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Facts About Noise #6

Conflicting Information about How to Use the NRR

Do you know how to use the NRR values that are required on the packaging of all hearing protection devices sold in the United States? If you do, you are one of a kind!

EPA Requirement: The only law (passed by the U.S. Congress) regulating how to use the NRR, is actually the EPA labeling regulation, dating back to 1981. This law directs the user to deduct the NRR from the noise level at hand, in order to get the noise level at the ear. That is pretty straightforward: Noise level [98 dB] minus Hearing Protector NRR [25 dB] = Noise at the Ear, 73 dB.

OSHA’s Field Manual: Although OSHA has no legislative authority, the agency has in its field manual directed their inspectors to use the following formula for how to apply the NRR.

NIOSH, Criteria for a Recommended Standard, Occupational Noise Exposure, June 1999: NIOSH recommends that Subject Fit data in accordance with ANSI S12.6-1997 be used. (To our knowledge no U.S. manufacturer has made "Subject fit" test data available). NIOSH recommends the following de-rating of hearing protector NRR’s, if subject fit data is not available.

The above de-ratings apply only when the noise measurement was made with a dB(C) scale. When only a dB(A) scale measurement is available, the de-rated NRR’s should be reduced by seven dB. Observe that earmuffs require the lowest de-rating.

OSHA Web Site, January 1999: OSHA recommends that manufacturers include a secondary label for NRR-SF. The SF (Subject Fit) refers to a NRR value achieved with the new ANSI S12.6-1997, using naive subjects. Naive subjects are defined as individuals having no previous experience in the use of hearing protection. (Authors comment: The method assures lower NRR’s, but we are no longer testing hearing protectors, we are testing test subjects. Better products will not necessarily get higher NRR’s. How about testing the safety record of new cars by having drivers without license drive a test course, and the car without dents gets the highest rating). The naive subjects are part of the ANSI standard, why OSHA bears no blame for this situation.

Read more: OSHA's Hearing Conservation Requirements


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