threshold limit value (TLV)

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.