391-1000

Education How to Use the Noise Reduction Rating (NRR) G The NRR describes the average sound level reduction (attenuation) provided by a hearing protection device (HPD) in a laboratory test. Since the NRR is based on laboratory testing, it does not take into account the loss of protection that occurs when hearing protectors are not fit properly or when they are not worn for the entire time that the wearer is exposed to noise For most wearers, the NRR identified on the current EPA label (shown here) significantly overestimates the protection of the hearing protector in the workplace. This rating is based on an “experimenter fit” method of measuring HPD attenuation. Hearing Protection Using the EPA Noise Reduction Rating (Experimenter Fit) The NRR on the EPA label shown to the right is based on the average amount of attenuation provided by an HPD when it is worn by 10 different people during a laboratory test. During this test, the person conducting the test fits the hearing protector on each person. This “experimenter fit” method results in ratings as high as 33 dB. Since research indicates that these ratings overestimate the protection that many wearers will receive in the real world, 3M RECOMMENDS REDUCING THE NRR before attempting to estimate the effectiveness of an HPD as follows: United States Technical Service 1 800 243-4630 Sales Assistance 1 800 896-4223 2000 Resource Guide 1. Subtract 7 dB from the NRR if noise is measured on the Aweighted decibel scale (dBA). (Skip this step if noise is measured on the C-weighted dB scale) 2. Divide the result of step 1 (NRR7) by 2. This is known as “derating”. in the real world. For more information about the NRR (SF), contact 3M Technical Service at 800 243-4630. Estimating Noise Reduction for Individual Users The labeled values of noise reduction are An Example of Reducing the NRR based on laboratory 8-hour TWA noise exposure: 93 dBA tests. It is not possible to NRR of hearing protectors: 29 dB use these data Subtract 7 dB from the NRR: 29 dB - 7 dB = 22 dB to reliably Divide by 2: 22 ÷ 2 = 11 dB predict levels of protection Subtract 11 dB from the achieved by a 8-hour TWA noise exposure: 93 dBA - 11 dB = 82 dB given Decide if 82 dB (known as the “Protected Exposure”) individual in is below the PEL for noise a particular environment. To ensure A New Rating: NRR (SF) protection, those wearing hearing A new “subject fit” method of protectors for occupational measuring HPD attenuation will be exposures must be enrolled in a used in the future to calculate a hearing conservation program. Nondifferent rating; the NRR (SF). The occupational users should have a people (subjects) in this laboratory hearing evaluation by an audiologist, test fit their own protector according physician, or other qualified to the manufacturer’s instructions professional, on a regular basis. without the help of the person conducting the test. Compared to the NRR shown on the current EPA label, the NRR (SF) is usually a lower rating that may be closer to the performance of the hearing protector G12 Canada Technical Service 1 800 267-4414 Sales Assistance 1 800 265-1840 ext. 6137