Understanding Ratings

Understanding Ratings Poster PDF

In addition to NRR, the hearing protector packaging displays other rating numbers (SNR and SLC80). What do these rating numbers mean?

Howard Leight® hearing protectors are packaged to be shipped throughout the world. While customers in the U.S. are familiar with the NRR labeling required by the EPA, they may be a bit confused with packaging that includes other rating numbers. The following summary explains the rating numbers seen on Howard Leight® packaging:

NRR [Noise Reduction Rating] – This rating is used in the United States, and is accepted for use in a variety of other countries. The current range of NRRs available in the U.S. market extends from 0 to 33 decibels. Published by the U.S. Environmental Protection Agency in 1979,1 the NRR labeling requirement is a standardized format for all hearing protectors distributed in the U.S. The EPA defines the type face size, font, wording and placement on the package for the NRR label. 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 labeling required by EPA.

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. For example, a protectormight 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.

SLC80 [Sound Level Conversion] – The SLC80 is a rating numberused in Australia and NewZealand.3 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. Packaging will often show the SLC80, followed by the classification (i.e. SLC80 27, Class 5).

Table 1. Rating numbers commonly used for hearing protectors.

Symbol Definition Where Used
NRR Noise Reduction Rating United States
SNR Single Number Rating European Union
SLC80 Sound Level Conversion Australia/New Zealand

Customers should not be concerned when they see several different attenuation ratings on a package. Each rating number is based upon differing test standards, test frequencies and calculation methods, and any given hearing protector generates different numbers depending on the rating method used. For example, the Howard Leight® LaserLite® single-use earplug displays the following ratings:

NRR 32
SNR 35 (H=34, M=32, L=31)
SLC80 25.0 (Class 4)

Since the NRR is the only rating method currently recognized by OSHA, customers are advised to only use the NRR for OSHA-compliant hearing conservation programs in the U.S.

— Brad Witt, MA, CCC-A
Director of Hearing Conservation
Howard Leight®



1 The EPA labeling standard is defined in Code of Federal Regulations (CFR) 40, Part 211, Subpart B – Hearing Protective Devices.
2 The SNR rating and HML descriptors are defined in ISO 4869-2, Acoustics – Hearing Protectors.
3 The SLC80 is defined in Australian/New Zealand Standard 1270:2002, Acoustics – Hearing Protectors.



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