General Overview

Coffee as a beverage was introduced in Europe during the sixteenth century, first in Germany and then throughout the European continent during the following century, especially to France and Holland. Afterwards, it spread to the rest of the world.

Since coffee will not keep its characteristic smell and flavour for long, after roasting and grinding, industrial establishments to roast and grind coffee have become needed wherever coffee is consumed. The establishments are usually small or medium-sized plants, but large factories do exist, mainly to produce regular as well as instant (soluble) coffee.

It is difficult to estimate the number of workers employed by the coffee industry. Some of the smaller plants do not keep registries, and figures are not entirely reliable. Considering a total consumption of approximately 100 million 60 kg bags of coffee during the year 1995, the worldwide coffee trade represents about US$50 million. Table 1 lists selected coffee-importing countries, giving an idea of the present world consumption.

Table 1. Selected coffee importers (in tonnes).

Source: FAO 1992.

Coffee manufacturing is a relatively simple process, including cleaning, roasting, grinding and packing processes, as shown in figure 1. However, modern technology has led to complex processes, with an increase in speed of production and requiring laboratories for quality-control testing of the product.

Figure 1. Flow chart of coffee manufacturing.

Coffee beans arrive at factories in 60 kg bags, which are unloaded mechanically or manually. In the latter case, usually two workers hold a bag and place it upon another worker’s head. This worker will carry the bag to be stored. Even when transportation is done on coveyor belts, some physical effort with high energy consumption is required.

The use of instant coffee has steadily increased, reaching approximately 20% of the world consumption. Instant coffee is obtained through a complex process in which blasts of hot air blow over coffee extracts, followed by evaporation, cooling and lyophilization (freeze drying), varying in details from one factory to another. In the manufacture of decaffeinated coffee, which represents over 10% of the consumption in the United States and in Europe, some plants still utilize chlorinated solvents (such as methylene chloride), which is removed by a blast of water vapour.

Potential Risks and Health Effects

To start coffee processing, bags are opened with a small knife, and the beans are thrown inside a bin to be cleaned. The work area is noisy and a large amount of residual particulate material remains in suspension, released from the cleaning machine.

Roasting exposes workers to risks of burns and thermal discomfort. Bean mixing, or blending, is done automatically, as is grinding, in areas which may be deficient in lighting due to interference from suspended coffee dust. Dirt may accumulate, noise levels may be high and mechanization requires work at a high speed.

After grinding, bags of different materials and sizes are filled and then packed, usually in cardboard boxes. When performed manually, these operations require high-speed repetitive motion of hands and arms. Cardboard boxes are transported to storage areas and then to their final destination.

The strong odour characteristic of the coffee industry may bother workers inside the plants, and the surrounding community as well. The significance of this problem as a potential health risk has not yet been clarified. The odour of coffee is due to a mixture of different products; research is ongoing to identify individual effects of these chemicals. Some components of the coffee dust and some of the odour-producing substances are known to be allergens.

Potential risks in instant-coffee plants are similar to those in regular coffee production; in addition, there are risks due to hot steam and boiler explosions. In the removal of caffeine, even when performed automatically, the risk of solvent exposure may be present.

Other potential risks which may affect workers’ health are similar to those found in food industries in general. Risks for accidents arise from cuts from knives used in bag opening, burns during roasting and crushing during grinding operations, especially in old machinery without automatic machine guarding. There are fire and explosion hazards from the large amounts of dust, unsafe electric wiring and gas used for heating the roasters.

Several hazards may be found in the coffee industry including, among others: hearing loss due to excessive noise, thermal stress during roasting, poisoning from pesticides and musculoskeletal disorders, especially affecting the backs of workers who lift and carry heavy bags.

Allergic disorders affecting the eye, skin or respiratory system may occur in any area in a coffee plant. It is the coffee dust which is associated with bronchitis with lung function impairment; rhinitis and conjunctivitis are also concerns (Sekimpi et al. 1996). Allergic reactions to contaminants of bags previously used for other materials, such as castor bean seeds, have also occurred (Romano et al. 1995).

Repetitive-motion disorders may result from high-speed motion in packing operations, especially where workers are not warned of the risk.

In less developed countries, effects of occupational risks may develop early because conditions of work may be inadequate and, moreover, other social and public health factors may contribute to disease. Such factors include: low salaries, inadequate medical care and social security, improper housing and sanitation, low levels of education, illiteracy, endemic diseases and malnutrition.

Preventive Measures

Machine guarding, general ventilation and local exhaust systems, noise abatement, housekeeping and cleaning, decreased bag weights, substitutes of solvents used in caffeine extraction, periodic inspection and preventive maintenance of boilers are examples of preventive measures that are required for ensuring adequate levels of industrial hygiene and safety. Odour intensity may be reduced through modification of roasting procedures. The organization of work can be modified so that repetitive-motion disorders may be avoided through alteration of working position and rhythm, as well as the introduction of systematic breaks and regular exercises, among other practices.

Periodic health screening should stress evaluation of exposure to herbicides and pesticides, spinal disorders and early signs of repetitive-motion disorders. Scratch tests using extracts from coffee beans, even if not universally accepted as completely reliable, may be useful in the identification of hypersusceptible individuals. Lung function tests may aid in the early diagnosis of obstructive respiratory conditions.

Health education is an important instrument to enable workers to identify health risks and their consequences and to become aware of their right to a healthy working environment.

Governmental action is required, through legislation and enforcement; employers’ participation is needed in providing and maintaining adequate working conditions.

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In most established markets around the world, soft drinks now rank first among manufactured beverages, surpassing even milk and coffee in terms of per capita consumption.

Including ready-to-drink, packaged products and bulk mixes for fountain dispensing, soft drinks are available in almost every conceivable size and flavour and in virtually every channel of retail distribution. Complementing this universal availability, much of the soft drink category’s growth can be attributed to convenient packaging. As consumers have become increasingly mobile, they have opted for easier-to-carry packaged goods. With the advent of the aluminium can and, more recently, the resealable plastic bottle, soft drink packaging has become lighter and more portable.

Stringent quality-control standards and state-of-the-art water treatment processes also have afforded the soft drink industry a high degree of confidence regarding product purity. Moreover, the manufacturing or bottling plants that produce soft drinks have evolved into highly mechanized, efficient and spotlessly clean food-processing facilities.

As early as the 1960s, most bottlers were producing beverages through machinery that ran at 150 bottles per minute. As product demand has continued to skyrocket, soft drink manufacturers have shifted to faster machinery. Thanks to advances in production technology, filling lines now are able to run in excess of 1,200 containers per minute, with minimal downtime except for product or flavour changes. This highly automated environment has allowed soft drink manufacturers to reduce the number of employees required to operate the lines (see figure 1). Still, as production efficiencies have risen dramatically, plant safety has remained an ever-important consideration.

Figure 1. Control panel in an automated soft drink plant in Novosibirsk, Russia.

Soft drink bottling or manufacturing involves five major processes, each with its own safety issues that must be evaluated and controlled:

1. treating water
2. compounding ingredients
3. carbonating product
4. filling product
5.  packaging.

See figure 2.

Figure 2. Flow chart of basic bottling operations.

Soft drink manufacturing starts with water, which is treated and cleansed to meet exacting quality-control standards, usually exceeding the quality of the local water supply. This process is critical to achieving high product quality and consistent taste profiles.

As ingredients are being compounded, the treated water is piped into large, stainless-steel tanks. This is the stage at which various ingredients are added and mixed. Diet beverages are mixed with artificial, non-nutritive sweeteners such as aspartame or saccharin, whereas regularly sweetened drinks typically use liquid sugars like fructose or sucrose. It is during this stage of the production process that food colouring may be added. Flavoured, sparkling waters receive the desired flavouring at this stage, while plain waters are stored in the mixing tanks until the filling line calls for them. It is common for bottling companies to purchase concentrate from other firms.

In order for carbonation (absorption of carbon dioxide (CO₂)) to occur, soft drinks are cooled using large, ammonia-based refrigeration systems. This is what gives carbonated products their effervescence and texture. CO₂ is stored in a liquid state and piped into carbonation units as needed. This process can be manipulated to control the required rate of beverage absorption. Depending upon the product, soft drinks may contain from 15 to 75 psi of CO₂. Fruit-flavoured soft drinks tend to have less carbonation than colas or sparkling water. Once carbonated, the product is ready to be dispensed into bottles and cans.

The filling room usually is separated from the rest of the facility, protecting open product from any possible contaminants. Again, the highly automated filling operation requires a minimal number of personnel. See figure 3 . Filling room operators monitor the equipment for efficiency, adding bulk lids or caps to the capping operation as necessary. Empty bottles and cans are transported automatically to the filling machine via bulk material-handling equipment.

Figure 3. Soft drink canning line showing filling operations.

Stringent quality-control procedures are followed throughout the production process. Technicians measure many variables, including CO₂, sugar content and taste, to ensure that finished drinks meet required quality standards.

Packaging is the last stage prior to warehousing and delivery. This process also has become highly automated. Meeting various marketplace requirements, bottles or cans enter the packaging machinery and may be wrapped with cardboard to form cases or placed into reusable plastic trays or shells. The packaged products then enter a palletizing machine, which automatically stacks them onto pallets. (See figure 4.) Next, the loaded pallets are moved—typically via fork-lift—to a warehouse, where they are stored.

Figure 4. Eight-packs of 2-litre soft drink plastic bottles on the way to an automatic palletizer.

Hazard Prevention

Lifting-related injuries—especially to employees’ backs and shoulders—are not uncommon in the beverage business. While many technological advances have been made in material handling over the years, the industry continues to seek safer, more efficient ways to move heavy product.

Certainly, employees must be provided with the proper training on safe work practices. Injuries also can be minimized by limiting exposure to lifting through enhanced work-station design. Adjustable tables can be used to raise or lower material to waist level, for example, so that employees do not have to bend and lift as much. In this manner, most weight-related stress is transferred to a piece of equipment instead of the human body. All beverage manufacturers should implement ergonomics programmes that identify work-related hazards and minimize the risks—either through modification or by developing better equipment. A reasonable means to that end is job rotation, which reduces employee exposure to high-risk tasks.

The use of machine guarding is another critical component of safe beverage manufacturing. Equipment such as fillers and conveyors move at high speeds and, if left unguarded, could snag employee clothing or body parts, causing potentially severe injuries. Conveyors, pulleys, gears and spindles must have appropriate covers to prevent employee contact. Overhead conveyors can create an additional hazard of falling cases. Netting or wire-mesh screens should be installed to protect against this danger. Maintenance programmes should dictate that all guarding which is removed for repair be replaced as soon as repair work is completed.

Since wet conditions are prevalent in the filling room, adequate drainage is necessary to keep liquid from accumulating on nearby walkways. In order to avoid slip-and-fall injuries, proper efforts must be made to keep floors as dry as possible. While steel-toed shoes usually are not required in the filling room, slip-resistant soles are highly recommended. Shoes should be selected based on the slip coefficient of the sole. Additionally, all electrical equipment should be properly grounded and protected from any moisture. Employees must take precautions to dry the areas around equipment before any electrical work begins.

Good housekeeping practices and routine inspections also are beneficial in keeping the workplace hazard-free. By taking these comparatively simple steps, management can be sure that all equipment is in good operating condition and properly stored. Emergency equipment such as fire extinguishers and eyewash stations also should be inspected for proper operation.

Although most of the chemicals present in bottling plants are not extremely hazardous, every operation uses flammable substances, acids, caustics, corrosives and oxidants. Appropriate work practices should be developed so employees know how to work safely with these chemicals. They must be taught how properly to store, handle and dispose of the chemicals and how to wear protective gear. Training should cover the location and operation of emergency response equipment. Eyewash stations and showers can minimize injury to anyone who is accidentally exposed to a hazardous chemical.

It also is necessary to install equipment such as chemical booms and dykes, as well as absorbent material, to be used in the event of a spill. Properly designed hazardous chemical storage facilities will minimize the risk of employee injury, too. Flammables should be separated from corrosives and oxidants.

The large tanks used for mixing ingredients, which need to be entered and cleaned routinely, are considered confined spaces. See the box on confined spaces in this chapter for information on the related hazards and precautions.

Mechanized equipment has become increasingly complex, often controlled by remote computers, pneumatic lines or even gravity. Employees must be sure that this equipment has been de-energized before it is serviced. Proper de-energizing procedures must be developed to guarantee the safety of those who maintain and repair this equipment. Energy must be shut off and locked out at its source so that the unit being serviced cannot be accidentally energized, causing potentially fatal injuries to service employees or nearby line operators.

Safety training and written de-energizing procedures are critical for each piece of equipment. Emergency stop switches should be strategically placed on all equipment. Interlocked safety devices are used to stop the equipment automatically when doors are opened or light beams are interrupted. Employees must be informed, however, that these devices cannot be relied upon to completely de-energize the equipment, but only to stop it in an emergency. Emergency stop switches cannot take the place of a proven de-energizing procedure for equipment maintenance.

Chlorine, which is used in the water treatment area, could be hazardous in the event of an accidental release. Chlorine typically comes in steel cylinders, which should be stored in an isolated, well-ventilated area and secured from tipping. Employees should be trained to follow safe cylinder-changing procedures. They also should be taught how to take quick, decisive action if an accidental release of chlorine occurs. In the late 1990s new chlorine compounds are gradually replacing the need for chlorine gas. Although still hazardous, these compounds are much safer to handle than gas.

Ammonia is used as a refrigerant in bottling operations. Typically, large ammonia systems can create a health hazard in the event of a leak or a spill. Bottling facilities should develop emergency response procedures to identify the responsibilities of involved employees. Those who are required to respond to such an emergency must be trained in spill response and respirator use. In the event of a leak or spill, respirators should be immediately available, and all non-essential personnel evacuated to safe areas until the situation is controlled.

CO₂, which is used in the filling operation, also can create health concerns. If filling rooms and adjacent work areas are not adequately ventilated, CO₂ accumulation can displace oxygen in employees’ breathing zones. Facilities should be monitored regularly for elevated CO₂ levels and, if they are detected, ventilation systems should be inspected to determine the cause for this occurence. Additional ventilation may be required to correct the situation.

Technological advances have made available better sound-absorption material for insulating or muffling motors and gears in most equipment. Still, given the function and size of filling equipment, noise levels generally exceed 90 dBA in this area. Employees who are exposed to this level of noise for an 8-hour weighted average must be protected. Good hearing protection programmes should include research on better ways to control noise; employee education on related health effects; personal noise protection; and training on how to use hearing protection devices, the wearing of which must be enforced in high-noise areas. Employee hearing must be routinely checked.

Fork-lifts are operated throughout the bottling plant and their safe use is imperative. In addition to demonstrating their driving skills, potential operators must understand fork-lift safety principles. Licenses are commonly issued to show that a minimum level of competency has been achieved. Fork-lift safety programmes should include a pre-use inspection process, whereby the vehicles are checked to ensure that all safety equipment is in place and working. Any deficient conditions should be immediately reported and corrected. Gas or liquid petroleum (LP) fork-lifts generate carbon monoxide as a by-product of combustion. Such emissions can be minimized by keeping the fork-lift engines tuned to manufacturers’ specifications.

Personal protective equipment (PPE) is common throughout the bottling facility. Filling-room employees wear eye and ear protection. Sanitation crews wear face, hand and foot protection that is appropriate for the chemicals they are exposed to. While slip-resistant shoes are recommended throughout the plant, maintenance employees should also have the added protection of steel-toed shoes. The key to a good PPE programme is to identify and evaluate the potential hazards associated with each job and to determine whether those hazards can be eliminated through engineering changes. If not, PPE must be selected to address the specific hazard at hand.

Management’s role is critical in identifying hazards and developing practices and procedures to minimize them in the workplace. Once developed, these practices and procedures must be communicated to employees so that they can perform their jobs safely.

As plant technology continues to advance—providing better equipment, new guards and protective devices—soft drink bottlers will have even more ways to maintain the safety of their workforce.

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Process Overview

The making of the concentrate is the first step in the production of a carbonated soft drink. At the beginnings of the industry, in the nineteenth century, both concentrate and soft drink were manufactured in the same facility. Sometimes the concentrate was sold to the consumers, who would make their own soft drinks. As the carbonated soft drink business has grown, the concentrate and the soft drink manufacturing have become specialized. Today, a concentrate manufacturing plant sells its product to various bottling companies.

Concentrate plants are constantly optimizing their operation through systems automation. As the demand for concentrate increases, automation has allowed the manufacturer to satisfy the demand without expanding the size of the manufacturing plant. Packaging size has increased too. Early in the industry, 1/2-, 1- and 5-gallon containers were the most common. Today 40- and 50-gallon drums and even tank trucks with capacities of 3,000 to 4,000 gallons are used.

Operations in a concentrate manufacturing plant can be divided into five basic processes:

1. treating water
2. receiving raw materials
3. concentrate manufacturing
4. concentrate and additives filling
5. shipping finished products.

Each of these processes has safety hazards that must be evaluated and controlled. Water is a very important ingredient in the concentrate and it must have excellent quality. Each concentrate plant treats water until it reaches the desired quality and is free from micro-organisms. Water treatment is monitored during all stages.

When the plant receives the compounding ingredients, inspection, sampling and analysing of the ingredients in the quality-control department are begun. Only materials that have passed the tests will be used in the concentrate manufacturing process. Some of the raw materials are received in tank trucks and require special handling. Also, packaging material is received, evaluated and analysed in the same way as the raw materials.

During the manufacturing of concentrate, treated water and liquid and solid ingredients are pumped into stainless-steel tanks, where they are mixed, homogenized and/or extracted in accordance with the manufacturing instructions. The tanks have capacities of 50 gallons, 10,000 gallons and even more. These tanks are completely clean and sanitized at the time of mixing.

Once the concentrate is manufactured, the filling stage is started. All the products are piped into the filling room. Filling machines are strictly cleaned and sanitized before the filling process starts. Most of the filling machines are dedicated to specific container sizes. The product is kept inside pipes and tanks at times during the filling process in order to avoid contamination. Each container should be labelled with the product name and handling hazards (if necessary). Full containers are moved by conveyors to the packaging area. Containers are placed on pallets and wrapped in plastic or tied before they are stored. Besides the concentrates, additives to be used in the preparation of carbonated soft drinks are packed. Many of these additives are packed in plastic bags and placed in boxes.

Once at the warehouse, the products are divided and prepared to be sent to the different bottling companies. These products should be labelled following all government regulations. If products are going to another country, the product must be labelled in accordance with the other country’s labelling requirements.

Production of fruit juices

Fruit juices are made from a wide variety of fruits, including oranges and other citrus fruits, apples, grapes, cranberries, pineapples, mangoes and so forth. In many cases, various fruit juices are blended. Usually, the fruit is processed into a concentrate near where it is grown, then shipped to a fruit juice packager. Fruit juices can be sold as concentrates, frozen concentrates (especially orange juice) and as the diluted juice. Often sugar and preservatives are added.

Once received at the processing plant, the oranges are washed, graded to remove damaged fruit, separated according to size and sent to the juice extractors. There the oils are extracted from the peel, and then the juice extracted by crushing. The pulpy juice is screened to remove seeds and pulp, which often end up as cattle feed. If the orange juice is intended for sale as “not from concentrate”, it is then pasteurized. Otherwise the juice is sent to evaporators, which remove most of the water by heat and vacuum, then chilled, to produce the frozen, concentrated orange juice. This process also removes many oils and essences which are blended back into the concentrate before shipping to the juice packager.

The frozen concentrate is shipped to the packager in refrigerated trucks or tankers. Many dairies package orange juice using the same equipment used to package milk. (See the article “Dairy products industry” elsewhere in this volume.) The concentrate is diluted with filtered water, pasteurized and packaged under sterile conditions. Depending on the amount of water added, the final product can be cans of frozen orange juice concentrate or ready-to-serve orange juice.

Michael McCann

Hazard Prevention

Hazards in a concentrate manufacturing plant vary depending on the products manufactured and the size of the plant.

Concentrate plants have a low injury rate due to a high degree of automation and mechanized handling. Materials are handled by fork-lifts, and full containers are placed on pallets by automatic palletizers. Although, employees generally do not have to use excessive force to get the job done, lifting related injuries remain a concern. Major hazards include engines and equipment in motion, objects falling from overhead containers, energy hazards in repair and maintenance, confined space hazards in cleaning mixing tanks, noise, fork-lift accidents and hazardous chemical cleaning agents. See the article “Soft drink bottling and canning” for more information on hazards and precautions.

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Fruit juices are made from a wide variety of fruits, including oranges and other citrus fruits, apples, grapes, cranberries, pineapples, mangoes and so forth. In many cases, various fruit juices are blended. Usually, the fruit is processed into a concentrate near where it is grown, then shipped to a fruit juice packager. Fruit juices can be sold as concentrates, frozen concentrates (especially orange juice) and as the diluted juice. Often sugar and preservatives are added.

Once received at the processing plant, the oranges are washed, graded to remove damaged fruit, separated according to size and sent to the juice extractors. There the oils are extracted from the peel, and then the juice extracted by crushing. The pulpy juice is screened to remove seeds and pulp, which often end up as cattle feed. If the orange juice is intended for sale as “not from concentrate”, it is then pasteurized. Otherwise the juice is sent to evaporators, which remove most of the water by heat and vacuum, then chilled, to produce the frozen, concentrated orange juice. This process also removes many oils and essences which are blended back into the concentrate before shipping to the juice packager.

The frozen concentrate is shipped to the packager in refrigerated trucks or tankers. Many dairies package orange juice using the same equipment used to package milk. (See the article “Dairy products industry” elsewhere in this volume.) The concentrate is diluted with filtered water, pasteurized and packaged under sterile conditions. Depending on the amount of water added, the final product can be cans of frozen orange juice concentrate or ready-to-serve orange juice.

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Overview of the Sector

The beverage industry consists of two major categories and eight sub-groups. The non-alcoholic category is comprised of soft drink syrup manufacture; soft drink and water bottling and canning; fruit juices bottling, canning and boxing; the coffee industry and the tea industry. Alcoholic beverage categories include distilled spirits, wine and brewing.

Evolution of the industry

Although many of these beverages, including beer, wine and tea, have been around for thousands of years, the industry has developed only over the past few centuries.

The beverage products industry, viewed as an aggregate group, is highly fragmented. This is evident by the number of manufacturers, methods of packaging, production processes and final products. The soft drink industry is the exception to the rule, as it is quite concentrated. Although the beverage industry is fragmented, ongoing consolidation since the 1970s is changing that.

Since the early 1900s beverage companies have evolved from regional firms that mainly produced goods for local markets, to today’s corporate giants that make products for international markets. This shift began when companies in this manufacturing sector adopted mass production techniques that let them expand. Also during this time period there were advances in product packaging and processes that greatly increased product shelf life. Air-tight containers for tea prevented absorption of moisture, which is the principle cause of loss of flavour. In addition, the advent of refrigeration equipment enabled lager beers to be brewed during the summer months.

Economic importance

The beverage industry employs several million people worldwide, and each type of beverage grosses billions of dollars in revenue each year. Indeed, in several small, developing countries, the production of coffee is the major support of the entire economy.

Characteristics of the Workforce

Though the ingredients and production of beverages vary, generally the characteristics of those employed in this industry have many commonalties. The process of harvesting raw materials, whether they be coffee beans, barley, hops or grapes, employs low-income, unskilled individuals or families. In addition to being their main source of income, the harvest determines a large part of their culture and lifestyle.

In contrast, the processing of the product involves automated and mechanized operations, usually employing a semi-skilled, blue-collar workforce. In the production facility and warehouse areas, some of the common jobs include packaging and filling machine operator, fork-lift operator, mechanic and manual labourer. The training for these positions is completed onsite with extensive on-the-job instruction. As technology and automation evolve, the workforce diminishes in number and technical training becomes more important. This semi-skilled manufacturing workforce is usually supported by a highly skilled technical group consisting of industrial engineers, manufacturing managers, cost accountants and quality assurance/food safety technicians.

The beverage industry for the most part distributes its products to wholesalers using common carriers. However, soft drink manufacturers usually employ drivers to deliver their products directly to individual retailers. These drivers-salesworkers account for about one-seventh of the workers in the soft drink industry.

The more health-conscious atmosphere in Europe and North America in the 1990s has led to a flat market in the alcoholic beverage industry, with demand shifting to non-alcoholic beverages. Both alcoholic and non-alcoholic beverages, however, are expanding considerably in developing nations in Asia, South America and to some extent Africa. Because of this expansion, numerous local jobs are being created to meet production and distribution needs.

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This article discusses situations and chains of events leading to accidents attributable to contact with the moving part of machines. People who operate and maintain machinery run the risk of being involved in serious accidents. US statistics suggest that 18,000 amputations and over 800 fatalities in the United States each year are assignable to such causes. According to the US National Institute for Occupational Safety and Health (NIOSH), the “caught in, under, or between” category of injuries in their classification ranked highest among the most important kinds of occupational injuries in 1979. Such injuries generally involved machines (Etherton and Myers 1990). “Contact with moving machine part” has been reported as the principal injury event in just over 10% of occupational accidents ever since this category was introduced into Swedish occupational-injury statistics in 1979.

Most machines have moving parts that can cause injury. Such moving parts may be found at the point of operation where work is performed on the material, such as where cutting, shaping, boring or deforming takes place. They may be found in the apparatus which transmits energy to the parts of the machine carrying out the work, such as flywheels, pulleys, connecting rods, couplers, cams, spindles, chains, cranks and gears. They may be found in other moving parts of the machine such as wheels on mobile equipment, gear motors, pumps, compressors and so forth. Hazardous machine movements can also be found among other sorts of machinery, especially in the auxiliary pieces of equipment which handle and transport such loads as work pieces, materials, waste or tools.

All parts of a machine that move in the course of the performance of work may contribute to accidents causing injury and damages. Both rotating and linear machine movements, as well as their sources of power, can be dangerous:

Rotating motion. Even smooth rotating shafts can grip an item of clothing and, for example, draw a person’s arm into a hazardous position. The danger in a rotating shaft increases if it has projecting parts or uneven or sharp surfaces, such as adjusting screws, bolts, slits, notches or cutting edges. Rotating machine parts give rise to “nip points” in three different ways:

1. There are the points between two rotating parts that rotate in opposite directions and have parallel axes, such as gears or cog-wheels, carriage rollers or mangles.
2. There are the points of contact between rotating parts and parts in linear movement, such as found between a power-transmission belt and its pulley, a chain and a sprocket, or a rack and pinion.
3. Rotating machine movements can give rise to the risk of cuts and crushing injuries when they take place in close proximity to stationary objects—this sort of condition exists between a worm conveyor and its housing, between the spokes of a wheel and the machine bed, or between a grinding wheel and a tool jig.

Linear movements. Vertical, horizontal and reciprocating motion can cause injury in several ways: a person may receive a shove or blow from a machine part, and may be caught between the machine part and some other object, or may be cut by a sharp edge, or sustain a nip injury by being trapped between the moving part and another object (figure 1).

Figure 1. Examples of mechanical movements that can injure a person

Power sources. Frequently, external sources of power are employed to run a machine which may involve considerable quantities of energy. These include electric, steam, hydraulic, pneumatic and mechanical power systems, all of which, if released or uncontrolled, can give rise to serious injuries or damage. A study of accidents that occurred over one year (1987 to 1988) among farmers in nine villages in northern India showed that fodder-cutting machines, all otherwise of the same design, are more dangerous when powered by a motor or tractor. The relative frequency of accidents involving more than a minor injury (per machine) was 5.1 per thousand for manual cutters and 8.6 per thousand for powered cutters (Mohan and Patel 1992).

Injuries Associated with Machine Movements

Since the forces associated with machine movements are often quite large, it can be presumed that the injuries to which they give rise will be serious. This presumption is confirmed by several sources. “Contact with moving machinery or material being machined” accounted for only 5% of all occupational accidents but for as much as 10% of fatal and major accidents (fractures, amputations and so on) according to British statistics (HSE 1989). Studies of two vehicle-manufacturing workplaces in Sweden point in the same direction. Accidents caused by machine movements gave rise to twice the number of days of sick leave, as measured by median values, compared to non-machine-related accidents. Machine-related accidents also differed from other accidents with regard to part of the body injured: The results indicated that 80% of the injuries sustained in “machine” accidents were to the hands and fingers, while the corresponding proportion for “other” accidents was 40% (Backström and Döös 1995).

The risk situation at automated installations has turned out to be both different (in terms of type of accident, sequence of events and degree of injury severity) and more complicated (both in technical terms and with regard to the need for specialized skills) than at installations where conventional machinery is used. The term automated is herein meant to refer to equipment which, without the direct intervention of a human being, can either initiate a machine movement or change its direction or function. Such equipment requires sensor devices (e.g., position sensors or microswitches) and/or some form of sequential controls (e.g., a computer program) to direct and monitor their activities. Over recent decades, a programmable logic controller (PLC) has been increasingly employed as the control unit in production systems. Small computers are now the most common means used for controlling production equipment in the industrialized world, while other means of control, such as electro-mechanical units, are becoming less and less common. In the Swedish manufacturing industry, the use of numerically controlled (NC) machines increased by 11 to 12% per year over the 1980s (Hörte and Lindberg 1989). In modern industrial production, being injured by “moving parts of machines” is increasingly becoming equivalent to being injured by “computer-controlled machine movements”.

Automated installations are found in more and more sectors of industry, and they have an increasing number of functions. Stores management, materials handling, processing, assembly and packaging are all being automated. Series production has come to resemble process production. If the feeding, machining and ejection of work pieces are mechanized, the operator no longer needs to be in the risk zone during the course of regular, undisturbed production. Research studies of automated manufacturing have shown that accidents occur primarily in the handling of disturbances affecting production. However, people can also get in the way of machine movements in performing other tasks, such as cleaning, adjusting, resetting, controlling and repairing.

When production is automated and the process is no longer under the direct control of the human being, the risk of unexpected machine movements increases. Most operators who work with groups or lines of inter-linked machines have experienced such unexpected machine movements. Many automation accidents occur as a result of just such movements. An automation accident is an accident in which the automatic equipment controlled (or should have controlled) the energy giving rise to the injury. This means that the force which injures the person comes from the machine itself (e.g., the energy of a machine movement). In a study of 177 automation accidents in Sweden, it was found that injury was caused by the “unexpected start” of a part of a machine in 84% of cases (Backström and Harms-Ringdahl 1984). A typical example of an injury caused by a computer-controlled machine movement is shown in figure 2.

Figure 2. A typical example of an injury caused by a computer-controlled machine movement

One of the studies referred to above (Backström and Döös 1995) showed that automatically controlled machine movements were causally linked to longer periods of sick leave than injuries due to other kinds of machine movements, the median value being four times higher at one of the workplaces. The injury pattern of automation accidents was similar to that for other machine accidents (mainly involving hands and fingers), but the tendency was for the former kind of injuries to be more serious (amputations, crushes and fractures).

Computer control, like manual, has weaknesses from the perspective of reliability. There is no guarantee that a computer program will operate without error. The electronics, with their low signal levels, may be sensitive to interference if not properly protected, and the consequences of resultant failures are not always possible to predict. Furthermore, programming changes are often left undocumented. One method used to compensate for this weakness is, for example, by operating “double” systems in which there are two independent chains of functional components and a method for monitoring such that both chains display the same value. If the systems display different values, this indicates a failure in one of them. But there is a possibility that both chains of components may suffer from the same fault and that they both can be put out of order by the same disturbance, thereby giving a false positive reading (as both systems agree). However, in only a few of the cases investigated has it been possible to trace an accident to computer failure (see below), despite the fact that it is common for a single computer to control all the functions of an installation (even the stopping of a machine as a result of the activation of a safety device). As an alternate, consideration may be given to providing a tried-and-tested system with electro-mechanical components for safety functions.

Technical Problems

In general, it can be said that a single accident has many causes, including technical, individual, environmental and organizational ones. For preventive purposes, an accident is best looked at not as an isolated event, but as a sequence of events or a process (Backström 1996). In the case of automation accidents, it has been shown that technical problems are frequently part of such a sequence and occur either at one of the early stages of the process or close to the injury event of the accident. Studies in which technical problems involved in automation accidents have been examined suggest that these lie behind 75 to 85% of the accidents. At the same time, in any specific case, there are usually other causes, such as those of an organizational nature. Only in one-tenth of cases has it been found that the direct source of the energy giving rise to an injury could be attributed to technical failure—for example, a machine movement taking place despite the machine’s being in the stop position. Similar figures have been reported in other studies. Usually, a technical problem led to trouble with the equipment, so that the operator had to switch tasks (e.g., to re-position a part that was in a crooked position). The accident then occurred during the implementation of the task, prompted by the technical failure. A quarter of the automation accidents were preceded by a disturbance in the materials flow such as a part becoming stuck or getting into a crooked or otherwise faulty position (see figure 3).

Figure 3. Types of technical problems involved in automation accidents (number of accidents =127)

In a study of 127 accidents involving automation, 28 of these accidents, described in figure 4, were further investigated to determine the types of technical problems which were involved as causal factors (Backström and Döös, in press). The problems specified in the accident investigations were most frequently caused by jammed, defective or worn-out components. In two cases, a problem was caused by a computer-program error, and in one by electromagnetic interference. In more than half of the cases (17 out of 28), faults had been present for some time but not remedied. Only in 5 of the 28 cases where a technical failure or deviation was referred to, had the defect not manifested itself previously. Some faults had been repaired only to reappear later. Certain defects had been present right from the time of installation, while others resulted from wear and the impact of the environment.

The proportion of automation accidents occurring in the course of the correction of a disturbance to production comes to between one-third and two-thirds of all cases, according to most studies. In other words, there is general agreement that handling production disturbances is a hazardous occupational task. The variation in the extent to which such accidents occur has many explanations, among them those related to the type of production and to how occupational tasks are classified. In some studies of disturbances, only problems and machine stops in the course of regular production have been considered; in others, a wider range of problems have been treated—for example, those involved in the setting up of work.

A very important measure in the prevention of automation accidents is to prepare procedures for removing the causes of production disturbances so that they are not repeated. In a specialized study of production disturbances at time of accident (Döös and Backström 1994), it was found that the most common task to which disturbances gave rise was the freeing or the correcting of the position of a work piece that had become stuck or wrongly placed. This type of problem initiated one of two rather similar sequences of events: (1) the part was freed and came into its correct position, the machine received an automatic signal to start, and the person was injured by the machine movement initiated, (2) there was not time for the part to be freed or repositioned before the person was injured by a machine movement that came unexpectedly, more quickly or was of greater force than the operator expected. Other disturbance-handling involved prompting a sensor impulse, freeing a jammed machine part, carrying out simple kinds of fault tracing, and arranging for restart (see figure 4).

Figure 4. Type of disturbance handling at time of accident (number of accidents =76)

Worker Safety

The categories of personnel which tend to be injured in automation accidents depend on how work is organized—that is, on which occupational group performs the hazardous tasks. In practice, this is a matter of which person at the workplace is assigned to deal with problems and disturbances on a routine basis. In modern Swedish industry, active interventions are usually demanded from the persons operating the machine. This is why, in the previously mentioned vehicle-manufacturing workplace study in Sweden (Backström and Döös, accepted for publication), it was found that 82% of the people who sustained injuries from automated machines were production workers or operators. Operators also had a higher relative accident frequency (15 automation accidents per 1,000 operators per year) than maintenance workers (6 per 1,000). The findings of studies which indicate that maintenance workers are more affected are at least partly to be explained by the fact that operators are not allowed to enter machining areas in some companies. In organizations with a different type of task distribution, other categories of personnel—setters, for example—may be given the task of solving any production problems that arise.

The most common corrective measure taken in this connection in order to raise the level of personal safety is to protect the person from hazardous machine movements by using some kind of safety device, such as machine guarding. The main principle here is that of “passive” safety—that is, the provision of protection that does not require action on the part of the worker. It is, however, impossible to judge the effectiveness of protective devices without very good acquaintance with the actual work requirements at the machine in question, a form of knowledge which is normally possessed only by machine operators themselves.

There are many factors that can put even what is apparently good machine protection out of action. In order to perform their work, operators may need to disengage or circumvent a safety device. In one study (Döös and Backström 1993), it was found that such disengagement or circumvention had taken place in 12 out of 75 of the automation accidents covered. It is often a matter of the operator’s being ambitious, and no longer willing to accept either production problems or the delay to the production process involved in correcting disturbances in accordance with instructions. One way of avoiding this problem is to make the protective device imperceptible, so that it does not affect the pace of production, product quality or task performance. But this is not always possible; and where there are repeated disturbances to production, even minor inconveniences can prompt people not to utilize safety devices. Again, routines should be made available to remove the causes of production disturbances so that these are not repeated. A lack of a means of confirming that safety devices really function according to specifications is a further significant risk factor. Faulty connections, start signals that remain in the system and later give rise to unexpected starts, build-up in air pressure, and sensors that have come loose may all cause failure of protective equipment.

Summary

As has been shown, technical solutions to problems may give rise to new problems. Although injuries are caused by machine movements, which are essentially technical by nature, this does not automatically mean that the potential for their eradication lies in purely technical factors. Technical systems will continue to malfunction, and people will fail to handle the situations to which these malfunctions give rise. The risks will continue to exist, and can be held in check only by a wide variety of means. Legislation and control, organizational measures at individual companies (in the form of training, safety rounds, risk analysis and the reporting of disturbances and near accidents), and an emphasis on steady, ongoing improvements are all needed as complements to purely technical development.

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Tools are such a common part of our lives that it is sometimes difficult to remember that they may pose hazards. All tools are manufactured with safety in mind, but occasionally an accident may occur before tool-related hazards are recognized. Workers must learn to recognize the hazards associated with the different types of tools and the safety precautions required to prevent those hazards. Appropriate personal protective equipment, such as safety goggles or gloves, should be worn for protection from potential hazards that may be encountered while using portable power tools and hand tools.

Hand Tools

Hand tools are non-powered and include everything from axes to wrenches. The greatest hazards posed by hand tools result from misuse, use of the wrong tool for the job, and improper maintenance. Some of the hazards associated with the use of hand tools include but are not limited to the following:

• Using a screwdriver as a chisel may cause the tip of the screwdriver to break off and fly, hitting the user or other employees.

• If a wooden handle on a tool such as a hammer or an axe is loose, splintered or cracked, the head of the tool may fly off and strike the user or another worker.

• A wrench must not be used if its jaws are sprung, because it might slip.

• Impact tools such as chisels, wedges or drift pins are unsafe if they have mushroomed heads which might shatter on impact, sending sharp fragments flying.

The employer is responsible for the safe condition of tools and equipment provided to employees, but the employees have the responsibility to use and maintain the tools properly. Workers should direct saw blades, knives or other tools away from aisle areas and other employees working in close proximity. Knives and scissors must be kept sharp, as dull tools can be more hazardous than sharp ones. (See figure 1.)

Figure 1. A screwdriver

Safety requires that floors be kept as clean and dry as possible to prevent accidental slips when working with or around dangerous hand tools. Although sparks produced by iron and steel hand tools are not normally hot enough to be sources of ignition, when working with or around flammable materials, spark-resistant tools made from brass, plastic, aluminium or wood may be used to prevent spark formation.

Power Tools

Power tools are hazardous when improperly used. There are several types of power tools, usually categorized according to the power source (electric, pneumatic, liquid fuel, hydraulic, steam and explosive powder actuated). Employees should be qualified or trained in the use of all power tools used in their work. They should understand the potential hazards associated with the use of power tools, and observe the following general safety precautions to prevent those hazards from occurring:

• Never carry a tool by the cord or hose.
• Never yank the cord or the hose to disconnect it from the receptacle.
• Keep cords and hoses away from heat, oil and sharp edges.
• Disconnect tools when they are not in use, before servicing, and when changing accessories such as blades, bits and cutters.
• All observers should stay a safe distance away from the work area.
• Secure work with clamps or a vise, freeing both hands to operate the tool.
• Avoid accidental starting. The worker should not hold a finger on the switch button while carrying a plugged-in tool. Tools which have lock-on controls should be disengaged when power is interrupted so that they do not start up automatically upon restoration of power.
• Tools should be maintained with care and kept sharp and clean for best performance. Instructions in the user’s manual should be followed for lubrication and changing accessories.
• Workers should assure they have good footing and balance when using power tools. Appropriate apparel should be worn, as loose clothing, ties or jewellery can become caught in moving parts.
• All portable electric tools that are damaged shall be removed from use and tagged “Do Not Use” to prevent electrical shock.

Protective Guards

Hazardous moving parts of power tools need to be safeguarded. For example, belts, gears, shafts, pulleys, sprockets, spindles, drums, flywheels, chains or other reciprocating, rotating or moving parts of equipment must be guarded if such parts are exposed to contact by workers. Where necessary, guards should be provided to protect the operator and others with respect to hazards associated with:

• the point of operation
• in-running nip points
• rotating and reciprocating parts
• flying chips and sparks, and mist or spray from metal-working fluids.

Safety guards must never be removed when a tool is being used. For example, portable circular saws must be equipped with guards. An upper guard must cover the entire blade of the saw. A retractable lower guard must cover the teeth of the saw, except when it makes contact with the work material. The lower guard must automatically return to the covering position when the tool is withdrawn from the work. Note the blade guards in the illustration of a power saw (figure 2).

Figure 2. A circular saw with guard

Safety Switches and Controls

The following are examples of hand-held power tools which must be equipped with a momentary contact “on-off” control switch:

• drills, tappers and fastener drivers
• horizontal, vertical and angle grinders with wheels larger than 2 inches (5.1 cm) in diameter
• disc and belt sanders
• reciprocating and sabre saws.

These tools also may be equipped with a lock-on control, provided that turnoff can be accomplished by a single motion of the same finger or fingers that turn it on.

The following hand-held power tools may be equipped with only a positive “on-off” control switch:

• platen sanders
• disc sanders with discs 2 inches (5.1 cm) or less in diameter
• grinders with wheels 2 inches (5.1 cm) or less in diameter
• routers and planers
• laminate trimmers, nibblers and shears
• scroll saws and jigsaws with blade shanks ¼ inch (0.64 cm) wide or less.

Other hand-held power tools which must be equipped with a constant pressure switch that will shut off the power when the pressure is released include:

• circular saws having a blade diameter greater than 2 inches (5.1 cm)
• chain-saws
• percussion tools without positive accessory-holding means.

Electric Tools

Workers using electric tools must be aware of several dangers. The most serious of these is the possibility of electrocution, followed by burns and slight shocks. Under certain conditions, even a small amount of current can result in fibrillation of the heart which may result in death. A shock also may cause a worker to fall off a ladder or other elevated work surfaces.

To reduce the potential of injury to workers from shock, tools must be protected by at least one of the following means:

• Grounded by a three-wire cord (with a ground wire). Three-wire cords contain two current-carrying conductors and a grounding conductor. One end of the grounding conductor connects to the tool’s metal housing. The other end is grounded through a prong on the plug. Any time an adapter is used to accommodate a two-hole receptacle, the adapter wire must be attached to a known ground. The third prong should never be removed from the plug. (See figure 3.)
• Double insulated. The worker and the tools are protected in two ways: (1) by normal insulation on the wires inside, and (2) by a housing that cannot conduct electricity to the operator in the event of a malfunction.
• Powered by a low-voltage isolation transformer.
• Connected through ground fault circuit interrupters. These are permanent and portable devices which instantaneously disconnect a circuit when it seeks ground through a worker’s body or through grounded objects.

Figure 3. An electric drill

These general safety practices should be followed in using electric tools:

• Electric tools should be operated within their design limitations.
• Gloves and safety footwear are recommended during use of electric tools.
• When not in use, tools should be stored in a dry place.
• Tools should not be used if wires or connectors are frayed, bent or damaged.
• Electric tools should not be used in damp or wet locations.
• Work areas should be well lighted.

Powered Abrasive Wheels

Powered abrasive grinding, cutting, polishing and wire buffing wheels create special safety problems because the wheels may disintegrate and throw off flying fragments.

Before abrasive wheels are mounted, they should be inspected closely and sound (or ring) tested by tapping gently with a light non-metallic instrument to be sure that they are free from cracks or defects. If wheels are cracked or sound dead, they could fly apart in operation and must not be used. A sound and undamaged wheel will give a clear metallic tone or “ring”.

To prevent the wheel from cracking, the user should be sure it fits freely on the spindle. The spindle nut must be tightened enough to hold the wheel in place without distorting the flange. Follow the manufacturer’s recommendations. Care must be taken to assure that the spindle wheel will not exceed the abrasive wheel specifications. Due to the possibility of a wheel disintegrating (exploding) during start-up, the worker should never stand directly in front of the wheel as it accelerates to full operating speed. Portable grinding tools need to be equipped with safety guards to protect workers not only from the moving wheel surface, but also from flying fragments in case of breakage. In addition, when using a powered grinder, these precautions should be observed:

• Always use eye protection.
• Turn off the power when tool is not in use.
• Never clamp a hand-held grinder in a vise.

Pneumatic Tools

Pneumatic tools are powered by compressed air and include chippers, drills, hammers and sanders. Although there are several potential dangers encountered in the use of pneumatic tools, the main one is the danger of getting hit by one of the tool’s attachments or by some kind of fastener the worker is using with the tool. Eye protection is required and face protection is recommended when working with pneumatic tools. Noise is another hazard. Working with noisy tools such as jackhammers requires proper, effective use of appropriate hearing protection.

When using a pneumatic tool, the worker must check to assure that it is fastened securely to the hose to prevent a disconnection. A short wire or positive locking device attaching the air hose to the tool will serve as an added safeguard. If an air hose is more than½ inch (1.27 cm) in diameter, a safety excess flow valve should be installed at the source of the air supply to shut off the air automatically in case the hose breaks. In general, the same precautions should be taken with an air hose that are recommended for electric cords, because the hose is subject to the same kind of damage or accidental striking, and it also presents a tripping hazard.

Compressed-air guns should never be pointed toward anyone. Workers should never “dead-end” the nozzle against themselves or anyone else. A safety clip or retainer should be installed to prevent attachments, such as a chisel on a chipping hammer, from being unintentionally shot from the barrel. Screens should be set up to protect nearby workers from being struck by flying fragments around chippers, riveting guns, air hammers, staplers or air drills.

Airless spray guns that atomize paints and fluids at high pressures (1,000 pounds or more per square inch) must be equipped with automatic or manual visual safety devices that will prevent activation until the safety device is manually released. Heavy jackhammers can cause fatigue and strains which may be reduced by the use of heavy rubber grips that provide a secure handhold. A worker operating a jackhammer must wear safety glasses and safety shoes to protect against injury if the hammer slips or falls. A face shield also should be used.

Fuel-Powered Tools

Fuel-powered tools are usually operated using small gasoline-powered internal combustion motors. The most serious potential dangers associated with the use of fuel-powered tools comes from hazardous fuel vapours that can burn or explode and give off dangerous exhaust fumes. The worker must be careful to handle, transport and store the gasoline or fuel only in approved flammable liquid containers, according to proper procedures for flammable liquids. Before the tank for a fuel-powered tool is refilled, the user must shut down the engine and allow it to cool to prevent accidental ignition of hazardous vapours. If a fuel-powered tool is used inside a closed area, effective ventilation and/or protective equipment is necessary to prevent exposure to carbon monoxide. Fire extinguishers must be available in the area.

Explosive Powder-Actuated Tools

Explosive powder-actuated tools operate like a loaded gun and should be treated with the same respect and precautions. In fact, they are so dangerous that they must be operated only by specially trained or qualified employees. Suitable ear, eye and face protection are essential when using a powder-actuated tool. All powder-actuated tools should be designed for varying powder charges so that the user can select a powder level necessary to do the work without excessive force.

The muzzle end of the tool should have a protective shield or guard centred perpendicularly on the barrel to protect the user from any flying fragments or particles that might create a hazard when the tool is fired. The tool must be designed so that it will not fire unless it has this kind of safety device. To prevent the tool from firing accidentally, two separate motions are required for firing: one to bring the tool into position, and another to pull the trigger. The tools must not be able to operate until they are pressed against the work surface with a force at least 5 pounds greater than the total weight of the tool.

If a powder-actuated tool misfires, the user should wait at least 30 seconds before trying to fire it again. If it still will not fire, the user should wait at least another 30 seconds so that the faulty cartridge is less likely to explode, then carefully remove the load. The bad cartridge should be put in water or otherwise safely disposed of in accordance with employer’s procedures.

If a powder-actuated tool develops a defect during use, it should be tagged and taken out of service immediately until it is properly repaired. Precautions for the safe use and handling of powder-actuated tools include the following:

• Powder-actuated tools should not be used in explosive or flammable atmospheres except upon issuance of a hot-work permit by an authorized person.
• Before using the tool, the worker should inspect it to determine that it is clean, that all moving parts operate freely and that the barrel is free from obstructions.
• The tool should never be pointed at anybody.
• The tool should not be loaded unless it is to be used immediately. A loaded tool should not be left unattended, especially where it may be available to unauthorized persons.
• Hands should be kept clear of the barrel end.

In using powder-actuated tools to apply fasteners, the following safety precautions should be considered:

• Do not fire fasteners into material that would let them pass through to the other side.
• Do not drive fasteners into materials like brick or concrete any closer than 3 inches (7.6 cm) to an edge or corner, or into steel any closer than ½ inch (1.27 cm) to a corner or edge.
• Do not drive fasteners into very hard or brittle material that might chip, shatter or make the fasteners ricochet.
• Use an alignment guide when shooting fasteners into existing holes. Do not drive fasteners into a spalled area caused by an unsatisfactory fastening.

Hydraulic Power Tools

The fluid used in hydraulic power tools must be approved for the expected use and must retain its operating characteristics at the most extreme temperatures to which it will be exposed. The manufacturer’s recommended safe operating pressure for hoses, valves, pipes, filters and other fittings must not be exceeded. Where there is a potential for a leak under high pressure in an area where sources of ignition, such as open flames or hot surfaces, may be present, the use of fire-resistant fluids as the hydraulic medium should be considered.

Jacks

All jacks—lever and ratchet jacks, screw jacks and hydraulic jacks—must have a device that stops them from jacking up too high. The manufacturer’s load limit must be permanently marked in a prominent place on the jack and should not be exceeded. Use wooden blocking under the base if necessary to make the jack level and secure. If the lift surface is metal, place a 1-inch-thick (2.54 cm) hardwood block or equivalent between the underside of the surface and the metal jack head to reduce the danger of slippage. A jack should never be used to support a lifted load. Once the load has been lifted, it should immediately be supported by blocks.

To set up a jack, make certain of the following conditions:

1. The base rests on a firm level surface.
2. The jack is correctly centred.
3. The jack head bears against a level surface.
4. The lift force is applied evenly.

Proper maintenance of jacks is essential for safety. All jacks must be inspected before each use and lubricated regularly. If a jack is subjected to an abnormal load or shock, it should be thoroughly examined to make sure it has not been damaged. Hydraulic jacks exposed to freezing temperatures must be filled with an adequate antifreeze liquid.

Summary

Workers who use hand and power tools and who are exposed to the hazards of falling, flying, abrasive and splashing objects and materials, or to hazards of harmful dusts, fumes, mists, vapours or gases, must be provided with the appropriate personal equipment necessary to protect them from the hazard. All hazards involved in the use of power tools can be prevented by workers following five basic safety rules:

1. Keep all tools in good condition with regular maintenance.
2. Use the right tool for the job.
3. Examine each tool for damage before use.
4. Operate tools according to the manufacturer’s instructions.
5. Select and use appropriate protective equipment.

Employees and employers have a responsibility to work together to maintain established safe work practices. If a an unsafe tool or hazardous situation is encountered, it should be brought to the attention of the proper individual immediately.

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A system can be defined as a set of interdependent components combined in such a way as to perform a given function under specified conditions. A machine is a tangible and particularly clear-cut example of a system in this sense, but there are other systems, involving men and women on a team or in a workshop or factory, which are far more complex and not so easy to define. Safety suggests the absence of danger or risk of accident or harm. In order to avoid ambiguity, the general concept of an unwanted occurrence will be employed. Absolute safety, in the sense of the impossibility of a more or less unfortunate incident occurring, is not attainable; realistically one must aim for a very low, rather than a zero probability of unwanted occurrences.

A given system may be looked upon as safe or unsafe only with respect to the performance that is actually expected from it. With this in mind, the safety level of a system can be defined as follows: “For any given set of unwanted occurrences, the level of safety (or unsafeness) of a system is determined by the probability of these occurrences taking place over a given period of time”. Examples of unwanted occurrences that would be of interest in the present connection include: multiple fatalities, death of one or several persons, serious injury, slight injury, damage to the environment, harmful effects on living beings, destruction of plants or buildings, and major or limited material or equipment damage.

Purpose of the Safety System Analysis

The object of a system safety analysis is to ascertain the factors which have a bearing on the probability of the unwanted occurrences, to study the way in which these occurrences take place and, ultimately, to develop preventive measures to reduce their probability.

The analytic phase of the problem can be divided into two main aspects:

1. identification and description of the types of dysfunction or maladjustment
2. identification of the sequences of dysfunctions that combine one with another (or with more “normal” occurrences) to lead ultimately to the unwanted occurrence itself, and the assessment of their likelihood.

Once the various dysfunctions and their consequences have been studied, the system safety analysts can direct their attention to preventive measures. Research in this area will be based directly on earlier findings. This investigation of preventive means follows the two main aspects of the system safety analysis.

Methods of Analysis

System safety analysis may be conducted before or after the event (a priori or a posteriori); in both instances, the method used may be either direct or reverse. An a priori analysis takes place before the unwanted occurrence. The analyst takes a certain number of such occurrences and sets out to discover the various stages that may lead up to them. By contrast, an a posteriori analysis is carried out after the unwanted occurrence has taken place. Its purpose is to provide guidance for the future and, specifically, to draw any conclusions that may be useful for any subsequent a priori analyses.

Although it may seem that an a priori analysis would be very much more valuable than an a posteriori analysis, since it precedes the incident, the two are in fact complementary. Which method is used depends on the complexity of the system involved and on what is already known about the subject. In the case of tangible systems such as machines or industrial facilities, previous experience can usually serve in preparing a fairly detailed a priori analysis. However, even then the analysis is not necessarily infallible and is sure to benefit from a subsequent a posteriori analysis based essentially on a study of the incidents that occur in the course of operation. As to more complex systems involving persons, such as work shifts, workshops or factories, a posteriori analysis is even more important. In such cases, past experience is not always sufficient to permit detailed and reliable a priori analysis.

An a posteriori analysis may develop into an a priori analysis as the analyst goes beyond the single process that led up to the incident in question and starts to look into the various occurrences that could reasonably lead to such an incident or similar incidents.

Another way in which an a posteriori analysis can become an a priori analysis is when the emphasis is placed not on the occurrence (whose prevention is the main purpose of the current analysis) but on less serious incidents. These incidents, such as technical hitches, material damage and potential or minor accidents, of relatively little significance in themselves, can be identified as warning signs of more serious occurrences. In such cases, although carried out after the occurrence of minor incidents, the analysis will be an a priori analysis as regards more serious occurrences that have not yet taken place.

There are two possible methods of studying the mechanism or logic behind the sequence of two or more events:

1. The direct, or inductive, method starts with the causes in order to predict their effects.
2. The reverse, or deductive, method looks at the effects and works backwards to the causes.

Figure 1 is a diagram of a control circuit requiring two buttons (B₁ and B₂) to be pressed simultaneously in order to activate the relay coil (R) and start the machine. This example may be used to illustrate, in practical terms, the direct and reverse methods used in system safety analysis.

Figure 1. Two-button control circuit

Direct method

In the direct method, the analyst begins by (1) listing faults, dysfunctions and maladjustments, (2) studying their effects and (3) determining whether or not those effects are a threat to safety. In the case of figure 1, the following faults may occur:

• a break in the wire between 2 and 2´

• unintentional contact at C₁ (or C₂) as a result of mechanical blocking

• accidental closing of B₁ (or B₂)

• short circuit between 1 and 1´.

The analyst can then deduce the consequences of these faults, and the findings can be set out in tabular form (table 1).

Table 1. Possible dysfunctions of a two-button control circuit and their consequences

* Occurrence with a direct influence on the reliability of the system
** Occurrence responsible for a serious reduction in the safety level of the system
*** Dangerous occurrence to be avoided

See text and figure 1.

In table 1 consequences which are dangerous or liable to seriously reduce the safety level of the system can be designated by conventional signs such as ***.

Note: In table 1 a break in the wire between 2 and 2´ (shown in figure 1) results in an occurrence that is not considered dangerous. It has no direct effect on the safety of the system; however, the probability of such an incident occurring has a direct bearing on the reliability of the system.

The direct method is particularly appropriate for simulation. Figure 2 shows an analog simulator designed for studying the safety of press-control circuits. The simulation of the control circuit makes it possible to verify that, so long as there is no fault, the circuit is actually capable of ensuring the required function without infringing the safety criteria. In addition, the simulator can allow the analyst to introduce faults in the various components of the circuit, observe their consequences and thus distinguish those circuits that are properly designed (with few or no dangerous faults) from those which are poorly designed. This type of safety analysis may also be performed using a computer.

Figure 2. Simulator for the study of press-control circuits

Reverse method

In the reverse method, the analyst works backwards from the undesirable occurrence, incident or accident, towards the various previous events to determine which may be capable of resulting in the occurrences to be avoided. In figure 1, the ultimate occurrence to be avoided would be the unintentional starting of the machine.

• The starting of the machine may be caused by an uncontrolled activation of the relay coil (R).

• The activation of the coil may, in turn, result from a short circuit between 1 and 1´ or from an unintentional and simultaneous closing of switches C₁ and C₂.

• Unintentional closing of C₁ may be the consequence of a mechanical blocking of C₁ or of the accidental pressing of B₁. Similar reasoning applies to C₂.

The findings of this analysis can be represented in a diagram which resembles a tree (for this reason the reverse method is known as “fault tree analysis”), such as depicted in figure 3.

Figure 3. Possible chain of events

The diagram follows logical operations, the most important of which are the “OR” and “AND” operations. The “OR” operation signifies that [X₁] will occur if either [A] or [B] (or both) take place. The “AND” operation signifies that before [X₂] can occur, both [C] and [D] must have taken place (see figure 4).

Figure 4. Representation of two logical operations

The reverse method is very often used in a priori analysis of tangible systems, especially in the chemical, aeronautical, space and nuclear industries. It has also been found extremely useful as a method to investigate industrial accidents.

Although they are very different, the direct and reverse methods are complementary. The direct method is based on a set of faults or dysfunctions, and the value of such an analysis therefore largely depends on the relevance of the various dysfunctions taken into account at the start. Seen in this light, the reverse method seems to be more systematic. Given knowledge of what types of accidents or incidents may happen, the analyst can in theory apply this method to work back towards all the dysfunctions or combinations of dysfunctions capable of bringing them about. However, because all the dangerous behaviours of a system are not necessarily known in advance, they can be discovered by the direct method, applied by simulation, for example. Once these have been discovered, the hazards can be analysed in greater detail by the reverse method.

Problems of System Safety Analysis

The analytical methods described above are not just mechanical processes which need only to be applied automatically in order to reach useful conclusions for improving system safety. On the contrary, analysts encounter a number of problems in the course of their work, and the usefulness of their analyses will depend largely on how they set about solving them. Some of the typical problems that may arise are described below.

Understanding the system to be studied and its operating conditions

The fundamental problems in any system safety analysis are the definition of the system to be studied, its limitations and the conditions under which it is supposed to operate throughout its existence.

If the analyst takes into account a subsystem that is too limited, the result may be the adoption of a series of random preventive measures (a situation in which everything is geared to preventing certain particular types of occurrence, while equally serious hazards are ignored or underestimated). If, on the other hand, the system considered is too comprehensive or general in relation to a given problem, it may result in excessive vagueness of concept and responsibilities, and the analysis may not lead to the adoption of appropriate preventive measures.

A typical example which illustrates the problem of defining the system to be studied is the safety of industrial machines or plant. In this kind of situation, the analyst may be tempted to consider only the actual equipment, overlooking the fact that it has to be operated or controlled by one or more persons. Simplification of this kind is sometimes valid. However, what has to be analysed is not just the machine subsystem but the entire worker-plus-machine system in the various stages of the life of the equipment (including, for example, transport and handling, assembly, testing and adjusting, normal operation, maintenance, disassembly and, in some cases, destruction). At each stage the machine is part of a specific system whose purpose and modes of functioning and malfunctioning are totally different from those of the system at other stages. It must therefore be designed and manufactured in such a way as to permit the performance of the required function under good safety conditions at each of the stages.

More generally, as regards safety studies in firms, there are several system levels: the machine, workstation, shift, department, factory and the firm as a whole. Depending on which system level is being considered, the possible types of dysfunction—and the relevant preventive measures—are quite different. A good prevention policy must make allowance for the dysfunctions that may occur at various levels.

The operating conditions of the system may be defined in terms of the way in which the system is supposed to function, and the environmental conditions to which it may be subject. This definition must be realistic enough to allow for the actual conditions in which the system is likely to operate. A system that is very safe only in a very restricted operating range may not be so safe if the user is unable to keep within the theoretical operating range prescribed. A safe system must thus be robust enough to withstand reasonable variations in the conditions in which it functions, and must tolerate certain simple but foreseeable errors on the part of the operators.

System modelling

It is often necessary to develop a model in order to analyse the safety of a system. This may raise certain problems which are worth examining.

For a concise and relatively simple system such as a conventional machine, the model is almost directly derivable from the descriptions of the material components and their functions (motors, transmission, etc.) and the way in which these components are interrelated. The number of possible component failure modes is similarly limited.

Modern machines such as computers and robots, which contain complex components like microprocessors and electronic circuits with very large-scale integration, pose a special problem. This problem has not been fully resolved in terms either of modelling or of predicting the different possible failure modes, because there are so many elementary transistors in each chip and because of the use of diverse kinds of software.

When the system to be analysed is a human organization, an interesting problem encountered in modelling lies in the choice and definition of certain non-material or not fully material components. A particular workstation may be represented, for example, by a system comprising workers, software, tasks, machines, materials and environment. (The “task” component may prove difficult to define, for it is not the prescribed task that counts but the task as it is actually performed).

When modelling human organizations, the analyst may opt to break down the system under consideration into an information subsystem and one or more action subsystems. Analysis of failures at different stages of the information subsystem (information acquisition, transmission, processing and use) can be highly instructive.

Problems associated with multiple levels of analysis

Problems associated with multiple levels of analysis often develop because starting from an unwanted occurrence, the analyst may work back towards incidents that are more and more remote in time. Depending on the level of analysis considered, the nature of the dysfunctions that occur varies; the same applies to the preventive measures. It is important to be able to decide at what level analysis should be stopped and at what level preventive action should be taken. An example is the simple case of an accident resulting from a mechanical failure caused by the repeated utilization of a machine under abnormal conditions. This may have been caused by a lack of operator training or from poor organization of work. Depending on the level of analysis considered, the preventive action required may be the replacement of the machine by another machine capable of withstanding more severe conditions of use, the use of the machine only under normal conditions, changes in personnel training, or a reorganization of work.

The effectiveness and scope of a preventive measure depend on the level at which it is introduced. Preventive action in the immediate vicinity of the unwanted occurrence is more likely to have a direct and rapid impact, but its effects may be limited; on the other hand, by working backwards to a reasonable extent in the analysis of events, it should be possible to find types of dysfunction that are common to numerous accidents. Any preventive action taken at this level will be much wider in scope, but its effectiveness may be less direct.

Bearing in mind that there are several levels of analysis, there may also be numerous patterns of preventive action, each of which carries its own share of the work of prevention. This is an extremely important point, and one need only return to the example of the accident presently under consideration to appreciate the fact. Proposing that the machine be replaced by another machine capable of withstanding more severe conditions of use places the onus of prevention on the machine. Deciding that the machine should be used only under normal conditions means placing the onus on the user. In the same way, the onus may be placed on personnel training, organization of work or simultaneously on the machine, the user, the training function and the organization function.

For any given level of analysis, an accident often appears to be the consequence of the combination of several dysfunctions or maladjustments. Depending on whether action is taken on one dysfunction or another, or on several simultaneously, the pattern of preventive action adopted will vary.

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Warehousing has long been a global industry; warehouses are integrally linked to commerce and transportation of goods—by rail, sea, air and road. Warehouses may be classified by the type of products stored: food products stored in dry, chilled or frozen sections; clothing or textiles; construction equipment or materials; machinery or machine parts. In the United States in 1995, for exemple, 1,877,000 workers were employed in trucking and warehousing (BLS 1996); this statistic cannot presently be disaggregated into workers by warehouse type or category. Warehouses might sell directly to external (retail) or internal (wholesale) customers, and the quantities retrieved for customers may be either full-pallet or less-than-full-pallet (one or more cases selected from a single pallet). Mechanical means (fork-lifts, conveyors or automatic storage and retrieval systems (AS/RS)) may be used to transport full-pallet or less-than-full-pallet loads; or workers, working without pallet movers and conveyors, may manually handle stored materials. Regardless of the nature of the business, the products stored or the mode of transportation servicing the warehouse, the basic layout is quite uniform, although the operational scale, terminology and technology will likely differ. (For additional information on AS/RS in warehousing, see Martin 1987.)

Products are delivered by shippers or suppliers to a receiving dock, where they are then entered into either a manual or computerized inventory system, assigned a storage rack or “slot” location (an address) and then transported to that location, usually by mechanical means (conveyors, AS/RS, fork-lift trucks or tractors). Once a customer order is received, the desired containers or cases must be retrieved from their slot location. Where full pallets are retrieved, mechanical means (a fork-lift or tractor operator) are used (see figure 1). When less than a full pallet load (one or more cases from a rack or slot) is to be retrieved, manual material handling is required, using a worker called a selector, who will choose the desired number of cases and place them either onto a mechanical pallet mover, a push cart or a conveyor. The individual customer order is assembled onto a pallet or similar container for shipment to the customer; a label, tag or other mark containing invoice/billing and/or routing instructions is then applied. This task may be performed by the order selector or fork-lift operator, or, where conveyors are used to deliver single cases for final assembly, by an assembler. When the order is ready for shipment, it is loaded by mechanical means onto the truck, trailer, railroad car or ship. (See figure 2).

Figure 1. A fork-lift truck in a warehouse in the United Kingdom being loaded with apples.

Figure 2. A dockworker in the United Kingdom using lifting machines to move quarters of beef.

Approximately 60% of the work activity in the warehouse is directly related to travel; the remainder relates to manual material handling. Aside from the important work of clerks, dispatchers, cleaners, supervisors and managers, the main work of the warehouse relating to the transporting and handling of goods is performed primarily by two classes of workers: fork-lift operators and selectors.

Intense worldwide competition and the rapid entrance of new firms have created the drive for increased labour and space efficiency, spawning a new discipline called warehouse management systems (WMSs) (Register 1994). These systems are becoming increasingly less expensive and more powerful; they rely on computer networks, bar coding, computer software and radio-frequency communications systems to vastly increase management and control of warehouse inventory and operations, allowing warehouses to improve customer order response times and responsiveness while dramatically increasing inventory accuracy and reducing costs (Firth 1995).

WMSs essentially computerize inventory and order dispatch systems. When incoming product from a supplier or shipper arrives at the receiving dock, bar code scanners record the product code and name, instantly updating the inventory database while assigning the incoming product an address in the warehouse. A fork-lift operator is then alerted to pick up and deliver the stock via a radio-frequency communications system mounted on the vehicle.

Orders from customers are received by another computer program which looks up the product address and availability of each item ordered in the inventory database and then sorts the customer order by the most efficient travel path to minimize travel. Labels with the product name, code and location are printed out for use by the order selectors who must then fill this order. While these features clearly help improve customer service and improve efficiency, they are important preconditions for engineered work standards (EWSs), which may pose additional health and safety hazards for both fork-lift operators and order selectors.

Information about each order—the number of cases, travel distances and so on—which is generated by the order dispatch programme can be further combined with standard or allowed times for each activity to calculate an overall standard time for selecting a particular customer order; it would be extremely time-consuming and difficult to retrieve this information without the use of the computer hardware and databases. Computer monitoring can then be used to record the elapsed time on each order, compare the actual with the allowed time and then compute an efficiency index, which any supervisor or manager can look up by pressing a few computer keys.

Warehouse EWSs have spread from the United States to Australia, Canada, the United Kingdom, Germany, Austria, Finland, Sweden, Italy, South Africa, the Netherlands and Belgium. While WMS systems themselves do not necessarily add safety and health hazards, there is considerable evidence to suggest that the resulting increased workload, lack of control over work pace and the impact of increased frequency of lifting contribute significantly to increased injury risk. In addition, the time pressure imposed by work standards may force workers to take risky short cuts and not utilize proper safe work methods. These risks and hazards are described below.

Hazards

In the most basic warehouse, regardless of the level of technology and computerization, there are a myriad of basic health and safety hazards; modern WMSs can be linked with a different order of health and safety hazards.

Basic health hazards begin with potentially toxic materials which may be stored in warehouses; examples include petroleum products, solvents and dyestuffs. These require proper labelling, employee education and training and an effective hazard communication programme (including MSDSs) for all affected workers, who often know little about the health effects of what they are handling, much less proper handling, spill and clean-up procedures. (See, for example, the ILO Chemicals Convention, 1990 (No. 170), and Recommendation, 1990 (No. 177).) Noise may be present from gasoline or LP-powered fork-lifts, conveyors, ventilation systems and pneumatically-actuated equipment. Additionally, workers who operate such equipment may be subject to whole-body vibration. (See, for example, the ILO Working Environment (Air Pollution, Noise and Vibration) Convention, 1977 (No. 148), and Recommendation, 1977 (No. 156).)

Both fork-lift operators and selectors may be exposed to diesel and gasoline exhaust from trucks at the loading and receiving docks, as well as from fork-lifts. Lighting may not be adequate for fork-lift and other vehicle traffic or for ensuring proper identification of products desired by customers. Workers assigned to work in cold and frozen storage areas may experience cold stress from exposure to cold temperatures and air recirculation systems; temperatures in many freezer storage areas can approach –20ºC, even without wind chill factors being considered. Moreover, since few warehouses are air conditioned during warm months, warehouse workers, particularly those performing manual material handling, may be exposed to heat stress problems.

Safety hazards and risks are also many and varied. Besides the more obvious hazards evident when pedestrians and any motor-driven vehicle are put into the same work area, many of the injuries occurring among warehouse workers include slips, trips and falls from floors not kept free of ice, water or spilled product or that are poorly maintained; a number of injuries involve fork-lift operators who slip or fall while mounting or dismounting their fork-lift trucks.

Workers are often exposed to falling product from overhead racks. Workers may be caught in or between fork-lift masts, forks and cargo, resulting in serious physical injury. Wooden pallets handled by workers often result in exposure to slivers and related puncture wounds. Using knives to cut apart boxes and cases often results in cuts and lacerations. Workers who move boxes or containers on or off conveyors may be exposed to in-running nip points. Selectors, assemblers and other workers engaged in manual material handling are exposed to varying degrees of risk of developing low-back pain and other related injuries. Weight-lifting regulations and recommended methods for materials handling are discussed elsewhere in the Encyclopaedia.

Recordable injuries and lost workday cases in the US warehouse industry, for example, are considerably higher than those for all industry.

Data regarding injuries (and particular back injuries) among grocery order selectors, the group at greatest risk from lifting-related injuries, are not available on a national or international scale. The US NIOSH, however, has studied lifting and other related injuries at two grocery warehouses in the United States (see US NIOSH) and found that “all order selectors have an elevated risk for musculoskeletal disorders, including low-back pain, because of the combination of adverse job factors, all contributing to fatigue, a high metabolic load and the workers’ inability to regulate their work rate because of the work requirements” (NIOSH 1995).

A comprehensive application of ergonomics to the warehouse should not be confined to lifting and to order selectors. A wide focus is required, involving detailed job analysis, careful measurement and assessment (part of the job analysis begins with the job safety analyses below). A more comprehensive look at the design of racks and shelves is required, as is establishment of a closer working relationship with suppliers to design or retrofit fork-lift controls to reduce ergonomic risk factors (extensive reaches, foot flexion and extension, winging, awkward neck and body positions) and to design containers that are less heavy and bulky, with handles or grips to reduce lifting risk.

Corrective Actions

Basic health hazards

Employers, workers and trade unions should cooperate to develop and implement an effective hazard communication programme which emphasizes the three following fundamentals:

1. adequate labelling of all toxic substances
2. availability of detailed MSDSs that provide more detailed information about health effects, fire, reactivity, PPE, first aid, spill clean-up and other emergency procedures
3. regular and relevant worker training in proper handling of these substances.

Lack of an effective hazard communication programme is one of the most frequent standards violations cited in this industry by the US Occupational Safety and Health Administration (OSHA).

Noise and vibration from mechanical equipment, conveyors and other sources require frequent noise and vibration testing and worker training, as well as engineering controls where needed. These controls are most effective when applied at the source of the noise in the form of noise insulation, mufflers and other controls (since most fork-lift operators are seated on top of the engine, vibration and noise dampening at this point are generally most effective). Lighting should be checked frequently and maintained at levels sufficient to reduce vehicle-pedestrian accidents and ensure that product identification and other information can be easily read. Heat (or cold) stress prevention programmes should be implemented for workplaces in warm and humid climates and for selectors or fork-lift operators assigned to cold storage or freezer rooms, to ensure that workers receive adequate breaks, fluids, training and information and that other preventive measures are implemented. Finally, where diesel or petroleum-based fuels are used, exhaust systems should be periodically tested for emissions of carbon monoxide and nitrogen oxides to ensure that they are within safe levels. Proper maintenance of vehicles and restricting their use to adequately ventilated areas will also help reduce the risk of over-exposure to these emissions.

Safety hazards for fork-lift and vehicle operators

Vehicle-pedestrian accidents are a constant risk in any warehouse. Pedestrian lanes should be clearly marked and respected. All vehicle operators should receive training in the safe operation of the vehicle, including traffic rules and speed limits; refresher training should also be considered. Mirrors should be installed at busy intersections or at blind corners to enable vehicle operators to check for traffic or pedestrians before proceeding, and operators should sound their horn before proceeding; back-up beepers or signals may also be considered. Dockplates from loading and receiving docks to the truck, railroad car or barge need to be sufficient to support the load and adequately secured.

Table 2 gives a job safety analysis for fork-lift operators, with recommendations.

Table 2. Job safety analysis: Fork-lift operator.

Implementing ergonomic solutions will require closer coordination with fork-lift and vehicle manufacturers; relying solely upon operator training and traffic rules will not eliminate hazards by itself. In addition, safety and health regulatory agencies have prepared mandatory standards for the design and use of fork-lifts—for example, requiring overhead guards to offer protection against falling objects (see figure 3).

Figure 3. An overhead guard fitted to a fork-lift truck.

Safety hazards for order selectors

Table 3 is a job safety analysis listing most of the corrective actions necessary to reduce the safety and lifting hazards for order selectors. However, just as improved fork-lift design to reduce ergonomic risk factors requires closer coordination with vehicle manufacturers, reducing safety and lifting hazards for order selectors requires similar coordination with designers of racking systems, consultants who design and install warehouse control systems and engineered standards systems and the vendors who store their products in the warehouse. The latter can be enlisted to design products that are less bulky, weigh less and have better handles or grips. Rack manufacturers can be very helpful in designing and retrofitting rack systems which allow the selector to stand upright during selection.

Table 3. Job safety analysis: Order selector.

Consultants who design and install warehouse control systems and engineered standards need to be more aware of the health and safety risks concerning the effect of work intensification on manual material-handling injuries. NIOSH (1993a, 1995) has recommended that more objective forms of determining fatigue allowance, such as oxygen consumption or heart rate, be used. They have also recommended that the height of the pallet being constructed (the “cube”) be limited to no more than 150 cm, and that there be an “order break” after one pallet has been assembled by the order selector, thus increasing the frequency of recovery periods between orders. In addition to more frequent breaks, NIOSH has recommended restricting overtime for workers based on engineered standards, considering worker rotation and installing “light duty” programmes for order selectors who return from injury or leave.

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Pipelines, marine vessels, tank trucks, rail tank cars and so forth are used to transport crude oils, compressed and liquefied hydrocarbon gases, liquid petroleum products and other chemicals from their point of origin to pipeline terminals, refineries, distributors and consumers.

Crude oils and liquid petroleum products are transported, handled and stored in their natural liquid state. Hydrocarbon gases are transported, handled and stored in both the gaseous and liquid states and must be completely confined in pipelines, tanks, cylinders or other containers prior to use. The most important characteristic of liquefied hydrocarbon gases (LHGs) is that they are stored, handled and shipped as liquids, taking up a relatively small amount of space and then expanding into a gas when used. For example, liquefied natural gas (LNG) is stored at –162°C, and when it is released the difference in storage and atmospheric temperatures causes the liquid to expand and gasify. One gallon (3.8 l) of LNG converts to approximately 2.5 m³ of natural gas at normal temperature and pressure. Because liquefied gas is much more “concentrated” than compressed gas, more useable gas can be transported and provided in the same size container.

Pipelines

It is generally the case that all crude oils, natural gas, liquefied natural gas, liquefied petroleum gas (LPG) and petroleum products flow through pipelines at some time in their migration from the well to a refinery or gas plant, then to a terminal and eventually to the consumer. Aboveground, underwater and underground pipelines, varying in size from several centimetres to a metre or more in diameter, move vast amounts of crude oil, natural gas, LHGs and liquid petroleum products. Pipelines run throughout the world, from the frozen tundra of Alaska and Siberia to the hot deserts of the Middle East, across rivers, lakes, seas, swamps and forests, over and through mountains and under cities and towns. Although the initial construction of pipelines is difficult and expensive, once they are built, properly maintained and operated, they provide one of the safest and most economical means of transporting these products.

The first successful crude-oil pipeline, a 5-cm-diameter wrought iron pipe 9 km long with a capacity of about 800 barrels a day, was opened in Pennsylvania (US) in 1865. Today, crude oil, compressed natural gas and liquid petroleum products are moved long distances through pipelines at speeds from 5.5 to 9 km per hour by large pumps or compressors located along the route of the pipeline at intervals ranging from 90 km to over 270 km. The distance between pumping or compressor stations is determined by the pump capacity, viscosity of the product, size of the pipeline and the type of terrain crossed. Regardless of these factors, pipeline pumping pressures and flow rates are controlled throughout the system to maintain a constant movement of product within the pipeline.

Types of pipelines

The four basic types of pipelines in the oil and gas industry are flow lines, gathering lines, crude trunk pipelines and petroleum product trunk pipelines.

• Flow lines. Flow lines move crude oil or natural gas from producing wells to producing field storage tanks and reservoirs. Flow lines may vary in size from 5 cm in diameter in older, lower-pressure fields with only a few wells, to much larger lines in multi-well, high-pressure fields. Offshore platforms use flow lines to move crude and gas from wells to the platform storage and loading facility. A lease line is a type of flow line which carries all of the oil produced on a single lease to a storage tank.

• Gathering and feeder lines. Gathering lines collect oil and gas from several locations for delivery to central accumulating points, such as from field crude oil tanks and gas plants to marine docks. Feeder lines collect oil and gas from several locations for delivery direct into trunk lines, such as moving crude oil from offshore platforms to onshore crude trunk pipelines. Gathering lines and feeder lines are typically larger in diameter than flow lines.

• Crude trunk pipelines. Natural gas and crude oil are moved long distances from producing areas or marine docks to refineries and from refineries to storage and distribution facilities by 1- to 3-m- or larger-diameter trunk pipelines.

• Petroleum product trunk pipelines. These pipelines move liquid petroleum products such as gasoline and fuel oil from refineries to terminals, and from marine and pipeline terminals to distribution terminals. Product pipelines may also distribute products from terminals to bulk plants and consumer storage facilities, and occasionally from refineries direct to consumers. Product pipelines are used to move LPG from refineries to distributor storage facilities or large industrial users.

Regulations and standards

Pipelines are constructed and operated to meet safety and environmental standards established by regulatory agencies and industry associations. Within the United States, the Department of Transportation (DOT) regulates the operation of pipelines, the Environmental Protection Agency (EPA) regulates spills and releases, the Occupational Safety and Health Administration (OSHA) promulgates standards covering worker health and safety, and the Interstate Commerce Commission (ICC) regulates common carrier pipelines. A number of industry organizations, such as the American Petroleum Institute and the American Gas Association, also publish recommended practices covering pipeline operations.

Pipeline construction

Pipeline routes are planned using topographic maps developed from aerial photogrammetric surveys, followed by actual ground surveying. After planning the route, obtaining right-of-way and permission to proceed, base camps are established and a means of access for construction equipment is required. Pipelines can be constructed working from one end to another or simultaneously in sections which are then connected.

The first step in laying pipeline is to construct a 15- to 30-m-wide service road along the planned route to provide a stable base for the pipe-laying and pipe-joining equipment and for underground pipeline excavation and backfill equipment. The pipe sections are laid on the ground alongside the service road. The ends of the pipe are cleaned, the pipe is bent horizontally or vertically, as necessary, and the sections are held in position by chocks above the ground and joined by multi-pass electrical arc-welding. The welds are checked visually and then with gamma radiation to assure that no defects are present. Each connected section is then coated with liquid soap and air-pressure tested to detect leaks.

The pipeline is cleaned, primed and coated with a hot, tar-like material to prevent corrosion and wrapped in an outer layer of heavy paper, mineral wool or plastic. If the pipe is to be buried, the bottom of the trench is prepared with a sand or gravel bed. The pipe may be weighed down by short, concrete sleeves to prevent its lifting out of the trench from groundwater pressure. After the underground pipeline is placed in the trench, the trench is backfilled and the surface of the ground returned to normal appearance. After coating and wrapping, aboveground piping is lifted up onto prepared stanchions or casements, which may have various design features such as anti-earthquake shock absorption. Pipelines may be insulated or have heat trace capabilities to keep products at desired temperatures throughout transport. All pipeline sections are hydrostatically tested prior to entering gas or liquid hydrocarbon service.

Pipeline operations

Pipelines may be either privately owned and operated, carrying only the owner’s products, or they may be common carriers, required to carry any company’s products provided that the pipeline’s product requirements and tariffs are met. The three major pipeline operations are pipeline control, pumping or compressor stations and delivery terminals. Storage, cleaning, communication and shipment are also important functions.

• Pipeline control. Regardless of the product being transported, the size and length of the pipeline or the terrain, pipeline pumping stations, pressures and flow rates are completely controlled in order to ensure appropriate flow rates and continuous operations. Typically an operator and computer control the pumps, valves, regulators and compressors throughout the pipeline system from a central location.

• Oil pumping and gas compressor stations. Crude oil and petroleum products pumping stations and gas compressor stations are located at wellheads and along the pipeline route as needed to maintain pressure and volume. Pumps are driven by electric motors or diesel engines, and turbines may be powered by fuel oil, gas or steam. Many of these stations are automatically controlled and not staffed at most times. Pumps, with and without vapour return lines or pressure equalizing lines, are commonly used in smaller pipelines for transport of LNG, LPG and compressed natural gas (CNG). Pressure drop detectors are installed to signal any leaks in pipelines, and excess flow valves or other flow limiting devices are used to minimize the rate of flow in case of a pipeline leak. Storage vessels and reservoirs may be isolated from main pipelines by manually operated or remote control valves or fusible link valves.

• Pipeline product storage. Crude and petroleum product pipeline terminals have breakout storage tanks to which shipments may be diverted, where they are held until required by a refinery, terminal or user (see figure 1). Other tanks at pipeline pumping stations contain fuel for operating diesel-driven pump motors or for running electrical generators. Because gas fields produce continuously and gas pipelines operate continuously, during times of reduced demand, such as summertime, liquefied natural and petroleum gases are stored underground in natural caverns or salt domes until needed.

• Pipeline cleaning. Pipelines are cleaned on a scheduled basis or as necessary in order to continue flow by reducing friction and maintaining as large a diameter interior as possible. A special cleaning device, called a pig or go-devil, is placed into the pipeline and pushed along by the flow of oil from one pumping station to the next. As the pig passes through the pipeline it scrapes off any dirt, wax or other deposits which have built up inside the pipeline walls. When it reaches a pumping station, the pig is removed, cleaned and reinserted into the pipeline to travel to the next station.

• Communications. It is important that there be communication and agreement concerning schedules, pumping rates and pressures and emergency procedures between pipeline stations and operators and those shipping and receiving crude oil, gas and petroleum products. Some pipeline companies have private telephone systems which transmit the signal along the pipeline, while others use radios or public telephones. Many pipelines use ultra-high-frequency microwave transmitter systems for computer communications between control centres and pumping stations.

• Petroleum product shipment. Petroleum products may be shipped a number of different ways on pipelines. A company operating a refinery may blend a specific grade of its own gasoline with appropriate additives (additize) and ship a batch through a pipeline directly to its own terminal for distribution to its customers. Another method is for a refinery to produce a batch of gasoline, called a frangible or specification product, which is blended to meet a common carrier pipeline company’s product specifications. The gasoline is placed into the pipeline for delivery to any company’s terminals which are connected to the pipeline system. In a third method, products are shipped by companies to each other’s terminals and exchanged in order to avoid extra transportation and handling. Frangible and exchange products are usually blended and additized at the terminal which receives the product from the pipeline, to meet the specific requirements of each company operating from the terminal. Finally, some products are delivered by pipeline from terminals and refineries direct to large commercial consumers—jet fuel to airports, gas to gas distribution companies and fuel oil to electric generating plants.

• Product receipt and delivery. Pipeline operators and terminal operators should jointly establish programmes to provide for the safe receipt and transfer of products and to coordinate actions in case an emergency occurs on the pipeline or at the terminal during shipment which requires shutdown or diversion of product.

Figure 1. A terminal operator transfers product the Pasagoula Refinery into holding tanks in the Deraville Terminal near Atlanta, Georgia, US.

American Petroleum Institute

Instructions for receiving pipeline deliveries should include verification of the availability of the storage tanks to hold the shipment, opening and aligning tank and terminal valves in anticipation of delivery, checking to assure that the proper tank is receiving product immediately after the start of delivery, conducting required sampling and testing of batches at the start of delivery, performing batch changes and tank switches as required, monitoring receipts to assure that overfills do not occur and maintaining communications between the pipeline and the terminal. The use of written communications between terminal workers, especially when shift changes occur during product transfer, should be considered.

Batch shipments and interface

Although pipelines originally were used to move only crude oil, they evolved into carrying all types and different grades of liquid petroleum products. Because petroleum products are transported in pipelines by batches, in succession, there is commingling or mixing of the products at the interfaces. The product intermix is controlled by one of three methods: downgrading (derating), using liquid and solid spacers for separation or reprocessing the intermix. Radioactive tracers, colour dyes and spacers may be placed into the pipeline to identify where the interfaces occur. Radioactive sensors, visual observation or gravity tests are conducted at the receiving facility to identify different pipeline batches.

Petroleum products are normally transported through pipelines in batch sequences with compatible crude oils or products adjoining one another. One method of maintaining product quality and integrity, downgrading or derating, is accomplished by lowering the interface between the two batches to the level of the least affected product. For example, a batch of high-octane premium gasoline is typically shipped immediately before or after a batch of lower-octane regular gasoline. The small quantity of the two products which has intermixed will be downgraded to the lower octane rating regular gasoline. When shipping gasoline before or after diesel fuel, a small amount of diesel interface is allowed to blend into the gasoline, rather than blending gasoline into the diesel fuel, which could lower its flashpoint. Batch interfaces are typically detected by visual observation, gravitometers or sampling.

Liquid and solid spacers or cleaning pigs may be used to physically separate and identify different batches of products. The solid spacers are detected by a radioactive signal and diverted from the pipeline into a special receiver at the terminal when the batch changes from one product to another. Liquid separators may be water or another product that does not commingle with either of the batches it is separating and is later removed and reprocessed. Kerosene, which is downgraded (derated) to another product in storage or is recycled, can also be used to separate batches.

A third method of controlling the interface, often used at the refinery ends of pipelines, is to return the interface to be reprocessed. Products and interfaces which have been contaminated with water may also be returned for reprocessing.

Environmental protection

Because of the large volumes of products which are transported by pipelines on a continuous basis, there is opportunity for environmental damage from releases. Depending on company and regulatory safety requirements and the pipeline’s construction, location, weather, accessibility and operation, a considerable amount of product may be released should a break in the line or leak occur. Pipeline operators should have emergency response and spill contingency plans prepared and have containment and clean-up materials, personnel and equipment available or on call. Simple field solutions such as building earth dykes and drainage ditches can be quickly implemented by trained operators to contain and divert spilled product.

Maintaining pipelines and worker health and safety

The first pipelines were made of cast iron. Modern trunk pipelines are constructed of welded, high-strength steel, which can withstand high pressures. Pipe walls are periodically tested for thickness to determine whether internal corrosion or deposits have occurred. Welds are checked visually and with gamma radiation to assure that no defects are present.

Plastic pipe may be used for low-pressure, small-diameter flow lines and gathering lines in gas and crude-oil-producing fields, since plastic is light in weight and easy to handle, assemble and move.

When a pipeline is separated by cutting, spreading flanges, removing a valve or opening the line, an electrostatic arc may be created by impressed cathodic protection voltage, corrosion, sacrificial anodes, nearby high-voltage power lines or stray ground currents. This should be minimized by grounding (earthing) the pipe, de-energizing the cathodic rectifiers closest to both sides of the separation and connecting a bonding cable to each side of the piping prior to starting work. As additional pipeline sections, valves and so on are added to an existing line, or during construction, they should first be bonded to the pipelines in place.

Work on pipelines should cease during electrical storms. Equipment used to lift and place pipe should not be operated within 3 m of high-voltage electric lines. Any vehicles or equipment working in the vicinity of high-voltage lines should have trailing grounding straps attached to the frames. Temporary metal buildings should also be grounded.

Pipelines are specially coated and wrapped to prevent corrosion. Cathodic electrical protection may also be required. After the pipeline sections are coated and insulated, they are joined by special clamps connected to metallic anodes. The pipeline is subjected to a grounded source of direct current of sufficient capacity so that the pipeline acts as a cathode and does not corrode.

All pipeline sections are hydrostatically tested prior to entering gas or liquid hydrocarbon service and, depending on regulatory and company requirements, at regular intervals during the life of the pipeline. Air must be eliminated from pipelines prior to hydrostatic testing, and hydrostatic pressure built up and reduced at safe rates. Pipelines are regularly patrolled, usually by aerial surveillance, to visually detect leaks, or monitored from the control centre to detect a drop in flow rate or pressure, which would signify that a break in the pipeline has occurred.

Pipeline systems are provided with warning and signalling systems to alert operators so they may take corrective action in an emergency. Pipelines may have automatic shutdown systems which activate emergency pressure valves upon sensing increased or reduced pipeline pressure. Manually or automatically operated isolation valves are typically located at strategic intervals along pipelines, such as at pumping stations and at both sides of river crossings.

An important consideration when operating pipelines is to provide a means of warning contractors and others who may be working or conducting excavations along the pipeline route, so that the pipeline is not inadvertently ruptured, breached or punctured, resulting in a vapour or gas explosion and fire. This is usually done by regulations which require construction permits or by pipeline companies and associations providing a central number which contractors can call prior to excavation.

Because crude oil and flammable petroleum products are transported in pipelines, the possibility exists for fire or explosion in case of a line break or release of vapour or liquid. Pressure should be reduced to a safe level before working on high-pressure pipelines. Combustible gas testing should be conducted and a permit issued prior to repair or maintenance involving hot work or hot tapping on pipelines. The pipeline should be cleared of flammable liquids and vapours or gas prior to starting work. If a pipeline cannot be cleared and an approved plug is used, safe work procedures should be established and followed by qualified workers. The line should be vented a safe distance from the hot work area to relieve any build-up of pressure behind the plug.

Proper safety procedures should be established and followed by qualified workers when hot tapping pipelines. If welding or hot tapping is conducted in an area where a spill or leak has occurred, the outside of the pipe should be cleaned of liquid, and contaminated soil should be removed or covered to prevent ignition.

It is very important to notify operators at the nearest pumping stations on each side of the operating pipeline where maintenance or repair is to be performed, in case shutdown is required. When crude oil or gas is being pumped into pipelines by producers, the pipeline operators must provide specific instructions to the producers as to actions to take during repair, maintenance or in an emergency. For example, prior to tie-in of production tanks and lines to pipelines, all gate valves and bleeders for the tanks and lines involved in the tie-in should be closed and locked or sealed until the operation is completed.

Normal safety precautions concerning pipe and materials handling, toxic and hazardous exposures, welding and excavation apply during pipeline construction. Workers clearing right-of-way should protect themselves from climatic conditions; poisonous plants, insects and snakes; falling trees and rocks; and so on. Excavations and trenches should be sloped or shored to prevent collapse during underground pipeline construction or repair (see the article “Trenching” in the chapter Construction). Workers should follow safe work practices when opening and de-energizing electrical transformers and switches.

Pipeline operating and maintenance personnel often work alone and are responsible for long stretches of pipeline. Atmospheric testing and the use of personal and respiratory protective equipment is needed to determine oxygen and flammable vapour levels and protect against toxic exposures to hydrogen sulphide and benzene when gauging tanks, opening lines, cleaning spills, sampling and testing, shipping, receiving and performing other pipeline activities. Workers should wear dosimeters or film badges and avoid exposure when working with density gauges, source holders or other radioactive materials. The use of personal and respiratory protective equipment should be considered for exposure to burns from the hot protective tar used in pipe-coating operations and from toxic vapours which contain polynuclear aromatic hydrocarbons.

Marine Tankers and Barges

The majority of the world’s crude oil is transported by tankers from producing areas such as the Middle East and Africa to refineries in consumer areas such as Europe, Japan and the United States. Oil products were originally transported in large barrels on cargo ships. The first tanker ship, which was built in 1886, carried about 2,300 SDWT (2,240 pounds per ton) of oil. Today’s supertankers can be over 300 m long and carry almost 200 times as much oil (see figure 2). Gathering and feeder pipelines often end at marine terminals or offshore platform loading facilities, where the crude oil is loaded into tankers or barges for transport to crude trunk pipelines or refineries. Petroleum products also are transported from refineries to distribution terminals by tanker and barge. After delivering their cargoes, the vessels return in ballast to loading facilities to repeat the sequence.

Figure 2. SS Paul L. Fahrney oil tanker.

American Petroleum Institute

Liquefied natural gas is shipped as a cryogenic gas in specialized marine vessels with heavily insulated compartments or reservoirs (see figure 3). At the delivery port, the LNG is off-loaded to storage facilities or regasification plants. Liquefied petroleum gas may be shipped both as a liquid in uninsulated marine vessels and barges and as a cryogenic in insulated marine vessels. Additionally, LPG in containers (bottled gas) may be shipped as cargo on marine vessels and barges.

Figure 3. LNG Leo tanker loading at Arun, Sumatra, Indonesia.

American Petroleum Institute

LPG and LNG marine vessels

The three types of marine vessels used for transport of LPG and LNG are:

• vessels with reservoirs pressurized up to 2 mPa (LPG only)

• vessels with heat-insulated reservoirs and a reduced pressure of 0.3 to 0.6 mPa (LPG only)

• cryogenic vessels with heat-insulated reservoirs pressurized close to atmospheric pressure (LPG and LNG).

Shipment of LHGs on marine vessels requires constant safety awareness. Transfer hoses must be suitable for the correct temperatures and pressures of the LHGs being handled. To prevent a flammable mixture of gas vapour and air, inert gas (nitrogen) blanketing is provided around reservoirs, and the area is continually monitored to detect leaks. Before loading, storage reservoirs should be inspected to ensure that they are free of contaminants. If reservoirs contain inert gas or air, they should be purged with LHG vapour prior to loading the LHG. Reservoirs should be constantly inspected to ensure integrity, and safety valves should be installed to relieve the LHG vapour generated at maximum heat load. Marine vessels are provided with fire suppression systems and have comprehensive emergency response procedures in place.

Crude oil and petroleum products marine vessels

Oil tankers and barges are vessels designed with the engines and quarters at the rear of the vessel and the remainder of the vessel divided into special compartments (tanks) to carry crude oil and liquid petroleum products in bulk. Cargo pumps are located in pump rooms, and forced ventilation and inerting systems are provided to reduce the risk of fires and explosions in pump rooms and cargo compartments. Modern oil tankers and barges are built with double hulls and other protective and safety features required by the United States Oil Pollution Act of 1990 and the International Maritime Organization (IMO) tanker safety standards. Some new ship designs extend double hulls up the sides of the tankers to provide additional protection. Generally, large tankers carry crude oil and small tankers and barges carry petroleum products.

• Supertankers. Ultra-large and very large crude carriers (ULCCs and VLCCs) are restricted by their size and draft to specific routes of travel. ULCCs are vessels whose capacity is over 300,000 SDWTs, and VLCCs have capacities ranging from 160,000 to 300,000 SDWTs. Most large crude carriers are not owned by oil companies, but are chartered from transportation companies which specialize in operating these super-sized vessels.

• Oil tankers. Oil tankers are smaller than VLCCs, and, in addition to ocean travel, they can navigate restricted passages such as the Suez and Panama Canals, shallow coastal waters and estuaries. Large oil tankers, which range from 25,000 to 160,000 SDWTs, usually carry crude oil or heavy residual products. Smaller oil tankers, under 25,000 SDWT, usually carry gasoline, fuel oils and lubricants.

• Barges. Barges operate mainly in coastal and inland waterways and rivers, alone or in groups of two or more, and are either self-propelled or moved by tugboat. They may carry crude oil to refineries, but more often are used as an inexpensive means of transporting petroleum products from refineries to distribution terminals. Barges are also used to off-load cargo from tankers offshore whose draft or size does not allow them to come to the dock.

Barge and ship loading and unloading

Vessel-to-shore procedures, safety checklists and guidelines should be established and agreed upon by terminal and marine vessel operators. The International Safety Guide for Oil Tankers and Terminals (International Chamber of Shipping 1978) contains information and samples of checklists, guidelines, permits and other procedures covering safe operations when loading or unloading vessels, which may be used by vessel and terminal operators.

Although marine vessels sit in water and are thereby intrinsically grounded, there is a need to provide protection from static electricity which can build up during loading or unloading. This is accomplished by bonding or connecting metal objects on the dock or loading/unloading apparatus to the metal of the vessel. Bonding is also accomplished by use of conductive loading hose or piping. An electrostatic spark of ignitable intensity may also be generated when lowering equipment, thermometers or gauging devices into compartments immediately after loading; enough time must be allowed for the static charge to dissipate.

Ship-to-shore electric currents, which are different from static electricity, may be generated by cathodic protection of the vessel’s hull or dock, or by galvanic potential differences between the vessel and the shore. These currents also build up in metal loading/unloading apparatus. Insulating flanges may be installed within the length of the loading arm and at the point where flexible hoses connect to the shore pipeline system. When the connections are broken, there is no opportunity for a spark to jump from one metal surface to another.

All vessels and terminals need mutually agreed upon emergency response procedures in case of a fire or release of product, vapour or toxic gas. These must cover emergency operations, stopping product flow and emergency removal of a vessel from the dock. The plans should consider communications, fire-fighting, vapour cloud mitigation, mutual aid, rescue, clean-up and remediation measures.

Fire protection portable equipment and fixed systems should be in accord with government and company requirements and appropriate to the size, function, exposure potential and value of the dock and wharf facilities. The International Safety Guide for Oil Tankers and Terminals (International Chamber of Shipping 1978) contains a sample fire notice which may be used as a guide by terminals for dock fire prevention.

Marine vessel health and safety

In addition to the usual maritime working hazards, transporting crude oil and flammable liquids by marine vessel creates a number of special health, safety and fire prevention situations. These include surging and expansion of liquid cargo, flammable vapour hazards during transport and when loading and unloading, possibility of pyrophoric ignition, toxic exposures to materials such as hydrogen sulphide and benzene and safety considerations when venting, flushing and cleaning compart-ments. The economics of operating modern tankers requires them to be at sea for extended periods of time with only short intervals in port to load or unload cargo. This, together with the fact that tankers are highly automated, creates unique mental and physical demands on the few crew members used to operate the vessels.

Fire and explosion protection

Emergency plans and procedures should be developed and implemented that are appropriate for the type of cargo on board and other potential hazards. Fire-fighting equipment must be supplied. Response team members who have shipboard fire-fighting, rescue and spill clean-up responsibilities should be trained, drilled and equipped to handle potential emergencies. Water, foam, dry chemicals, halon, carbon dioxide and steam are used as cooling, inhibiting and smothering fire-fighting agents aboard marine vessels, although halon is being phased out due to environmental concerns. The requirements for vessel fire-fighting equipment and systems are established by the country under whose flag the vessel sails and by company policy, but usually follow the recommendations of the 1974 International Convention for the Safety of Life at Sea (SOLAS).

Strict control of flames or naked lights, lighted smoking materials and other sources of ignition, such as welding or grinding sparks, electrical equipment and unprotected light bulbs, is required on vessels at all times to reduce the risk of fire and explosion. Prior to conducting hot work on board marine vessels, the area should be examined and tested to assure that conditions are safe, and permits should be issued for each specific task allowed.

One method of preventing explosions and fires in the vapour space of cargo compartments is to maintain the level of oxygen below 11% by making the atmosphere inert with a noncombustible gas. Sources for inert gas are exhaust gases from the vessel’s boilers or an independent gas generator or a gas turbine fitted with an afterburner. The 1974 SOLAS Convention implies that vessels carrying cargo with flashpoints below 60°C should have compartments fitted with inert systems. Vessels using inert gas systems should maintain cargo compartments in non-flammable conditions at all times. Inert gas compartments should be constantly monitored to assure safe conditions and should not be allowed to become flammable, because of the danger of ignition from pyrophoric deposits.

Confined spaces

Confined spaces on marine vessels, such as cargo compartments, paint lockers, pump rooms, fuel tanks and spaces between double hulls, must be treated the same as any confined space for entry, hot work and cold work. Tests for oxygen content, flammable vapours and toxic substances, in that order, must be conducted prior to entering confined spaces. A permit system should be established and followed for all confined space entry, safe (cold) work and hot work, which indicates safe exposure levels and required personal and respiratory protective equipment. In waters of the United States, these tests may be conducted by qualified individuals called “marine chemists”.

Compartments on marine vessels such as cargo tanks and pump rooms are confined spaces; when cleaning those which have been made inert or have flammable vapour, toxic or unknown atmospheres, they should be tested, and special safety and respiratory protection procedures should be followed. After crude oil has been unloaded, a small amount of residue, called clingage, remains on the interior surfaces of the compartments, which may then be washed and filled with water for ballast. One method of reducing the amount of residue is to install fixed equipment which removes up to 80% of the clingage by washing down the sides of inerted compartments with crude oil during unloading.

Pumps, valves and equipment

A work permit should be issued and safe work procedures followed, such as bonding, draining and vapour freeing, flammable vapour and toxic exposure testing, and providing stand-by fire protection equipment when operations, maintenance or repair requires opening cargo pumps, lines, valves or equipment on board marine vessels.

Toxic exposures

There is an opportunity for vented gases such as flue gas or hydrogen sulphide to reach the decks of vessels, even from specially designed vent systems. Testing should be continuously conducted to determine inert gas levels on all vessels and hydrogen sulphide levels on vessels which contain or previously carried sour crude oil or residual fuel. Tests should be conducted for benzene exposure on vessels carrying crude oil and gasoline. Inert gas scrubber effluent water and condensate water is acidic and corrosive; PPE should be used when contact is possible.

Environmental protection

Marine vessels and terminals should establish procedures and provide equipment to protect the environment from spills on water and land, and from releases of vapour to the air. The use of large vapour recovery systems at marine terminals is growing. Care must be taken to comply with air pollution requirements when vessels vent compartments and enclosed spaces. Emergency response procedures should be established, and equipment and trained personnel should be available to respond to spills and releases of crude oil and flammable and combustible liquids. A responsible person should be designated to ensure that notifications are made to both the company and the appropriate authorities should a reportable spill or release occur.

In the past, the oil-contaminated ballast water and tank washings were flushed out of the compartments at sea. In 1973, the International Convention for Prevention of Pollution from Ships established requirements that before the water is discharged at sea, the oily residue must be separated and retained on board for eventual onshore processing. Modern tankers have segregated ballast systems, with different lines, pumps and tanks than those used for cargo (in accordance with international recommen-dations), so that there is no possibility of contamination. Older vessels still carry ballast in cargo tanks, so special procedures, such as pumping oily water into designated onshore tanks and processing facilities, must be followed when discharging ballast in order to prevent pollution.

Motor Vehicle and Railroad Transport of Petroleum Products

Crude oil and petroleum products were initially transported by horse-drawn tank wagons, then by railroad tank cars and finally by motor vehicles. Following receipt at terminals from marine vessels or pipelines, bulk liquid petroleum products are delivered by non-pressure tank trucks or rail tank cars directly to service stations and consumers or to smaller terminals, called bulk plants, for redistribution. LPG, gasoline anti-knock compounds, hydrofluoric acid and many other products, chemicals and additives used in the oil and gas industry are transported in pressure tank cars and tank trucks. Crude oil may also be transported by tank truck from small producing wells to gathering tanks, and by tank truck and railroad tank car from storage tanks to refineries or main pipelines. Packaged petroleum products in bulk bins or drums and pallets and cases of smaller containers are carried by package truck or railroad box car.

Government regulations

Transportation of petroleum products by motor vehicle or railroad tank car is regulated by government agencies throughout most of the world. Agencies such as the US DOT and the Canadian Transport Commission (CTC) have established regulations governing the design, construction, safety devices, testing, preventive maintenance, inspection and operation of tank trucks and tank cars. Regulations governing railroad tank car and tank truck operations typically include tank pressure and pressure relief device testing and certification before being placed into initial service and at regular intervals thereafter. The Association of American Railroads and the National Fire Protection Association (NFPA) are typical of organizations which publish specifications and requirements for the safe operation of tank cars and tank trucks. Most governments have regulations or adhere to United Nations Conventions which require the identification of and information concerning hazardous materials and petroleum products which are shipped in bulk or in containers. Railroad tank cars, tank trucks and package trucks are placarded to identify any hazardous products being transported and to provide emergency response information.

Railroad tank cars

Railroad tank cars are constructed of carbon steel or aluminium and may be pressurized or unpressurized. Modern tank cars can hold up to 171,000 l of compressed gas at pressures up to 600 psi (1.6 to 1.8 mPa). Non-pressure tank cars have evolved from small wooden tank cars of the late 1800s to jumbo tank cars which transport as much as 1.31 million litres of product at pressures up to 100 psi (0.6 mPa). Non-pressure tank cars may be individual units with one or multiple compartments or a string of interconnected tank cars, called a tank train. Tank cars are loaded individually, and entire tank trains can be loaded and unloaded from a single point. Both pressure and non-pressure tank cars may be heated, cooled, insulated and thermally protected against fire, depending on their service and the products transported.

All railroad tank cars have top- or bottom-liquid or vapour valves for loading and unloading and hatch entries for cleaning. They are also equipped with devices intended to prevent the increase of internal pressure when exposed to abnormal con-ditions. These devices include safety relief valves held in place by a spring which can open to relieve pressure and then close; safety vents with rupture discs that burst open to relieve pressure but cannot reclose; or a combination of the two devices. A vacuum relief valve is provided for non-pressure tank cars to prevent vacuum formation when unloading from the bottom. Both pressure and non-pressure tank cars have protective housings on top surrounding the loading connections, sample lines, thermometer wells and gauging devices. Platforms for loaders may or may not be provided on top of cars. Older non-pressure tank cars may have one or more expansion domes. Fittings are provided on the bottom of tank cars for unloading or cleaning. Head shields are provided on the ends of tank cars to prevent puncture of the shell by the coupler of another car during derailments.

LNG is shipped as a cryogenic gas in insulated tank truck and rail pressure tank cars. Pressure tank trucks and rail tank cars for LNG transport have a stainless steel inner reservoir suspended in an outer reservoir of carbon steel. The annular space is a vacuum filled with insulation to maintain low temperatures during shipment. To prevent gas from igniting back to the tanks, they are equipped with two independent, remotely controlled fail-safe emergency shut-off valves on the filling and discharge lines and have gauges on both the inside and outside reservoirs.

LPG is transported on land in specially designed rail tank cars (up to 130 m³ capacity) or tank trucks (up to 40 m³ capacity). Tank trucks and rail tank cars for LPG transport are typically uninsulated steel cylinders with spherical bottoms, equipped with gauges, thermometers, two safety relief valves, a gas level meter and maximum fill indicator and baffles.

Rail tank cars transporting LNG or LPG should not be overloaded, since they may sit on a siding for some period of time and be exposed to high ambient temperatures, which could cause overpressure and venting. Bond wires and grounding cables are provided at rail and tank truck loading racks to help neutralize and dissipate static electricity. They should be connected before operations commence and not disconnected until operations are complete and all valves are closed. Truck and rail loading facilities are typically protected by fire water spray or mist systems and fire extinguishers.

Tank trucks

Petroleum products and crude oil tank trucks are typically constructed of carbon steel, aluminium or a plasticized fibreglass material, and vary in size from 1,900-l tank wagons to jumbo 53,200-l tankers. The capacity of tank trucks is governed by regulatory agencies, and usually is dependent upon highway and bridge capacity limitations and the allowable weight per axle or total amount of product allowed.

There are pressurized and non-pressurized tank trucks, which may be non-insulated or insulated depending on their service and the products transported. Pressurized tank trucks are usually single compartment, and non-pressurized tank trucks may have single or multiple compartments. Regardless of the number of compartments on a tank truck, each compartment must be treated individually, with its own loading, unloading and safety-relief devices. Compartments may be separated by single or double walls. Regulations may require that incompatible products and flammable and combustible liquids carried in different compartments on the same vehicle be separated by double walls. When pressure testing compartments, the space between the walls should also be tested for liquid or vapour.

Tank trucks have either hatches which open for top loading, valves for closed top- or bottom-loading and unloading, or both. All compartments have hatch entries for cleaning and are equipped with safety relief devices to mitigate internal pressure when exposed to abnormal conditions. These devices include safety relief valves held in place by a spring which can open to relieve pressure and then close, hatches on non-pressure tanks which pop open if the relief valves fail and rupture discs on pressurized tank trucks. A vacuum relief valve is provided for each non-pressurized tank truck compartment to prevent vacuum when unloading from the bottom. Non-pressurized tank trucks have railings on top to protect the hatches, relief valves and vapour recovery system in case of a rollover. Tank trucks are usually equipped with breakaway, self-closing devices installed on compartment bottom loading and unloading pipes and fittings to prevent spills in case of damage in a rollover or collision.

Rail tank car and tank truck loading and unloading

While railroad tank cars are almost always loaded and unloaded by workers assigned to these specific duties, tank trucks may be loaded and unloaded by either loaders or drivers. Tank cars and tank trucks are loaded at facilities called loading racks, and may be top loaded through open hatches or closed connections, bottom loaded through closed connections, or a combination of both.

Loading

Workers who load and unload crude oil, LPG, petroleum products, and acids and additives used in the oil and gas industry, should have a basic understanding of the characteristics of the products handled, their hazards and exposures and the operating procedures and work practices needed to perform the job safely. Many government agencies and companies require the use and completion of inspection forms upon receipt and shipment and prior to loading and unloading railroad tank cars and tank trucks. Tank trucks and railroad tank cars may be loaded through open hatches on the top or through fittings and valves at the top or bottom of each tank or compartment. Closed connections are required when pressure loading and where vapour recovery systems are provided. If loading systems do not activate for any reason (such as improper operation of the vapour recovery system or a fault in the grounding or bonding system), by-pass should not be attempted without approval. All hatches should be closed and securely latched during transit.

Workers should follow safe work practices to avoid slips and falls when top loading. If loading controls use pre-set meters, loaders must be careful to load the correct products into the assigned tanks and compartments. All compartment hatches should be shut when bottom loading, and when top loading, only the compartment being loaded should be open. When top loading, splash loading should be avoided by placing the loading tube or hose close to the bottom of the compartment and starting to load slowly until the opening is submerged. During manual top loading operations, loaders should remain in attendance, not tie down the loading shut-off (deadman) control and not overfill the compartment. Loaders should avoid exposures to product and vapour by standing upwind and averting the head when top loading through open hatches and by wearing protective equipment when handling additives, obtaining samples and draining hoses. Loaders should be aware of and follow prescribed response actions in case of a hose or line rupture, spill, release, fire or other emergency.

Unloading and delivery

When unloading tank cars and tank trucks, it is important first to assure that each product is unloaded into the proper designated storage tank and that the tank has sufficient capacity to hold all of the product being delivered. Although valves, fill pipes, lines and fill covers should be colour coded or otherwise marked to identify the product contained, the driver should still be responsible for product quality during delivery. Any misdelivery of product, mixing or contamination should be immediately reported to the recipient and to the company to prevent serious consequences. When drivers or operators are required to additize products or obtain samples from storage tanks following delivery to assure product quality or for any other reason, all safety and health provisions specific to the exposure should be followed. Persons engaged in delivery and unloading operations should remain in the vicinity at all times and know what to do in an emergency, including notification, stopping product flow, cleaning spills and when to leave the area.

Pressurized tanks may be unloaded by compressor or pump, and unpressurized tanks by gravity, vehicle pump or recipient pump. Tank trucks and tank cars which carry lubrication or industrial oils, additives and acids are sometimes unloaded by pressurizing the tank with an inert gas such as nitrogen. Tank cars or tank trucks may need to be heated using steam or electric coils in order to unload heavy crude oils, viscous products and waxes. All of these activities have inherent dangers and exposures. Where required by regulation, unloading should not commence until the vapour recovery hoses have been connected between the delivery tank and the storage tank. When delivering petroleum products to residences, farms and commercial accounts, drivers should gauge any tank which is not equipped with a vent alarm in order to prevent an overfill.

Loading-rack fire protection

Fires and explosions at top and bottom tank car and tank truck loading racks may occur from causes such as electrostatic build-up and incendiary spark discharge in a flammable atmosphere, unauthorized hot work, flashback from a vapour recovery unit, smoking or other unsafe practices.

Sources of ignition, such as smoking, running internal combustion engines and hot work activity, should be controlled at the loading rack at all times, and particularly during loading or other operations when a spill or release may occur. Loading racks may be equipped with portable fire extinguishers and manually or automatically operated foam, water or dry chemical fire extinguishing systems. If vapour recovery systems are in use, flame arrestors should be provided to prevent flashback from the recovery unit to the loading rack.

Drainage should be provided at loading racks to divert product spills away from the loader, tank truck or tank car and the loading rack pad. Drains should be provided with fire traps to prevent migration of flames and vapours through sewer systems. Other loading-rack safety considerations include emergency shut-down controls placed at loading spots and other strategic locations in the terminal and automatic pressure-sensing valves which stop product flow to the rack in case of a leak in the product lines. Some companies have installed automatic brake lock systems on their tank truck fill connections, which lock the brakes and will not allow the truck to be moved from the rack until the fill lines have been disconnected.

Electrostatic ignition hazards

Some products such as intermediate distillates and low-vapour-pressure fuels and solvents tend to accumulate electrostatic charges. When loading tank cars and tank trucks, there is always an opportunity for electrostatic charges to be generated by friction as product goes through lines and filters and by splash loading. This can be mitigated by designing loading racks to allow for relaxation time in piping downstream from pumps and filters. Compartments should be checked to assure that they do not contain any unbonded or floating objects which could act as static accumulators. Bottom loaded compartments may be provided with internal cables to help dissipate electrostatic charges. Sample containers, thermometers or other items should not be lowered into compartments until a waiting period of at least 1 minute has elapsed, to allow any electrostatic charge which has accumulated in the product to dissipate.

Bonding and grounding are important considerations in dissipating electrostatic charges which build up during loading operations. By keeping the fill pipe in contact with the metal side of the hatch when top loading, and through the use of metal loading arms or conductive hose when loading through closed connections, the tank truck or tank car is bonded to the loading rack, maintaining the same electrical charge between the objects so that a spark is not created when the loading tube or hose is removed. The tank car or tank truck may also be bonded to the loading rack by use of a bonding cable, which carries any accumulated charge from a terminal on the tank to the rack, where it is then grounded by a grounding cable and rod. Similar bonding precautions are needed when unloading from tank cars and tank trucks. Some loading racks are provided with electronic connectors and sensors which will not allow loading pumps to activate until a positive bond is achieved.

During cleaning, maintenance or repair, pressurized LPG tank cars or tank trucks are usually opened to the atmosphere, allowing air to enter the tank. In order to prevent combustion from electrostatic charges when loading these cars for the first time after such activities, it is necessary to reduce the oxygen level below 9.5% by blanketing the tank with inert gas, such as nitrogen. Precautions are needed to prevent liquid nitrogen from entering the tank if the nitrogen is provided from portable containers.

Switch loading

Switch loading occurs when intermediate- or low-vapour-pressure products such as diesel fuel or fuel oil are loaded into a tank car or tank truck compartment which previously contained a flammable product such as gasoline. The electrostatic charge generated during loading can discharge in an atmosphere which is within the flammable range, with a resultant explosion and fire. This hazard can be controlled when top loading by lowering the fill tube to the bottom of the compartment and loading slowly until the end of the tube is submerged to avoid splash loading or agitation. Metal to metal contact should be maintained during loading in order to provide a positive bond between the loading tube and the tank hatchway. When bottom loading, initial slow fill or splash deflectors are used to reduce static build-up. Prior to switch loading, tanks which cannot be drained dry may be flushed out with a small amount of the product to be loaded, to remove any flammable residue in sumps, lines, valves and onboard pumps.

Shipping products by rail box cars and package vans

Petroleum products are shipped by motor truck package vans and railroad box cars in metal, fibre and plastic containers of various sizes, from 55-gallon (209-l) drums to 5-gallon (19-l) pails and from 2-1/2-gallon (9.5-l) to 1-quart (.95-l) containers, in corrugated boxes, usually on pallets. Many industrial and commercial petroleum products are shipped in large metal, plastic or combination intermediate bulk containers ranging in size from 380 to over 2,660 l capacity. LPG is shipped in large and small pressure containers. In addition, samples of crude oil, finished products and used products are shipped by mail or express freight carrier to laboratories for assay and analysis.

All of these products, containers and packages have to be handled in accordance with government regulations for hazardous chemicals, flammable and combustible liquids and toxic materials. This requires the use of hazardous materials manifests, shipping documents, permits, receipts and other regulatory requirements, such as marking the outsides of packages, containers, motor trucks and box cars with proper identification and a hazard warning label. Proper utilization of tank trucks and tank cars is important to the petroleum industry. Because storage capacity is finite, delivery schedules need to be met, from the delivery of crude oil to keep refineries running to the delivery of gasoline to service stations, and from the delivery of lubricants to commercial and industrial accounts to the delivery of heating oil to homes.

LPG is supplied to consumers by bulk tank trucks which pump directly into smaller onsite storage tanks, both above ground and below ground (e.g., service stations, farms, commercial and industrial consumers). LPG is also delivered to consumers by truck or van in containers (gas cylinders or bottles). LNG is delivered in special cryogenic containers which have an inner fuel tank surrounded by insulation and an outer shell. Similar containers are provided for vehicles and appliances which use LNG as a fuel. Compressed natural gas is normally delivered in conventional compressed gas cylinders, such as those used on industrial lift trucks.

In addition to the normal safety and health precautions required in rail car and package trucking operations, such as moving and handling heavy objects and operating industrial trucks, workers should be familiar with the hazards of the products they are handling and delivering, and know what to do in case of a spill, release or other emergency. For example, intermediate bulk containers and drums should not be dropped out of box cars or from the tailgates of trucks onto the ground. Both companies and government agencies have established special regulations and requirements for drivers and operators who are involved in the transport and delivery of flammable and hazardous petroleum products.

Tank truck and package van drivers often work alone and may have to travel great distances for a number of days to deliver their loads. They work both day and night and in all sorts of weather conditions. Manoeuvring super-sized tank trucks into service stations and customer locations without hitting parked vehicles or fixed objects requires patience, skill and experience. Drivers should have the physical and mental characteristics required for this work.

Driving tank trucks is different from driving package vans in that the liquid product tends to shift forward as the truck stops, backwards as the truck accelerates and from side to side as the truck turns. Tank truck compartments should be fitted with baffles which restrict the movement of product during transport. Considerable skill is required by drivers to overcome the inertia created by this phenomenon, called “mass in motion”. Occasionally, tank truck drivers are required to pump out storage tanks. This activity requires special equipment, including suction hose and transfer pumps, and safety precautions, such as bonding and grounding to dissipate electrostatic build-up and to prevent any release of vapours or liquids.

Motor vehicle and rail car emergency response

Drivers and operators should be familiar with notification requirements and emergency response actions in case of a fire or a release of product, gas or vapour. Product identification and hazard warning placards in compliance with industry, association or national marking standards are posted on trucks and rail cars to allow emergency responders to determine the precautions needed in case of a spill or release of vapour, gas or product. Motor vehicle drivers and train operators may also be required to carry material safety data sheets (MSDSs) or other documentation describing the hazards and precautions for handling the products being transported. Some companies or government agencies require that vehicles transporting flammable liquids or hazardous materials carry first aid kits, fire extinguishers, spill clean-up materials and portable hazard warning devices or signals to alert motorists if the vehicle is stopped alongside a highway.

Special equipment and techniques are required if a tank car or tank truck needs to be emptied of product as the result of an accident or rollover. Removal of product through fixed piping and valves or by using special knock-out plates on tank truck hatches is preferred; however, under certain conditions holes may be drilled in tanks using prescribed safe work procedures. Regardless of the method of removal, tanks should be grounded and a bond connection provided between the tank being emptied and the receiving tank.

Cleaning tank cars and tank trucks

Entering a tank car or tank truck compartment for inspection, cleaning, maintenance or repair is a hazardous activity requiring that all ventilation, testing, gas freeing and other confined-space entry and permit system requirements be followed in order to assure a safe operation. Cleaning tank cars and tank trucks is not any different from cleaning petroleum-product storage tanks, and all the same safety and health exposure precautions and procedures apply. Tank cars and tank trucks may contain residue of flammable, hazardous or toxic materials in sumps and unloading piping, or have been unloaded using an inert gas, such as nitrogen, so that what may appear to be a clean, safe space is not. Tanks which have contained crude oil, residues, asphalt or high-melting-point products may need to be steam or chemically cleaned prior to ventilation and entry, or may have a pyrophoric hazard. Ventilating tanks to free them from vapours and toxic or inert gases may be accomplished by opening the lowest and furthest valve or connection on each tank or compartment and placing an air eductor at the furthest top opening. Monitoring should be performed prior to entry without respiratory protection to assure that all of the corners and low spots in the tank, such as sumps, have been thoroughly vented, and ventilation should continue while working in the tank.

Aboveground Tank Storage of Liquid Petroleum Products

Crude oil, gas, LNG and LPG, processing additives, chemicals and petroleum products are stored in aboveground and underground atmospheric (non-pressure) and pressure storage tanks. Storage tanks are located at the ends of feeder lines and gathering lines, along truck pipelines, at marine loading and unloading facilities and in refineries, terminals and bulk plants. This section covers aboveground atmospheric storage tanks in refinery, terminal and bulk plant tank farms. (Information concerning aboveground pressure tanks is covered below, and information concerning underground tanks and small aboveground tanks is in the article “Motor vehicle fuelling and servicing operations”.)

Terminals and bulk plants

Terminals are storage facilities which generally receive crude oil and petroleum products by trunk pipeline or marine vessel. Terminals store and redistribute crude oil and petroleum products to refineries, other terminals, bulk plants, service stations and consumers by pipelines, marine vessels, railroad tank cars and tank trucks. Terminals may be owned and operated by oil companies, pipeline companies, independent terminal operators, large industrial or commercial consumers or petroleum product distributors.

Bulk plants are usually smaller than terminals and typically receive petroleum products by rail tank car or tank truck, normally from terminals but occasionally direct from refineries. Bulk plants store and redistribute products to service stations and consumers by tank truck or tank wagon (small tank trucks of approximately 9,500 to 1,900 l capacity). Bulk plants may be operated by oil companies, distributors or independent owners.

Tank farms

Tank farms are groupings of storage tanks at producing fields, refineries, marine, pipeline and distribution terminals and bulk plants which store crude oil and petroleum products. Within tank farms, individual tanks or groups of two or more tanks are usually surrounded by enclosures called berms, dykes or fire walls. These tank farm enclosures may vary in construction and height, from 45-cm earth berms around piping and pumps inside dykes to concrete walls that are taller than the tanks they surround. Dykes may be built of earth, clay or other materials; they are covered with gravel, limestone or sea shells to control erosion; they vary in height and are wide enough for vehicles to drive along the top. The primary functions of these enclosures are to contain, direct and divert rain water, physically separate tanks to prevent the spread of fire in one area to another, and to contain a spill, release, leak or overflow from a tank, pump or pipe within the area.

Dyke enclosures may be required by regulation or company policy to be sized and maintained to hold a specific amount of product. For example, a dyke enclosure may need to contain at least 110% of the capacity of the largest tank therein, allowing for the volume displaced by the other tanks and the amount of product remaining in the largest tank after hydrostatic equilibrium is reached. Dyke enclosures may also be required to be constructed with impervious clay or plastic liners to prevent spilled or released product from contaminating soil or groundwater.

Storage tanks

There are a number of different types of vertical and horizontal aboveground atmospheric and pressure storage tanks in tank farms, which contain crude oil, petroleum feedstocks, intermediate stocks or finished petroleum products. Their size, shape, design, configuration, and operation depend on the amount and type of products stored and company or regulatory requirements. Aboveground vertical tanks may be provided with double bottoms to prevent leakage onto the ground and cathodic protection to minimize corrosion. Horizontal tanks may be constructed with double walls or placed in vaults to contain any leakage.

Atmospheric cone roof tanks

Cone roof tanks are aboveground, horizontal or vertical, covered, cylindrical atmospheric vessels. Cone roof tanks have external stairways or ladders and platforms, and weak roof to shell seams, vents, scuppers or overflow outlets; they may have appurtenances such as gauging tubes, foam piping and chambers, overflow sensing and signalling systems, automatic gauging systems and so on.

When volatile crude oil and flammable liquid petroleum products are stored in cone roof tanks there is an opportunity for the vapour space to be within the flammable range. Although the space between the top of the product and the tank roof is normally vapour rich, an atmosphere in the flammable range can occur when product is first put into an empty tank or as air enters the tank through vents or pressure/vacuum valves when product is withdrawn and as the tank breathes during temperature changes. Cone roof tanks may be connected to vapour recovery systems.

Conservation tanks are a type of cone roof tank with an upper and lower section separated by a flexible membrane designed to contain any vapour produced when the product warms up and expands due to exposure to sunlight in the daytime and to return the vapour to the tank when it condenses as the tank cools down at night. Conservation tanks are typically used to store aviation gasoline and similar products.

Atmospheric floating roof tanks

Floating roof tanks are aboveground, vertical, open top or covered cylindrical atmospheric vessels that are equipped with floating roofs. The primary purpose of the floating roof is to minimize the vapour space between the top of the product and the bottom of the floating roof so that it is always vapour rich, thus precluding the chance of a vapour-air mixture in the flammable range. All floating roof tanks have external stairways or ladders and platforms, adjustable stairways or ladders for access to the floating roof from the platform, and may have appurtenances such as shunts which electrically bond the roof to the shell, gauging tubes, foam piping and chambers, overflow sensing and signalling systems, automatic gauging systems and so on. Seals or boots are provided around the perimeter of floating roofs to prevent product or vapour from escaping and collecting on the roof or in the space above the roof.

Floating roofs are provided with legs which may be set in high or low positions depending on the type of operation. Legs are normally maintained in the low position so that the greatest possible amount of product can be withdrawn from the tank without creating a vapour space between the top of the product and the bottom of the floating roof. As tanks are brought out of service prior to entry for inspection, maintenance, repair or cleaning, there is a need to adjust the roof legs into the high position to allow room to work under the roof once the tank is empty. When the tank is returned to service, the legs are readjusted into the low position after it is filled with product.

Aboveground floating roof storage tanks are further classified as external floating roof tanks, internal floating roof tanks or covered external floating roof tanks.

External (open top) floating roof tanks are those with floating covers installed on open-top storage tanks. External floating roofs are usually constructed of steel and provided with pontoons or other means of flotation. They are equipped with roof drains to remove water, boots or seals to prevent vapour releases and adjustable stairways to reach the roof from the top of the tank regardless of its position. They may also have secondary seals to minimize release of vapour to the atmosphere, weather shields to protect the seals and foam dams to contain foam in the seal area in case of a fire or seal leak. Entry onto external floating roofs for gauging, maintenance or other activities may be considered confined-space entry, depending on the level of the roof below the top of the tank, the products contained in the tank and government regulations and company policy.

Internal floating roof tanks usually are cone roof tanks which have been converted by installing buoyant decks, rafts or internal floating covers inside the tank. Internal floating roofs are typically constructed of various types of sheet metal, aluminium, plastic or metal-covered plastic expanded foam, and their construction may be of the pontoon or pan type, solid buoyant material, or a combination of these. Internal floating roofs are provided with perimeter seals to prevent vapour from escaping into the portion of the tank between the top of the floating roof and the exterior roof. Pressure/vacuum valves or vents are usually provided at the top of the tank to control any hydrocarbon vapours which may accumulate in the space above the internal floater. Internal floating roof tanks have ladders installed for access from the cone roof to the floating roof. Entry onto internal floating roofs for any purpose should be considered confined-space entry.

Covered (external) floating roof tanks are basically external floating roof tanks that have been retrofitted with a geodesic dome, snow cap or similar semi-fixed cover or roof so that the floating roof is no longer open to the atmosphere. Newly constructed covered external floating roof tanks may incorporate typical floating roofs designed for internal floating roof tanks. Entry onto covered external floating roofs for gauging, maintenance or other activities may be considered confined-space entry, depending on the construction of the dome or cover, the level of the roof below the top of the tank, the products contained in the tank and government regulations and company policy.

Pipeline and marine receipts

An important safety, product quality and environmental concern in tank storage facilities is to prevent intermixing of products and overfilling tanks by developing and implementing safe operating procedures and work practices. Safe operation of storage tanks depends on receiving product into tanks within their defined capacity by designating receiving tanks prior to delivery, gauging tanks to determine the available capacity and ensuring that valves are properly aligned and that only the receiving tank inlet is opened, so the correct amount of product is delivered into the assigned tank. Drains in dyke areas surrounding tanks receiving product should normally be kept closed during receipt in case an overfill or spill occurs. Overfill protection and prevention can be accomplished by a variety of safe operating practices, including manual controls and automatic detection, signalling and shut-down systems and a means of communication, all of which should be mutually understood and acceptable to product transfer personnel at the pipeline, marine vessel and terminal or refinery.

Government regulations or company policy may require that automatic product level detection devices and signal and shut-down systems be installed on tanks receiving flammable liquids and other products from trunk pipelines or marine vessels. Where such systems are installed, electronic system integrity tests should be conducted on a regular basis or prior to product transfer, and if the system fails, transfers should follow manual receipt procedures. Receipts should be monitored manually or automatically, onsite or from a remote control location, to ensure that operations are proceeding as planned. Upon completion of transfer, all valves should be returned to normal operating position or set for the next receipt. Pumps, valves, pipe connections, bleeder and sample lines, manifold areas, drains and sumps should be inspected and maintained to assure good condition and to prevent spills and leakage.

Tank gauging and sampling

Tank storage facilities should establish procedures and safe work practices for gauging and sampling crude oil and petroleum products which take into consideration the potential hazards involved with each product stored and each type of tank in the facility. Although tank gauging is often done using automatic mechanical or electronic devices, manual gauging should be performed at scheduled intervals to assure the accuracy of the automatic systems.

Manual gauging and sampling operations usually require the operator to climb to the top of the tank. When gauging floating roof tanks, the operator then has to descend onto the floating roof unless the tank is fitted with gauging and sampling tubes that are accessible from the platform. With cone roof tanks, the gauger must open a roof hatch in order to lower the gauge into the tank. Gaugers should be aware of the confined-space entry requirements and potential hazards when entering onto covered floating roofs or down upon open-top floating roofs which are below established height levels. This may require the use of monitoring devices, such as oxygen, combustible gas and hydrogen sulphide detectors and personal and respiratory protective equipment.

Product temperatures and samples may be taken at the same time as manual gauging is conducted. Temperatures may also be recorded automatically and samples obtained from built-in sample connections. Manual gauging and sampling should be restricted while tanks are receiving product. Following the completion of receipt, a relaxation period of from 30 minutes to 4 hours, depending on the product and company policy, should be required to allow any electrostatic build-up to dissipate before conducting manual sampling or gauging. Some companies require that communications or visual contact be established and maintained between gaugers and other facility personnel when descending upon floating roofs. Entry onto tank roofs or platforms for gauging, sampling or other activities should be restricted during thunderstorms.

Tank venting and cleaning

Storage tanks are taken out of service for inspection, testing, maintenance, repair, retrofitting and tank cleaning as needed or at regular intervals dependent on government regulations, company policy and operating service requirements. Although tank venting, cleaning and entry is a potentially hazardous operation, this work can be accomplished without incident, provided that proper procedures are established and safe work practices followed. Without such precautions, injury or damage can occur from explosions, fires, lack of oxygen, toxic exposures and physical hazards.

Preliminary preparations

A number of preliminary preparations are required after it has been decided that a tank needs to be taken out of service for inspection, maintenance or cleaning. These include: scheduling storage and supply alternatives; reviewing the tank history to determine whether it has ever contained leaded product or has previously been cleaned and certified lead free; determining the amount and type of products contained and how much residue will remain in the tank; inspecting the outside of the tank, the surrounding area and the equipment to be used for product removal, vapour freeing and cleaning; assuring that personnel are trained, qualified and familiar with facility permit and safety procedures; assigning job responsibilities in accordance with the facility’s confined-space entry and hot- and safe-work permit requirements; and holding a meeting between terminal and tank cleaning personnel or contractors before tank cleaning or construction starts.

Control of ignition sources

After the removal of all available product from the tank through fixed piping, and before any water draws or sample lines are opened, all sources of ignition should be removed from the surrounding area until the tank is declared vapour free. Vacuum trucks, compressors, pumps and other equipment which is electrically or motor driven should be located upwind, either on top of or outside the dyke area, or, if inside the dyke area, at least 20 m from the tank or any other sources of flammable vapours. Tank preparation, venting and cleaning activities should cease during electrical storms.

Removing residue

The next step is to remove as much remaining product or residue in the tank as possible through pipeline and waterdraw connections. A safe-work permit may be issued for this work. Water or distillate fuel may be injected into the tank through fixed connections to help float product out of the tank. Residue removed from tanks that have contained sour crude should be kept wet until disposal to avoid spontaneous combustion.

Isolating the tank

After all available product has been removed through fixed piping, all piping connected to the tank, including product lines, vapour recovery lines, foam piping, sample lines and so on, should be disconnected by closing the valves nearest the tank and inserting blinds in the lines on the tank side of the valve to prevent any vapours from entering the tank from the lines. The portion of piping between the blinds and the tank should be drained and flushed. Valves outside the dyke area should be closed and locked or tagged. Tank pumps, internal mixers, cathodic protection systems, electronic gauging and level detection systems and so on should be disconnected, de-energized and locked or tagged out.

Vapour freeing

The tank is now ready to be made vapour free. Intermittent or continuous vapour testing should be conducted and work in the area restricted during tank ventilation. Natural ventilation, through opening the tank to the atmosphere, is not usually preferred, since it is neither as fast nor as safe as forced ventilation. There are a number of methods of mechanically venting a tank, depending on its size, construction, condition and internal configuration. In one method, cone roof tanks may be vapour freed by placing an eductor (a portable ventilator) at a hatch on the top of the tank, starting it slowly while a hatch at the bottom of the tank is opened and then setting it on high speed to draw air and vapours through the tank.

A safe- or hot-work permit should be issued covering ventilation activities. All blowers and eductors should be securely bonded to the tank shell to prevent electrostatic ignition. For safety purposes, blowers and eductors should preferably be operated by compressed air; however, explosion-proof electric- or steam-driven motors have been used. Internal floating roof tanks may need to have the portions above and below the floating roof vented separately. If vapours are discharged from a bottom hatch, a vertical tube at least 4 m above ground level and no lower than the surrounding dyke wall is needed in order to prevent vapours from collecting at low levels or reaching a source of ignition before dissipating. If necessary, vapours may be directed to the facility vapour recovery system.

As ventilation progresses, the remaining residue can be washed down and removed through the open bottom hatch by water and suction hoses, both of which should be bonded to the tank shell to prevent electrostatic ignition. Tanks which have contained sour crude oil or high-sulphur residual products may generate spontaneous heat and ignite as they dry out during ventilation. This should be avoided by wetting the inside of the tank with water to blanket the deposits from air and prevent a rise in temperature. Any iron sulphide residue should be removed from the open hatch to prevent ignition of vapours during ventilation. Workers engaged in washdown, removal and wetting activities should wear appropriate personal and respiratory protection.

Initial entry, inspection and certification

An indication of the progress being made in vapour freeing the tank can be obtained by monitoring vapours at the point of eduction during ventilation. Once it appears that the flammable vapour level is below that established by regulatory agencies or company policy, entry can be made into the tank for inspection and testing purposes. The entrant should wear appropriate personal and air-supplied respiratory protection; after testing the atmosphere at the hatch and obtaining an entry permit, the worker may enter the tank to continue testing and inspection. Checks for obstructions, falling roofs, weak supports, holes in the floor and other physical hazards should be conducted during the inspection.

Cleaning, maintenance and repair

As ventilation continues and the vapour levels in the tank drop lower, permits may be issued allowing entry by workers with appropriate personal and respiratory equipment, if needed, to start cleaning the tank. Monitoring for oxygen, flammable vapours and toxic atmospheres should continue, and if the levels inside the tank exceed those established for entry, the permit should automatically expire and the entrants should immediately leave the tank until the safe level is again achieved and the permit is reissued. Ventilation should continue during cleaning operations as long as any residue or sludge remains in the tank. Only low-voltage lighting or approved flashlights should be used during inspection and clean-up.

After tanks have been cleaned and dried, a final inspection and testing should be conducted before maintenance, repair or retrofitting work is started. Careful inspection of sumps, wells, floor plates, floating roof pontoons, supports and columns is needed to assure that no leaks have developed which allowed product to enter these spaces or seep beneath the floor. Spaces between foam seals and weather shields or secondary containment should also be inspected and tested for vapours. If the tank has previously contained leaded gasoline, or if no tank history is available, a lead-in-air test should be conducted and the tank certified lead free before workers are allowed inside without air-supplied respiratory equipment.

A hot-work permit should be issued covering welding, cutting and other hot work, and a safe-work permit issued to cover other repair and maintenance activities. Welding or hot work can create toxic or noxious fumes inside the tank, requiring monitoring, respiratory protection and continued ventilation. When tanks are to be retrofitted with double bottoms or internal floating roofs, a large hole is often cut into the side of the tank to provide unrestricted access and avoid the need for confined-space entry permits.

Blast cleaning and painting the outside of tanks usually follows tank cleaning and is completed before the tank is returned to service. These activities, together with cleaning and painting tank farm piping, may be performed while tanks and pipes are in service, by implementing and following prescribed safety procedures, such as conducting monitoring for hydrocarbon vapours and stopping blast cleaning while nearby tanks are receiving flammable liquid products. Blast cleaning with sand has the potential for hazardous exposure to silica; therefore, many government agencies and companies require the use of special non-toxic blast cleaning materials or grit, which may be collected, cleaned and recycled. Special vacuum collection blast cleaning devices may be used in order to avoid contamination when cleaning leaded paint from tanks and piping. Following blast cleaning, spots in the tank walls or piping suspected of having leaks and seeps should be tested and repaired before being painted.

Returning the tank to service

In preparation for return to service upon completion of tank cleaning, inspection, maintenance or repair, the hatches are closed, all blinds are removed and the piping is reconnected to the tank. Valves are unlocked, opened and aligned, and mechanical and electrical devices are reactivated. Many government agencies and companies require tanks to be hydrostatically tested to assure that there are no leaks before they are returned to service. Since a considerable amount of water is required to obtain the necessary pressure head for an accurate test, a water bottom topped with diesel fuel is often used. Upon completion of the testing, the tank is emptied and made ready to receive product. After receipt is completed and a relaxation time has elapsed, the legs on floating roof tanks are reset into the low position.

Fire protection and prevention

Whenever hydrocarbons are present in closed containers such as storage tanks in refineries, terminals and bulk plants, the potential exists for release of liquids and vapours. These vapours could mix with air in the flammable range and, if subjected to a source of ignition, cause an explosion or fire. Regardless of the capability of fire protection systems and personnel in the facility, the key to fire protection is fire prevention. Spills and releases should be stopped from entering sewers and drainage systems. Small spills should be covered with wet blankets, and larger spills with foam, to prevent vapours from escaping and mixing with air. Sources of ignition in areas when hydrocarbon vapours may be present should be eliminated or controlled. Portable fire extinguishers should be carried on service vehicles and located at accessible and strategic positions throughout the facility.

The establishment and implementation of safe work procedures and practices such as hot- and safe- (cold-) work permit systems, electrical classification programmes, lockout/tagout programmes, and employee and contractor training and education is critical to preventing fires. Facilities should develop preplanned emergency procedures, and employees should be knowledgeable in their responsibilities for reporting and responding to fires and evacuation. Telephone numbers of responsible persons and agencies to be notified in case of an emergency should be posted at the facility and a means of communication provided. Local fire departments, emergency response, public safety and mutual aid organizations should also be aware of the procedures and familiar with the facility and its hazards.

Hydrocarbon fires are controlled by one or a combination of methods, as follows:

• Removing fuel. One of the best and easiest methods of controlling and extinguishing a hydrocarbon fire is to shut off the source of fuel by closing a valve, diverting product flow or, if a small amount of product is involved, controlling exposures while allowing the product to burn away. Foam may also be used to cover hydrocarbon spills to prevent vapours from being emitted and mixing with the air.

• Removing oxygen. Another method is to shut off the supply of air or oxygen by smothering fires with foam or water fog, or by using carbon dioxide or nitrogen to displace air in enclosed spaces.

• Cooling. Water fog, mist or spray and carbon dioxide may be used to extinguish certain petroleum product fires by cooling the temperature of the fire below the product’s ignition temperature and by stopping vapours from forming and mixing with air.

• Interrupting combustion. Chemicals such as dry powders and halon extinguish fires by interrupting the chemical reaction of the fire.

Storage tank fire protection

Storage tank fire protection and prevention is a specialized science which depends on the interrelationship of tank type, condition and size; product and amount stored in the tank; tank spacing, dyking and drainage; facility fire protection and response capabilities; outside assistance; and company philosophy, industry standards and government regulations. Storage tank fires may be easy or very difficult to control and extinguish, depending primarily on whether the fire is detected and attacked during its initial inception. Storage tank operators should refer to the numerous recommended practices and standards developed by organizations such as the American Petroleum Institute (API) and the US National Fire Protection Association (NFPA), which cover storage tank fire prevention and protection in great detail.

If open-top floating roof storage tanks are out of round or if the seals are worn or not tight against the tank shells, vapours can escape and mix with air, forming flammable mixtures. In such situations, when lightning strikes, fires may occur at the point where the roof seals meet the shell of the tank. If detected early, small seal fires can often be extinguished by a hand-carried dry powder extinguisher or with foam applied from a foam hose or foam system.

If a seal fire cannot be controlled with hand extinguishers or hose streams, or if a large fire is in progress, foam may be applied onto the roof through fixed or semi-fixed systems or by large foam monitors. Precautions are necessary when applying foam onto the roofs of floating roof tanks; if too much weight is placed on the roof, it may tilt or sink, allowing a large surface area of product to be exposed and become involved in the fire. Foam dams are used on floating roof tanks to trap foam in the area between the seals and the tank shell. As the foam settles, water drains out under the foam dams and should be removed through the tank roof drain system to avoid overweighing and sinking the roof.

Depending on government regulations and company policy, storage tanks may be provided with fixed or semi-fixed foam systems which include: piping to the tanks, foam risers and foam chambers on the tanks; subsurface injection piping and nozzles inside the bottom of tanks; and distribution piping and foam dams on the tops of tanks.With fixed systems, foam-water solutions are generated in centrally located foam houses and pumped to the tank through a piping system. Semi-fixed foam systems typically use portable foam tanks, foam generators and pumps which are brought to the tank involved, connected to a water supply and connected to the tank’s foam piping.

Water-foam solutions may also be centrally generated and distributed within the facility through a system of piping and hydrants, and hoses would be used to connect the nearest hydrant to the tank’s semi-fixed foam system. Where tanks are not provided with fixed or semi-fixed foam systems, foam may be applied onto the tops of tanks, using foam monitors, fire hoses and nozzles. Regardless of the method of application, in order to control a fully involved tank fire, a specific amount of foam must be applied using special techniques at a specific concentration and rate of flow for a minimum amount of time depending primarily on the size of the tank, the product involved and the surface area of the fire. If there is not enough foam concentrate available to meet the required application criteria, the possibility of control or extinguishment is minimal.

Only trained and knowledgeable fire-fighters should be allowed to use water to fight liquid petroleum tank fires. Instantaneous eruptions, or boil-overs, can occur when water turns into steam upon direct application onto tank fires involving crude or heavy petroleum products. As water is heavier than most hydrocarbon fuels, it will sink to the bottom of a tank and, if enough is applied, fill the tank and push the burning product up and over the top of the tank.

Water is typically used to control or extinguish spill fires around the outside of tanks so that valves can be operated to control product flow, to cool the sides of involved tanks to prevent boiling liquid–expanding vapour explosions (BLEVEs—see the section “Fire hazards of LHGs” below) and to reduce the effect of heat and flame impingement on adjacent tanks and equipment. Because of the need for specialized training, materials and equipment, rather than allow employees to attempt to extinguish tank fires, many terminals and bulk plants have established a policy to remove as much product as possible from the involved tank, protect adjacent structures from heat and flame and allow the remaining product in the tank to burn under controlled conditions until the fire burns out.

Terminal and bulk plant health and safety

Storage tank foundations, supports and piping should be regularly inspected for corrosion, erosion, settling or other visible damage to prevent loss or degradation of product. Tank pressure/vacuum valves, seals and shields, vents, foam chambers, roof drains, water draw-off valves and overfill detection devices should be inspected, tested and maintained on a regular schedule, including removal of ice in the winter. Where flame arrestors are installed on tank vents or in vapour recovery lines, they have to be inspected and cleaned regularly and kept free of frost in the winter to ensure proper operation. Valves on tank outlets which close automatically in case of fire or drop in pressure should be checked for operability.

Dyke surfaces should drain or slope away from tanks, pumps and piping to remove any spilled or released product to a safe area. Dyke walls should be maintained in good condition, with drain valves kept closed except when draining water and dyke areas excavated as needed to maintain design capacity. Stairways, ramps, ladders, platforms and railings to loading racks, dykes and tanks should be maintained in a safe condition, free of ice, snow and oil. Leaking tanks and piping should be repaired as soon as possible. The use of victaulic or similar couplings on piping within dyked areas which could be exposed to heat should be discouraged to prevent lines from opening during fires.

Safety procedures and safe work practices should be established and implemented, and training or education provided, so that terminal and bulk plant operators, maintenance personnel, tank truck drivers and contractor personnel can work safely. These should include, as a minimum, information concerning the basics of hydrocarbon fire ignition, control and extinguishment; hazards and protection from exposures to toxic substances such as hydrogen sulphide and polynuclear aromatics in crude oil and residual fuels, benzene in gasoline and additives such as tetraethyl lead and methyl-tert-butyl ether (MTBE); emergency response actions; and normal physical and climatic hazards associated with this activity.

Asbestos or other insulation may be present in the facility as protection for tanks and piping. Appropriate safe-work and personal protective measures should be established and followed for handling, removing and disposing of such materials.

Environmental protection

Terminal operators and employees should be aware of and comply with government regulations and company policies covering environmental protection of ground and surface water, soil and air from pollution by petroleum liquids and vapours, and for handling and removing hazardous waste.

• Water contamination. Many terminals have oil/water separators to handle contaminated water from tank containment areas, run-off from loading racks and parking areas and water drained from tanks and open-top tank roofs. Terminals may be required to meet established water quality standards and obtain permits before discharging water.

• Air pollution. Air pollution prevention includes minimizing releases of vapours from valves and vents. Vapour recovery units collect vapours from loading racks and marine docks, even when tanks are vented prior to entry. These vapours are either processed and returned to storage as liquids or burned.

• Spills on land and water. Government agencies and companies may require that oil storage facilities have spill prevention control and counter-measure plans, and that personnel be trained and aware of the potential hazards, notifications to be made and the actions to take in case of a spill or release. In addition to handling spills within the terminal facility, personnel are often trained and equipped to respond to offsite emergencies, such as a tank truck rollover.

• Sewage and hazardous waste. Terminals may be required to meet regulatory requirements and obtain permits for discharge of sewage and oily waste to public or privately owned treatment works. Various government requirements and company procedures may apply to the onsite storage and handling of hazardous waste such as asbestos insulation, tank cleaning residue and contaminated product. Workers should be trained in this activity and be made aware of the potential hazards from exposures which could occur.

LHG Storage and Handling

Bulk storage tanks

LHGs are stored in large bulk storage tanks at the point of process (gas and oil fields, gas plants and refineries) and at the point of distribution to the consumer (terminals and bulk plants). The two most commonly used methods of bulk storage of LHGs are:

• Under high pressure at ambient temperature. LHG is stored in steel pressure tanks (at 1.6 to 1.8 mPa) or in underground impermeable rock or salt formations.

• Under pressure close to atmospheric at low temperature. LHG is stored in thin-walled, heat-insulated steel storage tanks; in reinforced concrete tanks above and below ground; and in underground cryogenic storage tanks. Pressure is maintained close to atmospheric (0.005 to 0.007 mPa) at a temperature of –160°C for LNG stored in cryogenic underground storage tanks.

LPG bulk storage vessels are either cylindrically (bullet) shaped horizontal tanks (40 to 200 m³) or spheres (up to 8,000 m³). Refrigerated storage is typical for storage in excess of 2,400 m³. Both horizontal tanks, which are fabricated in shops and transported to the storage site, and spheres, which are built onsite, are designed and constructed in accordance with rigid specifications, codes and standards.

The design pressure of storage tanks should not be less than the vapour pressure of the LHG to be stored at the maximum service temperature. Tanks for propane-butane mixtures should be designed for 100% propane pressure. Consideration should be given to additional pressure requirements resulting from the hydrostatic head of the product at maximum fill and the partial pressure of non-condensible gases in the vapour space. Ideally, liquefied hydrocarbon gas storage vessels should be designed for full vacuum. If not, vacuum relief valves must be provided. Design features should also include pressure relief devices, liquid level gauges, pressure and temperature gauges, internal shut-off valves, back flow preventers and excess flow check valves. Emergency fail-safe shut-down valves and high level signals may also be provided.

Horizontal tanks are either installed aboveground, placed on mounds or buried underground, typically downwind from any existing or potential sources of ignition. If the end of a horizontal tank ruptures from over-pressurization, the shell will be propelled in the direction of the other end. Therefore, it is prudent to place an aboveground tank so that its length is parallel to any important structure (and so that neither end points toward any important structure or equipment). Other factors include tank spacing, location, and fire prevention and protection. Codes and regulations specify minimum horizontal distances between pressurized liquefied hydrocarbon gas storage vessels and adjoining properties, tanks and important structures as well as potential sources of ignition, including processes, flares, heaters, power transmission lines and transformers, loading and unloading facilities, internal combustion engines and gas turbines.

Drainage and spill containment are important considerations in designing and maintaining liquid hydrocarbon gas tank storage areas in order to direct spills to a location where they will minimize risk to the facility and surrounding areas. Dyking and impounding may be used where spills present a potential hazard to other facilities or to the public. Storage tanks are not usually dyked, but the ground is graded so that vapours and liquids do not collect underneath or around the storage tanks, in order to keep burning spills from impinging upon storage tanks.

Cylinders

LHGs for use by consumers, either LNG or LPG, are stored in cylinders at temperatures above their boiling points at normal temperature and pressure. All LNG and LPG cylinders are provided with protective collars, safety valves and valve caps. The basic types of consumer cylinders in use are:

• vapour withdrawal (1/2 to 50 kg) cylinders used by consumers, with larger ones usually refillable on an exchange basis with the supplier

• liquid withdrawal cylinders for dispensing into small consumer-owned refillable cylinders

• motor vehicle fuel cylinders, including vehicle cylinders (40 kg) permanently installed as fuel tanks on motor vehicles and filled and used in the horizontal position, and industrial truck cylinders designed to be stored, filled and handled in the upright position, but used in the horizontal position.

Properties of hydrocarbon gases

According to the NFPA, flammable (combustible) gases are those which burn in the normal concentrations of oxygen in air. The burning of flammable gases is similar to flammable hydrocarbon liquid vapours, as a specific ignition temperature is needed to initiate the burning reaction, and each will burn only within a certain defined range of gas-air mixtures. Flammable liquids have a flashpoint, which is the temperature (always below the boiling point) at which they emit sufficient vapours for combustion. There is no apparent flashpoint for flammable gases, since they are normally at temperatures above their boiling points, even when liquefied, and are therefore always at temperatures well in excess of their flashpoints.

The NFPA (1976) defines compressed and liquefied gases as follows:

• “Compressed gases are those which at all normal atmospheric temperatures inside their containers, exist solely in the gaseous state under pressure.”

• “Liquefied gases are those which at normal atmospheric temperatures inside their containers, exist partly in the liquid state and partly in the gaseous state, and are under pressure as long as any liquid remains in the container.”

The major factor which determines the pressure inside the vessel is the temperature of the liquid stored. When exposed to the atmosphere, the liquefied gas very rapidly vaporizes, travelling along the ground or water surface unless dispersed into the air by wind or mechanical air movement. At normal atmospheric temperatures, about one-third of the liquid in the container will vaporize.

Flammable gases are further classified as fuel gas and industrial gas. Fuel gases, including natural gas (methane) and LPGs (propane and butane), are burned with air to produce heat in ovens, furnaces, water heaters and boilers. Flammable industrial gases, such as acetylene, are used in processing, welding, cutting and heat-treating operations. The differences in combustion properties of LNG and LPGs are shown in table 1.

Table 1. Typical approximate combustion properties of liquified hydrocarbon gases.

Safety hazards of LPG and LNG

The safety hazards applicable to all LHGs are associated with flammability, chemical reactivity, temperature and pressure. The most serious hazard with LHGs is the unplanned release from containers (canisters or tanks) and contact with an ignition source. Release can occur by failure of the container or valves for a variety of reasons, such as overfilling a container or from overpressure venting when the gas expands due to heating.

The liquid phase of LPG has a high coefficient of expansion, with liquid propane expanding 16 times and liquid butane 11 times as much as water with the same rise in temperature. This property must be considered when filling containers, as free space must be left for the vapour phase. The correct quantity to be filled is determined by a number of variables, including the nature of the liquefied gas, temperature at time of filling and expected ambient temperatures, size, type (insulated or uninsulated) and location of container (above or below ground). Codes and regulations establish allowable quantities, known as “filling densities”, which are specific for individual gases or families of similar gases. Filling densities may be expressed by weight, which are absolute values, or by liquid volume, which must always be temperature corrected.

The maximum amount that LPG pressure containers should be filled with liquid is 85% at 40 ºC (less at higher temperatures). Because LNG is stored under low temperatures, LNG containers may be liquid filled from 90% to 95%. All containers are provided with overpressure relief devices which normally discharge at pressures relating to liquid temperatures above normal atmospheric temperatures. As these valves cannot reduce the internal pressure to atmospheric, the liquid will always be at a temperature above its normal boiling point. Pure compressed and liquefied hydrocarbon gases are non-corrosive to steel and most copper alloys. However, corrosion can be a serious problem when sulphur compounds and impurities are present in the gas.

LPGs are 1-1/2 to 2 times heavier than air and, when released in air, tend to quickly disperse along the ground or water surface and collect in low areas. However, as soon as the vapour is diluted by air and forms a flammable mixture, its density is essentially the same as air, and it disperses differently. Wind will significantly reduce the dispersion distance for any size of leak. LNG vapours react differently from LPG. Because natural gas has a low vapour density (0.6), it will mix and disperse rapidly in open air, reducing the chance of forming a flammable mixture with air. Natural gas will collect in enclosed spaces and form vapour clouds which could be ignited. Figure 4 indicates how a liquefied natural gas vapour cloud spreads downwind in different spill situations.

Figure 4. Extension of LNG vapour cloud downwind from different spills (wind speed 8.05 km/h).

Although LHG is colourless, when released in air its vapours will be noticeable due to the condensation and freezing of water vapour contained in the atmosphere which is contacted by the vapour. This may not occur if the vapour is near ambient temperature and its pressure is relatively low. Instruments are available which can detect the presence of leaking LHG and signal an alarm at levels as low as 15 to 20% of the lower flammable limit (LFL). These devices may also stop all operations and activate suppression systems, should the concentrations of gas reach 40 to 50% of the LFL. Some industrial operations provide forced ventilation to keep leaking fuel-air concentrations below the lower flammable limit. Heater and furnace burners may also have devices which automatically stop the flow of gas if the flame is extinguished.

LHG leakage from tanks and containers may be minimized by the use of limiting and flow control devices. When decompressed and released, LHG will flow out of containers with a low negative pressure and low temperature. The auto refrigeration temperature of the product at the lower pressure must be considered when selecting materials of construction for containers and valves, to prevent metal embrittlement followed by rupture or failure due to exposure to low temperatures.

LHG can contain water in both its liquid and gaseous phases. Water vapour can saturate gas in a specific amount at a given temperature and pressure. If the temperature or pressure changes, or the water vapour content exceeds the evaporation limits, the water condenses. This can create ice plugs in valves and regulators and form hydrocarbon hydrate crystals in pipelines, devices and other apparatus. These hydrates can be decomposed by heating the gas, lowering the gas pressure or introducing materials, such as methanol, which reduce the water vapour pressure.

There are differences in the characteristics of compressed and liquefied gases which must be considered from safety, health and fire aspects. As an example, the differences in the characteristics of compressed natural gas and LNG are illustrated in table 2.

Table 2. Comparison of characteristics of compressed and liquified gas.

Health hazards of LHGs

The primary occupational injury concern in handling LHGs is the potential hazard of frostbite to the skin and eyes from contact with liquid during handling and storage activities including sampling, measuring, filling, receiving and delivery. As with other fuel gases, when improperly burned, compressed and liquefied hydrocarbon gases will emit undesirable levels of carbon monoxide.

Under atmospheric pressures and low concentrations, compressed and liquefied hydrocarbon gases are normally non-toxic, but they are asphyxiants—they will displace oxygen (air) if released in enclosed or confined spaces. Compressed and liquefied hydrocarbon gases may be toxic if they contain sulphur compounds, especially hydrogen sulphide. Because LHGs are colourless and odourless, safeguards include adding odourants, such as mercaptans, to consumer fuel gases to aid in leak detection. Safe work practices should be implemented to protect workers from exposure to mercaptans and other additives during storage and injection. Exposure to LPG vapours in concentrations at or above the LFL may cause a general central nervous system depression similar to anaesthesia gases or intoxicants.

Fire hazards of LHGs

Failure of liquefied gas (LNG and LPG) containers constitutes a more severe hazard than failure of compressed gas containers, as they release greater quantities of gas. When heated, liquefied gases react differently from compressed gases, because they are two-phase (liquid-vapour) products. As the temperature rises, the vapour pressure of the liquid is increased, resulting in increased pressure inside the container. The vapour phase first expands, followed by expansion of the liquid, which then compresses the vapour. The design pressure for LHG vessels is therefore assumed to be near that of the gas pressure at maximum possible ambient temperature.

When a liquefied gas container is exposed to fire, a serious condition can occur if the metal in the vapour space is allowed to heat. Unlike the liquid phase, the vapour phase absorbs little heat. This allows the metal to heat rapidly until a critical point is reached at which an instantaneous, catastrophic explosive failure of the container occurs. This phenomenon is known as a BLEVE. The magnitude of a BLEVE depends on the amount of liquid vaporizing when the container fails, the size of the pieces of exploded container, the distance they travel and the areas they impact. Uninsulated LPG containers may be protected against a BLEVE by applying cooling water to those areas of the container which are in the vapour phase (not in contact with LPG).

Other more common fire hazards associated with compressed and liquefied hydrocarbon gases include electrostatic discharge, combustion explosions, large open-air explosions and small leaks from pump seals, containers, valves, pipes, hoses and connections.

• Electrostatic charges may be generated when LHG is shipped in pipelines, when loaded and unloaded, in blending and filtering and during tank cleaning.

• Combustion explosions result when escaping gas or vapour is contained in a confined space or structure and combines with air to create a flammable mixture. When this flammable mixture contacts a source of ignition, it burns instantaneously and rapidly, producing extreme heat. The very hot air expands quickly, causing a considerable rise in pressure. If the space or structure is not strong enough to contain this pressure, a combustion explosion occurs.

• Flammable gas fires result when there is no confinement of the escaping gas or vapours, or ignition occurs when only a small amount of gas has been released.

• Large open-air explosions occur when a massive failure of a container releases a large vapour cloud of gas which is ignited before it disperses.

Controlling sources of ignition in hazardous areas is essential for the safe handling of compressed and liquefied hydrocarbon gases. This may be accomplished by establishing a permit system to authorize and control hot work, smoking, operation of motor vehicles or other internal combustion engines, and the use of open flames in areas where compressed and liquefied hydrocarbon gas is transported, stored and handled. Other safeguards include the use of properly classified electrical equipment and bonding and grounding systems to neutralize and dissipate static electricity.

The best means of reducing the fire hazard of leaking compressed or liquefied hydrocarbon gas is to stop the release, or shut off the flow of product, if possible. Although most LHGs will vaporize upon contact with air, lower vapour pressure LPGs, such as butane, and even some higher vapour pressure LPGs, such as propane, will pool if ambient temperatures are low. Water should not be applied to these pools, as it will create turbulence and increase the rate of vaporization. Vaporization from pool spills can be controlled by the careful application of foam. Water, if correctly applied against a leaking valve or small rupture, can freeze upon contact with the cold LHG and block the leak. LHG fires require controlling heat impingement upon storage tanks and containers by the application of cooling water. While compressed and liquefied hydrocarbon gas fires can be extinguished by the use of water spray and dry powder extinguishers, it is often more prudent to allow controlled burning so that a combustible explosive vapour cloud does not form and re-ignite should the gas continue to escape after the fire is extinguished.

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