OSHA's 5 dB Exchange Rate: Why 95 dBA Allows Half the Time of 90

An employer who hears "95 dBA is only 5 dB louder than 90 dBA" and assumes that means a small difference in allowable exposure time is wrong, and the gap matters for scheduling and PPE decisions. Under OSHA's 29 CFR 1910.95 Table G-16, the permissible exposure duration at 95 dBA is 4 hours, half of the 8 hours allowed at 90 dBA. That halving is not a coincidence of the numbers in the table, it is the direct result of a design choice called the exchange rate, and it is the single most misunderstood number in occupational noise compliance.

What is an exchange rate in noise exposure measurement?

An exchange rate (also called a doubling rate) is the number of decibels a sound level has to rise before the permissible exposure time is cut in half, or has to fall before the permissible time doubles. OSHA's Table G-16 in 29 CFR 1910.95 uses a 5 dB exchange rate: 90 dBA for 8 hours, 95 dBA for 4 hours, 100 dBA for 2 hours, 105 dBA for 1 hour, 110 dBA for 30 minutes, and 115 dBA for 15 minutes or less. Every 5 dB step up the table cuts the allowed time in half. This is an energy-averaging convention baked into the regulation itself, not a separate calculation an employer has to perform, but it is the reason small-sounding changes in measured sound level translate into large changes in how long an employee can work in that noise without additional controls.

Sound level (dBA)	Permissible exposure duration
90	8 hours
92	6 hours
95	4 hours
97	3 hours
100	2 hours
102	1.5 hours
105	1 hour
110	30 minutes
115	15 minutes or less

Why does OSHA use 5 dB instead of a different number?

OSHA's 5 dB exchange rate dates back to research from the 1960s-era Committee on Hearing, Bioacoustics, and Biomechanics (CHABA), which assumed that intermittent noise exposures with quiet recovery periods carried somewhat less risk than continuous exposure at the same average level, and set the rate to reflect that. The National Institute for Occupational Safety and Health (NIOSH) uses a different, more conservative assumption. Its Criteria for a Recommended Standard on occupational noise exposure, most recently revised in NIOSH Publication 98-126, recommends an 85 dBA exposure limit averaged over 8 hours using a 3 dB exchange rate, on the basis that hearing damage tracks total sound energy more closely than the 5 dB assumption allows for. Under a 3 dB rate, each 3 dB increase halves the allowable time, so 100 dBA drops from OSHA's 2-hour allowance to roughly 15 minutes under the NIOSH recommendation. OSHA has not adopted the 3 dB rate or the 85 dBA limit as its enforceable permissible exposure limit (PEL); 90 dBA with a 5 dB exchange rate remains the regulatory standard.

How does the exchange rate affect the hearing conservation action level?

The exchange rate question comes up most often around the 85 dBA action level in 1910.95(c), the 8-hour time-weighted average that triggers enrollment in a hearing conservation program, audiometric testing, and training. OSHA calculates that 85 dBA action level using the same 5 dB exchange rate as the PEL table, which is why a facility's noise dosimetry and its hearing testing enrollment decisions have to be built on the same exchange-rate assumption the regulation uses, not a NIOSH-based 3 dB calculation that will flag a different, typically larger, set of employees as exposed. Mixing exchange rates inside one compliance program, for example using a dosimeter default set to 3 dB while reporting against the OSHA 5 dB PEL, produces numbers that don't match the regulatory text and can misstate who belongs in the program.

What should an employer actually do with this difference?

For OSHA compliance purposes, dosimeters and sound level meters used to determine PEL and action-level status need their exchange rate set to 5 dB, matching Table G-16, and the resulting time-weighted averages are what belong in the record an inspector will ask for. Some employers choose to also track exposure under the stricter 3 dB NIOSH assumption as an internal best-practice benchmark, since a workforce that is compliant under the 5 dB rate can still include employees NIOSH would flag as at elevated risk under the 3 dB rate. That is a voluntary program decision, not a regulatory requirement, and it should be documented separately from the OSHA-required 5 dB figures so the two don't get confused during an audit.

How does Foster handle exchange-rate consistency across a noise program?

Foster's field technicians set dosimetry and sound level meter instruments to the 5 dB OSHA exchange rate as the default for every on-site testing engagement, because that is the figure that has to reconcile against Table G-16 in an inspection. When a client wants the stricter NIOSH 3 dB benchmark tracked alongside it for internal risk management, Foster's Compliance Workspace keeps that as a separate labeled metric on the employee or area record, rather than letting one number overwrite the other. That separation matters most when a facility's exposure profile sits in the gap between the two standards, since that is exactly where an employer deciding how to prioritize engineering controls or hearing protector upgrades needs to see both numbers clearly, not a blended one. For the testing side of the program that the action level triggers, see how who can legally perform the audiometric test is determined once an employee is enrolled.

Frequently Asked Questions

Does a 5 dB increase in sound level really cut allowed exposure time in half?

Yes, under OSHA's Table G-16. The table is built on a 5 dB exchange rate, so going from 90 dBA (8 hours) to 95 dBA (4 hours) halves the permissible exposure duration, and the pattern continues up the table in 5 dB steps.

Is NIOSH's 3 dB exchange rate required by OSHA?

No. NIOSH recommends the 3 dB rate and an 85 dBA limit in its criteria document, but OSHA's enforceable standard under 29 CFR 1910.95 still uses a 90 dBA PEL with a 5 dB exchange rate. Some employers track both for internal risk purposes.

Which exchange rate should my dosimeter be set to?

For OSHA compliance recordkeeping, set it to 5 dB to match Table G-16 and the 85 dBA action level calculation. If you also want a NIOSH-based internal benchmark, run that as a separately labeled measurement, not a substitute for the OSHA figure.

Why does this matter for hearing conservation program enrollment?

The 85 dBA action level that decides who gets enrolled in audiometric testing and training is itself calculated using the 5 dB exchange rate. Using a different exchange rate assumption can change which employees your calculation says are exposed at or above that level.

Sources

• OSHA 29 CFR 1910.95, Occupational Noise Exposure (Table G-16)
• NIOSH Publication 98-126, Criteria for a Recommended Standard: Occupational Noise Exposure