Monthly Round Up of Important Ideas and Standards in
Industrial Hygiene and Safety
N THIS ISSUE: What are Occupational Exposure Limits?
Both scientific and governmental organizations have developed occupational exposure limits (OELs) to protect workers from ill effects of working with chemical substances. The American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLV) “refer to airborne concentrations of chemical substances and represent conditions under which it is believed that nearly all workers may repeatedly exposed, day after day, over a working lifetime, without adverse health effects.” In the U.S. OELs also include OSHA Permissible Exposure Limits (PEL), the National Institute of Occupational Safety& Heath (NIOSH) Recommended Exposure Limits (REL), and to a lesser extent, the American Industrial Hygiene Association (AIHA) Workplace Environmental Exposure Levels (WEEL) and manufacturers.
While these standards have been valuable, there are thousands of chemicals used in the workplace. In some cases Control Banding is used to assess these and other chemicals. It assigns a level of health hazards or risk, exposure potentials, and suggests control measures such as ventilation, engineering controls, or containment. There are also OELs from different countries, especially in Europe that may be helpful.
In order to create an OEL, toxicologists try to determine a dose response. It is the amount of chemical needed to get a response and is the fundamental concept of toxicology. The dose response is shown as a dose-response curve, which is determined by experimentation. The toxicologist will design a protocol using a lab animal that is most likely to respond to a chemical that best reflects possible exposure in humans. From these experiments, a LD50 (lethal dose to 50% of the animal population) or LC50 (lethal concentration to 50% of the animal population) is determined. Results from these and other factors are used to develop a proposed OEL. It may include a protection factor of 10X, 100X, or greater, based upon the relative toxicity of the chemical.
OEL-creating organizations may take the results of a number of experiments to develop their standards. Panels of industrial hygienists and scientists will create the final OEL Governmental rule-making organizations may also include labor, industry, and governmental representative in making their OELs.
As new information becomes available, just as treatment methods may be improved in medicine, OELs may be updated. In the meantime, industrial hygienists and safety professionals must use the most stringent OELs, whether private or governmental, along with their knowledge of the chemical process to best protect employees.
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