3. health services provided voluntarily by the employer.


Specialized services are the most effective but also the most expensive in terms of direct costs. Experiences from Sweden indicate that the lowest injury rates on construction sites worldwide and a very low risk for occupational diseases among construction workers are associated with extensive preventive work through specialized service systems. In the Swedish model, called Bygghälsan, technical and medical prevention have been combined. Bygghälsan operates through regional centres and mobile units. During the severe economic recession of the late 1980s, however, Bygghälsan severely cut back its health service activities.

In countries that have occupational health legislation, construction companies usually buy the needed health services from companies serving general industries. In such cases, the training of occupational health personnel is important. Without special knowledge of the circumstances surrounding construction, medical personnel cannot provide effective preventive occupational health programmes for construction companies.

Some large multinational companies have well-developed occupational safety and health programmes that are part of the culture of the enterprise. The cost-benefit calculations have proved these activities economically profitable. Nowadays, occupational safety programmes are included in quality management of most international companies.

Mobile health clinics

Because construction sites are often situated far from any established providers of health services, mobile health service units may be necessary. Practically all countries that have specialized occupational health services for construction workers use mobile units for delivering the services. The mobile unit’s advantage is the saving of work time by bringing the services to worksites. Mobile health centres are contained in a specially equipped bus or trailer and are especially suitable for all types of screening procedures, such as periodic health examinations. Mobile services should be careful to arrange in advance for collaboration with local providers of health services in order to secure follow-up evaluation and treatment for workers whose test results suggest a health problem.

Standard equipment for a mobile unit includes a basic laboratory with a spirometer and an audiometer, an interview room and x-ray equipment, when needed. It is best to design module units as multipurpose spaces so they can be used for different types of projects. The Finnish experience indicates that mobile units are also suitable for epidemiological studies, which can be incorporated into occupational health programmes, if properly planned in advance.

Contents of preventive occupational health services

Identification of risk at construction sites should guide medical activity, although this is secondary to prevention through proper design, engineering and work organization. Risk identification requires a multidisciplinary approach; this requires close collaboration between the occupational health personnel and the enterprise. A systematic workplace survey of risks using standardized checklists is one option.

Preplacement and periodic health examinations are usually conducted according to requirements set by legislation or guidance provided by authorities. The examination’s content depends on the exposure history of each worker. Short work contracts and frequent turnover of the construction workforce can result in “missed” or “inappropriate” health examinations, a failure to follow up on findings or unwarranted duplication of health examinations. Therefore, regular standard periodic examinations are recommended for all workers. A standard health examination should contain: an exposure history; symptom and illness histories with special emphasis on musculoskeletal and allergic diseases; a basic physical examination; and audiometry, vision, spirometry and blood pressure tests. The examinations should also provide health education and information on how to avoid occupational risks known to be common.

Surveillance and Prevention of Key Construction-related Problems

Musculoskeletal disorders and their prevention

Musculoskeletal disorders have multiple origins. Lifestyle, hereditary susceptibility and ageing, combined with improper physical strain and minor injuries, are commonly accepted risk factors for musculoskeletal disorders. The types of musculoskeletal problems have different exposure patterns in different construction professions.

There is no reliable test to predict an individual’s risk for acquiring a musculoskeletal disorder. Medical prevention of musculoskeletal disorders is based on guidance in ergonomic matters and lifestyles. Preplacement and periodic examinations can be used for this purpose. Non-specific strength testing and routine x rays of the skeletal system have no specific value for prevention. Instead, early detection of symptoms and a detailed work history of musculoskeletal symptoms can be used as a basis for medical counselling. A programme that performs periodic symptom surveys to identify work factors that can be changed has been shown to be effective.

Often, workers who have been exposed to heavy physical loads or strain think the work keeps them fit. Several studies have proved that this is not the case. Therefore, it is important that, in the context of health examinations, the examinees be informed about proper ways to maintain their physical fitness. Smoking has also been associated with lumbar disk degeneration and low-back pain. Therefore, anti-smoking information and therapy should be included in the periodic health examinations, too (Workplace Hazard and Tobacco Education Project 1993).

Occupational noise-induced hearing loss

The prevalence of noise-induced hearing loss varies among construction occupations, depending on levels and duration of exposure. In 1974, less than 20% of Swedish construction workers at age 41 had normal hearing in both ears. Implementation of a comprehensive hearing conservation programme increased the proportion in that age group having normal hearing to almost 40% by the late 1980s. Statistics from British Columbia, Canada, show that construction workers generally suffer significant loss of hearing after working more than 15 years in the trades (Schneider et al. 1995). Some factors are thought to increase susceptibility to occupational hearing loss (e.g., diabetic neuropathy, hypercholesterolemia and exposure to certain ototoxic solvents). Whole-body vibration and smoking may have an additive effect.

A large-scale programme for hearing conservation is advisable for the construction industry. This type of programme requires not only collaboration at the worksite level, but also supportive legislation. Hearing conservation programmes should be specific in work contracts.

Occupational hearing loss is reversible in the first 3 or 4 years after initial exposure. Early detection of hearing loss will provide opportunities for prevention. Regular testing is recommended to detect the earliest possible changes and to motivate workers to protect themselves. At the time of testing, the exposed workers should be educated in the principles of personal protection, as well as the maintenance and proper use of protection devices.

Occupational dermatitis

Occupational dermatitis is prevented mainly by hygienic measures. The proper handling of wet cement and skin protection are effective in promoting hygiene. During health examinations, it is important to stress the importance of avoiding skin contact with wet cement.

Occupational lung diseases

Asbestosis, silicosis, occupational asthma and occupational bronchitis can be found among construction workers, depending on their past work exposures (Finnish Institute of Occupational Health 1987).

There is no medical method to prevent the development of carcinomas after someone has been sufficiently exposed to asbestos. Regular chest x rays, every third year, are the most common recommendation for medical surveillance; there is some evidence that x-ray screening improves the outcome in lung cancer (Strauss, Gleanson and Sugarbaker 1995). Spirometry and anti-smoking information are usually included in the periodic health examination. Diagnostic tests for the early diagnosis of asbestos-related malignant tumours are not available.

Malignant tumours and other lung diseases related to asbestos exposure are widely underdiagnosed. Therefore, many construction workers eligible for compensation remain without benefits. In the late 1980s and early 1990s, Finland conducted a nationwide screening of workers exposed to asbestos. The screening revealed that only one-third of the workers with asbestos-related diseases and who had access to occupational health services had been diagnosed earlier (Finnish Institute of Occupational Health 1994).

Special needs of migrant workers

Depending on the construction site, the social context, sanitary conditions and climate may present important risks to construction workers. Migrant workers often suffer from psychosocial problems. They have a higher risk of work-related injuries than native workers. Their risk of carrying infectious diseases, such as HIV/AIDS, tuberculosis, and parasitic diseases must be taken into account. Malaria and other tropical diseases are problems for workers in areas where they are endemic.

In many large construction projects, a foreign workforce is used. A preplacement medical examination should be conducted in the home country. Also, the spreading of contagious diseases must be prevented through proper vaccination programmes. In the host countries, proper vocational training, health and safety education, and housing should be organized. Migrant workers should be provided the same access to health care and social security as native workers (El Batawi 1992).

In addition to preventing construction-related ailments, the health practitioner should work to promote positive changes in lifestyle, which can improve a worker’s health overall. Avoiding alcohol and smoking are the most important and fruitful themes for health promotion for construction workers. It has been estimated that a smoker costs the employer 20 to 30% more than a non-smoking worker. Investments in anti-smoking campaigns pay not only in the short term, with lower accident risks and shorter sick leaves, but also in the long term, with lower risks of cardiovascular pulmonary diseases and cancer. In addition, tobacco smoke has harmful multiplier effects with most dusts, especially with asbestos.

Economic benefits

It is difficult to prove any direct economic benefit of occupational health services to an individual construction company, especially if the company is small. Indirect cost-benefit calculations show, however, that accident prevention and health promotion are economically beneficial. Cost-benefit calculations of investments in preventive programmes are available for companies to use internally. (For a model used extensively in Scandinavia, see Oxenburg 1991.)




Underground construction work includes tunnelling for roads, highways and railroads and laying pipelines for sewers, hot water, steam, electrical conduits, telephone lines. Hazards in this work include hard physical labour, crystalline silica dust, cement dust, noise, vibration, diesel engine exhaust, chemical vapours, radon and oxygen-deficient atmospheres. Occasionally this work must be done in a pressurized environment. Underground workers are at risk for serious and often fatal injuries. Some hazards are the same as those of construction on the surface, but they are amplified by working in a confined environment. Other hazards are unique to underground work. These include being struck by specialized machinery or being electrocuted, being buried by roof falls or cave-ins and being asphyxiated or injured by fires or explosions. Tunnelling operations may encounter unexpected impoundments of water, resulting in floods and drowning.

The construction of tunnels requires a great deal of physical effort. Energy expenditure during manual work is usually from 200 to 350 W, with a great part of static load of the muscles. Heart rate during work with compressed-air drills and pneumatic hammers reaches 150 to 160 per minute. Work is often done in unfavourable cold and humid microclimatic conditions, sometimes in cumbersome work postures. It is usually combined with exposure to other risk factors which depend on the local geological conditions and on the type of technology used. This heavy workload can be an important contribution to heat stress.

The need for heavy manual labour can be reduced by mechanization. But mechanization brings its own hazards. Large and powerful mobile machines in a confined environment introduce risks of serious injury to persons working nearby, who may be struck or crushed. Underground machinery also may generate dust, noise, vibration and diesel exhaust. Mechanization also results in fewer jobs, which reduces the number of persons exposed but at the expense of unemployment and all of its attendant problems.

Crystalline silica (also known as free silica and quartz) occurs naturally in many different types of rock. Sandstone is practically pure silica; granite may contain 75%; shale, 30%; and slate, 10%. Limestone, marble and salt are, for practical purposes, completely free of silica. Considering that silica is ubiquitous in the earth’s crust, dust samples should be taken and analysed at least at the start of an underground job and whenever the type of rock changes as work progresses through it.

Respirable silica dust is generated whenever silica-bearing rock is crushed, drilled, ground or otherwise pulverized. The main sources of airborne silica dust are compressed-air drills and pneumatic hammers. Work with these tools most often occurs in the fore part of the tunnel and, therefore, workers in these areas are the most heavily exposed. Dust suppression technology should be applied in all instances.

Blasting generates not only flying debris, but also dust and nitrogen oxides. To prevent excessive exposure, the customary procedure is to prevent re-entry to the affected area until the dust and gases have cleared. A common procedure is to blast at the end of the last work shift of the day and to clear out debris during the next shift.

Cement dust is generated when cement is mixed. This dust is a respiratory and mucous membrane irritant in high concentrations, but chronic effects have not been observed. When it settles on skin and mixes with sweat, however, cement dust can cause dermatoses. When wet concrete is sprayed in place, it too can cause dermatoses.

Noise can be significant in underground construction work. Principal sources include pneumatic drills and hammers, diesel engines and fans. Since the underground work environment is confined, there is also considerable reverberant noise. Peak noise levels can exceed 115 dBA, with time-weighted average noise exposure equivalent to 105 dBA. Noise-reducing technology is available for most equipment and should be applied.

Underground construction workers can also be exposed to whole-body vibration from mobile machinery and to hand-arm vibration from pneumatic drills and hammers. The levels of acceleration transmitted to the hands from pneumatic tools can reach about 150 dB (comparable to 10 m/s2). Harmful effects of hand-arm vibration can be aggravated by a cold and damp working environment.

If soil is highly saturated with water or if construction is conducted under water, the work environment may have to be pressurized to keep water out. For underwater work, caissons are used. When workers in such a hyperbaric environment make too rapid a transition to normal air pressure, they risk decompression sickness and related disorders. Since the absorption of most toxic gases and vapours depends on their partial pressure, more may be absorbed at higher pressure. Ten ppm of carbon monoxide (CO) at 2 atmospheres of pressure, for example, will have the effect of 20 ppm CO at 1 atmosphere.

Chemicals are used in underground construction in a variety of ways. For example, insufficiently coherent layers of rock may be stabilized with an infusion of urea formaldehyde resin, polyurethane foam or mixtures of sodium water glass with formamide or with ethyl and butyl acetate. Consequently, vapours of formaldehyde, ammonia, ethyl or butyl alcohol or di-isocyanates may be found in the tunnel atmosphere during application. Following application, these contaminants may escape into the tunnel from the surrounding walls, and it may therefore be difficult to fully control their concentrations, even with intensive mechanical ventilation.

Radon occurs naturally in some rock and may leak into the work environment, where it will decay into other radioactive isotopes. Some of these are alpha emitters that may be inhaled and increase the risk of lung cancer.

Tunnels constructed in inhabited areas can also be contaminated with substances from surrounding pipes. Water, heating and cooking gas, fuel oil, petrol and so on may leak into a tunnel or, if pipes carrying these substances are broken during excavation, they may escape into the work environment.

The construction of vertical shafts using mining technology poses similar health problems to those of tunnelling. In terrain where organic substances are present, products of microbiological decomposition may be expected.

Maintenance work in tunnels used for traffic differs from similar work on the surface mainly in the difficulty of installing safety and control equipment, for example, ventilation for electric arc welding; this may influence the quality of safety measures. Work in tunnels in which pipelines for hot water or steam are present is associated with great heat load, demanding a special regime of work and breaks.

Oxygen deficiency may occur in tunnels either because oxygen is displaced by other gases or because it is consumed by microbes or by the oxidation of pyrites. Microbes may also release methane or ethane, which not only displace oxygen but, in sufficient concentration, may create the risk of explosion. Carbon dioxide (commonly called blackdamp in Europe) is also generated by microbial contamination. The atmospheres in spaces which have been closed for a long time may contain mostly nitrogen, practically no oxygen and 5 to 15% carbon dioxide.

Blackdamp penetrates into the shaft from the surrounding terrain due to changes in the atmospheric pressure. The composition of the air in the shaft may change very quickly—it may be normal in the morning, but be deficient in oxygen by the afternoon.


Prevention of exposure to dust should in the first place be implemented by technical means, such as wet drilling (and/or drilling with LEV), wetting of the material before it is pulled down and loaded to the transport, LEV of mining machines and mechanical ventilation of tunnels. Technical control measures may not be sufficient to lower the concentration of respirable dust to an acceptable level in some technological operations (e.g., during drilling and sometimes also in the case of wet drilling), and therefore it may be necessary to supplement the protection of the workers engaged in such operations by the use of respirators.

The efficiency of technical control measures must be checked by monitoring the concentration of airborne dust. In the case of fibrogenic dust, it is necessary to arrange the programme of monitoring in such a way that it allows the registration of the exposure of individual workers. The individual exposure data, in connection with data about each worker’s health, are necessary for the assessment of the risk of pneumoconiosis in particular work conditions, as well as for the assessment of the efficiency of control measures in the long-run. Last but not least, the individual registration of exposure is necessary for evaluating the ability of individual workers to continue in their jobs.

Due to the nature of underground work, protection against noise depends mostly on the personal protection of hearing. Effective protection against vibrations, on the other hand, can be achieved only by eliminating or decreasing the vibration by mechanization of risky operations. PPE is not effective. Similarly, the risk of diseases due to physical overload of the upper extremities can be lowered only by mechanization.

Exposure to chemical substances can be influenced by the selection of appropriate technology (e.g., the use of formaldehyde resins and formamide should be eliminated), by good maintenance (e.g., of diesel engines) and by adequate ventilation. Organization and work regime precautions are sometimes very effective, especially in the case of the prevention of dermatoses.

Work in underground spaces in which the composition of the air is not known demands strict adherence to safety rules. Entering such spaces without isolating breathing apparatuses must not be allowed. The work should be done only by a group of at least three people—one worker in the underground space, with breathing apparatus and safety harness, the others outside with a rope to secure the inside worker. In case of accident it is necessary to act quickly. Many lives have been lost in efforts to save the victim of an accident when the safety of the rescuer was disregarded.

Pre-placement, periodic and post-employment preventive medical examinations are a necessary part of the health and safety precautions for workers in tunnels. The frequency of periodic examinations and the type and scope of special examinations (x ray, lung functions, audiometry and so on) should be individually determined for each workplace and for each job according to the working conditions.

Prior to groundbreaking for underground work, the site should be inspected and soil samples should be taken in order to plan the excavation. Once work is underway, the work site should be inspected daily to prevent roof falls or cave-ins. The workplace of solitary workers should be inspected at least twice each shift. Fire suppression equipment should be strategically placed throughout the underground work site.



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Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides