Hearing Protection - Noise Duration to Determine Need

Permissible noise exposures require hearing protection for employees exposed to occupational noise at specific decibel levels for specific time periods.

OSHA defines continuous noises as having an interval between occurrences of the maximum noise level that is one second or less. Noises not meeting this definition are considered impact or impulse noises (loud momentary explosions of sound) and exposures to this type of noise cannot exceed 140 dB. (Powder-actuated nail guns, punch presses, or drop hammers are examples of tools that create impact or impulse noises.)

As a general rule, the louder the noise, the shorter the exposure time before hearing protection is required.

Here is an example:

"Employees may be exposed to a noise level of 90 dB for 8 hours per day before requiring hearing protection. However, if the noise level reaches 115 dB, then hearing protection is required if the anticipated exposure exceeds 15 minutes."

OSHA produces a document titled Hearing Conservation. This PDF provides a detailed discussion of the requirements for a comprehensive hearing conservation program. This document and the OSHA standard 29 CFR 1910.95 (Occupational Noise Exposure) are excellent resources.

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