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Noise Exposure Limit Calculator: OSHA vs. NIOSH

How long you can safely be exposed to a given noise level depends on which exposure standard you use β€” OSHA and NIOSH give meaningfully different answers.

The "exchange rate" sets how allowed time drops as dB rises

An exchange rate defines how much the permitted exposure time is cut every time noise increases by that many decibels. A 5 dB exchange rate is far more forgiving of loud spikes than a 3 dB exchange rate.

OSHA: 90 dBA for 8 hours, 5 dB exchange rate

OSHA's legal permissible exposure limit (PEL) allows 8 hours of exposure at 90 dBA. Allowed time is cut in half for every 5 dB increase β€” so 95 dBA is limited to 4 hours, and 100 dBA to 2 hours.

NIOSH: 85 dBA for 8 hours, 3 dB exchange rate

NIOSH's recommended exposure limit (REL), based on more recent hearing-damage research, sets the 8-hour baseline at 85 dBA and halves allowed time for every 3 dB increase β€” so 88 dBA drops to 4 hours and 91 dBA to 2 hours, a much steeper curve than OSHA's.

OSHA sets a legal floor, NIOSH sets a health recommendation

OSHA is an enforceable regulatory limit; NIOSH is a research-based recommendation with no legal force. Many hearing-health experts and some employers voluntarily follow the stricter NIOSH limit even though only OSHA is legally required in US workplaces.

The general formula behind both standards

Allowed time (hours) = 8 Γ· 2^((measured dB βˆ’ baseline dB) Γ· exchange rate). Plug in 90 and 5 for OSHA, or 85 and 3 for NIOSH, to get the permitted duration at any noise level.

Why a 5 dB difference in exchange rate matters so much

Because decibels are logarithmic, a small change in exchange rate compounds fast over a full day. At 100 dBA, OSHA's rule allows 2 hours, while NIOSH's stricter 3 dB exchange rate allows only about 15 minutes β€” nearly an eightfold gap at the same noise level.

Hearing damage accumulates even under the legal limit

Staying within OSHA's PEL is legally compliant, but it does not guarantee no hearing loss over a career β€” this is exactly why NIOSH's tighter, research-driven REL exists as a health-based recommendation rather than a matching legal standard.

Frequently Asked Questions

Which standard should I actually use to protect my hearing?

For legal compliance in a US workplace, OSHA's limit applies. For genuinely protecting long-term hearing health, most audiologists recommend following the stricter NIOSH limit whenever practical, since it reflects newer research on cumulative noise damage.

Does wearing hearing protection change these numbers?

These limits describe unprotected noise exposure at the ear. Properly fitted hearing protection (earplugs or earmuffs) effectively reduces the dB level reaching your ear, which extends your safe exposure time, but its real-world attenuation is often lower than the rating on the package.