What Does Noise Reduction Rating (NRR) Mean? August 02 2018
Many of us are aware of the risks associated to our hearing with high noise level exposure, having experienced at one time or another the discomfort associated with loud noises. Perhaps we’ve been warned at some point that intense sounds can ultimately lead to impaired hearing. In fact OSHA has a chart that depicts what it considers permissible noise exposure levels. While we might understand the importance of hearing protection, especially in industrial environments, we might also lack knowledge of the key characteristics of effective hearing protection.
One of these characteristics of hearing protection is Noise Reduction Rating (NRR), which is a unit of measurement used to determine the effectiveness of hearing protection devices to decrease sound exposure within a given working environment. Classified by their potential to reduce noise in decibels (dB), a term used to categorize the power or density of sound, hearing protectors must be tested and approved by the American National Standards (ANSI) in accordance with the Occupational Safety & Health Administration (OSHA). The higher the NRR number associated with a hearing protector, the greater the potential for noise reduction.
When hearing protection is worn, your level of exposure to noise is based on the NRR of the protection device being used. We might assume that your level of protection is a one to one correspondence to the NRR. Unfortunately, this is not the case. While the NRR is measured in decibels, the hearing protector being used does not reduce the surrounding decibel level by the exact number of decibels associated with that protector’s NRR. For example, if you are at a rock concert where the level of noise exposure is 100 dB and you are wearing earplugs with an NRR 33dB, your level of exposure would not be reduced to 67 dB. Instead, to determine the actual amount of noise, in decibels, reduction applied, you take the NRR number (in dB), subtract seven, and then divide by two. Given the previous example, your noise reduction equation would look like the following: (33-7)/2 = 13. This means that if you are at a rock concert with a level of noise exposure at 100 dB and you are wearing a hearing protector with an NRR 33 dB, your new level of noise exposure is 87 dB. If you are wearing a product with an NRR of 27 it would deduct 10 decibels (27-7/2=10).
Armed with this information, we can now more reliably and more confidently select a hearing protection device that suits our needs.