Noise Exposure / Hearing Conservation

Noise exposure is the occupational health hazard the hearing-conservation programme under OSHA 29 CFR 1910.95 is built to prevent, and the standard triggers the programme at the 85 dBA time-weighted average — the Action Level — at which the worker begins to accumulate the noise dose that produces the noise-induced hearing loss over years. The programme has five parts: the noise monitoring that finds who is at the action level, the audiometric testing that baselines the worker and tracks the threshold shift, the hearing protector the employer provides, the training, and the recordkeeping. The engineering controls — the enclosure, the damper, the quiet machine — are the preferred control, and the hearing protector is the fallback when the engineering cannot bring the level down.

The tension in the noise standard is the gap between the OSHA numbers and the NIOSH numbers. OSHA sets the Action Level at 85 dBA and the Permissible Exposure Limit at 90 dBA TWA, with the five-dB exchange rate that halves the allowed time per five-dB increase; NIOSH recommends the REL at 85 dBA and the three-dB exchange rate the physics of hearing loss actually follows, so the OSHA PEL permits exposure the NIOSH limit does not. The standard threshold shift on the audiogram — the early hearing loss the programme is designed to catch — is the leading indicator the recordable hearing loss is the lagging one, and the worksite that acts on the threshold shift prevents the recordable. See PPE, PEL, and TLV.