The adoption of individual hearing protector fit testing continues to gain traction in industry as a powerful tool for helping to improve occupational hearing conservation programs. The driving force behind this growing trend is the ability to accurately estimate the attenuation a given hearing protector provides for an individual. This is in contrast to the traditional approach of relying solely on single number ratings, such as the Noise Reduction Rating (NRR) used in the U.S. or Single Number Rating (SNR) used in Europe. 

The benefits of hearing protector fit testing are being realized by employers and employees alike. Hearing protector fit testing is a recommended best practice in multiple countries and is now mandated by the U.S. Department of Defense for certain categories of personnel. The following text describes the recent evolution of hearing protection fit testing, and the use of these systems and their adoption by industry, regulators and health advocacy groups. 

What Is It?

Hearing protector fit testing is the measurement of the amount of noise reduction (or attenuation) a hearing protector provides as it was fitted by a specific individual. This real-world measurement is referred to as a “Personal Attenuation Rating” or PAR. The purpose of hearing protector fit testing is to verify that the attenuation achieved is appropriate for the individual using it and to help validate which hearing protectors can be used successfully in specific work environments.

Why It’s Needed

Until recently, the most practical way for employers to quantify the amount of noise reduction a hearing protector provided to an individual in the workplace, as required by many regulatory agencies globally, was to use a “single number rating” based on a laboratory test. Examples include the Noise Reduction Rating (NRR) used in the U.S., Single Number Rating (SNR) used in Europe, and the Sound Level Conversion (SLC80) used in Australia and New Zealand. 

Historically, studies have shown that, although these ratings may be a simple and convenient way to select hearing protectors, they are not always good at predicting the attenuation individuals will receive when using the hearing protector in the workplace. Evidence shows there can be a large range in attenuation achieved by individuals for the same model of hearing protector. A 2008 study shows the wide distribution of Personal Attenuation Ratings (PARs) in a population of workers. Some workers receive more attenuation than the NRR would predict, while others receive much less. (Figure 1). 

The main sources of this variability include individual differences in training and proficiency at inserting hearing protectors properly. Multiple studies have shown that a portion of a population does not achieve the necessary amount of attenuation on the first fit test. A 2013 study found that of 327 experienced users tested, 17% had to be re-trained before achieving an adequate fit (Figure 2). Another key source of fit variability is due to differences in individual ear canal size (too big or too small) or shape (sharp bends), such that those workers need to switch to a different model before achieving adequate fit. 

How It Works 

There are a variety of Field Attenuation Estimation System (FAES) technologies available on the market that are intended to assess the attenuation provided by a given fit of a hearing protector on an individual user. Attenuation is measured at various frequencies. Some systems then use the attenuation values to compute a PAR. The test methods can be divided into two different categories: (1) Subjective methods depend on the listener’s response, and (2) objective methods measure a physical quantity of sound pressure level. Three fit testing technologies available today include: 

Field-REAT (subjective). Field-REAT (Real Ear Attenuation at Threshold) is similar to an audiometric hearing testing. In a quiet setting, the threshold of hearing (the softest level a person can hear a test signal), is measured without the hearing protector in place, and then again with the hearing protector. The difference between the two thresholds is attributed to the attenuation provided by the hearing protector. This procedure must be repeated for each frequency and then the attenuation values can be used to calculate PAR.

Loudness Balancing (subjective). Loudness balancing is a unique approach that requires the worker to compare the sound level of the test signal heard in one ear compared to the sound level heard in the other ear. The listener’s task is to adjust the loudness of the sound in one ear to match the level in the other ear. This is done both with and without a hearing protector in place. Since loudness balancing is done at a louder level than the hearing threshold, the test can be conducted with more background noise in the test room than Field-REAT.   

Field Microphone-in-Real-Ear (objective). Also known as F-MIRE, this method uses small microphones to measure the sound pressure level both outside and inside of the ear at the same time. 

The microphone assembly is attached to specially-probed hearing protectors that are fitted by the worker. F-MIRE is considered an objective measurement system since it does not depend on a response from the test subject. This allows both ears to be tested across multiple frequencies simultaneously in just a few seconds. It also allows for normal background noise (up to 85 dBA) to be present during the testing as compared to subjective FAES systems, which require quieter test environments. Some F-MIRE systems can also test earmuffs. 

There are many factors to consider when selecting a technology to use. A recent National Occupational Research Agenda (NORA) publication provides guidance on hearing protector fit testing and suggests factors to consider when selecting a fit test system, include:

•    The types hearing protectors used.
•    The amount of background noise present.
•    Time and resources available.
•    How data and results will be used.

System Performance

The ANSI/ASA S12.71-2018(R2022) standard, “American National Standard Performance Criteria for Systems that Estimate the Attenuation of Passive Hearing Protectors for Individual Users,” contains criteria that fit-test system manufacturers should apply to ensure accurate measurements and transparent reporting of results. A main requirement of this standard is that fit-test systems be evaluated by comparing their attenuation estimates to attenuation measured using the laboratory “gold standard,” real ear attenuation at threshold (REAT) method. 

The standard recognizes various technologies and methods for conducting hearing protection fit testing and differentiates minimum requirements for a fit-test system based on the method it uses. This standard is the first and only one of its kind worldwide. With a standard to reference, regulators may recommend use of systems that are in conformance with the standard.

Supported by Research 

Recent research shows many advantages to hearing protector fit testing, including:

1.    Reduced likelihood of hearing loss. A study titled “A Mixed-Methods Assessment of Hearing Conservation Program Effectiveness” looked at a company’s expenditures for different aspects of a company’s Hearing Conservation Program at 13 different facilities. They found that the four facilities that implemented hearing protector fit-testing had significantly lower rates of age-corrected hearing loss— Standard Threshold Shift (STS).

Fit-testing – a best practice not required by any current HCP regulation – may be a high-impact expense, i.e., one that can result in an outsized reduction in [Noise-Induced Hearing Loss] NIHL. A variety of fit-testing technologies ... appear to be becoming more integrated into hearing conservation programs that are based on best practices, rather than simple compliance with OSHA regulations.”

— Neitzel; Saylor et al, NHCA Spectrum ∙ Vol. 34 (3) ∙ 
December 2017

2.    Improved use of hearing protectors. A 2015 study of offshore oil rig inspectors found that 40% of workers were not getting sufficient attenuation on the initial fit test. Without the PAR results, these workers would not have been identified as being at risk for developing noise-induced hearing loss (NIHL). The authors concluded that the labeled Noise Reduction Rating (NRR) has little predictive value in determining the level of noise reduction a worker receives.

“Forty percent or more of the workers were not getting sufficient attenuation from their hearing protectors. Through training and re-fitting, NIOSH was able to help 85% or more of the workers receive the appropriate amount of noise reduction.”
“Without fit-testing, nearly half of the oil rig inspectors would have been at risk for developing noise-induced hearing loss from their job exposures.”

— Murphy, Themann, Taichi, Murata, US Centers for Disease Control and Prevention, NIOSH.  July 2015

3.    Ability to evaluate attenuation when combined with other Personal Protective Equipment (PPE). When using earmuffs, any interference with the seal of the cushion to the head can reduce the attenuation. This can be caused by a variety of objects, such as baseball caps, hairnets, the temples of safety eyewear, and other types of obstructions. Fit testing earmuffs can be done while wearing the usual combination of PPE to help identify causes of sound leakage and troubleshoot options to ensure the worker is adequately protected.

“Earmuffs are often selected as the preferred type of hearing protector due to ease-of-use and durability. On the other hand, earmuffs are more susceptible than earplugs to the interference and compatibility issues provided by other PPE when worn with earmuffs.”

— Macedo, Gorman, Berger. Australian Institute of Occ. Hygienists, 34th Annual Conference & Expo, December 2016

Key Benefits 

Why implement hearing protector fit testing? Incorporating fit testing into a Hearing Conservation Program (HCP) can offer a multitude of benefits. For example, conducting hearing fit testing helps employers to: 

1.  Identify workers with poorly fitting hearing protectors before the worker develops hearing loss.

2.  Create a unique training opportunity where employees can experience how correctly fitting hearing protectors impacts protection:

·    PAR results are seen immediately following test.
·    One-on-one training targets the specific fitting issues observed.
·    PAR improvements are seen immediately after re-training and re-inserting the earplug correctly.
·    Workers can feel and hear the difference when their hearing protectors are properly inserted.

3.  Refine hearing protector selection based on individually validated attenuation levels.

4.  Supplement hearing loss intervention strategies by helping to ensure employees with hearing shifts are properly trained and protected.

5.  Implement proactive, best practices approach to hearing loss prevention.

6.  Gain documentation of results that many fit-testing systems provide—which can be used for training and for analyzing if any changes need to be made to the hearing conservation program.

Highly Recommended 

The use of hearing protector fit testing is a recommended best practice by:

·    US Occupational Safety & Health Admin (OSHA)

·    National Institute of Occupational Safety & Health (NIOSH)

·    National Hearing Conservation Association (NHCA)

For many years, NIOSH has stated that workers should be individually fit-tested for hearing protection devices. However, due to the lack of commercially available fit test systems, NIOSH developed and recommended a method for derating the NRR to estimate worker hearing protector attenuation. 

Years of research has demonstrated that derating the NRR is an ineffective way to assess proper hearing protector fit, and that training and fit testing are needed to improve “as worn” attenuation. NIOSH now recommends that individual fit testing be utilized in lieu of the NIOSH hearing protector de-rating scheme.

“Research studies have suggested that when individuals are involved in the fitting process and receive positive feedback on the proper fit of their earplug, they will be more likely to have a positive attitude about protecting their hearing and will be more apt to use hearing protection correctly and consistently in the workplace. This positive outcome should result in reducing noise-induced hearing loss in the workplace.”

— Best Practice Bulletin:  OSHA, NIOSH and NHCA Alliance

“NIOSH recommends employers use individual, quantitative fit testing to evaluate the attenuation received by workers from their hearing protection devices.”

“Employers should integrate individual fit testing into their hearing loss prevention programs.”
— NIOSH Science Policy Update

Helps with OSHA Compliance

To be sold in the U.S., a hearing protector must be tested according to a standardized method and labeled with the NRR. OSHA’s noise standard 29 CFR 1910.95 requires employers to offer noise-exposed workers hearing protectors that can adequately reduce the hazardous noise exposure. The allowable methods for calculating the sufficiency of hearing protectors are included in Appendix B of the standard. Since the standard was written before the availability of fit-testing technology, using PAR values are not included in Appendix B. If the noise exposure is high enough that the noise reduction calculated using one of the allowable methods in Appendix B is insufficient, then feasible noise controls and/or dual hearing protection should be used.

However, an OSHA Letter of Interpretation states that fit testing can be used to meet the training requirements of section 1910.95 (i)(4) and the requirement to ensure proper initial fitting in section (i)(5)10:

OSHA 29 CFR 1910.95(i)(4): The employer shall provide training in the use and care of all hearing protectors provided to employees.

OSHA 29 CFR 1910.95(i)(5): The employer shall ensure proper initial fitting and supervise the correct use of all hearing protectors.

Although OSHA does not require fit testing, this interpretation letter specifically recognizes fit testing as an acceptable way to fulfill the initial fitting requirement. More information on OSHA’s guidance for using fit testing can be found in the OSHA Technical Manual, Section III, Chapter 5. (https://www.osha.gov/otm/section-3-health-hazards/chapter-5).

Summary

The rapidly increasing availability of real-world fit-test data is shedding light on just how unreliable single number ratings are for predicting noise attenuation for individuals. A growing body of published research shows that fit testing has the potential to improve the effectiveness of hearing conservation efforts. This evidence, along with acceptance by regulatory and occupational health agencies as a best practice, makes it clear that hearing protector fit testing is here to stay.