Sheet 30Mix-up sheet · Ergonomics, vibration and noise
Construction noise limits: 90 dBA and the 85 dBA trap
Construction's noise limit is 90 dBA averaged over 8 hours, with a 5 dB exchange rate, under 29 CFR 1926.52. The 85 dBA figure that keeps appearing next to it is the action level in the general-industry rule, 29 CFR 1910.95, where it starts a hearing conservation program.
OSHA's construction and general-industry rules and the NIOSH recommended exposure limit (REL)scroll →
Point
OSHA construction, 1926.52
OSHA general industry, 1910.95
NIOSH REL
8-hour limit
90 dBA
90 dBA
85 dBA
Exchange rate
5 dB
5 dB
3 dB
What 85 dBA means
No action level in the text
Action level for hearing conservation
The limit itself
Force
Enforceable
Enforceable
Recommendation
Construction still requires a continuing, effective hearing conservation program whenever exposures exceed the Table D-2 values; its own text simply has no 85 dBA trigger.
Talking point 02
How the 5 dB exchange rate works
Every 5 dB above 90 halves the time allowed. Table D-2 in 29 CFR 1926.52 gives 8 hours at 90 dBA, 4 hours at 95 and 1 hour at 105. A 3 dB rate halves faster: under the NIOSH recommendation, 85 dBA allows 8 hours and 88 dBA allows 4.
Steady noise can be read straight off the table. Noise that changes through the day adds up as a dose: the hours spent at each level divided by the hours allowed at that level, summed. A total over 1 is over the limit, so 2 hours at 95 dBA uses half the day's allowance by itself. Impact or impulse noise has a separate ceiling of 140 dB peak.
The parent sheet, ergonomics and noise, puts these numbers next to the other health topics in the domain.
Talking point 03
Estimating protection from an NRR
Start from the label
Plugs and muffs carry a noise reduction rating (NRR) measured in a lab. Take a muff rated NRR 31.
Subtract 7 for dBA data
The NRR is meant to come off a C-weighted reading. With dBA exposure data, OSHA's method in 1910.95 Appendix B removes 7 first: 31 − 7 = 24 dB.
Subtract from the exposure
A worker measured at 98 dBA over 8 hours is estimated at 98 − 24 = 74 dBA with the muffs on.
Know the field derating
OSHA's Technical Manual suggests halving the corrected figure again to allow for real-world fit, which would give 12 dB here. That is guidance; the Appendix B arithmetic is the regulatory method.
Talking point 04
Instruments and tests that sound alike
Sound level meter
Noise at one spot at one moment. Useful for finding the loud tool or the loud corner, and for deciding where engineering controls should go.
Noise dosimeter
Worn by the worker through the shift, it adds every level the worker passes through into a single dose.
Baseline audiogram
The reference hearing test, taken after at least 14 hours away from workplace noise under 1910.95. Every later test is compared with it.
Standard threshold shift
A change from baseline averaging 10 dB or more at 2,000, 3,000 and 4,000 Hz in either ear.
Talking point 05
Noise numbers in practice
Some cards need arithmetic. Use the exchange rate and the 7 dB correction from this sheet, and check which rule book the stem names.
Card 1 of 6 · 0 right
Card 1
Under OSHA's construction noise standard, how long may a worker be exposed each day to a steady 100 dBA before exceeding the permissible limit?
Pick an answer. A short note for each option, A to D, appears here.
AOne hour is the limit at 105 dBA, one more 5 dB step above 100.
BEight hours applies only at 90 dBA, the base of the exposure table.
CFour hours is the allowed time at 95 dBA, one step below the level in this question.
DCorrect: with a 5 dB exchange rate from 90 dBA for 8 hours, each 5 dB increase halves the time, giving 2 hours at 100 dBA.
Card 2
A worker's 8-hour noise exposure is 100 dBA. Using OSHA's method for dBA data (subtract 7 from the NRR) and no further derating, what is the estimated exposure while wearing earmuffs rated NRR 27?
Pick an answer. A short note for each option, A to D, appears here.
ASubtracting the full NRR of 27 skips the 7 dB correction OSHA applies when exposure is measured in dBA.
BThis subtracts 7 from the exposure instead of from the NRR, which misapplies the correction step.
CThis halves the full NRR without first subtracting 7, mixing a field derating with the wrong starting value.
DCorrect: with dBA data, OSHA subtracts 7 from the NRR, so 27 − 7 = 20 dB, and 100 − 20 gives an estimated 80 dBA.
Card 3
What is the PRIMARY purpose of comparing a noise-exposed worker's annual audiogram with the baseline audiogram?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: comparing annual and baseline audiograms detects a threshold shift while it is small, so protection, fit or training can be corrected in time.
BAudiograms measure the worker's hearing; tool noise is measured with a sound level meter or dosimeter.
CHearing tests in a conservation program protect workers already exposed; they are not a hiring screen.
DWho needs hearing protection is decided by exposure monitoring, not by audiometric results.
Card 4
Chipping, saw cutting and quiet periods alternate throughout a worker's shift. Which measurement BEST shows whether the worker's noise exposure exceeds the permissible limit?
Pick an answer. A short note for each option, A to D, appears here.
AA single reading at the loudest tool captures one moment and misses how exposure varies over the shift.
BManufacturer ratings come from test conditions and reflect neither site acoustics nor how long each tool runs.
CBoundary readings describe community noise, not the dose received at the worker's ear.
DCorrect: a personal dosimeter integrates every level and duration over the shift into a dose that can be compared with the limit.
Card 5
A supervisor sees a worker on a jackhammer crew with foam earplugs barely inserted, most of each plug sticking out of the ear. What should the supervisor do?
Pick an answer. A short note for each option, A to D, appears here.
AWaiting for annual training leaves the worker poorly protected on a jackhammer crew until then.
BThe NRR assumes correct fit; a barely inserted foam plug may give little attenuation.
CA higher-rated plug inserted the same shallow way still underperforms, so the fit problem remains.
DCorrect: protection depends on fit, so the supervisor coaches proper insertion on the spot and checks that the plugs are seated.
Card 6
A laborer spends 4 hours at a steady 95 dBA and the other 4 hours of the shift at 90 dBA. Using the noise dose method of 29 CFR 1926.52, how does the exposure compare with the limit?
Pick an answer. A short note for each option, A to D, appears here.
AEach level is judged by the time allowed at it, and the periods add up. Staying at or below 95 dBA does not by itself keep the dose under 1.
BFour hours at 95 dBA uses the whole day's allowance by itself, so the 4 hours at 90 dBA push the total past it.
CCorrect: 4/4 at 95 dBA plus 4/8 at 90 dBA gives a dose of 1.5, which is over the limit of 1.
DA dose of 1.0 would mean the whole day fit the allowance. The 4 hours at 90 dBA add another 0.5.