Hearing Protectors 2009: Rating, Evaluation and the NRR

Even with careful attention to administrative and engineering controls, hearing protection devices often are the first and only choice when it comes to protection from hazardous noise exposure. The good news is that hearing protection devices (HPD) certainly are capable of doing what we expect of them in most cases. Careful selection of the right HPD for the right reasons effectively can protect people in the workplace.

EPA has been responsible for regulating how HPD are labeled and evaluated since the 1970s. The agency is in the process of updating the rule (40CFR211 Subpart B) that governs the noise reduction rating (NRR) for a variety of reasons:

Some HPD on the market today were not even invented when the original rule was promulgated, and the old way of evaluating HPD may not pertain to them. Examples include electronic HPD, such as active noise cancellation earmuffs and level-dependent earplugs (designed to only provide protection in high levels of impulse noise).
The laboratory HPD evaluation system that the NRR is based on is outdated. EPA uses a 1974 procedure; the most recent ANSI revision to that procedure was completed in 2008.
The NRR is not representative of how hearing protectors work in actual field use. That's the reason OSHA applies the 50 percent “derating” for some applications, giving credit for half of the labeled protection when comparing the use of HPD to noise controls.
The EPA system was developed based on C-weighted noise exposure information. Since OSHA requires the use of A-weighted noise exposures for the Hearing Conservation Amendment, very few people collect and use C-weighted exposure information, causing OSHA to subtract 7 dB from the NRR even before the derating described above.
Individual variability is significant. The current NRR process results in a single number, when in reality, individual use techniques and differences in ear canal size and shape result in significant differences in the amount of protection provided. Even in the tightly controlled laboratory data, it is common to see variability among test subjects of 5 dB or more at some test frequencies.

The current proposal under consideration at EPA is to adopt updated test standards and to develop a rating label that reflects the variability that is to be expected from HPD. Rather than a single number NRR, it is likely that EPA will adopt something more akin to their estimated fuel economy labels for new cars.

The basic message is quite simple — depending on how the device is used, performance will vary. Figure I shows how a label reflecting a range of performance could work. Since the federal legislation empowering the EPA to regulate HPD labels uses the term “noise reduction rating,” it is likely that the new rating still will be an NRR — just an NRR that reflects a range of performance rather than a single number.

Based on what we know today, relying on a single number like the NRR for making decision about which HPD are acceptable is not good practice. Differences of 3 dB or less in NRR are inconsequential. Selection decisions based on comfort, ease of use and worker acceptance are far more beneficial than trying to use NRR as the sole indicator of which HPD are the right choice.

While it is EPA's responsibility to manage the testing and labeling process, it is up to OSHA to determine how to apply the EPA labels in practice. It is uncertain at this point how OSHA will use the EPA ratings for compliance purposes. New information on the developing story is available at http://www.nrrupdate.com.

EVALUATION

New technologies are emerging that allow individual fit testing of HPD. This process can go a long way toward improving HPD use by giving workers quantitative feedback about how they use HPD, and how they way they use it can effect performance. Most of the commercially available systems focus on testing earplugs; earmuffs tend to be simpler to use and less variable than earplugs.

Most systems provide a personal attenuation rating (PAR), which is a measure of HPD performance for the worker, given the earplug they use and the way they use it.

There is a range of technologies used to get to the final result. Some involve taking a modified hearing test with earplugs in place, and another hearing test with earplugs out. The difference in how loud a sound must be played in the test system to be perceived by the worker with earplugs in and out indicates how well the HPD is working for them. The FitCheck system, available from Michael and Associates (http://www.michaelassociates.com/fitcheck/fitcheck.htm), is one commercially available system that uses this technology.

Other systems use miniature microphones to measure sound levels inside and outside an HPD while it is in place. This process requires small microphones, and a way to get a microphone or measurement location beneath the earplug while it is in the ear. E-A-Rfit from Aearo Technologies (a 3M company) uses a specially prepared earplug with a measurement channel built in to allow for simultaneous measurement underneath and outside the earplug, with the difference showing how well the earplug is working. Details on E-A-Rfit are available at http://www.e-a-rfit.com.

Loudness balance is the approach taken by the VeriPro system from Sperian (http://www.howardleight.com/veripro). In this approach, workers using special headphones listen to the test system and adjust the volume until sounds are about equal in each ear. Put in one earplug and balance again — the amount that the plugged ear must be turned up to balance the unplugged ear shows how well the earplug is working. Repeat for the other ear to complete the test and generate the PAR.

Individual fit testing can be a great step forward in HPD management, because:

It can help train and motivate employees. By quantifying the difference in HPD performance with different insertion depths and techniques, these systems clearly show workers the importance of proper fit.
It helps train the trainer. Most people who issue HPD have no training in how to fit an earplug. Individual fit testing can help them to see what a good fit should look like, and the steps necessary to get an earplug to fit properly.
It helps with assigning and selecting HPDs. Quantifying HPD protection for individuals allows the selection of devices that are appropriate for the workers' anatomy and noise exposure.
It provides standard-threshold-shift (STS) follow up. OSHA requires that the HPD of people who show hearing loss in the hearing conservation program be re-evaluated for sufficiency and condition. The individual test provides that follow-up with a measure of assurance of sufficient protection.
It determines HPD adequacy/sufficiency. Comparing individual fit testing results to noise exposure information helps determine whether the HPD the worker chooses to use is providing enough protection.
It helps with auditing or comparing groups. Is there more hearing loss in Plant A than in Plant B? Individual fit testing can help determine the reason why.
It demonstrates adequacy of training. Did a worker “get it” during the HPD fitting portion of the hearing conservation training session? If so, it should be reflected in his or her individual fit test.
It provides documentation. These processes build a track record of HPD performance over time that can help determine if hearing loss is related to workplace noise exposure.

HDP are an essential part of effectively managing noise exposure in the workplace. Appropriate selection and application of new technologies like fit testing can greatly improve hearing loss prevention efforts.

Lee D. Hager is a hearing loss prevention consultant for Aearo Technologies, a 3M company. Most of all, he cares about your ears.