Step Four

Continuous exposure to hazardous materials will put the employees at risk of harmful effects from those materials. So it is necessary to establish a permissible level of exposure. All the guidelines for permissible levels of exposure are derived from the original work of the American Conference of Government Industrial Hygienists (ACGIH) who developed a concept they call threshold limit values (TLV). A TLV, which is a proprietary term, refers to the airborne concentration of a substance and represents conditions under which it is believed that nearly all workers may be repeatedly exposed to that substance day after day without adverse effect. The amount and nature of the information available for establishing a TLV also varies from substance to substance. Consequently, the precision of the estimated TLV is also subject to variation. The Occupational Safety and Health Administration–Permissible Exposure limit (OSHA-PEL) defines the average concentration permissible to a worker for a normal eight-hour workday and a forty-hour work week to which all workers may be repeatedly exposed, day after day, without adverse effect. The PEL or TLV concept is widely used throughout the world in spite of some well-founded objections, largely because there is no feasible alternative. The most significant objection pertains to the use of the averaging technique. It is argued that the effects on the body are not necessarily the same when they result from constant uniform exposure to low concentrations as they would be when they result from intermittent exposure to higher concentrations over the same period.