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Exposure Limits <br /> • Permissible exposure limit (PEL) <br /> • Threshold limit value (TLV) <br /> • Time-weighted average (TWA) <br /> • Short-term exposure limit (STEL) <br /> O OIRf—Bfneff b Lpfl RfMourpf Ic01 <br /> To guard against both acute and chronic health effects, scientists have <br /> identified exposure limits for different kinds of materials. Generally, these <br /> limits are the maximum quantity of a material that people can be exposed <br /> to without possibly suffering health effects. <br /> • The PEL, or permissible exposure limit, is often expressed as the <br /> quantity of hazardous chemical that an average employee can safely <br /> be exposed to in an 8-hour workday. <br /> • Threshold limit values (TLVs) are air quality standards developed <br /> by the American Conference of Governmental Industrial Hygienists. <br /> They are the model for many other air quality limits such as OSHA's <br /> PELs. TLVs are the amounts of materials in the air that almost all <br /> healthy adult workers are predicted to be able to tolerate without <br /> adverse effects. <br /> • Time-weighted average (TWA) refers to the average time over a given <br /> work period (such as an 8-hour workday) of a person's exposure. <br /> • And, the short-term exposure limit(STEL) is the maximum <br /> concentration to which workers can be exposed to a material or agent <br /> for a short period of time (15 minutes) for only four times throughout <br /> the day, with at least 1 hour between exposures. <br /> 14 <br />