Full definition
Personal protective devices (earplugs or earmuffs) that reduce the sound level reaching the inner ear, mandatory when noise exposure exceeds 85 dBA as an 8-hour time-weighted average (TWA) per OSHA 29 CFR 1910.95 and NOM-011-STPS-2001 (Mexico). For every 5 dB increase above 85 dBA, permissible exposure time halves (90 dBA = 4h, 95 dBA = 2h, 100 dBA = 1h). Types: (1) Earplugs — inserted into the ear canal; foam (disposable, NRR 29-33 dB, most attenuation), silicone/flanged (reusable, NRR 22-27 dB), and custom-molded (NRR 25-30 dB, best comfort for all-day use). (2) Earmuffs — cups over ears with foam cushions; NRR 20-30 dB; better for intermittent exposure (easy on/off); can mount on hard hat. (3) Electronic/active — amplify speech and ambient sounds while blocking impulse noise (gunshots, hammer blows); NRR 20-25 dB. Noise Reduction Rating (NRR): OSHA derates NRR by subtracting 7 dB and dividing by 2 for real-world effectiveness (lab NRR 33 → field ~13 dB). Dual protection (plug + muff) is required above 105 dBA. Per OSHA 29 CFR 1910.95, NOM-011-STPS-2001, and EN 352 (European). Hearing conservation program elements: noise survey, audiometric testing (annual baseline comparison), hearing protection selection and fitting, and worker training. Noise-induced hearing loss is permanent and irreversible — prevention is the only option.