Hearing Protection: OSHA's Targets and How to Check an NRR Against Your Noise

What OSHA requires: the three numbers to know

OSHA's noise rule for general industry, 29 CFR 1910.95, works with three numbers. An 8-hour average of 85 decibels, measured on the A scale, is the level at which the employer's hearing conservation program begins.

Once protectors are worn, they must bring the worker's exposure down at least to an 8-hour average of 90 decibels. For a worker whose hearing tests show a standard threshold shift, the target is stricter: 85 decibels or below.

The check is not done once and for all. The rule says the adequacy of the protectors must be re-evaluated whenever noise exposure rises enough that they may no longer be sufficient.

Check an NRR against your noise with OSHA's Appendix B

Appendix B of the rule, which OSHA marks as mandatory, tells employers how to use the NRR printed on a package. With a C-weighted 8-hour average, subtract the NRR. With an A-weighted average, first subtract 7 dB from the NRR, then subtract what remains from the average. Either way, the result is the estimated A-weighted average under the protector, and the estimator on this page does exactly that arithmetic, nothing more. With an A-weighted measurement and an NRR below 7 dB, the remainder is negative, so the estimate comes out above the measured level, as in the fifth worked example: that is the letter of Appendix B.

OSHA adds a limit to its own method: the values are realistic "only to the extent that the protectors are properly fitted and worn". Employers may also use one of three NIOSH methods instead of the NRR, NIOSH methods #1B1, #1B2 and #1B3.

NIOSH is blunter about the label. It writes that the package NRR "often does not reflect the actual protection provided for each worker", and that individual fit testing is "the best way to check if each worker is getting the amount of protection needed". A fit test gives a Personal Attenuation Rating (PAR), a number for one person wearing one protector, not for a product.

How long a noise level is allowed: OSHA Table G-16

Table G-16 of the same rule sets how long a worker may be exposed each day at a given sound level, read on the A scale at slow response. The table runs from 8 hours at 90 dBA through 4 hours at 95 dBA, 2 hours at 100 dBA and 1 hour at 105 dBA, down to half an hour at 110 dBA and a quarter hour or less at 115 dBA. The full table is below the estimator.

Real days are rarely one level. For a day made of several periods at different levels, the rule says "their combined effect should be considered, rather than the individual effect of each".

Types of protectors, and what the EPA label must show

NIOSH sorts earplugs into formable, pre-formed or custom, and describes earmuffs as "devices which completely surround the outer ear and are held in place by a headband or attached to a hardhat".

Whatever the type, EPA's labeling rule requires the package to state the Noise Reduction Rating, tested under ANSI STD S3.19-1974. For earmuffs that can be worn with the headband in more than one position, the label must give the worst case NRR. The month and year of production belong in the supporting information that comes with the protector.

Brands and models, from foam plugs to filtered and shooting protectors, are compared label by label on our ear plugs page.