This article addresses “machine” hazards, those which are specific to the appurtenances and hardware used in the industrial processes associated with pressure vessels, processing equipment, powerful machines and other intrinsically risky operations. This article does not address worker hazards, which implicate the actions and behaviour of individuals, such as slipping on working surfaces, falling from elevations and hazards from using ordinary tools. This article focuses on machine hazards, which are characteristic of an industrial job environment. Since these hazards threaten anyone present and may even be a threat to neighbours and the external environment, the analysis methods and the means for prevention and control are similar to the methods used to deal with risks to the environment from industrial activities.

Machine Hazards

Good quality hardware is very reliable, and most failures are caused by secondary effects like fire, corrosion, misuse and so on. Nevertheless, hardware may be highlighted in certain accidents, because a failing hardware component is often the most conspicuous or visibly prominent link of the chain of events. Although the term hardware is used in a broad sense, illustrative examples of hardware failures and their immediate “surroundings” in accident causation have been taken from industrial workplaces. Typical candidates for investigation of “machine” hazards include but are not limited to the following:

• pressure vessels and pipes

• motors, engines, turbines and other rotating machines

• chemical and nuclear reactors

• scaffolding, bridges, etc.

• lasers and other energy radiators

• cutting and drilling machinery, etc.

• welding equipment.

Effects of Energy

Hardware hazards can include wrong use, construction errors or frequent overload, and accordingly their analysis and mitigation or prevention can follow rather different directions. However, physical and chemical energy forms that elude human control often exist at the heart of hardware hazards. Therefore, one very general method to identify hardware hazards is to look for the energies that are normally controlled with the actual piece of equipment or machinery, such as a pressure vessel containing ammonia or chlorine. Other methods use the purpose or intended function of the actual hardware as a starting point and then look for the probable effects of malfunctions and failures. For example, a bridge failing to fulfil its primary function will expose subjects on the bridge to the risk of falling down; other effects of the collapse of a bridge will be the secondary ones of falling items, either structural parts of the bridge or objects situated on the bridge. Further down the chain of consequences, there may be derived effects related to functions in other parts of the system that were dependent on the bridge performing its function properly, such as the interruption of emergency response vehicular traffic to another incident.

Besides the concepts of “controlled energy” and “intended function”, dangerous substances must be addressed by asking questions such as, “How could agent X be released from vessels, tanks or pipe systems and how could agent Y be produced?” (either or both may be hazardous). Agent X might be a pressurized gas or a solvent, and agent Y might be an extremely toxic dioxin whose formation is favoured by the “right” temperatures in some chemical processes, or it could be produced by rapid oxidation, as the result of a fire. However, the possible hazards add up to much more than just the risks of dangerous substances. Conditions or influences might exist which allow the presence of a particular item of hardware to lead to harmful consequences to humans.

Industrial Work Environment

Machine hazards also involve load or stress factors that may be dangerous in the long run, such as the following:

• extreme working temperatures

• high intensities of light, noise or other stimuli

• inferior air quality

• extreme job demands or workloads.

These hazards can be recognized and precautions taken because the dangerous conditions are already there. They do not depend on some structural change in the hardware to come about and work a harmful result, or on some special event to effect damage or injury. Long-term hazards also have specific sources in the working environment, but they must be identified and evaluated through observing workers and the jobs, instead of just analysing hardware construction and functions.

Dangerous hardware or machine hazards are usually exceptional and rather seldom found in a sound working environment, but cannot be avoided completely. Several types of uncontrolled energy, such as the following risk agents, can be the immediate consequence of hardware malfunction:

• harmful releases of dangerous gas, liquids, dusts or other substances

• fire and explosion

• high voltages

• falling objects, missiles, etc.

• electric and magnetic fields

• cutting, trapping, etc.

• displacement of oxygen

• nuclear radiation, x rays and laser light

• flooding or drowning

• jets of hot liquid or steam.

Risk Agents

Moving objects. Falling and flying objects, liquid flows and jets of liquid or steam, such as listed, are often the first external consequences of hardware or equipment failure, and they account for a large proportion of accidents.

Chemical substances. Chemical hazards also contribute to worker accidents as well as affecting the environment and the public. The Seveso and Bhopal accidents involved chemical releases which affected numerous members of the public, and many industrial fires and explosions release chemicals and fumes to the atmosphere. Traffic accidents involving gasoline or chemical delivery trucks or other dangerous goods transports, unite two risk agents - moving objects and chemical substances.

Electromagnetic energy. Electric and magnetic fields, x rays and gamma rays are all manifestations of electromagnetism, but are often treated separately as they are encountered under rather different circumstances. However, the dangers of electromagnetism have some general traits: fields and radiation penetrate human bodies instead of just making contact on the application area, and they cannot be sensed directly, although very large intensities cause heating of the affected body parts. Magnetic fields are created by the flow of electric current, and intense magnetic fields are to be found in the vicinity of large electric motors, electric arc welding equipment, electrolysis apparatus, metal works and so forth. Electric fields accompany electric tension, and even the ordinary mains voltages of 200 to 300 volts cause the accumulation of dirt over several years, the visible sign of the field’s existence, an effect also known in connection with high-tension electrical lines, TV picture tubes, computer monitors and so on.

Electromagnetic fields are mostly found rather close to their sources, but electromagnetic radiation is a long-distance traveller, as radar and radio waves exemplify. Electromagnetic radiation is scattered, reflected and damped as it passes through space and meets intervening objects, surfaces, different substances and atmospheres, and the like; its intensity is therefore reduced in several ways.

The general character of the electromagnetic (EM) hazard sources are:

• Instruments are needed to detect the presence of EM fields or EM radiation.

• EM does not leave primary traces in the form of “contamination”.

• Dangerous effects are usually delayed or long-term, but immediate burns are caused in severe cases.

• X rays and gamma rays are damped, but not stopped, by lead and other heavy elements.

• Magnetic fields and x rays are stopped immediately when the source is de-energized or the equipment turned off.

• Electric fields can survive for long periods after turning the generating systems off.

• Gamma rays come from nuclear processes, and these radiation sources cannot be turned off as can many EM sources.

Nuclear radiation. The hazards associated with nuclear radiation are of special concern to workers in nuclear power plants and in plants working with nuclear materials such as fuel manufacturing and the reprocessing, transport and storage of radioactive matter. Nuclear radiation sources are also used in medicine and by some industries for measurement and control. One most common usage is in fire alarms/smoke detectors, which use an alpha-particle emitter like americium to monitor the atmosphere.

Nuclear hazards are principally centred around five factors:

• gamma rays

• neutrons

• beta particles (electrons)

• alpha particles (helium nuclei)

• contamination.

The hazards arise from the radioactive processes in nuclear fission and the decaying of radioactive materials. This sort of radiation is emitted from reactor processes, reactor fuel, reactor moderator material, from the gaseous fission products that may be developed, and from certain construction materials that become activated by exposure to radioactive emissions arising from reactor operation.

Other risk agents. Other classes of risk agents that release or emit energy include:

• UV radiance and laser light

• infrasound

• high-intensity sound

• vibration.

Triggering the Hardware Hazards

Both sudden and gradual shifts from the controlled - or “safe” - condition to one with increased danger can come about through the following circumstances, which can be controlled through appropriate organizational means such as user experience, education, skills, surveillance and equipment testing:

• wear and overloads

• external impact (fire or impact)

• ageing and failure

• wrong supply (energy, raw materials)

• insufficient maintenance and repair

• control or process error

• misuse or misapplication

• hardware breakdown

• barrier malfunction.

Since proper operations cannot reliably compensate for improper design and installation, it is important to consider the entire process, from selection and design through installation, use, maintenance and testing, in order to evaluate the actual state and conditions of the hardware item.

Hazard Case: The Pressurized Gas Tank

Gas can be contained in suitable vessels for storage or transport, like the gas and oxygen cylinders used by welders. Often, gas is handled at high pressure, affording a great increase in the storing capacity, but with higher accident risk. The key accidental phenomenon in pressurized gas storage is the sudden creation of a hole in the tank, with these results:

• the confinement function of the tank ceases

• the confined gas gets immediate access to the surrounding atmosphere.

The development of such an accident depends on these factors:

• the type and amount of gas in the tank

• the situation of the hole in relation to the tank’s contents

• the initial size and subsequent growth rate of the hole

• the temperature and pressure of the gas and the equipment

• the conditions in the immediate environment (sources of ignition, people, etc.).

The tank contents can be released almost immediately or over a period of time, and result in different scenarios, from the burst of free gas from a ruptured tank, to moderate and rather slow releases from small punctures.

The behaviour of various gases in the case of leakage

When developing release calculation models, it is most important to determine the following conditions affecting the system’s potential behaviour:

• the gas phase behind the hole (gaseous or liquid?)

• temperature and wind conditions

• the possible entry of other substances into the system or their possible presence in its surroundings

• barriers and other obstacles.

The exact calculations pertaining to a release process where liquefied gas escapes from a hole as a jet and then evaporates (or alternatively, first becomes a mist of droplets) are difficult. The specification of the later dispersion of the resultant clouds is also a difficult problem. Consideration must be given to the movements and dispersion of gas releases, whether the gas forms visible or invisible clouds and whether the gas rises or stays at ground level.

While hydrogen is a light gas compared to any atmosphere, ammonia gas (NH₃, with a molecular weight of 17.0) will rise in an ordinary air-like, oxygen-nitrogen atmosphere at the same temperature and pressure. Chlorine (Cl₂, with a molecular weight of 70.9) and butane (C₄H₁₀, mol. wt.58) are examples of chemicals whose gas phases are denser than air, even at ambient temperature. Acetylene (C₂H₂, mol. wt. 26.0) has a density of about 0.90g/l, approaching that of air (1.0g/l), which means that in a working environment, leaking welding gas will not have a pronounced tendency to float upwards or to sink downwards; therefore it can mix easily with the atmosphere.

But ammonia released from a pressure vessel as a liquid will at first cool as a consequence of its evaporation, and may then escape via several steps:

• Pressurized, liquid ammonia emanates from the hole in tank as jet or cloud.

• Seas of liquid ammonia can be formed on the nearest surfaces.

• The ammonia evaporates, thereby cooling itself and the near environment.

• Ammonia gas gradually exchanges heat with surroundings and equilibrates with ambient temperatures.

Even a cloud of light gas may not rise immediately from a liquid gas release; it may first form a fog - a cloud of droplets - and stay near the ground. The gas cloud’s movement and gradual mixing/dilution with the surrounding atmosphere depends on weather parameters and on the surrounding environment—enclosed area, open area, houses, traffic, presence of the public, workers and so on.

Tank Failure

Consequences of tank breakdown may involve fire and explosion, asphyxiation, poisoning and choking, as experience shows with gas production and gas handling systems (propane, methane, nitrogen, hydrogen, etc.), with ammonia or chlorine tanks, and with gas welding (using acetylene and oxygen). What actually initiates the formation of a hole in a tank has a strong influence on the hole “behaviour” - which in its turn influences the outflow of gas - and is crucial for the effectiveness of prevention efforts. A pressure vessel is designed and built to withstand certain conditions of use and environmental impact, and for handling a certain gas, or perhaps a choice of gases. The actual capabilities of a tank depend on its shape, materials, welding, protection, use and climate; therefore, evaluation of its adequacy as a container for dangerous gas must consider designer’s specifications, the tank’s history, inspections and tests. Critical areas include the welding seams used on most pressure vessels; the points where appurtenances such as inlets, outlets, supports and instruments are connected to the vessel; the flat ends of cylindrical tanks like railway tanks; and other aspects of even less optimal geometric shapes.

Welding seams are investigated visually, by x rays or by destructive test of samples, as these may reveal local defects, say, in the form of reduced strength that might endanger the overall strength of the vessel, or even be a triggering point for acute tank failure.

Tank strength is affected by the history of tank use - first of all by the normal wearing processes and the scratches and corrosion attacks typical of the particular industry and of the application. Other historical parameters of particular interest include:

• casual overpressure

• extreme heating or cooling (internal or external)

• mechanical impacts

• vibrations and stress

• substances that have been stored in or have passed through the tank

• substances used during cleansing, maintenance and repair.

The construction material - steel plate, aluminium plate, concrete for non-pressurized applications, and so on - can undergo deterioration from these influences in ways that are not always possible to check without overloading or destroying the equipment during testing.

Accident Case: Flixborough

The explosion of a large cloud of cyclohexane in Flixborough (UK) in 1974, which killed 28 persons and caused extensive plant damage, serves as a very instructive case. The triggering event was the breakdown of a temporary pipe serving as a substitute in a reactor unit. The accident was “caused” by a piece of hardware breaking down, but on closer investigation it was revealed that the breakdown followed from overload, and that the temporary construction was in fact inadequate for its intended use. After two months’ service, the pipe was exposed to bending forces due to a slight pressure rise of the 10-bar (10⁶ Pa) cyclohexane content at about 150°C. The two bellows between the pipe and the nearby reactors broke and 30 to 50 tonnes of cyclohexane was released and soon ignited, probably by a furnace some distance from the leak. (See figure 1.) A very readable account of the case is found in Kletz (1988).

Figure 1. Temporary connection between tanks at Flixborough

Hazard Analysis

The methods that have been developed to find the risks that may be relevant to a piece of equipment, to a chemical process or to a certain operation are referred to as “hazard analysis”. These methods ask questions such as: “What may possibly go wrong?” “Could it be serious?” and “What can be done about it?” Different methods of conducting the analyses are often combined to achieve a reasonable coverage, but no such set can do more than guide or assist a clever team of analysts in their determinations. The main difficulties with hazard analysis are as follows:

• availability of relevant data

• limitations of models and calculations

• new and unfamiliar materials, constructions and processes

• system complexity

• limitations on human imagination

• limitations on practical tests.

To produce usable risk evaluations under these circumstances it is important to stringently define the scope and the level of “ambitiousness” appropriate to the analysis at hand; for example, it is clear that one does not need the same sort of information for insurance purposes as for design purposes, or for the planning of protection schemes and the construction of emergency arrangements. Generally speaking, the risk picture must be filled in by mixing empirical techniques (i.e., statistics) with deductive reasoning and a creative imagination.

Different risk evaluation tools - even computer programs for risk analysis—can be very helpful. The hazard and operability study (HAZOP) and the failure mode and effect analysis (FMEA ) are commonly used methods for investigating hazards, especially in the chemical industry. The point of departure for the HAZOP method is the tracing of possible risk scenarios based on a set of guide words; for each scenario one has to identify probable causes and consequences. In the second stage, one tries to find means for reducing the probabilities or mitigating the consequences of those scenarios judged to be unacceptable. A review of the HAZOP method can be found in Charsley (1995). The FMEA method asks a series of “what if” questions for every possible risk component in order to thoroughly determine whatever failure modes may exist and then to identify the effects that they may have on system performance; such an analysis will be illustrated in the demonstration example (for a gas system) presented later in this article.

Fault trees and event trees and the modes of logical analysis proper to accident causation structures and probability reasoning are in no way specific to the analysis of hardware hazards, as they are general tools for system risk evaluations.

Tracing hardware hazards in an industrial plant

To identify possible hazards, information on construction and function can be sought from:

• actual equipment and plant

• substitutes and models

• drawings, electrical diagrams, piping and instrumentation (P/I) diagrams, etc.

• process descriptions

• control schemes

• operation modes and phases

• work orders, change orders, maintenance reports, etc.

By selecting and digesting such information, analysts form a picture of the risk object itself, its functions and its actual use. Where things are not yet constructed - or unavailable for inspection - important observations cannot be made and the evaluation must be based entirely on descriptions, intentions and plans. Such evaluation might seem rather poor, but in fact, most practical risk evaluations are made this way, either in order to seek authoritative approval for applications to undertake new construction, or to compare the relative safety of alternative design solutions. Real life processes will be consulted for the information not shown on the formal diagrams or described verbally by interview, and to verify that the information gathered from these sources is factual and represents actual conditions. These include the following:

• actual practice and culture

• additional failure mechanisms/construction details

• “sneak paths” (see below)

• common error causes

• risks from external sources/missiles

• particular exposures or consequences

• past incidents, accidents and near accidents.

Most of this additional information, especially sneak paths, is detectable only by creative, skilled observers with considerable experience, and some of the information would be almost impossible to trace with maps and diagrams. Sneak paths denote unintended and unforeseen interactions between systems, where the operation of one system affects the condition or operation of another system through other ways than the functional ones. This typically happens where functionally different parts are situated near each other, or (for example) a leaking substance drips on equipment beneath and causes a failure. Another mode of a sneak path’s action may involve the introduction of wrong substances or parts into a system by means of instruments or tools during operation or maintenance: the intended structures and their intended functions are changed through the sneak paths. By common-mode failures one means that certain conditions - like flooding, lightning or power failure - can disturb several systems at once, perhaps leading to unexpectedly large blackouts or accidents. Generally, one tries to avoid sneak-path effects and common-mode failures through proper layouts and introducing distance, insulation and diversity in working operations.

A Hazards Analysis Case: Gas Delivery from a Ship to a Tank

Figure 2 shows a system for delivery of gas from a transport ship to a storage tank. A leak could appear anywhere in this system: ship, transmission line, tank or output line; given the two tank reservoirs, a leak somewhere on the line could remain active for hours.

Figure 2. Transmission line for delivery of liquid gas from ship to storage tank

The most critical components of the system are the following:

• the storage tank

• the pipeline or hose between the tank and the ship

• other hoses, lines, valves and connections

• the safety valve on the storage tank

• the emergency shut-down valves ESD 1 and 2.

A storage tank with a large inventory of liquid gas is put at the top of this list, because it is difficult to stop a leak from a tank on short notice. The second item on the list - the connection to the ship - is critical because leaks in the pipe or hose and loose connections or couplings with worn gaskets, and variations among different ships, could release product. Flexible parts like hoses and bellows are more critical than rigid parts, and require regular maintenance and inspection. Safety devices like the pressure release valve on the top of the tank and the two emergency shut-down valves are critical, since they must be relied upon to reveal latent or developing failures.

Up to this point, the ranking of system components as to their importance with respect to reliability has been of a general nature only. Now, for analytical purposes, attention will be drawn to the particular functions of the system, the chief one of course being the movement of liquefied gas from the ship to the storage tank until the connected ship tank is empty. The overriding hazard is a gas leak, the possible contributory mechanisms being one of more of the following:

• leaking couplings or valves

• tank rupture

• rupture of pipe or hose

• tank breakdown.

Application of the FMEA method

The central idea of the FMEA approach, or “what if” analysis, is to record explicitly, for each component of the system, its failure modes, and for every failure to find the possible consequences to the system and to the environment. For standard components like a tank, pipe, valve, pump, flowmeter and so on, the failure modes follow general patterns. In the case of a valve, for instance, failure modes could include the following conditions:

• The valve cannot close on demand (there is reduced flow through an “open” valve).

• The valve leaks (there is residual flow through a “closed” valve).

• The valve cannot open on demand (the valve position oscillates).

For a pipeline, failure modes would consider items such as:

• a reduced flow

• a leak

• a flow stopped due to blockage

• a break in the line.

The effects of leaks seem obvious, but sometimes the most important effects may not be the first effects: what happens for example, if a valve is stuck in a half-open position? An on-off valve in the delivery line that does not open completely on demand will delay the tank filling process, a non-dangerous consequence. But if the “stuck half-open” condition arises at the same time that a closing demand is made, at a time when the tank is almost full, overfilling might result (unless the emergency shut-down valve is successfully activated). In a properly designed and operated system, the probability of both these valves being stuck simultaneously will be kept rather low.

Plainly a safety valve’s not operating on demand could mean disaster; in fact, one might justifiably state that latent failures are constantly threatening all safety devices. Pressure relief valves, for instance, can be defective due to corrosion, dirt or paint (typically due to bad maintenance), and in the case of liquid gas, such defects in combination with the temperature decrease at a gas leak could produce ice and thereby reduce or perhaps stop the flow of material through a safety valve. If a pressure relief valve does not operate on demand, pressure may build up in a tank or in connected systems of tanks, eventually causing other leaks or tank rupture.

For simplicity, instruments are not shown on figure 2; there will of course be instruments related to pressure, flow and temperature, which are essential parameters for monitoring the system state, relevant signals being transmitted to operator consoles or to a control room for control and monitoring purposes. Furthermore, there will be supply lines other than those intended for materials transport - for electricity, hydraulics and so forth - and extra safety devices. A comprehensive analysis must go through these systems as well and look for the failure modes and effects of these components also. In particular, the detective work on common-mode effects and sneak paths requires one to construct the integral picture of main system components, controls, instruments, supplies, operators, working schedules, maintenance and so on.

Examples of common-mode effects to consider in connection with gas systems are addressed by such questions as these:

• Are activation signals for delivery valves and emergency shut-down valves transmitted on a common line (cable, cabling channels)?

• Do two given valves share the same power line?

• Is maintenance performed by the same person according to a given schedule?

Even an excellently designed system with redundancy and independent power lines can suffer from inferior maintenance, where, for example, a valve and its back-up valve (the emergency shut-down valve in our case) have been left in a wrong state after a test. A prominent common-mode effect with an ammonia-handling system is the leak situation itself: a moderate leak can make all manual operations on plant components rather awkward - and delayed - due to the deployment of the required emergency protection.

Summary

The hardware components are very seldom the guilty parts in accident development; rather, there are root causes to be found in other links of the chain: wrong concepts, bad designs, maintenance errors, operator errors, management errors and so on. Several examples of the specific conditions and acts that may lead to failure development have already been given; a broad collection of such agents would take account of the following:

• collision

• corrosion, etching

• excessive loads

• failing support and aged or worn-out parts

• low-quality welding jobs

• missiles

• missing parts

• overheating or chilling

• vibration

• wrong construction material used.

Controlling the hardware hazards in a working environment requires the review of all possible causes and respect for the conditions that are found to be critical with the actual systems. The implications of this for the organization of risk management programmes are dealt with in other articles, but, as the foregoing list clearly indicates, the monitoring and control of hardware conditions can be necessary all the way back to the choice of concepts and designs for the selected systems and processes.

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This article examines the role of human factors in the accident causation process and reviews the various preventive measures (and their effectiveness) by which human error may be controlled, and their application to the accident causation model. Human error is an important contributing cause in at least 90 of all industrial accidents. While purely technical errors and uncontrollable physical circumstances may also contribute to accident causation, human error is the paramount source of failure. The increased sophistication and reliability of machinery means that the proportion of causes of accidents attributed to human error increases as the absolute number of accidents decreases. Human error is also the cause of many of those incidents that, although not resulting in injury or death, nevertheless result in considerable economic damage to a company. As such, it represents a major target for prevention, and it will become increasingly important. For effective safety management systems and risk identification programmes it is important to be able to identify the human component effectively through the use of general failure type analysis.

The Nature of Human Error

Human error can be viewed as the failure to reach a goal in the way that was planned, either from a local or wider perspective, due to unintentional or intentional behaviour. Those planned actions may fail to achieve the desired outcomes for the following four reasons:

1. Unintentional behaviour:

• The actions did not go as planned (slips).

• The action was not executed (lapses).

2. Intentional behaviour:

• The plan itself was inadequate (mistakes).

• There were deviations from the original plan (violations).

Deviations can be divided in three classes: skill-, rule- and knowledge-based errors.

1. At the skill-based level, behaviour is guided by pre-programmed action schemes. The tasks are routine and continuous, and feedback is usually lacking.
2. At the rule-based level, behaviour is guided by general rules. They are simple and can be applied many times in specific situations. The tasks consist of relatively frequent action sequences that start after a choice is made among rules or procedures. The user has a choice: the rules are not automatically activated, but are actively chosen.
3. Knowledge-based behaviour is shown in completely new situations where no rules are available and where creative and analytical thinking is required.

In some situations, the term human limitation would be more appropriate than human error. There also are limits to the ability to foresee the future behaviour of complex systems (Gleick 1987; Casti 1990).

Reason and Embrey’s model, the Generic Error Modelling System (GEMS) (Reason 1990), takes into account the error-correcting mechanisms on the skill-, rule- and knowledge-based levels. A basic assumption of GEMS is that day-to-day behaviour implies routine behaviour. Routine behaviour is checked regularly, but between these feedback loops, behaviour is completely automatic. Since the behaviour is skill-based, the errors are slips. When the feedback shows a deviation from the desired goal, rule-based correction is applied. The problem is diagnosed on the basis of available symptoms, and a correction rule is automatically applied when the situation is diagnosed. When the wrong rule is applied there is a mistake.

When the situation is completely unknown, knowledge-based rules are applied. The symptoms are examined in the light of knowledge about the system and its components. This analysis can lead to a possible solution the implementation of which constitutes a case of knowledge-based behaviour. (It is also possible that the problem cannot be solved in a given way and that further knowledge-based rules have to be applied.) All errors on this level are mistakes. Violations are committed when a certain rule is applied that is known to be inappropriate: the thinking of the worker may be that application of an alternative rule will be less time-consuming or is possibly more suitable for the present, probably exceptional, situation. The more malevolent class of violations involves sabotage, a subject that is not within the scope of this article. When organizations are attempting to eliminate human error, they should take into account whether the errors are on the skill-, rule- or knowledge-based level, as each level requires its own techniques (Groeneweg 1996).

Influencing Human Behaviour: An Overview

A comment often made with regard to a particular accident is, “Maybe the person did not realize it at the time, but if he or she had not acted in a certain way, the accident would not have happened.” Much of accident prevention is aimed at influencing the crucial bit of human behaviour alluded to in this remark. In many safety management systems, the solutions and policies suggested are aimed at directly influencing human behaviour. However, it is very uncommon that organizations assess how effective such methods really are. Psychologists have devoted much thought to how human behaviour can best be influenced. In this respect, the following six ways of exercising control over human error will be set forth, and an evaluation will be performed of the relative effectiveness of these methods in controlling human behaviour on a long-term basis (Wagenaar 1992). (See table 1.)

Table 1. Six ways to induce safe behaviour and assessment of their cost-effectiveness

Do not attempt to induce safe behaviour, but make the system “foolproof”

The first option is to do nothing to influence the behaviour of people but to design the workplace in such a way that whatever the employee does, it will not result in any kind of undesirable outcome. It must be acknowledged that, thanks to the influence of robotics and ergonomics, designers have considerably improved on the user-friendliness of workplace equipment. However, it is almost impossible to anticipate all the different kinds of behaviour that people may evince. Besides, workers often regard so-called foolproof designs as a challenge to “beat the system”. Finally, as designers are human themselves, even very carefully foolproof-designed equipment can have flaws (e.g., Petroski 1992). The additional benefit of this approach relative to existing hazard levels is marginal, and in any event initial design and installation costs may increase exponentially.

Tell those involved what to do

Another option is to instruct all workers about every single activity in order to bring their behaviour fully under the control of management. This will require an extensive and not very practical task inventory and instruction control system. As all behaviour is de-automated it will to a large extent eliminate slips and lapses until the instructions become part of the routine and the effect fades away.

It does not help very much to tell people that what they do is dangerous - most people know that very well - because they will make their own choices concerning risk regardless of attempts to persuade them otherwise. Their motivation to do so will be to make their work easier, to save time, to challenge authority and perhaps to enhance their own career prospects or claim some financial reward. Instructing people is relatively cheap, and most organizations have instruction sessions before the start of a job. But beyond such an instruction system the effectiveness of this approach is assessed to be low.

Reward and punish

Although reward and punishment schedules are powerful and very popular means for controlling human behaviour, they are not without problems. Reward works best only if the recipient perceives the reward to be of value at the time of receipt. Punishing behaviour that is beyond an employee’s control (a slip) will not be effective. For example, it is more cost-effective to improve traffic safety by changing the conditions underlying traffic behaviour than by public campaigns or punishment and reward programmes. Even an increase in the chances of being “caught” will not necessarily change a person’s behaviour, as the opportunities for violating a rule are still there, as is the challenge of successful violation. If the situations in which people work invite this kind of violation, people will automatically choose the undesired behaviour no matter how they are punished or rewarded. The effectiveness of this approach is rated as of medium quality, as it usually is of short-term effectiveness.

Increase motivation and awareness

Sometimes it is believed that people cause accidents because they lack motivation or are unaware of danger. This assumption is false, as studies have shown (e.g., Wagenaar and Groeneweg 1987). Furthermore, even if workers are capable of judging danger accurately, they do not necessarily act accordingly (Kruysse 1993). Accidents happen even to people with the best motivation and the highest degree of safety awareness. There are effective methods for improving motivation and awareness which are discussed below under “Change the environment”. This option is a delicate one: in contrast with the difficulty to further motivate people it is almost too easy to de-motivate employees to the extent that even sabotage is considered.

The effects of motivation enhancement programmes are positive only when coupled with behaviour modification techniques such as employee involvement.

Select trained personnel

The first reaction to an accident is often that those involved must have been incompetent. With hindsight, the accident scenarios appear straightforward and easily preventable to someone sufficiently intelligent and properly trained, but this appearance is a deceptive one: in actual fact the employees involved could not possibly have foreseen the accident. Therefore, better training and selection will not have the desirable effect. A base level of training is however a prerequisite for safe operations. The tendency in some industries to replace experienced personnel with inexperienced and inadequately trained people is to be discouraged, as increasingly complex situations call for rule- and knowledge-based thinking that requires a level of experience that such lower-cost personnel often do not possess.

A negative side-effect of instructing people very well and selecting only the highest-classified people is that behaviour can become automatic and slips occur. Selection is expensive, while the effect is not more than medium.

Change the environment

Most behaviour occurs as a reaction to factors in the working environment: work schedules, plans, and management expectations and demands. A change in the environment results in different behaviour. Before the working environment can be effectively changed, several problems must be solved. First, the environmental factors that cause the unwanted behaviour must be identified. Second, these factors must be controlled. Third, management must allow discussion about their role in creating the adverse working environment.

It is more practical to influence behaviour through creating the proper working environment. The problems that should be solved before this solution can be put into practice are (1) that it must be known which environmental factors cause the unwanted behaviour, (2) that these factors must be controlled and (3) that previous management decisions must be considered (Wagenaar 1992; Groeneweg 1996). All these conditions can indeed be met, as will be argued in the remainder of this article. The effectiveness of behaviour modification can be high, even though a change of environment may be quite costly.

The Accident Causation Model

In order to get more insight into the controllable parts of the accident causation process, an understanding of the possible feedback loops in a safety information system is necessary. In figure 1, the complete structure of a safety information system is presented that can form the basis of managerial control of human error. It is an adapted version of the system presented by Reason et al. (1989).

Figure 1. A safety information system 

Accident investigation

When accidents are investigated, substantial reports are produced and decision-makers receive information about the human error component of the accident. Fortunately, this is becoming more and more obsolete in many companies. It is more effective to analyse the “operational disturbances” that precede the accidents and incidents. If an accident is described as an operational disturbance followed by its consequences, then sliding from the road is an operational disturbance and getting killed because the driver did not wear a safety belt is an accident. Barriers may have been placed between the operational disturbance and the accident, but they failed or were breached or circumvented.

Unsafe act auditing

A wrong act committed by an employee is called a “substandard act” and not an “unsafe act” in this article: the notion of “unsafe” seems to limit the applicability of the term to safety, whereas it can also be applied, for example, to environmental problems. Substandard acts are sometimes recorded, but detailed information as to which slips, mistakes and violations were performed and why they were performed is hardly ever fed back to higher management levels.

Investigating the employee’s state of mind

Before a substandard act is committed, the person involved was in a certain state of mind. If these psychological precursors, like being in a state of haste or feeling sad, could be adequately controlled, people would not find themselves in a state of mind in which they would commit a substandard act. Since these states of mind cannot be effectively controlled, such precursors are regarded as “black box” material (figure 1).

General failure types

The GFT (general failure type) box in figure 1 represents the generating mechanisms of an accident - the causes of substandard acts and situations. Because these substandard acts cannot be controlled directly, it is necessary to change the working environment. The working environment is determined by 11 such mechanisms (table 2). (In the Netherlands the abbreviation GFT already exists in a completely different context, and has to do with ecologically sound waste disposal, and to avoid confusion another term is used: basic risk factors (BRFs) (Roggeveen 1994).)

Table 2. General failure types and their definitions

The GFT box is preceded by a “decision-maker’s” box, as these people determine to a large extent how well a GFT is managed. It is management’s task to control the working environment by managing the 11 GFTs, thereby indirectly controlling the occurrence of human error.

All these GFTs can contribute to accidents in subtle ways by allowing undesirable combinations of situations and actions to come together, by increasing the chance that certain persons will commit substandard acts and by failing to provide the means to interrupt accident sequences already in progress.

There are two GFTs that require some further explanation: maintenance management and defences.

Maintenance management (MM)

Since maintenance management is a combination of factors that can be found in other GFTs, it is not, strictly speaking, a separate GFT: this type of management is not fundamentally different from other management functions. It may be treated as a separate issue because maintenance plays an important role in so many accident scenarios and because most organizations have a separate maintenance function.

Defences (DF)

The category of defences is also not a true GFT, as it is not related to the accident causation process itself. This GFT is related to what happens after an operational disturbance. It does not generate either psychological states of mind or substandard acts by itself. It is a reaction that follows a failure due to the action of one or more GFTs. While it is indeed true that a safety management system should focus on the controllable parts of the accident causation chain before and not after the unwanted incident, nevertheless the notion of defences can be used to describe the perceived effectiveness of safety barriers after a disturbance has occurred and to show how they failed to prevent the actual accident.

Managers need a structure that will enable them to relate identified problems to preventive actions. Measures taken at the levels of safety barriers or substandard acts are still necessary, although these measures can never be completely successful. To trust “last line” barriers is to trust factors that are to a large extent out of management control. Management should not attempt to manage such uncontrollable external devices, but instead must try to make their organizations inherently safer at every level.

Measuring the Level of Control over Human Error

Ascertaining the presence of the GFTs in an organization will enable accident investigators to identify the weak and strong points in the organization. Given such knowledge, one can analyse accidents and eliminate or mitigate their causes and identify the structural weaknesses within a company and fix them before they in fact contribute to an accident.

Accident investigation

The task of an accident analyst is to identify contributing factors and to categorize them. The number of times a contributing factor is identified and categorized in terms of a GFT indicates the extent to which this GFT is present. This is often done by means of a checklist or computer analysis program.

It is possible and desirable to combine profiles from different but similar types of accidents. Conclusions based upon an accumulation of accident investigations in a relatively short time are far more reliable than those drawn from a study in which the accident profile is based upon a single event. An example of such a combined profile is presented in figure 2, which shows data relating to four occurrences of one type of accident.

Figure 2. Profile of an accident type

Some of the GFTs - design, procedures and incompatible goals - score consistently high in all four particular accidents. This means that in each accident, factors have been identified that were related to these GFTs. With respect to the profile of accident 1, design is a problem. Housekeeping, although a major problem area in accident 1, is only a minor problem if more than the first accident is analysed. It is suggested that about ten similar types of accidents be investigated and combined in a profile before far-reaching and possibly expensive corrective measures are taken. This way, the identification of the contributing factors and subsequent categorization of these factors can be done in a very reliable way (Van der Schrier, Groeneweg and van Amerongen 1994).

Identifying the GFTs within an organization pro-actively

It is possible to quantify the presence of GFTs pro-actively, regardless of the occurrence of accidents or incidents. This is done by looking for indicators of the presence of that GFT. The indicator used for this purpose is the answer to a straightforward yes or no question. If answered in the undesired way, it is an indication that something is not functioning properly. An example of an indicator question is: “In the past three months, did you go to a meeting that turned out to be cancelled?” If the employee answers the question in the affirmative, it does not necessarily signify danger, but it is indicative of a deficiency in one of the GFTs—communication. However, if enough questions that test for a given GFT are answered in a way that indicates an undesirable trend, it is a signal to management that it does not have sufficient control of that GFT.

To construct a system safety profile (SSP), 20 questions for each of the 11 GFTs have to be answered. Each GFT is assigned a score ranging from 0 (low level of control) to 100 (high level of control). The score is calculated relative to the industry average in a certain geographical area. An example of this scoring procedure is presented in the box. 

The indicators are pseudo-randomly drawn from a database with a few hundred questions. No two subsequent checklists have questions in common, and questions are drawn in such a way that each aspect of the GFT is covered. Failing hardware could, for instance, be the result of either absent equipment or defective equipment. Both aspects should be covered in the checklist. The answering distributions of all questions are known, and checklists are balanced for equal difficulty.

It is possible to compare scores obtained with different checklists, as well as those obtained for different organizations or departments or the same units over a period of time. Extensive validation tests have been done to ensure that all questions in the database have validity and that they are all indicative of the GFT to be measured. Higher scores indicate a higher level of control - that is, more questions have been answered in the “desired” way. A score of 70 indicates that this organization is ranked among the best 30 (i.e., 100 minus 70) of comparable organizations in this kind of industry. Although a score of 100 does not necessarily mean that this organization has total control over a GFT, it does means that with regard to this GFT the organization is the best in the industry.

An example of an SSP is shown in figure 3. The weak areas of Organization 1, as exemplified by the bars in the chart, are procedures, incompatible goals, and error enforcing conditions, as they score below the industry average as shown by the dark grey area. The scores on housekeeping, hardware and defences are very good in Organization 1. On the surface, this well-equipped and tidy organization with all safety devices in place appears to be a safe place to work. Organization 2 scores exactly at the industry average. There are no major deficiencies, and although the scores on hardware, housekeeping and defences are lower, this company manages (on the average) the human error component in accidents better than Organization 1. According to the accident causation model, Organization 2 is safer than Organization 1, although this would not necessarily be apparent in comparing the organizations in “traditional” audits.

Figure 3. Example of a system safety profile

If these organizations had to decide where to allocate their limited resources, the four areas with below average GFTs would have priority. However, one cannot conclude that, since the other GFT scores are so favourable, resources may be safely withdrawn from their upkeep, since these resources are what have most probably kept them at so high a level in the first place.

Conclusions

This article has touched upon the subject of human error and accident prevention. The overview of the literature regarding control of the human error component in accidents yielded a set of six ways by which one can try to influence behaviour. Only one, restructuring the environment or modifying behaviour in order to reduce the number of situations in which people are liable to commit an error, has a reasonably favourable effect in a well-developed industrial organization where many other attempts have already been made. It will take courage on the part of management to recognize that these adverse situations exist and to mobilize the resources that are needed to effect a change in the company. The other five options do not represent helpful alternatives, as they will have little or no effect and will be quite costly.

“Controlling the controllable” is the key principle supporting the approach presented in this article. The GFTs must be discovered, attacked and eliminated. The 11 GFTs are mechanisms that have proven to be part of the accident causation process. Ten of them are aimed at preventing operational disturbances and one (defences) is aimed at the prevention of the operational disturbance’s turning into an accident. Eliminating the impact of the GFTs has a direct bearing upon the abatement of contributing causes of accidents. The questions in the checklists are aimed at measuring the “health state” of a given GFT, from both a general and a safety point of view. Safety is viewed as an integrated part of normal operations: doing the job the way it should be done. This view is in accordance with the recent “quality oriented” management approaches. The availability of policies, procedures and management tools is not the chief concern of safety management: the question is rather whether these methods are actually used, understood and adhered to.

The approach described in this article concentrates upon systemic factors and the way in which management decisions can be translated into unsafe conditions at the workplace, in contrast to the conventional belief that attention should be directed towards the individual workers who perform unsafe acts, their attitudes, motivations and perceptions of risk.

An indication of the level of control your organization has over the GFT “Communication”

In this box a list of 20 questions is presented. The questions in this list have been answered by employees of more than 250 organizations in Western Europe. These organizations were operating in different fields, ranging from chemical companies to refineries and construction companies. Normally, these questions would be tailor-made for each branch. This list serves as an example only to show how the tool works for one of the GFTs. Only those questions have been selected that have proved to be so “general” that they are applicable in at least  80% of the industries.

In “real life” employees would not only have to answer the questions (anonymously), they would also have to motivate their answers. It is not sufficient to answer “Yes” on, for example, the indicator “Did you have to work in the past 4 weeks with an outdated procedure?” The employee would have to indicate which procedure it was and under which conditions it had to be applied. This motivation serves two goals: it increases the reliability of the answers and it provides management with information it can act upon.

Caution is also necessary when interpreting the percentile score: in a real measurement, each organization would be matched against a representative sample of branch-related organizations for each of the 11 GFTs. The distribution of percentiles is from May 1995, and this distribution does change slightly over time.

How to measure the “level of control”

Answer all 20 indicators with your own situation in mind and beware of the time limits in the questions. Some of the questions might not be applicable for your situation; answer them with “n.a.” It might be impossible for you to answer some questions; answer them with a question mark“?”.

After you have answered all questions, compare your answers with the reference answers. You get a point for each “correctly” answered question.

Add the number of points together. Calculate the percentage of correctly answered questions by dividing the number of points by the number of questions you have answered with either “Yes” or “No”. The “n.a.” and “?” answers are not taken into account. The result is a percentage between 0 and 100.

The measurement can be made more reliable by having more people answering the questions and by averaging their scores over the levels or functions in the organization or comparable departments.

Twenty questions about the GFT “Communication”

Possible answers to the questions: Y = Yes; N = No; n.a.  = not applicable; ?  = don’t know.

1. In the past 4 weeks has the telephone directory provided you with incorrect or insufficient information?
2. In the past 2 weeks has your telephone conversation been interrupted due to a malfunctioning of the telephone system?
3. Have you received mail in the past week that was not relevant to you?
4. Has there been an internal or external audit in the past 9 months of your office paper trail?
5. Was more than 20% of the information you received in the past 4 weeks labelled “urgent”?
6. Did you have to work in the past 4 weeks with a procedure that was difficult to read (e.g., phrasing or language problems)?
7. Have you gone to a meeting in the past 4 weeks that turned out not to be held at all?
8. Has there been a day in the past 4 weeks that you had five or more meetings?
9. Is there a “suggestion box” in your organization?
10. Have you been asked to discuss a matter in the past 3 months that later turned out to be already decided upon?
11. Have you sent any information in the past 4 weeks that was never received?
12. Have you received information in the past 6 months about changes in policies or procedures more than a month after it had been put into effect?
13. Have the minutes of the last three safety meetings been sent to your management?
14. Has “office” management stayed at least 4 hours at the location when making the last site visit?
15. Did you have to work in the past 4 weeks with procedures with conflicting information?
16. Have you received within 3 days feedback on requests for information in the past 4 weeks?
17. Do people in your organization speak different languages or dialects (different mother tongue)?
18. Was more than 80% of the feedback you received (or gave) from management in the past 6 months of a “negative nature”?
19. Are there parts of the location/workplace where it is difficult to understand each other due to extreme noise levels?
20. In the past 4 weeks, have tools and/or equipment been delivered that not had been ordered?

Reference answers:

1 = N; 2 = N; 3 = N; 4 = Y; 5 = N; 6 = N; 7 = N; 8 = N; 9 = N; 10 = N; 11 = N; 12 = N; 13 = Y; 14 = N; 15 = N; 16 = Y; 17 = N; 18 = N; 19 = Y; 20 = N.

Scoring GFT “Communication”

Percent score = (a/b) x 100

where a = no. of questions answered correctly

where b = no. of questions answered “Y” or “N”.

Back

The helicopter is a very special type of aircraft. It is used in every part of the world and serves a variety of purposes and industries. Helicopters vary in size from the smallest single-seat helicopters to giant heavy-lift machines with gross weights in excess of 100,000 kg, which is about the same size as a Boeing 757. The purpose of this article is to discuss some of the safety and health challenges of the machine itself, the different missions it are used for, both civilian and military, and the helicopter’s operating environment.

The helicopter itself presents some very unique safety and health challenges. All helicopters use a main rotor system. This is the lifting body for the machine and serves the same purpose as the wings on a conventional airplane. Rotor blades are a significant hazard to people and property because of their size, mass and rotational speed, which also makes them difficult to see from certain angles and in different lighting conditions.

The tail rotor is also a hazard. It is usually much smaller than the main rotor and turns at a very high rate, so it too is very difficult to see. Unlike the main rotor system, which sits atop the helicopter’s mast, the tail rotor is often near ground level. People should approach a helicopter from the front, in view of the pilot, to avoid coming into contact with the tail rotor. Extra care should be taken to identify or remove obstacles (such as bushes or fences) in a temporary or unimproved helicopter landing area. Contact with the tail rotor can cause injury or death as well as serious damage to the property or helicopter.

Many people recognize the characteristic slap sound of a helicopter’s rotor system. This noise is encountered only when the helicopter is in forward flight, and is not considered a health problem. The compressor section of the engine produces extremely loud noise, often in excess of 140 dBA, and unprotected exposure must be avoided. Hearing protection (ear plugs and a noise attenuating headset or helmet) should be worn when working in and around helicopters.

There are several other hazards to consider when working with helicopters. One is flammable or combustible liquids. All helicopters require fuel to run the engine(s). The engine and the main and tail rotor transmissions use oil for lubrication and cooling. Some helicopters have one or more hydraulic systems and use hydraulic fluid.

Helicopters build a static electric charge when the rotor system is turning and/or the helicopter is flying. The static charge will dissipate when the helicopter touches the ground. If an individual is required to grab a line from a hovering helicopter, as during logging, external lifts or rescue efforts, that person should let the load or line touch the ground before grabbing it in order to avoid a shock.

Rescue/air ambulance. The helicopter was originally designed with rescue in mind, and one of its most widespread uses is as an ambulance. These are often found at the scene of an accident or disaster (see figure 2). They can land in confined areas with qualified medical teams on board who care for the injured at the scene while en route to a medical facility. Helicopters are also used for non-emergency flights when speed of transport or patient comfort is required.

Offshore oil support. Helicopters are used to help supply offshore oil operations. They transport people and supplies between land and platform and between platforms.

Executive/personal transport. The helicopter is used for point-to-point transportation. This is usually done over short distances where geography or sluggish traffic conditions prevent rapid ground transportation. Corporations build helipads on company property to allow easy access to airports or to facilitate transportation between facilities.

Sightseeing. The use of helicopters in the tourist industry has seen continuous growth. The excellent view from the helicopter combined with its ability to access remote areas make it a popular attraction.

Law enforcement. Many police departments and governmental agencies use helicopters for this type of work. The helicopter’s mobility in crowded urban areas and remote rural areas makes it invaluable. The largest rooftop helipad in the world is at the Los Angeles Police Department.

Film operations. Helicopters are a staple in action movies. Other types of movies and film-based entertainment are filmed from helicopters.

News gathering. Television and radio stations employ helicopters for traffic spotting and news gathering. Their ability to land at the place where the news is happening makes them a valuable asset. Many of them are also equipped with microwave transceivers so they can send their stories, live, over fairly long distances, while en route.

Heavy lift. Some helicopters are designed to carry heavy loads at the end of external lines. Aerial logging is one application of this concept. Construction and oil exploration crews make extensive use of the helicopter’s capacity for lifting large or bulky objects into place.

Aerial application. Helicopters can be fitted with spray booms and loaded to dispense herbicides, pesticides and fertilizers. Other devices can be added that allow helicopters to fight fires. They can drop either water or chemical retardants.
 

Military

Rescue/aerial ambulance. The helicopter is used widely in humanitarian efforts. Many nations around the world have coast guards that engage in maritime rescue work. Helicopters are used to transport the sick and wounded from battle areas. Still others are sent to rescue or recover people from behind enemy lines.

Attack. Helicopters can be armed and used as attack platforms over land or sea. Weapon systems include machine guns, rockets and torpedoes. Sophisticated targeting and guidance systems are used to lock on to and destroy targets at longe range.

Transport. Helicopters of all sizes are used to transport people and supplies over land or sea. Many ships are equipped with helipads to facilitate offshore operations.

The Helicopter Operating Environment

The helicopter is used all over the world in a variety of ways (see, for example, figure 1 and figure 2). In addition, it is often working very near the ground and other obstructions. This requires constant vigilance from the pilots and those who work with or ride on the aircraft. By contrast, the fixed-wing aircraft environment is more predictable, since they fly (especially the commercial airplanes) primarily from airports whose airspace is tightly controlled.

Figure 1. H-46 helicopter landing in the Arizona, US, desert.

Figure 2.  5-76A Cougar helicopter landing in field at accident site.

The combat environment presents special dangers. The military helicopter also operates in a low-level environment and is subject to the same hazards. The proliferation of inexpensive, hand-carried, heat-seeking missiles represents another danger to rotorcraft. The military helicopter can use the terrain to hide itself or to mask its telltale signature, but when in the open it is vulnerable to small-arms fire and missiles.

Military forces also use night vision goggles (NVG) to enhance the pilot’s view of the area in low-light conditions. While the NVGs do increase the pilot’s ability to see, they have severe operating limitations. One major drawback is the lack of peripheral vision, which has contributed to mid-air collisions.

Accident Prevention Measures

Preventive measures can be grouped into several categories. Any one prevention category or item will not, in and of itself, prevent accidents. All of them must be used in concert to maximize their effectiveness.

Operational policies

Operational policies are formulated in advance of any operations. They are usually provided by the company with the operating certificate. They are crafted from governmental regulations, manufacturer’s recommended guidelines, industry standards, best practices and common sense. In general, they have proven to be effective in preventing incidents and accidents and include:

• Establishment of best practices and procedures. Procedures are essential for accident prevention. When not used, such as in early helicopter ambulance operations, there were extremely high accident rates. In the absence of regulatory guidance, pilots attempted to support humanitarian missions at night and/or in poor weather conditions with minimal training and helicopters that were ill equipped for such flights, leading to accidents.

• Crew resource management (CRM). CRM began as “cockpit resource management” but has since progressed to crew resource management. CRM is based on the idea that people in the crew should be free to discuss any situation among themselves to assure the successful completion of the flight. While many helicopters are flown by a single pilot, they are often working with other people who are either in the helicopter or on the ground. These people can provide information about the operation if consulted or allowed to speak. When such interaction occurs, CRM then becomes company resource management. Such collaboration is an acquired skill and should be taught to crews, company employees and others that work with and around helicopters.

• Provision of a threat-free company environment. Helicopter operations can be seasonal. This means long, tiring days. Crews should be able to end their duty day without fear of recrimination. If there are other, similar, operational deficiencies, crews should be permitted to openly identify, discuss and correct them.

• Physical hazards awareness. The helicopter presents an array of hazards. The aircraft’s dynamic components, its main and tail rotors, must be avoided. All passengers and crew members should be briefed on their location and on how to avoid coming into contact with them. The component’s surfaces should be painted to enhance their visibility. The helicopter should be positioned so that it is difficult for people to get to the tail rotor. Noise protection must be provided, especially to those with continuous exposure.

• Training for abnormal conditions. Training is often limited, if available at all, to practising autorotations for engine-out conditions. Simulators can provide exposure to a much wider range of atypical conditions without exposing the crew or machine to the real condition.

Crew practices

• Published procedures. One study of accidents has shown that, in more than half the cases, the accident would have been prevented had the pilot followed known, published procedures.

• Crew resource management. CRM should be used.

• Anticipating and avoiding known problems. Most helicopters are not equipped to fly in icing conditions and are prohibited from flying in moderate or severe turbulence, yet numerous accidents result from these circumstances. Pilots should anticipate and avoid these and other equally compromising conditions.

• Special or non-standard operations. Pilots must be thoroughly briefed for such circumstances.

Support operations

The following are crucial support operations for the safe use of helicopters:

• following published procedures

• briefing all passengers prior to boarding the helicopter

• keeping facilities free of obstructions

• keeping facilities well lit for night operations.

Back

Since the first sustained flight of a powered aircraft at Kitty Hawk, North Carolina (United States), in 1903, aviation has become a major international activity. It is estimated that from 1960 to 1989, the annual number of air passengers of regularly scheduled flights increased from 20 million to over 900 million (Poitrast and deTreville 1994). Military aircraft have become indispensable weapons systems for the armed forces of many nations. Advances in aviation technology, in particular the design of life support systems, have contributed to the rapid development of space programmes with human crews. Orbital space flights occur relatively frequently, and astronauts and cosmonauts work in space vehicles and space stations for extended periods of time.

In the aerospace environment, physical stressors that may affect the health of aircrew, passengers and astronauts to some degree include reduced concentrations of oxygen in the air, decreased barometric pressure, thermal stress, acceleration, weightlessness and a variety of other potential hazards (DeHart 1992). This article describes aeromedical implications of exposure to gravity and acceleration during flight in the atmosphere and the effects of microgravity experienced in space.

Gravity and Acceleration

The combination of gravity and acceleration encountered during flight in the atmosphere produces a variety of physiological effects experienced by aircrew and passengers. At the surface of the earth, the forces of gravity affect virtually all forms of human physical activity. The weight of a person corresponds to the force exerted upon the mass of the human body by the earth’s gravitational field. The symbol used to express the magnitude of the acceleration of an object in free fall when it is dropped near the earth’s surface is referred to as g, which corresponds to an acceleration of approximately 9.8 m/s² (Glaister 1988a; Leverett and Whinnery 1985).

Acceleration occurs whenever an object in motion increases its velocity. Velocity describes the rate of movement (speed) and direction of motion of an object. Deceleration refers to acceleration that involves a reduction in established velocity. Acceleration (as well as deceleration) is a vector quantity (it has magnitude and direction). There are three types of acceleration: linear acceleration, a change of speed without change in direction; radial acceleration, a change in direction without a change of speed; and angular acceleration, a change in speed and direction. During flight, aircraft are capable of manoeuvring in all three directions, and crew and passengers may experience linear, radial and angular accelerations. In aviation, applied accelerations are commonly expressed as multiples of the acceleration due to gravity. By convention, G is the unit expressing the ratio of an applied acceleration to the gravitational constant (Glaister 1988a; Leverett and Whinnery 1985).

Biodynamics

Biodynamics is the science dealing with the force or energy of living matter and is a major area of interest within the field of aerospace medicine. Modern aircraft are highly manoeuvrable and capable of flying at very high speeds, causing accelerative forces upon the occupants. The influence of acceleration upon the human body depends upon the intensity, rate of onset and direction of acceleration. The direction of acceleration is generally described by the use of a three-axis coordinate system (x, y, z) in which the vertical (z) axis is parallel to the long axis of the body, the x axis is oriented from front to back, and the y axis oriented side to side (Glaister 1988a). These accelerations can be categorized into two general types: sustained and transitory.

Sustained acceleration

The occupants of aircraft (and spacecraft operating in the atmosphere under the influence of gravity during launch and re-entry) commonly experience accelerations in response to aerodynamic forces of flight. Prolonged changes in velocity involving accelerations lasting longer than 2 seconds may result from changes in an aircraft’s speed or direction of flight. The physiological effects of sustained acceleration result from the sustained distortion of tissues and organs of the body and changes in the flow of blood and distribution of body fluids (Glaister 1988a).

Positive or headward acceleration along the z axis (+G_z) represents the major physiological concern. In civil air transportation, G_z accelerations are infrequent, but may occasionally occur to a mild degree during some take-offs and landings, and while flying in conditions of air turbulence. Passengers may experience brief sensations of weightlessness when subject to sudden drops (negative G_z accelerations), if unrestrained in their seats. An unexpected abrupt acceleration may cause unrestrained aircrew or passengers to be thrown against internal surfaces of the aircraft cabin, resulting in injuries.

In contrast to civil transport aviation, the operation of high- performance military aircraft and stunt and aerial spray planes may generate significantly higher linear, radial and angular accelerations. Substantial positive accelerations may be generated as a high-performance aircraft changes its flight path during a turn or a pull-up manoeuvre from a steep dive. The +G_z performance characteristics of current combat aircraft may expose occupants to positive accelerations of 5 to 7 G for 10 to 40 seconds (Glaister 1988a). Aircrew may experience an increase in the weight of tissues and of the extremities at relatively low levels of acceleration of only +2 G_z. As an example, a pilot weighing 70 kg who performed an aircraft manoeuvre which generated +2 G_z would experience an increase of body weight from 70 kg to 140 kg.

The cardiovascular system is the most important organ system for determining the overall tolerance and response to +G_z stress (Glaister 1988a). The effects of positive acceleration on vision and mental performance are due to decreases in blood flow and delivery of oxygen to eye and brain. The capability of the heart to pump blood to the eyes and brain is dependent upon its capability to exceed the hydrostatic pressure of blood at any point along the circulatory system and the inertial forces generated by the positive G_z acceleration. The situation may be likened to that of pulling upward a balloon partially full of water and observing the downward distension of the balloon because of the resultant inertial force acting upon the mass of water. Exposure to positive accelerations may cause temporary loss of peripheral vision or complete loss of consciousness. Military pilots of high- performance aircraft may risk development of G-induced blackouts when exposed to rapid onset or extended periods of positive acceleration in the +G_z axis. Benign cardiac arrhythmias frequently occur following exposure to high sustained levels of +G_z acceleration, but usually are of minimal clinical significance unless pre-existing disease is present; –G_z acceleration seldom occurs because of limitations in aircraft design and performance, but may occur during inverted flight, outside loops and spins and other similar manoeuvres. The physiological effects associated with exposure to –G_z acceleration primarily involve increased vascular pressures in the upper body, head and neck (Glaister 1988a).

Accelerations of sustained duration which act at right angles to the long axis of the body are termed transverse accelerations and are relatively uncommon in most aviation situations, with the exception of catapult and jet- or rocket-assisted take-offs from aircraft carriers, and during launch of rocket systems such as the space shuttle. The accelerations encountered in such military operations are relatively small, and usually do not affect the body in a major fashion because the inertial forces act at right angles to the long axis of the body. In general, the effects are less pronounced than in G_z accelerations. Lateral acceleration in ±G_y axis are uncommon, except with experimental aircraft.

Transitory acceleration

The physiological responses of individuals to transitory accelerations of short duration are a major consideration in the science of aircraft accident prevention and crew and passenger protection. Transitory accelerations are of such brief duration (considerably less than 1 second) that the body is unable to attain a steady-state status. The most common cause of injury in aircraft accidents results from the abrupt deceleration that occurs when an aircraft impacts the ground or water (Anton 1988).

When an aircraft impacts the ground, a tremendous amount of kinetic energy applies damaging forces to the aircraft and its occupants. The human body responds to these applied forces by a combination of acceleration and strain. Injuries result from deformation of tissues and organs and trauma to anatomic parts caused by collision with structural components of the aircraft cockpit and/or cabin.

Human tolerance to abrupt deceleration is variable. The nature of injuries will depend on the nature of the applied force (whether it primarily involves penetrating or blunt impact). At impact, the forces which are generated are dependent on the longitudinal and horizontal decelerations which are generally applied to an occupant. Abrupt decelerative forces are often categorized into tolerable, injurious and fatal. Tolerable forces produce traumatic injuries such as abrasions and bruises; injurious forces produce moderate to severe trauma which may not be incapacitating. It is estimated that an acceleration pulse of approximately 25 G maintained for 0.1 second is the limit of tolerability along the +G_z axis, and that about 15 G for 0.1 sec is the limit for the –G_z axis (Anton 1988).

Multiple factors affect human tolerance to short-duration acceleration. These factors include the magnitude and duration of the applied force, the rate of onset of the applied force, its direction and the site of application. It should be noted that people can withstand much greater forces perpendicular to the long axis of the body.

Protective Countermeasures

Physical screening of crew members to identify serious pre- existing diseases which might put them at increased risk in the aerospace environment is a key function of aeromedical programmes. In addition, countermeasures are available to crew of high-performance aircraft to protect against the adverse effects of extreme accelerations during flight. Crew members must be trained to recognize that multiple physiological factors may decrease their tolerance to G stress. These risk factors include fatigue, dehydration, heat stress, hypoglycemia and hypoxia (Glaister 1988b).

Three types of manoeuvres which crew members of high- performance aircraft employ to minimize adverse effects of sustained acceleration during flight are muscle tensing, forced expiration against a closed or partially closed glottis (back of the tongue) and positive-pressure breathing (Glaister 1988b; DeHart 1992). Forced muscle contractions exert increased pressure on blood vessels to decrease venous pooling and increase venous return and cardiac output, resulting in increased blood flow to the heart and upper body. While effective, the procedure requires extreme, active effort and may rapidly result in fatigue. Expiration against a closed glottis, termed the Valsalva manoeuver (or M-1 procedure) can increase pressure in the upper body and raise the intrathoracic pressure (inside the chest); however, the result is short lived and may be detrimental if prolonged, because it reduces venous blood return and cardiac output. Forcibly exhaling against a partially closed glottis is a more effective anti-G straining manoeuver. Breathing under positive pressure represents another method to increase intrathoracic pressure. Positive pressures are transmitted to the small artery system, resulting in increased blood flow to the eyes and brain. Positive-pressure breathing must be combined with the use of anti-G suits to prevent excessive pooling in the lower body and limbs.

Military aircrew practise a variety of training methods to enhance G tolerance. Crews frequently train in a centrifuge consisting of a gondola attached to a rotating arm which spins and generates +G_z acceleration. Aircrew become familiar with the spectrum of physiological symptoms which may develop and learn the proper procedures to control them. Physical fitness training, particularly whole-body strength training, also has been found to be effective. One of the most common mechanical devices used as protective equipment to reduce the effects of +G exposure consists of pneumatically inflated anti-G suits (Glaister 1988b). The typical trouser-like garment consists of bladders over the abdomen, thighs and calves which automatically inflate by means of an anti-G valve in the aircraft. The anti-G valve inflates in reaction to an applied acceleration upon the aircraft. Upon inflation, the anti-G suit produces a rise in the tissue pressures of the lower extremities. This maintains peripheral vascular resistance, reduces the pooling of blood in the abdomen and lower limbs and minimizes downward displacement of the diaphragm to prevent the increase in the vertical distance between the heart and brain that may be caused by positive acceleration (Glaister 1988b).

Surviving transitory accelerations associated with aircraft crashes is dependent on effective restraint systems and the maintenance of the cockpit/cabin integrity to minimize intrusion of damaged aircraft components into the living space (Anton 1988). The function of lap belts, harnesses and other types of restraint systems are to limit the movement of the aircrew or passengers and to attenuate the effects of sudden deceleration during impact. The effectiveness of the restraint system depends on how well it transmits loads between the body and the seat or vehicle structure. Energy-attenuating seating and rearward facing seats are other features in aircraft design which limit injury. Other accident-protection technology includes the design of airframe components to absorb energy and improvements in seat structures to reduce mechanical failure (DeHart 1992; DeHart and Beers 1985).

Microgravity

Since the 1960s, astronauts and cosmonauts have flown numerous missions into space, including 6 lunar landings by Americans. Mission duration has been from several days to a number of months, with a few Russian cosmonauts logging approximately 1-year flights. Subsequent to these space flights, a large body of literature has been written by physicians and scientists describing in-flight and post-flight physiological aberrations. For the most part, these aberrations have been attributed to exposure to weightlessness or microgravity. Although these changes are transient, with total recovery within several days to several months after returning to Earth, nobody can say with complete certitude whether astronauts would be so fortunate after missions lasting 2 to 3 years, as envisioned for a round trip to Mars. The major physiological aberrations (and countermeasures) can be categorized as cardiovascular, musculoskeletal, neurovestibular, haematological and endocrinological (Nicogossian, Huntoon and Pool 1994).

Cardiovascular hazards

Thus far, there have been no serious cardiac problems in space, such as heart attacks or heart failure, although several astronauts have developed abnormal heart rhythms of a transient nature, particularly during extra-vehicular activity (EVA). In one case, a Russian cosmonaut had to return to Earth earlier than planned, as a precautionary measure.

On the other hand, microgravity seems to induce a lability of blood pressure and pulse. Although this does not cause impaired health or crew performance during flight, approximately half of astronauts immediately post-flight do become extremely dizzy and giddy, with some experiencing fainting (syncope) or near fainting (pre-syncope). The cause of this intolerance to being vertical is thought to be a drop in blood pressure upon re-entering the earth’s gravitational field, combined with the dysfunction of the body’s compensatory mechanisms. Hence, a low blood pressure and decreasing pulse unopposed by the body’s normal response to such physiological aberrations results in these symptoms.

Although these pre-syncopal and syncopal episodes are transient and without sequelae, there remains great concern for several reasons. First, in the event that a returning space vehicle were to have an emergency, such as a fire, upon landing, it would be extremely difficult for astronauts to rapidly escape. Second, astronauts landing on the moon after periods of time in space would be prone to some extent to pre-fainting and fainting, even though the moon’s gravitational field is one-sixth that of Earth. And finally, these cardiovascular symptoms might be far worse or even lethal after very long missions.

It is for these reasons that there has been an aggressive search for countermeasures to prevent or at least ameliorate the microgravity effects upon the cardiovascular system. Although there are a number of countermeasures now being studied that show some promise, none so far has been proven truly effective. Research has focused on in-flight exercise utilizing a treadmill, bicycle ergometer and rowing machine. In addition, studies are also being conducted with lower body negative pressure (LBNP). There is some evidence that lowering the pressure around the lower body (using compact special equipment) will enhance the body’s ability to compensate (i.e., raise blood pressure and pulse when they fall too low). The LBNP countermeasure might be even more effective if the astronaut drinks moderate amounts of specially constituted salt water simultaneously.

If the cardiovascular problem is to be solved, not only is more work needed on these countermeasures, but also new ones must be found.

Musculoskeletal hazards

All astronauts returning from space have some degree of muscle wasting or atrophy, regardless of mission duration. Muscles at particular risk are those of the arms and legs, resulting in decreased size as well as strength, endurance and work capacity. Although the mechanism for these muscle changes is still ill-defined, a partial explanation is prolonged disuse; work, activity and movement in microgravity are almost effortless, since nothing has any weight. This may be a boon for astronauts working in space, but is clearly a liability when returning to a gravitational field, whether it be that of the moon or Earth. Not only could a weakened condition impede post-flight activities (including work on the lunar surface), it could also compromise rapid ground emergency escape, if required upon landing. Another factor is the possible requirement during EVA to do space vehicle repairs, which can be very strenuous. Countermeasures under study include in-flight exercises, electrical stimulation and anabolic medication (testosterone or testosterone-like steroids). Unfortunately, these modalities at best only retard muscle dysfunction.

In addition to muscle wasting, there is also a slow but inexorable loss of bone in space (about 300 mg per day, or 0.5% of total bone calcium per month) experienced by all astronauts. This has been documented by post-flight x rays of bones, particularly of those that bear weight (i.e., the axial skeleton). This is due to a slow but unremitting loss of calcium into the urine and faeces. Of great concern is the continuing loss of calcium, regardless of flight duration. Consequently, this calcium loss and bone erosion could be a limiting factor of flight, unless an effective countermeasure can be found. Although the precise mechanism of this very significant physiological aberration is not fully understood, it undoubtedly is due in part to the absence of gravitational forces on bone, as well as disuse, similar to muscle wasting. If bone loss were to continue indefinitely, particularly over long missions, bones would become so brittle that eventually there would be risk of fractures with even low levels of stress. Furthermore, with a constant flow of calcium into the urine via the kidneys, a possibility of renal stone formation exists, with accompanying severe pain, bleeding and infection. Clearly, any of these complications would be a very serious matter were they to occur in space.

Unfortunately, there are no known countermeasures that effectively prevent calcium loss during space flight. A number of modalities are being tested, including exercise (treadmill, bicycle ergometer and rowing machine), the theory being that such voluntary physical stresses would normalize bone metabolism, thereby preventing or at least ameliorating bone loss. Other countermeasures under investigation are calcium supplements, vitamins and various medications (such as diphosphonates—a class of medications that has been shown to prevent bone loss in patients with osteoporosis). If none of these simpler countermeasures prove to be effective, it is possible that the solution lies in artificial gravity that could be produced by continuous or intermittent rotation of the space vehicle. Although such motion could generate gravitational forces similar to that of the earth, it would represent an engineering “nightmare”, in addition to major add-on costs.

Neurovestibular hazards

More than half of the astronauts and cosmonauts suffer from space motion sickness (SMS). Although the symptoms vary somewhat from individual to individual, most suffer from stomach awareness, nausea, vomiting, headache and drowsiness. Often there is an exacerbation of symptoms with rapid head movement. If an astronaut develops SMS, it usually occurs within a few minutes to a few hours after launch, with complete remission within 72 hours. Interestingly, the symptoms sometimes recur after returning to the earth.

SMS, particularly vomiting, can not only be disconcerting to the crew members, it also has the potential to cause performance decrement in an astronaut who is ill. Furthermore, the risk of vomiting while in a pressure suit doing EVA cannot be ignored, as the vomitus could cause the life-support system to malfunction. It is for these reasons that no EVA activities are ever scheduled during the first 3 days of a space mission. If an EVA becomes necessary, for example, to do emergency repairs on the space vehicle, the crew would have to take that risk.

Much neurovestibular research has been directed toward finding a way to prevent as well as to treat SMS. Various modalities, including anti-motion-sickness pills and patches, as well as using pre-flight adaptation trainers such as rotating chairs to habituate astronauts, have been attempted with very limited success. However, in recent years it has been discovered that the antihistamine phenergan, given by injection, is an extremely effective treatment. Hence, it is carried onboard all flights and given as required. Its efficacy as a preventive has yet to be demonstrated.

Other neurovestibular symptoms reported by astronauts include dizziness, vertigo, dysequilibrium and illusions of self-motion and motion of the surrounding environment, sometimes making walking difficult for a short time post-flight. The mechanisms for these phenomena are very complex and are not completely understood. They could be problematical, particularly after a lunar landing following several days or weeks in space. As of now, there are no known effective countermeasures.

Neurovestibular phenomena are most likely caused by dysfunction of the inner ear (the semicircular canals and utricle-saccule), because of microgravity. Either erroneous signals are sent to the central nervous system or signals are misinterpreted. In any event, the results are the aforementioned symptoms. Once the mechanism is better understood, effective countermeasures can be identified.

Haematological hazards

Microgravity has an effect upon the body’s red and white blood cells. The former serve as a conveyor of oxygen to the tissues, and the latter as an immunological system to protect the body from invading organisms. Hence, any dysfunction could cause deleterious effects. For reasons not understood, astronauts lose approximately 7 to 17% of their red blood cell mass early in flight. This loss appears to plateau within a few months, returning to normal 4 to 8 weeks post-flight.

So far, this phenomenon has not been clinically significant, but, rather, a curious laboratory finding. However, there is clear potential for this loss of red blood cell mass to be a very serious aberration. Of concern is the possibility that with very long missions envisioned for the twenty-first century, red blood cells could be lost at an accelerated rate and in far greater quantities. If this were to occur, anaemia could develop to the point that an astronaut could become seriously ill. It is hoped that this will not be the case, and that the red blood cell loss will remain very small, regardless of mission duration.

In addition, several components of the white blood cell system are affected by microgravity. For example, there is an overall increase in the white blood cells, mainly neutrophils, but a decrease in lymphocytes. There is also evidence that some white blood cells do not function normally.

As of now, in spite of these changes, no illness has been attributed to these white blood cell changes. It is unknown whether or not a long mission will cause further decrease in numbers as well as further dysfunction. Should this occur, the body’s immune system would be compromised, making astronauts very susceptible to infectious disease, and possibly incapacitated by even minor illness that would otherwise easily be fended off by a normally functioning immunological system.

As with the red blood cell changes, the white blood cell changes, at least on missions of approximately one year, are not of clinical significance. Because of the potential risk of serious illness in-flight or post-flight, it is critical that research continue on the effects of microgravity on the haematological system.

Endocrinological hazards

During space flight, it has been noted that there are a number of fluid and mineral changes within the body due in part to changes in the endocrine system. In general, there is a loss of total body fluids, as well as calcium, potassium and calcium. A precise mechanism for these phenomena has eluded definition, although changes in various hormonal levels offer a partial explanation. To further confound matters, laboratory findings are often inconsistent among the astronauts who have been studied, making it impossible to discern a unitary hypothesis as to the cause of these physiological aberrations. In spite of this confusion, these changes have caused no known impairment of health of astronauts and no performance decrement in flight. What the significance of these endocrine changes are for very long flight, as well as the possibility that they may be harbingers of very serious sequelae, is unknown.

Acknowledgements: The authors would like to recognize the work of the Aerospace Medical Association in this area.

Back

Adapted from the 3rd edition Encyclopaedia article “Aviation - flying personnel” authored by H. Gartmann.

This article deals with the occupational safety and health of the crew members of civil aviation aircraft; see also the articles “Airport and flight control operations”, “Aircraft maintenance operations” and “Helicopters” for additional information.

Technical Crew Members

The technical personnel, or flight crew members, are responsible for the operation of the aircraft. Depending on aircraft type, the technical crew includes the pilot-in-command (PIC), the co-pilot (or first officer), and the flight engineer or a second officer (a pilot).

The PIC (or captain) has the responsibility for the safety of the aircraft, the passengers and the other crew members. The captain is the legal representative of the air carrier and is vested by the air carrier and the national aviation authority with the authority to carry out all actions necessary to fulfil this mandate. The PIC directs all duties on the flight deck and is in command of the entire aircraft.

The co-pilot takes his or her orders directly from the PIC and acts as the captain’s deputy upon delegation or in the latter’s absence. The co-pilot is the primary assistant to the PIC in a flight crew; in newer generation, two-person flight deck operations and in older two-engine aircraft, he or she is the only assistant.

Many older generation aircraft carry a third technical crew member. This person may be a flight engineer or a third pilot (usually called the second officer). The flight engineer, when present, is responsible for the mechanical condition of the aircraft and its equipment. New generation aircraft have automated many of the functions of the flight engineer; in these two-person operations, the pilots perform such duties as a flight engineer might otherwise perform that have not been automated by design.

On certain long-distance flights, the crew may be supplemented by a pilot with the qualifications of the PIC, an additional first officer and, when required, an additional flight engineer.

National and international laws stipulate that aircraft technical personnel may operate aircraft only when in possession of a valid licence issued by the national authority. In order to maintain their licences, technical crew members are given ground school training once every year; they are also tested in a flight simulator (a device that simulates real flight and flight emergency conditions) twice a year and in actual operations at least once a year.

Another condition for the receipt and renewal of a valid licence is a medical examination every 6 months for airline transport and commercial pilots over 40 years old, or every 12 months for commercial pilots under 40 years old and for flight engineers. The minimum requirements for these examinations are specified by the ICAO and by national regulations. A certain number of physicians experienced in aviation medicine may be authorized to provide such examinations by the national authorities concerned. These may include air ministry physicians, airforce flight surgeons, airline medical officers or private practitioners designated by the national authority.

Cabin Crew Members

The cabin crew (or flight attendants) are primarily responsible for passenger safety. Flight attendants perform routine safety duties; in addition, they are responsible for monitoring the aircraft cabin for security and safety hazards. In the event of an emergency, the cabin crew members are responsible for the organization of emergency procedures and for the safe evacuation of the passengers. In flight, cabin crew may need to respond to emergencies such as smoke and fire in the cabin, turbulence, medical trauma, aircraft decompressions, and hijackings or other terrorist threats. In addition to their emergency responsibilities, flight attendants also provide passenger service.

The minimum cabin crew ranges from 1 to 14 flight attendants, depending on the type of aircraft, the aircraft’s passenger capacity and national regulations. Additional staffing requirements may be determined by labour agreements. The cabin crew may be supplemented by a purser or service manager. The cabin crew is usually under the supervision of a lead or “in-charge” flight attendant, who, in turn, is responsible and reports directly to the PIC.

National regulations do not usually stipulate that the cabin crew should hold licences in the same way as the technical crew; however, cabin crew are required by all national regulations to have received appropriate instruction and training in emergency procedures. Periodic medical examinations are not usually required by law, but some air carriers require medical examinations for the purposes of health maintenance.

Hazards and Their Prevention

All air crew members are exposed to a wide variety of stress factors, both physical and psychological, to the hazards of an aircraft accident or other flight incident and to the possible contraction of a number of diseases.

Physical stress

Lack of oxygen, one of the main concerns of aviation medicine in the early days of flying, had until recently become a minor consideration in modern air transport. In the case of a jet aircraft flying at 12,000 m altitude, the equivalent altitude in the pressurized cabin is only 2,300 m and, consequently, symptoms of oxygen deficiency or hypoxia will not normally be encountered in healthy persons. Oxygen deficiency tolerance varies from individual to individual, but for a healthy, non-trained subject the presumed altitude threshold at which the first symptoms of hypoxia occur is 3,000 m.

With the advent of new generation aircraft, however, concerns about cabin air quality have resurfaced. Aircraft cabin air consists of air drawn from compressors in the engine and often also contains recirculated air from within the cabin. The flow rate of outside air within an aircraft cabin can vary from as little as 0.2 m³ per minute per person to 1.42 m³ per minute per person, depending upon aircraft type and age, and depending on location within the cabin. New aircraft use recirculated cabin air to a much greater degree than do older models. This air quality issue is specific to the cabin environment. The flight deck compartment air flow rates are often as high as 4.25 m³ per minute per crew member. These higher air flow rates are provided on the flight deck to meet the cooling requirements of the avionic and electronic equipment.

Complaints of poor cabin air quality from cabin crew and passengers have increased in recent years, prompting some national authorities to investigate. Minimal ventilation rates for aircraft cabins are not defined in national regulations. Actual cabin airflow is seldom measured once an aircraft is put into service, since there is no requirement to do so. Minimal air flow and the use of recirculated air, combined with other issues of air quality, such as the presence of chemical contaminants, micro-organisms, other allergens, tobacco smoke and ozone, require further evaluation and study.

Maintaining a comfortable air temperature in the cabin does not represent a problem in modern aircraft; however, the humidity of this air cannot be raised to a comfortable level, due to the large temperature difference between the aircraft interior and exterior. Consequently, both crew and passengers are exposed to extremely dry air, especially on long-distance flights. Cabin humidity depends on the cabin ventilation rate, passenger load, temperature and pressure. The relative humidity found on aircraft today varies from about 25% to less than 2%. Some passengers and crew members experience discomfort, such as dryness of the eyes, nose and throat, on flights that exceed 3 or 4 hours. There is no conclusive evidence of extensive or serious adverse health effects of low relative humidity on flight personnel. However, precautions should be taken to avoid dehydration; adequate intake of liquids such as water and juices should be sufficient to prevent discomfort.

Motion sickness (dizziness, malaise and vomiting due to the abnormal movements and altitudes of the aircraft) was a problem for civil aviation crews and passengers for many decades; the problem still exists today in the case of small sports aircraft, military aircraft and aerial acrobatics. In modern jet transport aircraft, it is much less serious and occurs less frequently due to higher aircraft speeds and take-off weights, higher cruising altitudes (which take the aircraft above the turbulence zones) and the use of airborne radar (which enables squalls and storms to be located and circumnavigated). Additionally, the lack of motion sickness also may be attributed to the more spacious, open design of today’s aircraft cabin, which provides a greater feeling of security, stability and comfort.

Other physical and chemical hazards

Aircraft noise, while a significant problem for ground personnel, is less serious for the crew members of a modern jet aircraft than was the case with the piston-engined plane. The efficiency of noise control measures such as insulation in modern aircraft have helped to eliminate this hazard in most flight environments. Additionally, improvements in communications equipment have minimized background noise levels from these sources.

Ozone exposure is a known but poorly monitored hazard for air crew and passengers. Ozone is present in the upper atmosphere as a result of the photochemical conversion of oxygen by solar ultraviolet radiation at altitudes used by commercial jet aircraft. The mean ambient ozone concentration increases with increasing latitude and is most prevalent during spring. It can also vary with weather systems, with the result of high ozone plumes descending down to lower altitudes.

Symptoms of ozone exposure include cough, upper airway irritation, tickle in the throat, chest discomfort, substantial pain or soreness, difficulty or pain in taking a deep breath, shortness of breath, wheezing, headache, fatigue, nasal congestion and eye irritation. Most people can detect ozone at 0.02 ppm, and studies have shown that ozone exposure at 0.5 ppm or more causes significant decrements in pulmonary function. The effects of ozone contamination are felt more readily by persons engaged in moderate to heavy activity than those who are at rest or engaged in light activity. Thus flight attendants (who are physically active in flight) have experienced the effects of ozone earlier and more frequently than technical crew or passengers on the same flight when ozone contamination was present.

In one study conducted in the late 1970s by the aviation authority in the United States (Rogers 1980), several flights (mostly at 9,150 to 12,200 m) were monitored for ozone contamination. Eleven per cent of the flights monitored were found to exceed that authority’s permissible ozone concentration limits. Methods of minimizing ozone exposure include choice of routes and altitudes that avoid areas of high ozone concentration and the use of air treatment equipment (usually a catalytic converter). The catalytic converters, however, are subject to contamination and loss of efficiency. Regulations (when they exist) do not require their periodic removal for efficiency testing, nor do they require monitoring of ozone levels in actual flight operations. Crew members, especially cabin crew, have requested that better monitoring and control of ozone contamination be implemented.

Another serious concern for technical and cabin crew members is cosmic radiation, which includes radiation forms that are transmitted through space from the sun and other sources in the universe. Most cosmic radiation that travels through space is absorbed by the earth’s atmosphere; however, the higher the altitude, the less the protection. The earth’s magnetic field also provides some shielding, which is greatest near the equator and decreases at the higher latitudes. Air crew members are exposed to cosmic radiation levels inflight that are higher than those received on the ground.

The amount of radiation exposure depends on the type and the amount of flying; for example, a crew member who flies many hours at high altitudes and high latitudes (e.g., polar routes) will receive the greatest amount of radiation exposure. The civil aviation authority in the United States (the FAA) has estimated that the long-term average cosmic radiation dose for air crew members ranges from 0.025 to 0.93 millisieverts (mSv) per 100 block hours (Friedberg et al. 1992). Based on FAA estimates, a crew member flying 960 block hours per year (or an average of 80 hours/month) would receive an estimated annual radiation dose of between 0.24 and 8.928 mSv. These levels of exposure are lower than the recommended occupational limit of 20 millisieverts per year (5-year average) established by the International Commission on Radiological Protection (ICRP).

The ICRP, however, recommends that occupational exposure to ionizing radiation should not exceed 2 mSv during pregnancy. In addition, the US National Council on Radiation Protection and Measurements (NCRP) recommends that exposure not exceed 0.5 mSv in any month once a pregnancy is known. If a crew member worked an entire month on flights with the highest exposures, the monthly dose rate could exceed the recommended limit. Such a pattern of flying over 5 or 6 months could result in an exposure which also would exceed the recommended pregnancy limit of 2 mSv.

The health effects of low-level radiation exposure over a period of years include cancer, genetic defects and birth defects to a child exposed in the womb. The FAA estimates that the added risk of fatal cancer resulting from exposure to inflight radiation would range from 1 in 1,500 to 1 in 94, depending on the type of routes and number of hours flown; the level of added risk of a serious genetic defect resulting from one parent’s exposure to cosmic radiation ranges from 1 in 220,000 live births to 1 in 4,600 live births; and the risk of mental retardation and childhood cancer in a child exposed in utero to cosmic radiation would range between 1 in 20,000 to 1 in 680, depending upon the type and amount of flying the mother did while pregnant.

The FAA report concludes that “radiation exposure is not likely to be a factor that would limit flying for a non-pregnant crew member” because even the largest amount of radiation received annually by a crew member working as much as 1,000 block hours a year is less than half the ICRP recommended average annual limit. However, for a pregnant crew member, the situation is different. The FAA calculates that a pregnant crew member working 70 block hours per month would exceed the recommended 5-month limit on about one-third of the flights they studied (Friedberg et al. 1992).

It should be stressed that these exposure and risk estimates are not universally accepted. Estimates are dependent upon assumptions about the types and mix of radioactive particles encountered at altitude and the weight or quality factor used to determine dose estimates for some of these forms of radiation. Some scientists believe that the actual radiation hazard to air crew members may be greater than described above. Additional monitoring of the flight environment with reliable instrumentation is needed to more clearly determine the extent of inflight radiation exposure.

Until more is known about exposure levels, air crew members should keep their exposure to all types of radiation as low as possible. With respect to inflight radiation exposure, minimizing the amount of flight time and maximizing the distance from the source of radiation can have a direct effect on the dose received. Reducing monthly and yearly flight time and/or selecting flights which fly at lower altitudes and latitudes will reduce exposure. An air crew member who has the ability to control his or her flight assignments might choose to fly fewer hours per month, to bid for a mix of domestic and international flights or to request leaves periodically. A pregnant air crew member might choose to take a leave for the duration of the pregnancy. Since the first trimester is the most crucial time to guard against radiation exposure, an air crew member planning a pregnancy also may want to consider a leave especially if she is flying long-distance polar routes on a regular basis and has no control over her flight assignments.

Ergonomic problems

The main ergonomic problem for technical crew is the need to work for many hours in a sitting but unsettled position and in a very limited working area. In this position (restrained by lap and shoulder harness), it is necessary to carry out a variety of tasks such as movements of the arms, legs and head in different directions, consulting instruments at a distance of about 1 m above, below, to the front and to the side, scanning the far distance, reading a map or manual at close distance (30 cm), listening through earphones or talking through a microphone. Seating, instrumentation, lighting, cockpit microclimate and radio communications equipment comfort have been and still remain the object of continuous improvement. Today’s modern flight deck, often referred to as the “glass cockpit”, has created yet another challenge with its use of leading-edge technology and automation; maintaining vigilance and situational awareness under these conditions has created new concerns for both the designers of aircraft and the technical personnel who fly them.

Cabin crew have an entirely different set of ergonomic problems. One main problem is that of standing and moving around during flight. During climb and descent, and in turbulence, the cabin crew is required to walk on an inclined floor; in some aircraft the cabin incline may remain at approximately 3% during cruise as well. Also, many cabin floors are designed in a manner that creates a rebound effect while walking, putting an additional stress on the flight attendants who are constantly moving about during a flight. Another important ergonomic problem for flight attendants has been the use of mobile carts. These carts can weigh up to 100 to 140 kg and must be pushed and pulled up and down the length of the cabin. Additionally, the poor design and maintenance of the braking mechanisms on many of these carts have caused an increase in repetitive-strain injuries (RSIs) among flight attendants. Air carriers and cart manufacturers are now taking a more serious look at this equipment, and new designs have resulted in ergonomic improvements. Additional ergonomic problems result from the need to lift and carry heavy or bulky items in restricted spaces or while maintaining uncomfortable body posture.

Workload

The workload for air crew members depends on the task, the ergonomic layout, the hours of work/duty and many other factors. The additional factors affecting the technical crew include:

• duration of rest time between present and last flight and the duration of sleep time during the rest period

• the pre-flight briefing and problems encountered during the pre-flight briefing

• delays preceding departure

• timing of flights

• meteorological conditions at the point of departure, en route and at the destination

• number of flight segments

• type of equipment being flown

• quality and quantity of radio communications

• visibility during descent, glare and protection from the sun

• turbulence

• technical problems with the aircraft

• experience of other crew members

• air traffic (especially at point of departure and destination)

• presence of air carrier or national authority personnel for purposes of checking crew competency.

Certain of these factors may be equally important for the cabin crew. In addition, the latter are subject to the following specific factors:

• pressure of time due to short duration of flight, high number of passengers and extensive service requirements

• extra services demanded by passengers, the character of certain passengers and, occasionally, verbal or physical abuse by passengers

• passengers requiring special care and attention (e.g., children, the disabled, the elderly, a medical emergency)

• extent of preparatory work

• lack of necessary service items (e.g., insufficient meals, beverages and so on) and equipment.

The measures taken by air carrier managements and government administrations to keep crew workload within reasonable limits include: improvement and extension of air-traffic control; reasonable limits on hours of duty and requirements for minimum rest provisions; execution of preparatory work by dispatchers, maintenance, catering and cleaning personnel; automation of cockpit equipment and tasks; the standardization of service procedures; adequate staffing; and the provision of efficient and easy-to-handle equipment.

Hours of work

One of the most important factors affecting both technical and cabin crew member occupational health and safety (and certainly the most widely discussed and controversial) is the issue of flight fatigue and recovery. This issue covers the broad spectrum of activity encompassing crew scheduling practices—length of duty periods, amount of flight time (daily, monthly and yearly), reserve or standby duty periods and availability of time for rest both while on flight assignment and at domicile. Circadian rhythms, especially sleep intervals and duration, with all their physiological and psychological implications, are especially significant for air crew members. Time shifts due either to night flights or to east/west or west/east travel across a number of time zones create the greatest problems. Newer generation aircraft, which have the capability of remaining aloft for up to 15 to 16 hours at a time, have exacerbated the conflict between airline schedules and human limitations.

National regulations to limit duty and flight periods and to provide minimum rest limitations exist on a nation by nation basis. In some instances, these regulations have not kept pace with technology or science, nor do they necessarily guarantee flight safety. Until recently there has been little attempt to standardize these regulations. Current attempts at harmonization have given rise to concerns among air crew members that those countries with more protective regulations may be required to accept lower and less adequate standards. In addition to national regulations, many air crew members have been able to negotiate more protective hours of service requirements in their labour agreements. While these negotiated agreements are important, most crew members feel that hours of service standards are essential to their health and safety (and to that of the flying public), and thus minimum standards should be adequately regulated by the national authorities.

Psychological stress

In recent years, aircraft crew have been confronted with a serious mental stress factor: the likelihood of hijacking, bombs and armed attacks on aircraft. Although security measures in civil aviation worldwide have been considerably increased and upgraded, the sophistication of terrorists has likewise increased. Air piracy, terrorism and other criminal acts remain a real threat to all air crew members. The commitment and cooperation of all national authorities as well as the force of worldwide public opinion are needed to prevent these acts. Additionally, air crew members must continue to receive special training and information on security measures and must be informed on a timely basis of suspected threats of air piracy and terrorism.

Air crew members understand the importance of starting flight duty in a sufficiently good mental and physical state to ensure that the fatigue and stresses occasioned by the flight itself will not affect safety. Fitness for flight duty may occasionally be impaired by psychological and physical stress, and it is the responsibility of the crew member to recognize whether or not he or she is fit for duty. Sometimes, however, these effects may not be readily apparent to the person under duress. For this reason, most airlines and air crew member associations and labour unions have professional standards committees to assist crew members in this area.

Accidents

Fortunately, catastrophic aircraft accidents are rare events; nonetheless, they do represent a hazard for air crew members. An aircraft accident is practically never a hazard resulting from a single, well-defined cause; in almost every instance, a number of technical and human factors coincide in the causal process.

Defective equipment design or equipment failure, especially as a result of inadequate maintenance, are two mechanical causes of aircraft accidents. One important, although relatively rare, type of human failure is sudden death due, for example, to myocardial infarction; other failures include sudden loss of consciousness (e.g., epileptic fit, cardiac syncope and fainting due to food poisoning or other intoxication). Human failure may also result from the slow deterioration of certain functions such as hearing or vision, although no major aircraft accident has been attributed to such a cause. Preventing accidents from medical causes is one of the most important tasks of aviation medicine. Careful personnel selection, regular medical examinations, surveys of absence due to illness and accidents, continuous medical contact with working conditions and industrial hygiene surveys can considerably decrease the danger of sudden incapacitation or slow deterioration in technical crew. Medical personnel should also routinely monitor flight scheduling practices to prevent fatigue-related incidents and accidents. A well-operated, modern airline of significant size should have its own medical service for these purposes.

Advances in aircraft accident prevention are often made as a result of careful investigation of accidents and incidents. Systematic screening of all, even minor, accidents and incidents by an accident investigation board comprising technical, operational, structural, medical and other experts is essential to determine all causal factors in an accident or incident and to make recommendations for preventing future occurrences.

A number of strict regulations exist in aviation to prevent accidents caused by use of alcohol or other drugs. Crew members should not consume quantities of alcohol in excess of what is compatible with professional requirements, and no alcohol at all should be consumed during and for at least 8 hours prior to flight duty. Illegal drug use is strictly prohibited. Drug use for medicinal purposes is strictly controlled; such drugs are generally not allowed during or immediately preceding flight, although exceptions may be allowed by a recognized flight physician.

The transport of hazardous materials by air is yet another cause of aircraft accident and incidents. A recent survey covering a 2-year period (1992 to 1993) identified over 1,000 aircraft incidents involving hazardous materials on passenger and cargo air carriers in one nation alone. More recently, an accident in the United States which resulted in the deaths of 110 passengers and crew involved the carriage of hazardous cargo. Hazardous materials incidents in air transportation occur for a number of reasons. Shippers and passengers may be unaware of the dangers presented by the materials they bring aboard aircraft in their baggage or offer for transport. Occasionally, unscrupulous persons may choose to illegally ship forbidden hazardous materials. Additional restrictions on the carriage of hazardous materials by air and improved training for air crew members, passengers, shippers and loaders may help to prevent future incidents. Other accident prevention regulations deal with oxygen supply, crew meals and procedures in case of illness.

Diseases

Specific occupational disease of crew members are not known or documented. However, certain diseases may be more prevalent among crew members than among persons in other occupations. Common colds and upper respiratory system infections are frequent; this may be due in part to the low humidity during flight, irregularities of schedules, exposure to att large number of people in a confined space and so on. A common cold, especially with upper respiratory congestion, that is not significant for an office worker may incapacitate a crew member if it prevents the clearing of pressure on the middle ear during ascent and, particularly, during descent. Additionally, illnesses that require some form of drug therapy may also preclude the crew member from engaging in work for a period of time. Frequent travel to tropical areas may also entail increased exposure to infectious diseases, the most important being malaria and infections of the digestive system.

The close confines of an aircraft for extended periods of time also carry an excess risk of airborne infectious diseases like tuberculosis, if a passenger or crew member has such a disease in its contagious stage.

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Aircraft maintenance operations are broadly distributed within and across nations and are performed by both military and civilian mechanics. Mechanics work at airports, maintenance bases, private fields, military installations and aboard aircraft carriers. Mechanics are employed by passenger and freight carriers, by maintenance contractors, by operators of private fields, by agricultural operations and by public and private fleet owners. Small airports may provide employment for a few mechanics, while major hub airports and maintenance bases may employ thousands. Maintenance work is divided between that which is necessary to maintain ongoing daily operations (line maintenance) and those procedures that periodically check, maintain and refurbish the aircraft (base maintenance). Line maintenance comprises en route (between landing and takeoff) and overnight maintenance. En route maintenance consists of operational checks and flight-essential repairs to address discrepancies noted during flight. These repairs are typically minor, such as replacing warning lights, tyres and avionic components, but may be as extensive as replacing an engine. Overnight maintenance is more extensive and includes making any repairs deferred during the day’s flights.

The timing, distribution and nature of aircraft maintenance is controlled by each airline company and is documented in its maintenance manual, which in most jurisdictions must be submitted for approval to the appropriate aviation authority. Maintenance is performed during regular checks, designated as A through D checks, specified by the maintenance manual. These scheduled maintenance activities ensure that the entire aircraft has been inspected, maintained and refurbished at appropriate intervals. Lower level maintenance checks may be incorporated into line maintenance work, but more extensive work is performed at a maintenance base. Aircraft damage and component failures are repaired as required.

Line Maintenance Operations and Hazards

En route maintenance is typically performed under a great time constraint at active and crowded flight lines. Mechanics are exposed to prevailing conditions of noise, weather and vehicular and aircraft traffic, each of which may amplify the hazards intrinsic to maintenance work. Climatic conditions may include extremes of cold and heat, high winds, rain, snow and ice. Lightning is a significant hazard in some areas.

Although the current generation of commercial aircraft engines are significantly quieter than previous models, they can still produce sound levels well above those set by regulatory authorities, particularly if the aircraft are required to use engine power in order to exit gate positions. Older jet and turboprop engines can produce sound level exposures in excess of 115 dBA. Aircraft auxiliary-power units (APUs), ground-based power and air-conditioning equipment, tugs, fuel trucks and cargo-handling equipment add to the background noise. Noise levels in the ramp or aircraft parking area are seldom below 80 dBA, thus necessitating the careful selection and routine use of hearing protectors. Protectors must be selected that provide excellent noise attenuation while being reasonably comfortable and permitting essential communication. Dual systems (ear plugs plus ear muffs) provide enhanced protection and allow accom-modation for higher and lower noise levels.

Mobile equipment, in addition to aircraft, may include baggage carts, personnel buses, catering vehicles, ground support equipment and jetways. To maintain departure schedules and customer satisfaction, this equipment must move quickly within often congested ramp areas, even under adverse ambient conditions. Aircraft engines pose the danger of ramp personel being ingested into jet engines or being struck by a propeller or exhaust blasts. Reduced visibility during night and inclement weather increase the risk that mechanics and other ramp personnel might be struck by mobile equipment. Reflective materials on work clothing help to improve visibility, but it is essential that all ramp personnel be well trained in ramp traffic rules, which must be rigorously enforced. Falls, the most frequent cause of serious injuries among mechanics, are discussed elsewhere in this Encyclopaedia.

Chemical exposures in the ramp area include de-icing fluids (usually containing ethylene or propylene glycol), oils and lubricants. Kerosene is the standard commercial jet fuel (Jet A). Hydraulic fluids containing tributyl phosphate cause severe but transient eye irritation. Fuel tank entry, while relatively rare on the ramp, must be included in a comprehensive confined- space-entry programme. Exposure to resin systems used for patching composite areas such as cargo hold panelling may also occur.

Overnight maintenance is typically performed under more controlled circumstances, either in line-service hangers or on inactive flight lines. Lighting, work stands and traction are far better than on the flight line but are likely to be inferior to those found in maintenance bases. Several mechanics may be working on an aircraft simultaneously, necessitating careful planning and coordination to control personnel movement, aircraft component activation (drives, flight control surfaces and so on) and chemical usage. Good housekeeping is essential to prevent clutter from air lines, parts and tools, and to clean spills and drips. These requirements are of even greater importance during base maintenance.

Base Maintenance Operations and Hazards

Maintenance hangars are very large structures capable of accommodating numerous aircraft. The largest hangars can simultaneously accommodate several wide-body aircraft, such as the Boeing 747. Separate work areas, or bays, are assigned to each aircraft undergoing maintenance. Specialized shops for the repair and refitting of components are associated with the hangars. Shop areas typically include sheet metal, interiors, hydraulics, plastics, wheels and brakes, electrical and avionics and emergency equipment. Separate welding areas, paint shops and non-destructive testing areas may be established. Parts-cleaning operations are likely to be found throughout the facility.

Paint hangars with high ventilation rates for workplace air contaminant controls and environmental pollution protection should be available if painting or paint stripping is to be performed. Paint strippers often contain methylene chloride and corrosives, including hydrofluoric acid. Aircraft primers typically contain a chromate component for corrosion protection. Top coats may be epoxy or polyurethane based. Toluene diisocyanate (TDI) is now seldom used in these paints, having been replaced with higher molecular weight isocyanates such as 4,4-diphenylmethane diisocyanate (MDI) or by prepolymers. These still present a risk of asthma if inhaled.

Engine maintenance may be performed within the maintenance base, at a specialized engine overhaul facility or by a sub-contractor. Engine overhaul requires the use of metalworking techniques including grinding, blasting, chemical cleaning, plating and plasma spray. Silica has in most cases been replaced with less hazardous materials in parts cleaners, but the base materials or coatings may create toxic dusts when blasted or ground. Numerous materials of worker health and environmental concern are used in metal cleaning and plating. These include corrosives, organic solvents and heavy metals. Cyanide is generally of the greatest immediate concern, requiring special emphasis in emergency preparedness planning. Plasma spray operations also merit particular attention. Finely divided metals are fed into a plasma stream generated using high-voltage electrical sources and plated onto parts with the concomitant generation of very high noise levels and light energies. Physical hazards include work at height, lifting and work in uncomfortable positions. Precautions include local exhaust ventilation, PPE, fall protection, training in proper lifting and use of mechanized lifting equipment when possible and ergonomic redesign. For example, repetitive motions involved in tasks such as wire tying may be reduced by use of specialized tools.

Military and Agricultural Applications

Military aircraft operations may present unique hazards. JP4, a more volatile jet fuel that Jet A, may be contaminated with n-hexane. Aviation gasoline, used in some propeller-driven aircraft, is highly flammable. Military aircraft engines, including those on transport aircraft, may use less noise abatement than those on commercial aircraft and may be augmented by afterburners. Aboard aircraft carriers the many hazards are significantly increased. Engine noise is augmented by steam catapults and afterburners, flight deck space is extremely limited, and the deck itself is in motion. Because of combat demands, asbestos insulation is present in some cockpits and around hot areas.

The need for lowered radar visibility (stealth) has resulted in the increased use of composite materials on fuselage, wings and flight control structures. These areas may be damaged in combat or from exposure to extremes of climate, requiring extensive repair. Repairs performed under field conditions may result in heavy exposures to resins and composite dusts. Beryllium is also common in military applications. Hydrazide may be present as part of auxiliary-power units, and anti-tank armament may include radioactive depleted uranium rounds. Precautions include appropriate PPE, including respiratory protection. Where possible, portable exhaust systems should be used.

Maintenance work on agricultural aircraft (crop dusters) may result in exposures to pesticides either as a single product or, more likely, as a mixture of products contaminating a single or multiple aircraft. Degradation products of some pesticides are more hazardous than the parent product. Dermal routes of exposure may be significant and may be enhanced by perspiration. Agricultural aircraft and external parts should be thoroughly cleaned before repair, and/or PPE, including skin and respiratory protection, should be used.

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United States

High levels of stress among air traffic controllers (ATCs) were first widely reported in the United States in the 1970 Corson Report (US Senate 1970), which focused on working conditions such as overtime, few regular work breaks, increasing air traffic, few vacations, poor physical work environment and “mutual resentment and antagonism” between management and labour. Such conditions contributed to ATC job actions in 1968–69. In addition, early medical research, including a major 1975–78 Boston University study (Rose, Jenkins and Hurst 1978), suggested that ATCs may face a higher risk of stress-related illness, including hypertension.

Following the 1981 US ATC strike, in which job stress was a major issue, the Department of Transportation again appointed a task force to examine stress and morale. The resulting 1982 Jones Report indicated that FAA employees in a wide variety of job titles reported negative results for job design, work organization, communication systems, supervisory leadership, social support and satisfaction. The typical form of ATC stress was an acute episodic incident (such as a near mid-air collision) along with interpersonal tensions stemming from management style. The task force reported that 6% of the ATC sample was “burned out” (having a large and debilitating loss of self-confidence in ability to do the job). This group represented 21% of those 41 years of age and older and 69% of those with 19 or more years of service.

A 1984 review by the Jones task force of its recommendations concluded that “conditions are as bad as in 1981, or perhaps a bit worse”. Major concerns were increasing traffic volume, inadequate staffing, low morale and an increasing burnout rate. Such conditions led to the re-unionization of US ATCs in 1987 with the election of the National Air Traffic Controllers Organization (NATCA) as their bargaining representative.

In a 1994 survey, New York City area ATCs reported continuing staffing shortages and concerns about job stress, shift work and indoor air quality. Recommendations for improving morale and health included transfer opportunities, early retirement, more flexible schedules, exercise facilities at work and increased staffing. In 1994, a greater proportion of Level 3 and 5 ATCs reported high burnout than ATCs in 1981 and 1984 national surveys (except for ATCs working in centres in 1984). Level 5 facilities have the highest level of air traffic, and Level 1, the lowest (Landsbergis et al. 1994). Feelings of burnout were related to having experienced a “near miss” in the past 3 years, age, years working as an ATC, working in high-traffic Level 5 facilities, poor work organization and poor supervisor and co-worker support.

Research also continues on appropriate shift schedules for ATCs, including the possibility of a 10-hour, 4-day shift schedule. The long-term health effects of the combination of rotating shifts and compressed work weeks are not known.

A collectively bargained programme to reduce ATC job stress in Italy

The company in charge of all civil air traffic in Italy (AAAV) employs 1,536 ATCs. AAAV and union representatives drew up several agreements between 1982 and 1991 to improve working conditions. These include:

1.  Modernizing radio systems and automating aeronautical information, flight data processing and air traffic management. This provided for more reliable information and more time for making decisions, eliminating many risky traffic peaks and providing for a more balanced workload.

2.  Reducing work hours. The operative work week is now 28 to 30 hours.

3. Changing shift schedules:

• rapid shift speed: one day on each shift

• one night shift followed by 2 days rest

• adjust of shift length to workload: 5 to 6 hours for morning; 7 hours for afternoon; 11 to 12 hours for night

• short naps on the night shift

• keeping shift rotation as regular as possible to allow better organization of personal, family and social life

• a long break (45 to 60 minutes) for a meal during work shifts.

4.  Reduce environmental stressors. Attempts have been made to reduce noise and provide more light.

5.  Improving the ergonomics of new consoles, screens and chairs.

6.  Improving physical fitness. Gyms are provided in the largest facilities.

Research during this period suggests that the programme was beneficial. The night shift was not very stressful; ATCs’ performance did not worsen significantly at the end of three shifts; only 28 ATCs were dismissed for health reasons in 7 years; and a large decline in “near misses” occurred despite major increases in air traffic.

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Some text was adapted from the 3rd edition Encyclopaedia article “Aviation - ground personnel” authored by E. Evrard.

Commercial air transport involves the interaction of several groups including governments, airport operators, aircraft operators and aircraft manufacturers. Governments are generally involved in overall air transport regulation, oversight of aircraft operators (including maintenance and operations), manufacturing certification and oversight, air traffic control, airport facilities and security. Airport operators can either be local governments or commercial entities. They are usually responsible for the general operation of the airport. Types of aircraft operators include general airlines and commercial transport (either privately or publicly owned), cargo carriers, corporations and individual aircraft owners. Aircraft operators in general are responsible for operation and maintenance of the aircraft, training of personnel and operation of ticketing and boarding operations. Responsibility for security can vary; in some countries the aircraft operators are responsible, and in others the government or airport operators are responsible. Manufacturers are responsible for design, manufacturing and testing, and for aircraft support and improvement. There are also international agreements con- cerning international flights.

This article deals with the personnel involved with all aspects of flight control (i.e., those who control commercial aircraft from takeoff to landing and who maintain the radar towers and other facilities used for flight control) and with those airport personnel who perform maintenance on and load aircraft, handle baggage and air freight and provide passenger services. Such personnel are divided into the following categories:

• air traffic controllers

• airways facilities and radar towers maintenance personnel

• ground crews

• baggage handlers

• passenger service agents.

Flight Control Operations

Government aviation authorities such as the Federal Aviation Administration (FAA) in the United States maintain flight control over commercial aircraft from takeoff to landing. Their primary mission involves the handling of airplanes using radar and other surveillance equipment to keep aircraft separated and on course. Flight control personnel work at airports, terminal radar approach control facilities (Tracons) and regional long-distance centres, and consist of air traffic controllers and airways facilities maintenance personnel. Airways facilities maintenance personnel maintain the airport control towers, air traffic Tracons and regional centres, radio beacons, radar towers and radar equipment, and consist of electronics technicians, engineers, electricians and facilities maintenance workers. The guidance of planes using instruments is accomplished following instrument flight rules (IFR). Planes are tracked using the General National Air Space System (GNAS) by air traffic controllers working at airport control towers, Tracons and regional centres. Air traffic controllers keep planes separated and on course. As a plane moves from one jurisdiction to another, responsibility for the plane is handed from one type of controller to another.

Regional centres, terminal radar approach control and airport control towers

Regional centres direct planes after they have reached high altitudes. A centre is the largest of the aviation authority’s facilities. Regional centre controllers hand off and receive planes to and from Tracons or other regional control centres and use radio and radar to maintain communication with aircraft. A plane flying across a country will always be under surveillance by a regional centre and passed along from one regional centre to the next.

The regional centres all overlap each other in the surveillance range and receive radar information from long-range radar facilities. Radar information is sent to these facilities via microwave links and telephone lines, thus providing a redundancy of information so that if one form of communication is lost, the other is available. Oceanic air traffic, which cannot be seen by radar, is handled by the regional centres via radio. Technicians and engineers maintain the electronic surveillance equipment and the uninterrupted power systems, which includes emergency generators and large banks of back-up batteries.

Air traffic controllers at Tracons handle planes flying at low altitudes and within 80 km of airports, using radio and radar to maintain communication with aircraft. Tracons receive radar tracking information from the airport surveillance radar (ASR). The radar tracking system identifies the plane moving in space but also queries the plane beacon and identifies the plane and its flight information. Personnel and work tasks at Tracons are similar to those at the regional centres.

Regional and approach control systems exist in two variants: non-automated or manual systems and automated systems.

With manual air traffic control systems, radio communications between controller and pilot are supplemented by information from primary or secondary radar equipment. The trace of the aeroplane can be followed as a mobile echo on display screens formed by cathode-ray tubes (see figure 1). Manual systems have been replaced by automated systems in most countries.

Figure 1. Air traffic controller at a manual local control centre radar screen.

With automated air traffic control systems, information on the aeroplane is still based on the flight plan and primary and secondary radar, but computers make it possible to present in alphanumeric form on the display screen all data concerning each aeroplane and to follow its route. Computers are also used to anticipate conflict between two or more aircraft on identical or converging routes on the basis of the flight plans and standard separations. Automation relieves the controller of many of the activities he or she carries out in a manual system, leaving more time for taking decisions.

Conditions of work are different in manual and automated control centre systems. In the manual system the screen is horizontal or sloping, and the operator leans forward in an uncomfortable position with his or her face between 30 and 50 cm from it. The perception of mobile echoes in the form of spots depends on their brightness and their contrast with the illuminance of the screen. As some mobile echoes have a very low luminous intensity, the working environment must be very weakly illuminated to ensure the greatest possible visual sensitivity to contrast.

In the automated system the electronic data display screens are vertical or almost vertical, and the operator can work in a normal sitting position with a greater reading distance. The operator has horizontally arranged keyboards within reach to regulate the presentation of the characters and symbols conveying the various types of information and can alter the shape and brightness of the characters. The lighting of the room can approach the intensity of daylight, for contrast remains highly satisfactory at 160 lux. These features of the automated system place the operator in a much better position to increase efficiency and reduce visual and mental fatigue.

Work is carried out in a huge, artificially lighted room without windows, which is filled with display screens. This closed environment, often far from the airports, allows little social contact during the work, which calls for great concentration and powers of decision. The comparative isolation is mental as well as physical, and there is hardly any opportunity of diversion. All this has been held to produce stress.

Each airport has a control tower. Controllers at airport control towers direct planes in and out of the airport, using radar, radio and binoculars to maintain communication with aircraft both while taxiing and while taking off and landing. Airport tower controllers hand off to or receive planes from controllers at Tracons. Most of the radar and other surveillance systems are located at the airports. These systems are maintained by technicians and engineers.

The walls of the tower room are transparent, for there must be perfect visibility. The working environment is thus completely different from that of regional or approach control. The air traffic controllers have a direct view of aircraft movements and other activities. They meet some of the pilots and take part in the life of the airport. The atmosphere is no longer that of a closed environment, and it offers a greater variety of interest.

Airways facilities maintenance personnel

Airways facilities and radar towers maintenance personnel consist of radar technicians, navigational and communication technicians and environmental technicians.

Radar technicians maintain and operate the radar systems, including airport and long-range radar systems. The work involves electronic equipment maintenance, calibration and troubleshooting.

Navigational and communication technicians maintain and operate the radio communications equipment and other related navigational equipment used in controlling air traffic. The work involves electronic equipment maintenance, calibration and troubleshooting.

Environmental technicians maintain and operate the aviation authority buildings (regional centres, Tracons and airport facilities, including the control towers) and equipment. The work requires running heating, ventilation and air-conditioning equipment and maintaining emergency generators, airport lighting systems, large banks of batteries in uninterrupted power supply (UPS) equipment and related electrical power equipment.

The occupational hazards for all three jobs include: noise exposure; working on or near live electrical parts including exposure to high voltage, x-ray exposure from klystron and magnitron tubes, fall hazards while working on elevated radar towers or using climbing poles and ladders to access towers and radio antenna and possibly PCBs exposure when handling older capacitors and working on utility transformers. Workers may also be exposed to microwave and radio-frequency exposure. According to a study of a group of radar workers in Australia (Joyner and Bangay 1986), personnel are not generally exposed to levels of microwave radiation exceeding 10 W/m² unless they are working on open waveguides (microwave cables) and components utilizing waveguide slots, or working within transmitter cabinets when high-voltage arcing is occurring. The environmental technicians also work with chemicals related to building maintenance, including boiler and other related water treatment chemicals, asbestos, paints, diesel fuel and battery acid. Many of the electrical and utility cables at airports are underground. Inspection and repair work on these systems often involves confined space entry and exposure to confined space hazards—noxious or asphyxiating atmospheres, falls, electrocution and engulfment.

Airways facilities maintenance workers and other ground crews in the airport operating area are frequently exposed to jet exhaust. Several airport studies where sampling of jet engine exhaust has been conducted demonstrated similar results (Eisenhardt and Olmsted 1996; Miyamoto 1986; Decker 1994): the presence of aldehydes including butyraldehyde, acetaldehyde, acrolein, methacrolein, isobutyraldehyde, propionaldehyde, croton-aldehyde and formaldehyde. Formaldehyde was present at significantly higher concentrations then the other aldehydes, followed by acetaldehyde. The authors of these studies have concluded that the formaldehyde in the exhaust was probably the main causative factor in the eye and respiratory irritation reported by exposed persons. Depending on the study, nitrogen oxides either were not detected or were present in concentrations below 1 part per million (ppm) in the exhaust stream. They concluded that neither nitrogen oxides nor other oxides play a major role in the irritation. Jet exhaust was also found to contain 70 different hydrocarbon species with up to 13 consisting mostly of olefins (alkenes). Heavy-metal exposure from jet exhaust has been shown not to pose a health hazard for areas surrounding airports.

Radar towers should be equipped with standard railings around the stairs and platforms to prevent falls and with interlocks to prevent access to the radar dish while it is operating. Workers accessing towers and radio antennas should use approved devices for ladder climbing and personal fall protection.

Personnel work on both de-energized and energized electrical systems and equipment. Protection from electrical hazards should involve training in safe work practices, lockout/tagout procedures and the use of personal protective equipment (PPE).

The radar microwave is generated by high-voltage equipment using a klystron tube. The klystron tube generates x rays and can be a source of exposure when the panel is opened, allowing personnel to come in close proximity to it to work on it. The panel should always remain in place except when servicing the klystron tube, and work time should be kept to a minimum.

Personnel should wear the appropriate hearing protection (e.g., ear plugs and/or ear muffs) when working around noise sources such as jet planes and emergency generators.

Other controls involve training in materials handling, vehicle safety, emergency response equipment and evacuation procedures and confined space entry procedures equipment (including direct-reading air monitors, blowers and mechanical retrieval systems).

Air traffic controllers and flight services personnel

Air traffic controllers work in regional control centres, Tracons and airport control towers. This work generally involves working at a console tracking planes on radar scopes and communicating with pilots by radio. Flight services personnel provide weather information for pilots.

The hazards to air traffic controllers include possible visual problems, noise, stress and ergonomic problems. At one time there was concern about x-ray emissions from the radar screens. This, however, has not turned out to be a problem at the operating voltages used.

Standards of fitness for air traffic controllers have been recommended by the International Civil Aviation Organization (ICAO), and detailed standards are set out in national military and civil regulations, those relating to sight and hearing being particularly precise.

Visual problems

The broad, transparent surfaces of air traffic control towers at airports sometimes result in dazzling by the sun, and reflection from surrounding sand or concrete can increase the luminosity. This strain on the eyes may produce headaches, though often of a temporary nature. It may be prevented by surrounding the control tower with grass and avoiding concrete, asphalt or gravel and by giving a green tint to the transparent walls of the room. If the colour is not too strong, visual acuity and colour perception remain adequate while the excess radiation that causes dazzle is absorbed.

Until about 1960 there was a good deal of disagreement among authors on the frequency of eyestrain among controllers from viewing radar screens, but it does seem to have been high. Since then, attention given to visual refractive errors in the selection of radar controllers, their correction among serving controllers and the constant improvement of working conditions at the screen have helped to lower it considerably. Sometimes, however, eyestrain appears among controllers with excellent sight. This may be attributed to too low a level of lighting in the room, irregular illumination of the screen, the brightness of the echoes themselves and, in particular, flickering of the image. Progress in viewing conditions and insistence on higher technical specifications for new equipment are leading to a marked reduction in this source of eyestrain, or even its elimination. Strain in accommodation has also been considered until recently to be a possible cause of eyestrain among operators who have worked very close to the screen for an hour without interruption. Visual problems are becoming much less frequent and are likely to disappear or to occur only very occasionally in the automated radar system, for example, when there is a fault in a scope or where the rhythm of the images is badly adjusted.

A rational arrangement of the premises is mainly one that facilitates the adaptation of the scope readers to the intensity of the ambient lighting. In a non-automated radar station, adaptation to the semi-darkness of the scope room is achieved by spending 15 to 20 minutes in another dimly lighted room. The general lighting of the scope room, the luminous intensity of the scopes and the brightness of the spots must all be studied with care. In the automated system the signs and symbols are read under an ambient lighting of from 160 to 200 lux, and the disadvantages of the dark environment of the non-automated system are avoided. With regard to noise, despite modern sound-insulating techniques, the problem remains acute in control towers installed near the runways.

Readers of radar screens and electronic display screens are sensitive to changes in the ambient lighting. In the non-automated system the controllers must wear glasses absorbing 80% of the light for between 20 and 30 minutes before entering their workplace. In the automated system special glasses for adaptation are no longer essential, but persons particularly sensitive to the contrast between the lighting of the symbols on the display screen and that of the working environment find that glasses of medium absorptive power add to the comfort of their eyes. There is also a reduction in eyestrain. Runway controllers are well advised to wear glasses absorbing 80% of the light when they are exposed to strong sunlight.

Stress

The most serious occupational hazard for air traffic controllers is stress. The chief duty of the controller is to make decisions on the movements of aircraft in the sector he or she is responsible for: flight levels, routes, changes of course when there is conflict with the course of another aircraft or when congestion in one sector leads to delays, air traffic and so on. In non-automated systems the controller must also prepare, classify and organize the information his or her decision is based on. The data available are comparatively crude and must first be digested. In highly automated systems the instruments can help the controller in taking decisions, and he or she may then only have to analyse data produced by teamwork and presented in rational form by these instruments. Although the work may be greatly facilitated, the responsibility for approving the decision proposed to the controller remains the controller’s, and his or her activities still give rise to stress. The responsibilities of the job, pressure of work at certain hours of dense or complex traffic, increasingly crowded air space, sustained concentration, rotating shift work and awareness of the catastrophe that may result from an error all create a situation of continuous tension, which may lead to stress reactions. The fatigue of the controller may assume the three classic forms of acute fatigue, chronic fatigue or overstrain and nervous exhaustion. (See also the article “Case Studies of Air Traffic Controllers in the United States and Italy”.)

Air traffic control calls for an uninterrupted service 24 hours a day, all year long. The conditions of work of controllers thus include shift work, an irregular rhythm of work and rest and periods of work when most other people are enjoying holidays. Periods of concentration and of relaxation during working hours and days of rest during a week of work are indispensable to the avoidance of operational fatigue. Unfortunately, this principle cannot be embodied in general rules, for the arrangement of work in shifts is influenced by variables that may be legal (maximum number of consecutive hours of work authorized) or purely professional (workload depending on the hour of the day or the night), and by many other factors based on social or family considerations. With regard to the most suitable length for periods of sustained concentration during work, experiments show that there should be short breaks of at least a few minutes after periods of uninterrupted work of from half an hour to an hour-and-a-half, but that there is no need to be bound by rigid patterns to achieve the desired aim: the maintenance of the level of concentration and the prevention of operational fatigue. What is essential is to be able to interrupt the periods of work at the screen with periods of rest without interrupting the continuity of the shift work. Further study is necessary to establish the most suitable length of the periods of sustained concentration and of relaxation during work and the best rhythm for weekly and annual rest periods and holidays, with a view to drawing up more unified standards.

Other hazards

There are also ergonomic issues while working at the consoles similar to those of computer operators, and there may be indoor air quality problems. Air traffic controllers also experience tone incidents. Tone incidents are loud tones coming into the headsets. The tones are of short duration (a few seconds) and have sound levels up to 115 dBA.

In flight services work, there are hazards associated with lasers, which are used in ceilorometer equipment used to measure cloud ceiling height, as well as ergonomic and indoor air quality issues.

Other flight control services personnel

Other flight control services personnel include flight standards, security, airport facilities renovation and construction, administrative support and medical personnel.

Flight standards personnel are aviation inspectors who conduct airline maintenance and flight inspections. Flight standards personnel verify the airworthiness of the commercial airlines. They often inspect airplane maintenance hangers and other airport facilities, and they ride in the cockpits of commercial flights. They also investigate plane crashes, incidents or other aviation-related mishaps.

The hazards of the job include noise exposure from aircraft, jet fuel and jet exhaust while working in hangers and other airport areas, and potential exposure to hazardous materials and blood-borne pathogens while investigating aircraft crashes. Flight standards personnel face many of the same hazards as airport ground crews, and thus many of the same precautions apply.

Security personnel include sky marshals. Sky marshals provide internal security on airplanes and external security at airport ramps. They are essentially police and investigate criminal activities related to aircraft and airports.

Airport facilities renovation and construction personnel approve all plans for airport modifications or new construction. The personnel are usually engineers, and their work largely involves office work.

Administrative workers include personnel in accounting, management systems and logistics. Medical personnel in the flight surgeon’s office provide occupational medical services to aviation authority workers.

Air traffic controllers, flight services personnel and personnel who work in office environments should have ergonomic training on proper sitting postures and on emergency response equipment and evacuation procedures.

Airport Operations

Airport ground crews conduct maintenance on and load aircraft. Baggage handlers handle passenger baggage and air freight, whereas passenger service agents register passengers and check passenger baggage.

All loading operations (passengers, baggage, freight, fuel, supplies and so on) are controlled and integrated by a supervisor who prepares the loading plan. This plan is given to the pilot prior to take-off. When all operations have been completed and any checks or inspections considered necessary by the pilot have been made, the airport controller gives authorization for take-off.

Ground crews

Aircraft maintenance and servicing

Every aircraft is serviced every time it lands. Ground crews performing routine turnaround maintenance; conduct visual inspections, including checking the oils; perform equipment checks, minor repairs and internal and external cleaning; and refuel and restock the aircraft. As soon as the aircraft lands and arrives in the unloading bays, a team of mechanics begins a series of maintenance checks and operations which vary with the type of aircraft. These mechanics refuel the aircraft, check a number of safety systems which must be inspected after each landing, investigate the logbook for any reports or defects the flight crew may have noticed during the flight and, where necessary, make repairs. (See also the article “Aircraft Maintenance Operations” in this chapter.) In cold weather, the mechanics may have to perform additional tasks, such as de-icing of wings, landing gear, flaps and so on. In hot climates special attention is paid to the condition of the aircraft’s tyres. Once this work has been completed, the mechanics can declare the aircraft flightworthy.

More thorough maintenance inspections and aircraft overhauls are performed at specific intervals of flying hours for each aircraft.

Fuelling aircraft is one of the most potentially hazardous servicing operations. The amount of fuel to be loaded is determined on the basis of such factors as flight duration, take-off weight, flight path, weather and possible diversions.

A cleaning team cleans and services the aircraft cabins, replacing dirty or damaged material (cushions, blankets and so on), empties the toilets and refills the water tanks. This team may also disinfect or disinfest the aircraft under the supervision of public health authorities.

Another team stocks the aircraft with food and drink, emergency equipment and supplies needed for passenger comfort. Meals are prepared under high standards of hygiene to eliminate the risk of food poisoning, particularly among the flight crew. Certain meals are deep frozen to –40ºC, stored at –29ºC and reheated in flight.

Ground service work includes the use of motorized and non-motorized equipment.

Baggage and air cargo loading

Baggage and cargo handlers move passenger baggage and air freight. Freight can range from fresh fruits and vegetables and live animals to radioisotopes and machinery. Because baggage and cargo handling requires physical effort and the use of mechanized equipment, workers may be more at risk for injuries and ergonomic problems.

Ground crews and baggage and freight handlers are exposed to many of the same hazards. These hazards include working outdoors in all types of weather, exposure to potential airborne contaminants from jet fuel and jet engine exhaust and exposure to prop wash and jet blast. Prop wash and jet blast can slam doors shut, knock people or unsecured equipment over, cause turboprop propellers to rotate and blow debris into engines or onto people. Ground crews are also exposed to noise hazards. A study in China showed ground crews were exposed to noise at aircraft engine hatches that exceeds 115 dBA (Wu et al. 1989). Vehicle traffic on the airport ramps and apron is very heavy, and the risk of accidents and collision is high. Fuelling operations are very hazardous, and workers may be exposed to fuel spills, leaks, fires and explosions. Workers on lifting devices, aerial baskets, platforms or access stands are at risk of falling. Job hazards also include rotating shift work carried out under pressure of time.

Strict regulations must be implemented and enforced for vehicle movement and driver training. Driver training should emphasize complying with speed limits, obeying off-limit areas and ensuring that there is adequate room for planes to manoeuvre. There should be good maintenance of ramp surfaces and efficient control of ground traffic. All vehicles authorized to operate on the airfield should be conspicuously marked so they can be readily identified by air traffic controllers. All equipment used by the ground crews should be regularly inspected and maintained. Workers on lifting devices, aerial baskets, platforms or access stands must be protected from falls either through the use of guardrails or personal fall protection equipment. Hearing protection equipment (earplugs and earmuffs) must be used for protection against noise hazards. Other PPE includes suitable work clothing depending on the weather, non-slip reinforced-toe-cap foot protection and appropriate eye, face, glove and body protection when applying de-icing fluids. Rigorous fire prevention and protection measures including bonding and grounding and prevention of electric sparking, smoking, open flames and the presence of other vehicles within 15 m of aircraft, must be implemented for refuelling operations. Fire-fighting equipment should be maintained and located in the area. Training on procedures to follow in the event of a fuel spill or fire should be conducted regularly.

Baggage and freight handlers should store and stack cargo securely and should receive training on proper lifting techniques and back postures. Extreme care should be used when entering and leaving aircraft cargo areas from carts and tractors. Appropriate protective clothing should be worn, depending on the type of cargo or baggage (such as gloves when handling live animal cargo). Baggage and freight conveyors, carousels and dispensers should have emergency shut-offs and built-in guards.

Passenger service agents

Passenger service agents issue tickets, register and check in passengers and passenger baggage. These agents may also guide passengers when boarding. Passenger service agents who sell airline tickets and check in passengers may spend all day on their feet using a video display unit (VDU). Precautions against these ergonomic hazards include resilient floor mats and seats for relief from standing, work breaks and ergonomic and anti-glare measures for the VDUs. In addition, dealing with passengers can be a source of stress, particularly when there are delays in flights or problems with making flight connections and so on. Breakdowns in the computerized airline reservations systems can also be a major source of stress.

Baggage check-in and weigh-in facilities should minimize the need for employees and passengers to lift and handle bags, and baggage conveyors, carousels and dispensers should have emergency shut-offs and built-in guards. Agents should also receive training on proper lifting techniques and back postures.

Baggage inspection systems use fluoroscopic equipment to examine baggage and other carry-on items. Shielding protects workers and the public from x-ray emissions, and if the shielding is not properly positioned, interlocks prevent the system from operating. According to an early study by the US National Institute for Occupational Safety and Health (NIOSH) and the Air Transport Association at five US airports, maximum documented whole-body x-ray exposures were considerably lower than maximum levels set by the US Food and Drug Administration (FDA) and the Occupational Safety and Health Administration (OSHA) (NIOSH 1976). Workers should wear whole-body monitoring devices to measure radiation exposures. NIOSH recommended periodic maintenance programmes to check effectiveness of shielding.

Passenger service agents and other airport personnel must be thoroughly familiar with the airport emergency evacuation plan and procedures.

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The transportation and warehousing industry is fraught with challenges to worker health and safety. Those involved in loading and unloading of cargo and in storing, stacking and retrieving materials are prone to musculoskeletal injuries, slips and falls due to uncertain, irregular or slippery work surfaces and being struck by falling objects. See figure 1. Those operating and maintaining vehicles and other machinery are not only vulnerable to such injuries but also to the toxic effects of fuels, lubricants and exhaust fumes. If ergonomic principles are not heeded in the design of seats, pedals and instrument panels, drivers of trains, planes and motor vehicles (those used in warehousing as well on roads) will not only be subject to musculoskeletal disorders and undue fatigue, but will also be prone to operating mishaps that can lead to accidents.

Figure 1. Lifting parcels above shoulder height is an ergonomic hazard.

Teamster Union

All workers—and the general public as well—may be exposed to toxic substances in the event of leaks, spills and fires. Since much of the work is done out-of-doors, transportation and warehousing workers are also subject to extremes of weather such as heat, cold, rain, snow and ice, which can not only make the work more arduous but also more dangerous. Aviation crews must adjust to changes in barometric pressure. Noise is a perennial problem for those operating or working near noisy vehicles and machinery.

Stress

Perhaps the most pervasive hazard in this industry is work stress. It has many sources:

Adjusting to work hours. Many workers in this industry are burdened by the necessity of adjusting to changing shifts, while flight crews who travel long east-west or west-east distances must adjust to changes in circadian body rhythms; both of these factors may cause drowsiness and fatigue. The danger of functional impairment due to fatigue has led to laws and regulations stipulating the number of hours or shifts that may be worked without a rest period. These are generally applicable to aviation flight crews, railroad train crews and, in most countries, drivers of road buses and trucks. Many of the last group are independent contractors or work for small enterprises and are frequently forced by economic pressures to flout these regulations. There are always emergencies dictated by problems with traffic, weather or accidents which require exceeding the work hours limits. Led by the airlines, large transportation companies are now using computers to track employees’ work schedules to verify their compliance with the regulations and to minimize the amount of down time for both workers and equipment.

Timetables. Most passenger and a good part of freight transport is guided by timetables stipulating departure and arrival times. The necessity of keeping to schedules which often allow too little leeway is often a very potent stressor for the drivers and their crews.

Dealing with the public. Meeting the sometimes unreasonable and often forcefully expressed demands of the public can be a significant source of stress for those dealing with passengers at terminals and ticket offices and en route. Drivers of road transport must contend with other vehicles, traffic regulations and diligent highway traffic officers.

Accidents. Accidents, whether due to equipment failure, human error or environmental conditions, place the transportation industry at or near the top of listings of occupational fatalities in most countries. Even when a particular worker’s injuries may not be serious, post-traumatic stress disorder (PTSD) can lead to profound and prolonged disability, and in some instances it can prompt changing to another job.

Isolation. Many employees in the transportation industry work alone with little or no human contact (e.g., truck drivers, workers in control rooms and in railroad switch and signal towers). If problems arise, there may be difficulty and delays in getting help. And, if they are not kept busy, boredom may lead to a drop in attentiveness that can presage accidents. Working alone, especially for those driving taxis, limousines and delivery trucks, is an important risk factor for felonious assaults and other forms of violence.

Being away from home. Transportation workers are frequently required to be away from home for periods of days or weeks (in the maritime industry, for months). In addition to the stress of living out of a suitcase, strange food and strange sleeping accommodations, there is the reciprocal stress of separation from family and friends.

Health problems

Most industrialized countries require transportation workers, especially drivers and operating crew members, to take periodic medical examinations to verify that their physical and mental capacities meet the requirements established by regulations. Visual and hearing acuity, colour vision, muscular strength and flexibility and freedom from causes of syncope are some of the factors tested for. Accommodations, however, make it possible for many individuals with chronic disorders or disabilities to work without danger to themselves or others. (In the United States, for example, employers are mandated by the federal Americans With Disabilities Act to provide such accommodations.)

Drugs and alcohol

Prescription and over-the-counter medications taken for a variety of disorders (e.g., hypertension, anxiety and other hyperkinetic conditions, allergies, diabetes, epilepsy, headaches and the common cold) may cause drowsiness and affect alertness, reaction time and coordination, especially when alcoholic beverages are also consumed. Abuse of alcohol and/or illegal drugs is found frequently enough among transportation workers to have led to voluntary or legislatively mandated drug testing programmes.

Summary

The health and safety of workers in the transportation and warehousing industry are critical considerations, not only for the workers themselves but also for the public being transported or involved as bystanders. Safeguarding health and safety, therefore, is the joint responsibility of the employers, the employees and their unions and governments on all levels.

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The transport sector encompasses industries that are involved in the transportation of goods and passengers throughout the world. This sector is structurally complex and vitally important to economies locally, nationally and globally.

Economic Importance

The transport sector is vitally important to the economic viability of nations. Transportation plays a key role in economically important factors such as employment, utilization of raw and manufactured goods, investment of private and public capital and generation of tax revenues.

In most industrialized countries, transport accounts for 2 to 12% of the paid employment (ILO 1992). In the United States alone, the Department of Transportation reported that in 1993, there were approximately 7.8 million employees in trucking-related firms (DOT 1995). The transport sector’s share in the gross domestic product (GDP) and total employment tends to decrease as the country’s income increases.

The transport sector is also a major consumer of raw materials and finished goods in most industrialized countries. For example, in the United States, the transport sector utilizes approximately 71% of all rubber produced, 66% of all petroleum refined, 24% of all zinc, 23% of all cement, 23% of all steel, 11% of all copper and 16% of all aluminium (Sampson, Farris and Shrock 1990).

Capital investment utilizing public and private funds to purchase trucks, ships, airplanes, terminals and other equipment and facilities easily exceeds hundreds of billions of dollars in industrialized countries.

The transport sector also plays a major role in generating revenues in the form of taxes. In industrialized countries, transport of passengers and freight is often heavily taxed (Sampson, Farris and Shrock 1990; Gentry, Semeijn and Vellenga 1995). Typically these taxes take the form of fuel taxes on gasoline and diesel fuels, and excise taxes on freight bills and passenger tickets, and easily exceed hundreds of billions of dollars annually.

Evolution of the Sector

In the early stages of the transport sector, geography greatly influenced what was the dominant mode of transportation. As advances were made in construction technology, it became possible to overcome many of the geographical barriers that limited the development of the transport sector. As a result, the modes of transport that have dominated the sector evolved in accordance with the technology available.

Initially, water travel over the oceans was the primary mode of transport of freight and passengers. As large rivers were navigated and canals were built, the volume of inland transport over the waterways increased significantly. In the late nineteenth century, transport over railways began to emerge as the dominant mode of transport. Rail transport, because of its ability to overcome natural barriers such as mountains and valleys through the use of tunnels and bridges, offered flexibility that waterways could not provide. Furthermore, unlike transport over waterways, transport over the rails was virtually unaffected by winter conditions.

Many national governments recognized the strategic and economic advantages of rail transport. Consequently, rail companies were awarded governmental financial assistance to facilitate the expansion of rail networks.

In the early twentieth century, the development of the combustion engine combined with the increased use of motor vehicles enabled road transport to become an increasingly popular mode of transport. As the highway and throughway systems were developed, road transport enabled door-to-door deliveries of goods. This flexibility far surpassed that of railways and waterways. Eventually, as advances were made in road construction and improvements were made to the internal combustion engine, in many parts of the world road transport became faster than rail transport. Consequently, road transport has become the most used mode of transport of goods and passengers.

The transport sector continued to evolve with the advent of airplanes. The use of airplanes as a means to transport freight and passengers began during the Second World War. Initially, airplanes were primarily used to transport mail and soldiers. However, as aircraft construction was perfected and an increasing number of persons learned to operate airplanes, air transport grew in popularity. Today, air transport is a very fast, reliable mode of transport. However, in terms of total tonnage, air transport handles only a very small percentage of freight.

Structure of the Sector

Information on the structure of rail systems in industrialized countries is generally reliable and comparable (ILO 1992). Similar information on road systems is somewhat less reliable. Information on the structure of waterways is reliable, having not changed substantially in the past few decades. However, similar information regarding developing countries is scarce and unreliable.

European countries developed economic and political blocs that have had a significant impact on the transport sector. In Europe, road transport dominates the movement of freight and passengers. Trucking, with a heavy emphasis on less-than-trailer-load freight, is conducted by small national and regional carriers. This industry is heavily regulated and highly fractured. Since the early 1970s, the total volume of freight transported by road has increased by 240%. Conversely, rail transport has declined by approximately 8% (Violland 1996). However, several European countries are working diligently to increase the efficiency of rail transport and are promoting intermodal transport.

In the United States, the primary mode of transport is over the roadways. The Department of Transportation, Office of Motor Carriers, reported in 1993 that there were over 335,000 firms operating medium and heavy trucks (DOT 1995). This included large companies that transport their own products, smaller private firms, and for-hire truckload and less-than-truckload common and contract carriers. The majority of these fleets (58%) operate six or fewer trucks. These companies operate a total of 1.7 million combination units, 4.4 million single-unit medium and heavy trucks and 3.8 million trailers. The road system in the United States increased by roughly 2% from 1980 to 1989 (ILO 1992).

The rail systems in the United States have declined, due primarily to the loss of Class 1 status of some rail lines, and due to the abandonment of less profitable lines. Canada has increased its rail system by some 40%, due mainly to a change in the classification system. The road system in Canada has decreased by 9% (ILO 1992).

In the industrialized nations of the Pacific Rim, there is great variability of the rail and road systems, due mainly to the different levels of industrialization of the respective countries. For example, rail and road networks in the Republic of Korea are similar to those in Europe, whereas in Malaysia, the rail and road networks are significantly smaller, but experiencing tremendous growth rates (over 53% for roads since 1980) (ILO 1992).

In Japan, the transport sector is heavily dominated by road transport, which accounts for 90.5% of the total Japanese freight transport tonnage. Approximately 8.2% of the tonnage is transported by water and 1.2% by rail (Magnier 1996).

Developing countries in Asia, Africa and Latin America typically suffer from inadequate transport systems. There is significant work underway to improve the systems, but a lack of hard currency, skilled workers and equipment inhibits the growth. Transport systems have grown significantly in Venezuela, Mexico and Brazil.

The Middle East in general has experienced growth in the transport sector, with countries such as Kuwait and Iran leading the way. It should be noted that due to the large size of the countries, sparse populations and arid climatic conditions, unique problems are encountered that limit the development of transport systems in this region.

An overview of railroad and road systems for selected countries and world regions is shown in figure 1 and figure 2.

Figure 1. World road network distribution 1988-89, kilometers.

Figure 2. World railroad network distribution, 1988-89, in kilometers.

Workforce Characteristics

The transportation sector contributes significantly to employment in most countries in both the private and public sectors. However, as per capita income increases, the impact of the sector on total employment decreases. The overall number of workers in the transport industries has declined steadily since the 1980s. This loss of workforce in the sector is due to several factors, especially technological advances that have automated many of the jobs related to the construction, maintenance and operation of transport systems. In addition, many countries have passed legislation which deregulated many transport-related industries; this has ultimately resulted in the loss of jobs.

Workers who are currently employed in transport-related industries must be highly skilled and competent. Due to the rapid advances in technology experienced in the transport sector, these workers and prospective workers must receive continual training and retraining.

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