Threshold Limit ValueTLV

A Threshold Limit Value — TLV — is the airborne concentration of a chemical the American Conference of Governmental Industrial Hygienists, the ACGIH, judges nearly all workers can be exposed to repeatedly without adverse health effect, published annually in the TLVs and BEIs booklet. The TLV comes in three forms: the TLV-TWA, the eight-hour time-weighted average for a normal workday, the TLV-STEL, the fifteen-minute short-term exposure limit not to be exceeded at any time during the day, and the TLV-C, the ceiling concentration never to be exceeded even instantaneously. The industrial hygienist uses the TLV to design the ventilation, select the respirator, and set the exposure-monitoring programme.

The TLV is a guideline, not a regulatory limit — the OSHA Permissible Exposure Limit, the PEL, is the enforceable one — and the practical difference is that the ACGIH revises the TLV on the science every year, where the OSHA PEL is mostly frozen at the 1971 levels the agency adopted and has not been able to update. The result is that the TLV for a chemical is usually lower — more health-protective — than the PEL for the same chemical, and the industrial hygienist who works to the TLV protects the worker where the PEL would not. The honest EHS programme monitors to the lower of the two and treats the OSHA PEL as the legal floor, not the health target. See PEL, SDS, and noise exposure.