Bad Assumptions About Hearing Protection #4: Cut the NRR in Half to Predict Real-World Protection

Bad Assumptions About Hearing Protection #4: Cut the NRR in Half to Predict Real-World Protection


Since the EPA promulgated its Noise Reduction Rating (NRR) on all hearing protector packaging since 1974, many studies have shown that attenuation achieved in the real-world is sometimes far below the laboratory NRR. There are a number of good reasons for this difference: users in the real-world might not receive proper training, or might adjust their hearing protectors for comfort rather than protection, or they may intentionally compromise the fit in order to hear co-workers and machine noises more clearly. 

A 50% de-rating method, defined by OSHA to determine feasibility of engineering controls, is often misapplied to try to predict real-world protection for workers in a Hearing Conservation Program. Such de-rating is arbitrary and usually wrong!

Using a fit-testing system for ear plugs, we visited eight industrial sites and measured real-world attenuation of 100 workers using ear plugs from a variety of manufacturers. Workers were instructed to fit their ear plugs just the same as they usually do. A Personal Attenuation Rating (PAR) was then measured on each ear. The PAR results showed that one-third of the workers achieved attenuation slightly higher than the published NRR, one-third of workers showed attenuation within 5 dB below the published NRR, and about one-third showed significantly lower attenuation (anywhere from 0 to 25 dB).

Recognizing this disparity between real-world and laboratory results, the EPA has announced its intention to update the NRR very soon. Instead of a single-number attenuation rating (31 dB, for example), the new NRR label will likely show a two-number range of measured attenuation for a given ear plug (18-29 dB, for example). The lower number indicates the expected attenuation for groups of workers with little or no training, while the higher number represents the expected attenuation for groups of workers with some individual training in hearing protector fitting.

Most experts agree that the new NRR range will provide a more realistic indicator to safety managers of how hearing protectors operate in the real world, but the new NRR still will not predict exactly how much protection an individual workers achieves.

That would require individual fit testing, which we’ll discuss in our next post.


Next: Bad Assumption #5: There’s No Way to Measure Real Attenuation on a Worker Wearing Ear Plugs


Blog Author:  Brad Witt  
Blog Catagories:  Personal Attenuation Rating  

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