ACGIH term for airborne concentration
of a substance below which all workers are believed to be protected while exposed
to it day after day for 8-hour periods. For gases and vapors, TLV is stated as parts per million (PPM)
of surrounding air, and for fumes
, mists, and dusts as milligrams per cubic meter (mg/m3) of surrounding air. ACGIH classifies TLV in three ways (1) TLV-TWA: time weighted average
concentration for a normal 8-hour workday or 40-hour workweek. (2) TLV-STEL: short term exposure limit
, or maximum concentration of a substance (a) for a continuous 15-minute exposure period
, (b) for maximum of 4 such periods per day, (c) with at least one 60-minute exposure-free period between two exposure periods, and (d) provided the daily
TLV-TWA is met.
(3) TLV-C: ceiling exposure limit
or maximum exposure concentration
that should not be exceeded under any circumstance, while meeting
the daily TLV-TWA.