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The United States Environmental Protection Agency (EPA) requires that all hearing protection devices be labeled with their associated noise reduction rating (NRR).[11] The NRR provides the estimated attenuation of the hearing protection device. The NRR obtained in the lab is often higher than the attenuation provided in the field."[12][13] To determine the amount of noise reduction afforded by a hearing protection device for the A weighted scale, OSHA recommends that 7 dB be subtracted from the NRR. This new NRR should be subtracted from the individuals time weighted average (TWA) noise exposure. It must then be determined if the attenuation is appropriate for the level of noise the individual is exposed to.[14]

There are several fit testing devices on the market that will measure the attenuation an individual receives when wearing their HPD. These systems typically use one of two methods to verify fit. The individual wears their HPD and a microphone is placed inside the ear canal and another microphone is placed outside of the ear. A sound is played and the difference between the microphones is the attenuation for that individual, known as the personal attenuation rating (PAR). In the second method, a series of sounds are played for the individual, and the lowest level that they can detect the sound is recorded. The individual then wears the HPD and the same sounds are played. The amount that the sound has to be increased so that the individual can hear it is the PAR.