How to Use the Noise Reduction Rating-July 2014

Monthly Round Up of Important Ideas and Standards in
Industrial Hygiene and Safety 

July 2014

IN THIS ISSUE: How to Use the Noise Reduction Rating 
The Noise Reduction Rating (NRR) requires manufacturers to identify the noise reduction capability of all hearing protectors. NRR is part of an EPA standard, based upon ANSI S3.19-1974, and it is a laboratory‐derived numerical estimate in decibels (dB) of the attenuation achieved by the hearing protector. Ratings for muffs or earplugs can range from 0 to 33 dB. Theoretically, wearer exposure can be calculated one of two ways:
  • Estimated Exposure = Noise Level (dBC) – NRR
  • Estimated Exposure = Noise Level (dBA) – NRR – 7 dB
Consider the following factors:
  • The most widely used earplugs, compressible foam earplugs, are often poorly fitted. Users are generally unaware of how to properly insert them. As a result, incorrectly compressed earplugs may give virtually no attenuation.
  • Hearing protectors may become lost, dirty, or damaged and replacements may not be readily available.
  • Eye wear or other personal protective equipment affects the seal of earmuffs.
  • Environmental factors such as heat or humidity affect effectiveness and usage for both earplugs and muffs.
  • Lack of employee recognition of the noise hazard or the importance of hearing protection impacts usage.
In recognition of these factors, OSHA recommends that when calculating employee exposure, NRR should be reduced by 50 percent. NIOSH recommends a 25 percent reduction in NRR for earmuffs, 50 percent for formable earplugs, and 70 percent for other earplugs. Both of these are rules of thumb and should only be used in conjunction with a comprehensive hearing protection program.Here are some steps that should be taken to protect workers’ hearing:
  • Reduce noise at the source to lessen the need for hearing protection.
  • Determine the jobs or areas where hearing protection is needed.
  • Provide a selection of hearing protectors and demonstrate their proper use.
  • Monitor the use of hearing protection and make them readily available.
  • Provide training on the hazards of noise and how employees can protect themselves against the effects of noise.

Noise is a significant hazard to workers in many industries. The CDC estimates that four million workers go to work each day in damaging noise. It is important employers recognize the hazards of noise and provide an effective hearing conservation program which should include the proper use of hearing protection.

For more information on this topic and to discuss your company’s safety and industrial hygiene needs callOccuSafe at (214) 662-6005 or visit us at 

OccuSafe Industrial Hygiene & Safety, Inc. provides skills and expertise to recognize, evaluate and control hazards and injuries in the areas of industrial hygiene, occupational safety and health. OccuSafe services companies of all sizes in a range of industries.

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