Canadian Occupational Safety

24 www.cos-mag.com Canadian Occupational Safety Standard occupational exposure limits must be reduced for workers on extended work schedules By Linda Johnson ne main characteristic of the workplace today is the steady decline of the 9-to-5 day. In Canada, about 30 per cent of all employees now work non-standard work schedules. These new sched- ules may entail work at night or on weekends, shifts, split-shifts or on- call work. Increasingly, they require people to work longer days. For safety managers, the move to extended shifts raises the possibility of increased exposure to chemical hazards among workers exposed to hazardous substances over a longer day. Occupational exposure limits are based on the standard work schedule, and managers need to adjust these established limits for work shifts longer than eight hours. By under- standing how to use the different adjustment models available, safety professionals can keep the chemi- cal exposure of workers on irregular shifts within reasonably safe levels. Non-standard shifts are used in many industries, such as construc- tion, manufacturing, health care and security. They are also becoming more common in industries that involve continuous process operations, such as chemical manufacturing, oil refin- eries, steel mills, drilling rigs and paper mills, which require two or three shifts in a 24-hour period. The trend to specialized production is also driving a need for extended shifts, says Simon Aubin, chemist and industrial hygienist at the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST) in Montreal. "Many manufacturing industries have been moving their production to foreign countries. What's left here is more specialized work, done by highly skilled, qualified workers, so the mandates are more specialized. They have shorter deadlines, so it often implies longer, irregular shifts to be able to deliver the job on time." In remote areas, too, many indus- tries have adopted a fly-in, fly-out routine. Workers will eat and sleep at the work site. Because they are there only for a certain length of time and they want to get as much done as pos- sible during that time, shifts will be much longer than normal. A similar situation prevails at many under- ground mines. "It may take you, say, 45 minutes to get down to the work site, so you won't end your day after seven or eight hours; you will stay in the mine for at least 10 or 12 hours. It's also the complexity of the work. To get it going at first, it could take longer than usual, so once you get started, you better do it for a longer time if you want to maximize your presence there," Aubin says. LONGER DAYS, SHORTER NIGHTS An occupational exposure limit (OEL) is the concentration of a chemi- cal in the workplace air to which most people can be exposed without expe- riencing harmful effects, according to the Canadian Centre for Occupa- tional Health and Safety (CCOHS), based in Hamilton, Ont. The amount is often expressed in milligrams per cubic metre (mg/m 3 ). In Canada, provincial OELs are largely based on the maxi- mum exposure limits for chemical substances established by the American Conference of Governmental Industrial Hygienists (ACGIH), which refers to the limits as thresh- old limit values (TLVs). These OELs vary among provinces, so safety managers in dif- ferent provinces will be adjusting different OELs. There are three types of exposure limits: • The time-weighted aver- age exposure value (T WAEV) is based on the average concen- tration of a chemical in the air in a worker's breathing zone for a normal eight-hour workday and 40-hour workweek. It is calculated by averaging the level of samples taken during a specific time period. • The short-term exposure value (STEV) is the average concentra- tion to which workers can be exposed for a short period (usually 15 minutes) without experiencing irritation, long-term or irreversible tissue damage or reduced alertness. • The ceiling value (CV) exposure limit is the maximum allowable limit regardless of exposure time. Employers must ensure that no worker is exposed to a substance that exceeds the OEL, the short-term exposure limit or the ceiling limit. To establish compliance with this requirement, an employer is required to have an acceptable workplace monitoring program in place. The difficulty for employers who have workers with irregular shifts is that because OELs are based on a normal work schedule, using an established OEL for workers with extended shifts creates the risk of increased exposure. During work, the body accumulates the contaminant to a particular level (the "body burden") and then eliminates the contaminant in the hours away from work. "The (OELs) are based on a regu- lar work schedule, which means eight hours a day, 40 hours a week. If you work eight hours while you're exposed to a contaminant, in theory you have a period of 16 hours for your body to recover. If you start working a 12-hour shift and have only 12 hours to recover, then you've had a higher dose during the time you worked and less time for recovery. That could increase the burden," says Marc-André Lavoie, registered occu- pational hygienist and president of Dartmouth, N.S.-based Risk Marcker. "So, in circumstances where there is a different schedule, you need to put some thought into how to main- tain the same level of safety for these unusual work shifts." ADJUSTING THE OEL Where people are working non-traditional shifts, the safety manager must adjust the established OELs. Often, the way of adjusting for irregular work shifts has been to reduce the exposure limit based on the increased work time. For example, British Columbia's OHS regulation specifies that if the length of a work- day is between eight and 10 hours, the employer will multiply the OEL by a factor of 0.7; if between 10 and 12, by a factor of 0.5; if between 12 and 16, by a factor of 0.25; and if more than 16 hours, by a factor of 0.1. However, other methods, or models, have been developed to modify the standard OELs so that they apply to non-standard work schedules. These models, three of which are commonly used today, take into consideration exposure and recovery times and require different types and complex- ity of information, such as the toxicity of the individual substance. The OELs and adjustment calculations must be interpreted and applied by profes- sional occupational hygienists. The Quebec Model, which fol- lowed a method devised in 1979 by the Occupational Safety and Health Administration (OSHA) in Washing- ton, D.C., was developed in the late 1990s by experts at the University of Montréal and the IRSST. It classifies chemicals into four categories. "The advantage of our approach is that it's adapted to the toxicologi- cal characteristics of the chemicals involved," Aubin says. "Our group of experts, based on current scientific knowledge, can say that a given sub- stance will be eliminated throughout 24 hours, or it may need a week or even more to be eliminated. This will determine what category the substance is put into. The longer the elimination time, the longer period [days or weeks] you have to adjust the OEL." Category I comprises substances regulated by a ceiling value, irritants with short-term effects and sub- stances whose maximum exposure limits are based on technological limitations. Substances that fall in this category need no adjustment. Category II contains acute toxi- cants. These have short-term effects, do not accumulate and have an adjustment factor derived from hours of work per day. Category III contains chronic toxi- cants. These have long-term effects, can accumulate and have an adjust- ment factor derived from hours worked per week (according to the "repetitive work cycle," the calendar period during which the work sched- ule is exactly repeated). Category IV contains substances that are both acute and chronic. These have both short- and long-term effects, and the adjustment factor selected will be based on either hours worked per day or per week, which- ever is more conservative.

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