When choosing the correct hearing protection for specific areas it is important to know what the meanings of the reduction rates mean to determine whether the specific type of protector will be suitable for employees. The following three noise reduction systems are commonly used when hearing protectors are tested for their attenuation:
1. NRR – Noise Reduction Rating
NRR stands for Noise Reduction Rating and is the greatest amount of sound reduction that a hearing protection device can provide. To get an accurate idea of the protection provided in dB(A) take the NRR value, subtract 7 and divide by 2. For example: An NRR rating of 25 offers a protection factor of 9 dB(A).
25 – 7 = 18
                                                                       18/2 = 9
This rating is used in the United States, and is accepted for use in a variety of other countries. The NRR labelling requirement is a standardized format for all hearing protectors distributed in the U.S. the NRR rating. The chart showing mean attenuation values and standard deviations at each of the seven test frequencies (from 125 Hz through 8000 Hz) is also part of the labelling required by EPA
2. SNR – Single Number Rating
This rating number is used by the European Union and affiliated countries.2 Tests are conducted at independent testing laboratories, using test frequencies which are slightly different than those used for the NRR rating. In addition to an overall rating, the SNR further rates protectors in terms of the particular noise environments in which they will be used – H for high-frequency noise environments, M for mid-frequency, and L for low-frequency. Note that the HML designation does not refer to noise level, rather the spectrum of the noise. Note that the HML designation does not refer to noise level, rather the spectrum of the noise. For example, a protector might be designated with SNR 26, H=32, M=23, L=14. The estimated attenuation changes according to the noise spectrum of the environment in which the protector is to be worn.
3. SLC80 – Sound Level Conversion
The SLC80 is a rating number used in Australia and New Zealand. It is an estimate of the amount of protection attained by 80% of users, based upon laboratory testing. Depending on the level of attenuation in the SLC rating, a classification is assigned to a protector: a Class 1 protector may be used in noise up to 90 dB, a Class 2 protector to 95 dB, a Class 3 protector to 100 dB, and so on in 5 dB increments
From the above information it is then not only beneficial but completely necessary to know what the noise levels are in your workplace so you can ensure that you purchase and choose the correct hearing protection for your employees
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