NRR: Now Really Relevant

In an effort to bring the noise reduction rating for hearing protection more in line with real-world usage, the Environmental Protection Agency is expected to announce a change in rating systems very soon. Are you ready?

For over 30 years, the U.S. Environmental Protection Agency (EPA) has used the noise reduction rating (NRR) to measure the attenuation of hearing protector devices (HPD). Based upon idealized laboratory testing, the NRR has been subjected not only to criticism for being too generous in predicting hearing protector attenuation, but also to a variety of de-rating schemes designed to compensate for variations in individual fit.

While it still will be known as the noise reduction rating and still be based on laboratory tests, the changes EPA is expected to make to the NRR will reflect a range of expected protection, instead of a single-number estimate. The lower number of the range will indicate how much attenuation minimally trained users can expect, while the higher number will indicate how much attenuation highly motivated, trained users can expect to achieve. Like EPA's new mileage estimation for cars, which takes into consideration a variety of usage factors, the new NRR also will consider the human factors involved with HPD use — specifically training and fit.

While this announcement no doubt will raise many questions before a final rule is enacted, safety professionals can begin to prepare for the changes by taking this opportunity to reassess the effectiveness of their hearing conservation programs (HCP) and perhaps integrate some new technologies just now becoming available. Here are three key elements to consider:


The establishment of any hearing conservation program is based on noise exposure levels, including both area noise levels measured with handheld sound level meters and personal exposure levels measured with dosimeters worn on a worker's collar or hard hat. OSHA requires a baseline recording of noise exposure at the start of any HCP, and follow-up measurements with any change in processes or equipment. Noise levels should be outlined on noise maps and posted throughout each facility.

Personal dosimetry provides a measure of each worker's ambient noise exposure level, but it does not provide any information on individual noise dose, or exposure levels while wearing hearing protection. However, recent advances in technology now make it feasible to measure the actual level of protection provided by HPDs while workers are on the job. This new style of in-ear dosimetry, available with systems such as QuietDose from Howard Leight, records daily noise exposure levels for workers under their hearing protectors to provide an accurate and complete measurement of personal noise dose.

In-ear dosimetry offers a number of benefits. By measuring and recording a worker's actual noise dose, with and without protection over their entire work shift, it provides real-time monitoring and alerts users when their individual noise dose approaches or exceeds safe limits. This not only helps workers to better identify when and where they must wear hearing protection, it also allows safety managers to more efficiently deploy workers, especially in extreme noise where dual protection often is required.


Many safety managers routinely ask, “How much attenuation do my workers achieve with their HPDs?” The expected EPA ratings change in NRR provides an ideal opportunity to perform fit testing on workers' earplugs to determine if they are receiving optimal protection for their noise environment. There are several new fit testing systems available, including VeriPRO from Howard Leight, EARFit from Aearo Technologies and FitCheck from Michael & Associates.

Fit-testing systems can help determine the actual real-world attenuation workers receive from their earplugs, taking the guesswork out of the hearing protector selection process. Fit testing gives workers the information they need to select hearing protection based on their personal attenuation rating (PAR) using their actual earplugs in their actual work environment. This information helps safety managers determine whether their workers are receiving optimal protection, require additional training on how to fit their earplugs or need to try a different model. Fit testing also confirms the value of offering choice. Hearing conservation program managers who only offer one model of earplug to noise-exposed workers unknowingly rob themselves of one of their best tools for preventing hearing loss: a comprehensive selection of protectors.


With this change in NRR, safety professionals should take time to evaluate the efficacy of their worker hearing safety training programs. OSHA's 29 CHR 1910.95 provides an outline of content to be included in training sessions (effects of noise exposure; use/selection/fitting HPDs; audiometric test procedures), though no guidelines are offered on depth or presentation of the information. Most hearing conservation training is performed in group sessions and is conducted by safety managers, industrial hygienists, occupational nurses and other hearing conservation professionals using videos, posters and other educational and motivational materials.

However, recent studies on the real-world attenuation of hearing protectors — i.e., those worn on the job — suggest that one-on-one training may be more effective. It long has been known that the best time to educate and motivate workers on the use of hearing protection is immediately after their audiometric test, when they actually can see their own results. In a recent earplug fit-testing study1, over 100 workers were evaluated with earplug fit testing during their standard shift. Workers were not pre-screened, and were tested with their own earplugs that they routinely wore on the job, with no modifications and no additional instruction.

The results showed a direct correlation between earplug fit and effective attenuation: fully one-third of workers achieved attenuation higher than published NRR for their earplugs; another third achieved attenuation within 5 dB of those ratings; and only the bottom one-third had attenuation that was more than 5 dB below published NRRs.

In analyzing the factors that contributed to good earplug fit, and hence, good attenuation, only one-on-one training had a strong correlation. The more often a worker had received individual training in the proper use of hearing protectors, the higher the probability that worker would achieve a good fit. In addition, the National Hearing Conservation Association (NHCA) and OSHA have endorsed fit testing as a recommended tactic in reducing occupational hearing loss as well as a metric to assess a HCP's overall effectiveness.2

Renee S. Bessette is marketing manager for Sperian Hearing Protection LLC.


  1. Howard Leight Acoustical Laboratory. “Assessing Fit Effectiveness of Earplugs.”

  2. HCA/OSHA Alliance. “Hearing Protection-Emerging Trends: Individual Fit Testing,” 2008.

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