How is noise dose calculated?

Dose = 100 × Σ(Cᵢ/Tᵢ), where Cᵢ is the hours spent at a given level and Tᵢ is the reference duration allowed at that level. Under OSHA, Tᵢ = 8 / 2^((L−90)/5).

What is the difference between OSHA and NIOSH noise limits?

OSHA uses a 5 dB exchange rate and a 90 dBA criterion (PEL). NIOSH recommends a more protective 3 dB exchange rate and an 85 dBA recommended exposure limit (REL). The same exposure yields a higher dose under NIOSH.

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Free Acoustics Toolkit · Industrial & Energy

OSHA Noise Dose & 8-Hour TWA Calculator

Enter the sound levels your workers are exposed to and how long they're exposed. This tool computes the total noise dose and 8-hour time-weighted average, and flags it against the OSHA action level (85 dBA) and permissible exposure limit (90 dBA) per 29 CFR 1910.95.

Method reviewed by CSTI's INCE Board-Certified engineers

Exposure inputs

Add a row for each area or task in the worker's day. Levels are A-weighted (dBA); times are hours.

Result

OSHA · 90 dBA criterion · 85 dBA action level

Noise dose

8-hour TWA

—dBA

The method (29 CFR 1910.95, Appendix A)

Reference duration Tᵢ = 8 / 2^((Lᵢ − 90) / 5) (OSHA 5 dB exchange)

Dose D = 100 × Σ ( Cᵢ / Tᵢ ) TWA = 16.61 × log₁₀(D / 100) + 90

Worked example: 6 h at 92 dBA and 2 h at 88 dBA (OSHA). T₉₂ = 8/2^(2/5) = 6.06 h; T₈₈ = 8/2^(−2/5) = 10.56 h. D = 100 × (6/6.06 + 2/10.56) = 118%, TWA = 16.61·log₁₀(1.18) + 90 = 91.2 dBA — over the PEL. NIOSH mode uses a 3 dB exchange and an 85 dBA criterion (Tᵢ = 8/2^((Lᵢ−85)/3)). Full-shift dosimetry per ANSI S1.25 gives the defensible number of record — this estimate sizes the problem. See 29 CFR 1910.95 and NIOSH 98-126.

Frequently asked

What is the OSHA noise exposure limit?

OSHA's permissible exposure limit (PEL) is a 90 dBA 8-hour time-weighted average — a 100% dose. The action level, which triggers a mandatory hearing conservation program, is an 85 dBA 8-hour TWA (a 50% dose).

When do I have to start a Hearing Conservation Program?

When employee exposure equals or exceeds an 85 dBA 8-hour TWA (50% dose), OSHA requires monitoring, audiometric testing, hearing protection, training, and recordkeeping. If this tool shows you at or above 50%, that obligation likely applies.

Why does NIOSH give a higher dose than OSHA?

NIOSH uses a more protective 3 dB exchange rate and an 85 dBA criterion, versus OSHA's 5 dB rate and 90 dBA. Under a 3 dB rule, every 3 dB increase halves the allowed time, so the same exposure accrues dose faster.