Test for determining the effectiveness hearing protection devices
Hearing protector fit-testing measures the degree of noise reduction obtained from an individual wearing a particular hearing protection device (HPD) - for example, an earplug or earmuff. Such measurements are necessary because noise attenuation varies across individuals (and sometimes can be close to zero) due to anatomical differences and inadequate training as to the proper wear and use.[2] Labeled HPD attenuation values (for example, the Noise Reduction Rating, or NRR) are average values that cannot predict noise attenuation for an individual; in addition, they are based on laboratory measurements which may overestimate the noise reduction obtained in the real world.[3]
Hearing protection devices such as earplugs or earmuffs must be worn correctly for the wearer to be protected from noise.[4] Correct use of hearing protection includes:
Choosing the most appropriate hearing protection device, both with appropriate level of attenuation and appropriate fit for the individual.[5] Ideally, the device should limit the sound intensity that reaches the ear to levels below 85 dBA. If the attenuation does not limit the noise levels to that level, other alternatives should be sought. If the attenuation is greater than that, it can also interfere with the HPD use by making it difficult to hear important sounds.[6]
Wearing or inserting the hearing protection device correctly so it seals the wearer's ear canal, using the "roll-pull-hold" method for foam earplugs, and ensuring earmuffs create an unbroken seal around each ear.[7]
Fit-testing hearing protection can facilitate an appropriate choice of hearing protection, and allow for the professional administering the fit-test to train users on proper techniques for wear.[8][9][10][11][12][13]
Requirements and Recommendations for HPD Fit Testing
Effective March 31, 2023, the Alberta Government added a requirement that employers fit test each employee who wears HPDs.[16] A trend towards recommending HPD fit-testing as a best practice is emerging in the European Union and the USA.[17][18]
Fit-testing methods
Fit testing is typically carried out using one of the available fit-testing hardware and software systems (also known as field attenuation estimation system (FAES).[19] Although all fit-testing systems measure the amount of sound reduction provided by hearing protection devices, different systems use different approaches to making this measurement.
The different methods[20] used to measure the attenuation provided by HPDs are as follows:
Real-ear attenuation at threshold (REAT)
REAT is the most commonly used type of fit-testing technology used in commercial systems. REAT systems are modeled on the "gold-standard" approach to measuring hearing protector attenuation as defined in acoustic standards such as
ISO
4869-1. This approach measures the difference in auditory (hearing) thresholds without hearing protection (unoccluded) and with hearing protection (occluded). Differences in occluded and unoccluded thresholds across one or more test frequencies are used to calculate the noise reduction. REAT systems rely on the subjective response of the person being tested to determine auditory thresholds much like a hearing test where the subject indicates when sound is heard at various frequencies.
According to the acoustic standards, REAT testing of hearing protection devices must be tested in an acoustic chamber with a diffuse sound field. Because such chambers are not mobile, portable fit-testing systems employing sound-isolating headphones have been developed to test earplugs.[22] For noncritical screening, REAT can be performed using a web browser and simple audio devices.[23]
Loudness balance
This method first has the subject listen to tones with headphones and "match" loudness between both ears until tones sound equally loud on both sides. Then an earplug is placed in one ear while the baseline procedure is repeated to match loudness in both ears. The increase in loudness required to balance represents the attenuation achieved in that ear. The second earplug is then placed in the other ear and the procedure is repeated a third time. The required increase in loudness this time represents the noise reduction achieved in the second ear. The loudness balance fit-testing approach provides individual personal attenuation ratings for each ear.[24]