Every 3 dBA increase in noise level halves the safe exposure duration

NIOSH uses a 3-dB exchange rate (also called the equal-energy rule): each 3 dBA increase in sound level cuts the allowable exposure time in half. At the REL of 85 dBA, the safe duration is 8 hours. At 88 dBA it is 4 hours, at 91 dBA it is 2 hours, and so on. The inverse also applies: if a shift is longer than 8 hours, the allowable noise level is lower. This exchange rate is stricter than OSHA’s 5-dB rule; using NIOSH’s rule provides greater hearing protection. The 3-dB exchange rate follows from the physics of acoustic energy: a 3 dBA increase doubles sound intensity.

Examples

85 dBA → 8 hours safe; 88 dBA → 4 hours; 91 dBA → 2 hours; 94 dBA → 1 hour; 97 dBA → 30 minutes. A performer rehearsing 3 hours at 91 dBA has used their full day’s dose.

Assessment

A musician practices at 94 dBA for 1.5 hours. Have they exceeded their NIOSH daily dose? Calculate the answer using the 3-dB exchange rate.