The answer depends on how loud the noise is and how long the person is exposed to the noise. Generally, more noise reduction is needed at high sound levels and for long exposure times. More protection is also required for workers who have a work-related hearing loss known as a Standard Threshold Shift (STS). Hearing protector ratings, such as the Noise Reduction Rating (NRR), were developed to help inform the buyer about the capability of the hearing protection device (HPD) in reducing noise exposure when worn correctly. The NRR of HPDs on the market today varies widely; from as little as 4 decibels (dB) to as much as 33 dB.
In the U.S., employers are required by OSHA to limit the 8-hour Time Weighted Average (TWA) daily noise exposure of most employees to 90 dBA or less.1 For workers who have already experienced a workrelated STS, the OSHA 8-hour TWA noise exposure limit is 85 dBA. Table G-16 from the OSHA Noise Regulation 29 CFR 1910.95 provides the noise exposure limits for various exposure times from 15 minutes up to 8 hours.1 ACGIH has established 85 dBA as the 8-hour Threshold Limit Value (TLV®) for noise.2