Many users in a group may obtain values close to the labeled NRR, but a substantial portion typically do not. The only way to determine a person’s attenuation level is with a fit test system.

    * By Lee D. Hager, Pegeen Smith
    * Sep 01, 2010

Editor’s note: Fit testing is not just for respirators. It is a good way to determine whether that worker’s hearing protector is adequately attenuating the noise to which he or she is exposed, especially in high-noise situations, the authors note in the following Q&A.

Q: Why should I consider fit testing hearing protectors?

A: Individual fit testing of hearing protection devices (HPDs) can lead to significant improvements in several aspects of your hearing conservation program.

* Train and motivate employees. Providing workers with a quantitative measure of how well their HPDs can work can help to ensure they understand proper use.

* Train the trainer. Most HPDs are distributed by people with limited experience in HPD fitting. Fit testing helps educate those who perform fit checks on what a proper HPD fit looks, sounds, and feels like to enhance their ability to train others.

* Helps select HPDs. Differences in ear canal size and shape and differences in a worker’s ability to prepare an ear plug for use are reflected in individual fit test results. Fit testing can help find the HPD that is right for the worker and noise environment.

* Provide standard-threshold-shift (STS) follow up. When hearing loss of a particular configuration is found in a noise-exposed worker, OSHA requires that the HPD used by that worker be assessed to determine whether it provides adequate noise reduction for the worker’s exposure. Fit testing can help provide the required OSHA follow-up.

* Determine HPD adequacy/sufficiency. Especially in high-noise situations, it can be important to make sure the HPD is providing enough noise reduction to lower the worker’s noise exposure sufficiently. Comparing noise exposure data with the HPD fit testing data helps employers make this determination for each individual employee.

* Audit departments. It can be useful in hearing conservation program administration to compare hearing loss results from different groups, sites, or departments. Fit testing is another piece of the puzzle that may help to identify individual employees who need additional assistance to wear hearing protection successfully.

* Demonstrate adequacy of training. Fit testing can be a quantifiable way to make sure trainees can properly fit and use their HPDs after training. Conducting fit testing after training is one way to document whether or not the training was effective.

* Provide documentation. Fit testing reports may be used to document how well the employee fitted the HPDs at the time of the test and which HPD was selected for that employee.

Q: How is fit testing done?

A: Some fit testing systems are based on subjective responses from the person being tested, while other systems measure the fit objectively. Fit testing systems that are based on subjective measurement techniques typically require the employee to participate in a hearing test with the HPD in place (occluded) and a second hearing test with the HPD out (unoccluded).

It may be a hearing test like the one conducted as part of the hearing conservation program, or it may be a different type of hearing test. Although the specifics vary from one system to the next, most, if not all, of the subjective fit test systems require the test subject to listen and respond to a sound signal or “auditory stimulus.”

By contrast, objective fit test techniques involve a direct measure of sound pressure level under the HPD while it is in the ear, for example, taking direct measurements of sound pressure levels inside and outside the ear canal while the HPD is in place and comparing those measurements to determine how much noise reduction the HPD provides.

Q: What are some of the barriers to using these technologies?

A: Subjective systems are just that: subjective. The systems depend on the employee to reliably and consistently respond to the test sounds and are subject to all of the variability that would be expected from a hearing test, such as background noise, employee cooperation, etc. Typically, audiologists are very pleased to obtain test-retest results within 5 dB for hearing tests in industrial settings. The accuracy of subjective fit tests could be expected to be no better.

Objective systems require that a measurement microphone be able to access the sound pressure level in the ear canal while the HPD is in place, using special test ear plugs equipped with a sound tube that can accommodate a measurement microphone. The system generates a test signal and performs all necessary measurements so the employee does not have to respond to the test sound.

Q: What kind of information can I expect to get from these systems?

A: Most systems generate a Personal Attenuation Rating (PAR) that reflects how much noise reduction the HPD is providing as it was fitted that day. Because there is no standardized way to calculate PAR, each system may use a different approach, and the results may not be comparable among systems.

Q: Is a PAR the same as an NRR?

A: No. The noise reduction rating (NRR) printed on the label of the HPD is intended to provide an estimate of the average amount of noise reduction a group of individuals might obtain when wearing a particular hearing protector. These ratings are based on a small group of test subjects who fit the devices in a laboratory setting. Unfortunately, it is not possible to predict the noise reduction obtained by an individual worker from the average noise reduction obtained by a group of test subjects. The PAR represents the noise reduction obtained by the individual worker during a given testing session, rather than a test panel.

Q: Is the employee’s fitting technique the only variable in hearing protector fit?

A: No. Every employee is slightly different. Even though gender, ethnicity, and age may influence the size or shape of ear canals, only a fit test can determine whether a particular HPD is right for that specific ear. In addition, human factors come into play. For a worker with dexterity issues, the need to prepare an HPD before use (for example, by rolling down a foam ear plug) may make it difficult to get enough noise reduction from the HPD for that worker.

Q: Is the noise reduction rating (NRR) on the label a reliable way to determine what level of noise reduction people are getting?
A: No. Research findings, including new research with the E-A-Rfit™ System, indicate the amount of noise reduction people obtain from their choice of HPD varies widely. While many users in a group may obtain values close to the labeled NRR, a substantial portion typically do not. The only way to determine the level of attenuation a person is receiving is with a fit test system. The reasons individuals fail to achieve NRR levels of protection are manifold due to such factors as fitting technique, motivation to wear the device correctly, and individual variation in ear canal anatomy that may influence the ability of the ear plug to fit their specific ear canals.
This article originally appeared in the September 2010 issue of Occupational Health & Safety.

About the Authors

Lee D. Hager is Hearing Loss Prevention Consultant for Sonomax Hearing Healthcare, Inc.

Pegeen Smith, MS, R.N., is a certified occupational health nurse who works for Technical Service at 3M Company. She is the Product Specialist for the E-A-Rfit™ Validation System and the leader of the Global E-A-Rfit™ Technical Service Team for 3M. She trains companies interested in the E-A-Rfit™ Validation System and assists them with the integration of this technology into their hearing conservation program.