|
102-275
Broadway |
MFL Occupational Health Centre, Inc. |
Today's workplaces often use different materials and equipment that may be harmful to workers' health. Occupational Exposure Limits and Threshold Limit Values are used to help find out if the work environment is harmful. This fact sheet discusses these terms and looks at their uses and short-comings.
Occupational Exposure Limit (OEL) is a general term for the amount of a workplace health hazard that most workers can be exposed to without harming their health. There are different OELs for different workplace health hazards, such as the amount of a chemical in the air and the loudness of noise. OELs may protect workers from both
Threshold Limit Values (TLVs) are the most common type of OEL. The American Conference of Governmental Industrial Hygienists (ACGIH) sets the TLVs to help evaluate workplace health hazards. TLVs are designed as guidelines to be used by people trained in industrial hygiene. There are TLVs for many workplace hazards including chemicals, vibration, heat, and ultraviolet light. Over 675 TLVs are for chemicals alone.
The ACGIH prints a TLV booklet each year that includes the new and changed TLVs. The booklet contains other useful information. For example, the skin notation says if the chemical causes harm by getting into the body through the skin. The booklet also says whether some chemicals cause cancer. In another book, the TLV Documentation, the ACGIH gives the reason why a specific amount was selected for the TLV. (See #1 and 2 on the Resource List.)
|
Types of TLVs for Chemicals in the Air TLV-TWA or time-weighted average is the amount of chemical in the air that most workers can be exposed to, day after day without harm to their health. It is based on working an 8-hour work shift and 40-hour work week. During the work shift the amount of chemical in the air may go up and down, above and below the TLV, but the average amount of chemical in eight hours should not be above the TLV. TLV-STEL or short-term exposure limit is the amount of chemical in the air averaged over 15 minutes that should not be exceeded during the workshift. TLV-C or ceiling is the amount of chemical in the air that should never be exceeded during the work shift. |
Most Manitoba workplaces are regulated by the provincial government. The Manitoba Workplace Health Hazard Regulation (53/88) says workers cannot be exposed to harmful materials at amounts more than the OEL. The regulation uses the 1987-1988 TLVs for OELs. It also says to use other available information. Other information includes the most recent TLVs. Therefore, the most recent TLVs should really be used for the OELs. The regulation has other requirements for OELs. This includes requiring the employer to set new OELs if
The regulation also says to keep exposures to certain cancer causing chemicals as close to zero as possible. A list of these chemicals is in the regulation.
The Manitoba mining industry and federally regulated workplaces use the most recent TLVs for OELs. The regulations for these workplaces are the Manitoba Operation of Mines Regulation (228/94) and Canada Labour Code Health and Safety Regulations Part X, respectively. There are two exceptions to the current TLVs in the Canada Labour Code. The OELs for grain dust and one type of asbestos are written directly into the code.
Collecting a personal air sample is the best way to find out the amount of chemical in the air that a worker is breathing. Workers wear portable equipment on their collars to collect a sample from the air as they work. The results give the average amount of chemical in the air. Spot or grab air samples are collected with many different types of equipment. They show the amount of chemical in the air at one point in time, but not the average amount of chemical in the air over time.
A worker's health can still be harmed even if his or her exposure to a health hazard is below the OEL. OELs are guidelines and not a line between safe and unsafe levels of exposure. Each worker is different. One worker's health can be harmed by exposure to a certain amount when another's is not. A worker may also have a medical problem that could be made worse by exposure to a chemical. For example, overexposure to carbon monoxide affects the heart. Therefore, exposure to carbon monoxide below the OEL could be a problem for people who have a heart condition.
OELs do not include all workplace factors. For example, they do not include the amount of chemical taken into the body through the skin. OELs do not account for heavy physical work. Workers may breathe in more chemical when doing heavy physical work. Also OELs do not protect pregnant women or the reproductive health of men and women.
In the 1980's a number of people in occupational health and safety raised concerns about how the TLVs were set. It was found that some TLVs were set at levels where workers had health symptoms. This is changing. Each year a few TLVs are reviewed and the level is often lowered. It is always important to pay attention to health symptoms, even if you are told that the chemicals in your workplace are at safe levels.
|
Units of measure for chemicals in the air or air concentration mg/m3 or milligrams per cubic meter is the weight of a chemical in a cubic meter of air. It is used for particles in the air including metal dusts, welding fumes and acid mists. It also applies to gases and vapours, such as carbon monoxide and formaldehyde. ppm or parts per million is the "parts" of a gas or vapour in the air for every million "parts" of air. It only applies to gases and vapours. fibres/cc fibres per cubic centimetre is the number of fibres in a cubic centimetre of air. It is used for fibres like asbestos. |
OELs do not protect all workers from cancer. There is no safe level of exposure for chemicals that cause cancer. Workers have a smaller chance of getting cancer if they are exposed
Therefore, use cancer causing chemicals as little as possible. Even though OELs and TLVs are supposed to protect most workers, it is good to keep exposures as low as possible.
OELs are usually set for 8-hour work shifts and can not be used for longer shifts. A new OEL should be set for longer shifts. This is often difficult to do. One method uses a formula that lowers an 8-hour OEL to account for the longer shifts. Patty's Industrial Hygiene book explains this method. (See # 3 on the Resource List.)
Many workplaces have more than one harmful chemical in the air. The OELs for the chemicals that can harm the body in a similar way, for example xylene and toluene, need to be grouped together. Sometimes workers will not be overexposed to each chemical by itself, but will be overexposed when grouping the OELs. The TLV booklet explains the method for grouping OELs. (See # 1 on the Resource List.)
Resource List
The MFL Occupational Health Centre's library has many resources about OELs and TLVs including:
June 1998
