OSHA's permissible exposure limit (PEL) is 90 dB, averaged over 8 hours, using a 5 dB exchange rate, meaning every 5 dB increase halves the permitted exposure time: 4 hours at 95 dB, 2 hours at 100 dB. Separately, the 85 dB action level triggers a required hearing conservation program even though it sits below the PEL. The same 5 dB exchange rate applies.
The two thresholds serve different purposes: above 90 dB as an 8-hour time-weighted average (TWA), feasible engineering or administrative controls are required; at 85 dB TWA, monitoring, hearing testing, training, and the availability of hearing protection begin. Program requirements cover the day-to-day obligations. In FY2025, occupational noise exposure was one of the ten most frequently cited Federal OSHA standards in the manufacturing sector.
