Ear protection equipment is classified by its Noise Reduction Rating (NRR), a grading that determines a device’s ability to decrease sound exposure in an environment. NRR is sometimes referred to as “hearing protection rating.” Organized by their potential to reduce noise in decibels (dB), a term used to measure the power or loudness 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. While many strive to have the NRR be a perfect “tell-all” number, it is still an estimate based on what 98% of the population will experience if the protection is properly fit, if not there can be differences by as much as 50%.
Currently the US Environmental Protection Agency is in the process of changing NRR rating labels. Instead of the former “one number” approach, the EPA has proposed changing the labels to indicate a range, from the minimally trained to the more proficient users, accounting for variability in usage and fit.
What does decibel exposure mean?
According to OSHA noise standards (documented at 29 CFR), hearing protection is required for any employee exposed to 85 decibels or higher over an 8-hour period or 100 decibels or greater over a 2-hour period. However, depending on your own environment, it might be beneficial to look into some ear protection if you are exposed to high levels of noise. Notice from the chart below that ear protection is needed on an exponential basis and that a small increase in noise decreases exposure time dramatically.
Some of the most common producers of noise levels that OSHA considers to be dangerous: lawnmowers, rock concerts, firearms, firecrackers, headset listening systems, motorcycles, tractors, power tools and industrial machinery. To illustrate what these numbers represent, here are some examples:
150 dB = Rock Concerts at Peak
140 dB = Firearms, Air-Raid Siren, Jet Engine
130 dB = Jackhammer
120 dB = Jet Plane Take-off, Amplified Music at 4-6 ft., Car Stereo, Band Practice
110 dB = Machinery, Model Airplanes
100 dB = Snowmobile, Chain saw, Pneumatic Drill
90 dB = Lawnmower, Shop Tools, Truck Traffic, Subway
80 dB = Alarm Clock, Busy Street
70 dB = Vacuum Cleaner
60 dB = Conversation, Dishwasher
50 dB = Moderate Rainfall
40 dB = Quiet room
30 dB = Whisper, Quiet Library
Keep in mind that 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 25dB, your level of exposure would not be reduced to 75 dB. Instead, there is a formula to determine the actual amount of decibel deduction applied.
Take the NRR number (in dB), subtract seven, and then divide by two. In the previous example, your noise reduction equation would look like the following: (25-7)/2 = 9. 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 25 dB, your new level of noise exposure is 91 dB. If you are wearing a product with an NRR of 27 it would deduct 10 decibels (27-7/2=10) or 100-10 = 90 dB.
If you are wearing hearing protectors in combination, like a pair of earplugs and earmuffs, you would not add the NRR numbers together. Instead you simply add five more decibels of protection to the device with the higher NRR. For example, using Earplugs (NRR 29) with Earmuffs (NRR 27) would provide a Noise Reduction Rating of approximately 34 decibels.
Hopefully that gives an idea of what the NRR is and how to calculate your exposure in certain loud and potentially harmful environments.