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Noise Reduction Coefficient (NRC)

Last updated: November 10, 2018

What Does Noise Reduction Coefficient (NRC) Mean?

The Noise Reduction Coefficient (NRC) is a scalar representation of the amount of sound energy absorbed after that energy strikes a particular surface.

An NRC of zero indicates a perfect reflection of the sound energy, and an NRC of one indicates a perfect absorption of it.

Safeopedia Explains Noise Reduction Coefficient (NRC)

The process of absorbing sound is referred to as “acoustic absorption.” When sound energy hits a surface, part of that energy is absorbed into the material and converted into heat rather than being reflected off the surface as sound energy. The NRC of a building is typically used to evaluate the acoustic properties of ceiling tiles, wall panels, and screens that are used for purposes such as reducing the amount of noise that workers are exposed to in a given area.

The use of material with a high NRC within a workplace setting is an effective way to protect employees from noise exposure, which is necessary when noise levels exceed a certain decibel (dB) level. In the United States, OSHA’s action limit for noise exposure is 85 dB. Workplaces that may have high amounts of noise exposure can include both industrial settings as well as office settings. As OSHA standard 1910.95 requires employers to use engineering or administrative controls for hazard control before using personal protective equipment (PPE), employers may have a duty to ensure that reasonable efforts are made to use building materials (e.g., ceiling tiles) with a high NRC if a large level of noise exposure can be anticipated.

A high-rated NRC does not guarantee effective sound absorption in every workplace because NRC testing only rates the ability to reduce noise at the 250, 500, 1,000, and 2,000 Hertz (Hz) frequency levels. Workplaces that feature a large amount of sound outside this range may receive little benefit from the use of material with a high NRC.

Due to the limited range of frequencies tested, the use of the NRC is also not appropriate for work environments that must maintain certain sensitive acoustic properties, such as recording studios. The standard used to calculate the NRC is defined by ASTM International’s C423 standard.


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