How OSHA measures noise on a construction site
OSHA regulates noise as an 8-hour Time-Weighted Average (TWA), not as a single peak reading. For construction the governing standard is 29 CFR 1926.52 (with hearing protection under 29 CFR 1926.101). The Permissible Exposure Limit (PEL) is 90 dBA as an 8-hour TWA. A worker can be exposed to louder noise for a shorter time, or quieter noise for longer — what matters is the total dose across the shift.
OSHA enforcement uses a 5 dB exchange (doubling) rate: every 5 dB rise in level cuts the allowable time in half. (NIOSH recommends a more protective 3 dB rate, but OSHA citations use 5 dB.)
The four-step calculation
- Allowed time per level (T).
T = 8 / 2^((L − 90) / 5). Levels below 80 dBA contribute nothing. - Daily dose.
D = 100 × Σ(C / T), where C is the actual hours at each level. - 8-hour TWA.
TWA = 16.61 × log₁₀(D / 100) + 90. - Compare. 100% dose = 90 dBA TWA (the PEL); 50% dose = 85 dBA.
OSHA permissible exposure durations (5 dB exchange rate)
From 29 CFR 1926.52 Table D-2. The table ends at 115 dBA. Above that the 5 dB exchange arithmetic still produces a number, but the rule does not sanction it — a jackhammer at 130 dBA has no permissible daily duration to look up, it has a control problem. Treat those rows as a stop sign, not a time budget.
| Sound level (dBA) | Max permissible time / day |
|---|---|
| 90 (PEL) | 8 hours |
| 95 | 4 hours |
| 100 | 2 hours |
| 105 | 1 hour |
| 110 | 30 minutes |
| 115 | 15 minutes (end of Table D-2) |
| 120 | Beyond Table D-2 — no permissible duration |
| 130 | Beyond Table D-2 — no permissible duration |
Construction vs. general industry: the 85 dBA question
This is the single most-confused point in noise compliance, and the confusion usually runs the wrong way. Construction does require a hearing conservation program: 29 CFR 1926.52(d)(1) says that “in all cases where the sound levels exceed the values shown herein, a continuing, effective hearing conservation program shall be administered.” What construction lacks is the program’s content. The element list (audiometric testing, annual training, protector fitting) and the 85 dBA action levelwere added to general industry by the 1983 Hearing Conservation Amendment at 29 CFR 1910.95(c)-(n) and never extended to Part 1926. OSHA acknowledged the gap in an advance notice of August 5, 2002 (67 FR 50610); no construction rule followed.
So a contractor owes a program and gets no checklist in the standard. OSHA filled that gap in a letter to a construction company on August 4, 1992: an effective program consists of monitoring, engineering, work practice and administrative controls, an individually fitted protector with an adequate noise reduction rating, training, baseline and annual audiometry, procedures to prevent further loss, and recordkeeping, and “every construction industry employer’s hearing conservation program must incorporate as many of the above elements as are feasible.” Treat 85 dBA as the working trigger: it is what a defensible program is built around, and in Washington it is the rule for construction work (WAC 296-155-145 applies chapter 296-817 WAC, which requires a hearing loss prevention program at 85 dBA TWA8).
Hearing protection: derate the NRR
The Noise Reduction Rating (NRR) printed on a package is a laboratory figure that real-world fit rarely achieves. With A-weighted readings, OSHA’s Technical Manual subtracts 7 dB from the NRR, and applies a further 50% safety factor, (NRR − 7) ÷ 2, when deciding whether engineering controls are needed; to judge a protector for hearing conservation, its inspectors subtract only the 7 dB. The table below uses the conservative 50% figure. Estimated protected level = TWA − effective attenuation. Dual protection (plugs + muffs) is not additive: take the higher NRR, subtract 7 dB, and add 5 dB for the second protector.
| Protector | Labeled NRR | Field-effective (≈) |
|---|---|---|
| Foam Earplugs | 32 | 13 dB |
| Earmuffs (High-Attenuation) | 31 | 12 dB |
| Earmuffs (Standard) | 27 | 10 dB |
| Pre-molded Earplugs | 25 | 9 dB |
| Electronic Earmuffs | 22 | 8 dB |
| Dual Protection (Plugs + Muffs) | 37 | 15 dB |
Worked examples
Example 1 — jackhammer + saw. 2 h with a jackhammer at 130 dBA (T ≈ 1.9 min = 0.031 h) and 3 h with a circular saw at 110 dBA (T = 30 min = 0.5 h). Dose D = 100 × (2 / 0.031 + 3 / 0.5) = 100 × (64 + 6) ≈ 7,000%. TWA = 16.61 × log₁₀(70) + 90 ≈ 121 dBA — far above the PEL. Even dual protection (NRR 37 → ~15 dB effective) only gets to ≈106 dBA: this task needs engineering controls, not just PPE.
Example 2 — full shift at 95 dBA. 8 h at 95 dBA (T = 4 h). Dose D = 100 × (8 / 4) = 200%. TWA = 16.61 × log₁₀(2) + 90 = 95 dBA — 5 dB over the PEL. Foam plugs (NRR 32 → ~13 dB effective) bring the estimated protected level to ≈82 dBA, below the PEL. Hearing protection is required, and a hearing-conservation program is strongly recommended.
What to do when exposure is over the limit
- Measure it. Confirm with a calibrated sound level meter or dosimeter — this estimate flags the task, it doesn’t document compliance.
- Engineer it down first. 1926.52(b) requires feasible engineering/administrative controls (mufflers, enclosures, isolation, rotation) before relying on PPE.
- Provide the right protector. 1926.101 requires protection that brings exposure within the Table D-2 limits — size it with the derated NRR above.
- Run a hearing-conservation program. Audiometric baseline + annual tests, training, and protector fitting — required at 85 dBA in general industry and best practice everywhere.
Frequently asked questions
What is the OSHA noise exposure limit for construction?
OSHA's Permissible Exposure Limit (PEL) for noise in construction is 90 dBA as an 8-hour Time-Weighted Average (TWA), set by 29 CFR 1926.52 Table D-2. Hearing protection is mandatory once a worker's exposure exceeds that 90 dBA TWA. Construction does NOT have a codified 85 dBA action level — that 85 dBA action level and the hearing-conservation program live in the general-industry standard 1910.95. NIOSH and OSHA both recommend the more protective 85 dBA limit and a hearing-conservation program for construction as best practice.
How is the 8-hour noise TWA calculated?
First compute the daily noise dose: D = 100 × Σ(C/T), where for each exposure C is the actual hours at that level and T is the maximum hours OSHA allows at that level. T comes from the 5 dB exchange rate: T = 8 / 2^((L−90)/5). Then convert the dose to an 8-hour TWA with the OSHA formula TWA = 16.61 × log₁₀(D/100) + 90. A dose of 100% equals exactly a 90 dBA TWA (the PEL); a dose of 50% equals 85 dBA.
What is the 5 dB exchange rate?
OSHA uses a 5 dB exchange (doubling) rate: every 5 dB increase in noise level halves the allowable exposure time. At 90 dBA you may be exposed 8 hours; at 95 dBA, 4 hours; at 100 dBA, 2 hours; at 105 dBA, 1 hour; at 110 dBA, 30 minutes; at 115 dBA, 15 minutes. (NIOSH recommends a more protective 3 dB exchange rate, but OSHA enforcement uses 5 dB.)
When is hearing protection required on a construction site?
Under 29 CFR 1926.52, hearing protection is required whenever a worker's noise exposure exceeds the 90 dBA 8-hour TWA PEL (or the equivalent Table D-2 duration limits) and feasible engineering or administrative controls have not reduced it below the limit. 1926.101 requires that the protector actually attenuate exposure to within the Table D-2 limits. As best practice (and as required in general industry at the 85 dBA action level), provide protection and a hearing-conservation program at 85 dBA.
How do I derate a hearing protector's NRR?
The Noise Reduction Rating (NRR) printed on the package is a laboratory value. OSHA's enforcement guidance (and NIOSH) derate it for real-world fit: the field-effective attenuation ≈ (NRR − 7) ÷ 2 for foam plugs (50% derating). The codified 1910.95 Appendix B 'two methods' value is NRR − 7. Estimated protected level = TWA − effective attenuation. Dual protection (plugs + muffs) is NOT additive — OSHA's Technical Manual says take the higher NRR and add 5 dB.
Does this calculator replace a noise dosimeter?
No. It is a planning estimate built from typical published sound-pressure levels for each tool/equipment type. Actual exposure depends on the specific equipment, distance, enclosure, reflective surfaces, and how long the tool actually runs. To determine compliance you must measure with a calibrated sound level meter or dosimeter. Use this tool to flag tasks that likely need protection and to size that protection — not as the official exposure record.
Sources & verification
- 29 CFR 1926.52 — Occupational noise exposure (construction)
- 29 CFR 1926.101 — Hearing protection (construction)
- 29 CFR 1910.95 — Occupational noise exposure (general industry)
- NIOSH Criteria for a Recommended Standard: Occupational Noise Exposure (Pub. 98-126)
- OSHA Technical Manual (OTM), Section III, Chapter 5 — Noise
OSHA figures verified 2026-10-05 against 29 CFR 1926.52 / 1926.101. This calculator is a planning estimate built from typical published sound levels — it is not a substitute for measurement with a calibrated dosimeter, and not legal advice. State-Plan states may impose additional requirements.
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