Abstract

Background

Global Burden of Disease studies identify hearing loss as the third leading cause of years lived with a disability. Their estimates point to large societal and individual costs from unaddressed hearing difficulties. Workplace noise is an important modifiable risk factor; if addressed, it could significantly reduce the global burden of disease.

In practice, providing hearing protection devices (HPDs) is the most common intervention to reduce noise exposure at work. However, lack of fit of HPDs, especially earplugs, can greatly limit their effectiveness. This may be the case for 40% of users. Testing the fit and providing instructions to improve noise attenuation might be effective. In the past two decades, hearing protection fit‐test systems have been developed and evaluated in the field. They are called field attenuation estimation systems. They measure the noise attenuation obtained by individual workers using HPDs. If there is a lack of fit, instruction for better fit is provided, and may lead to better noise attenuation obtained by HPDs.

Objectives

To assess: (1) the effects of field attenuation estimation systems and associated training on the noise attenuation obtained by HPDs compared to no instruction or to less instruction in workers exposed to noise; and (2) whether these interventions promote adherence to HPD use.

Search methods

We used CENTRAL, MEDLINE, five other databases, and two trial registers, together with reference checking, citation searching, and contact with study authors to identify studies. We imposed no language or date restrictions. The latest search date was February 2024.

Selection criteria

We included randomised controlled trials (RCTs), cluster‐RCTs, controlled before‐after studies (CBAs), and interrupted time‐series studies (ITSs) exploring HPD fit testing in workers exposed to noise levels of more than 80 A‐weighted decibels (or dBA) who use hearing protection devices. The unit 'dBA' reports on the use of a frequency‐weighting filter to adjust sound measurement results to better reflect how human ears process sound. The outcome noise attenuation had to be measured either as a personal attenuation rating (PAR), PAR pass rate, or both. PAR pass rate is the percentage of workers who passed a pre‐established level of sufficient attenuation from their HPDs, identified on the basis of their individual noise exposure.

Data collection and analysis

Two review authors independently assessed study eligibility, risk of bias, and extracted data. We categorised interventions as fit testing of HPDs with instructions at different levels (no instructions, simple instructions, and extensive instructions).

Main results

We included three RCTs (756 participants). We did not find any studies that examined whether fit testing and training contributed to hearing protector use, nor any studies that examined whether age, gender, or HPD experience influenced attenuation. We would have included any adverse effects if mentioned by the trial authors, but none reported them. None of the included studies blinded participants; two studies blinded those who delivered the intervention.

Effects of fit testing of HPDs with instructions (simple or extensive) versus fit testing of HPDs without instructions

Testing the fit of foam and premoulded earplugs accompanied by simple instructions probably does not improve their noise attenuation in the short term after the test (1‐month follow‐up: mean difference (MD) 1.62 decibels (dB), 95% confidence interval (CI) ‐0.93 to 4.17; 1 study, 209 participants; 4‐month follow‐up: MD 0.40 dB, 95% CI ‐2.28 to 3.08; 1 study, 197 participants; both moderate‐certainty evidence). The intervention probably does not improve noise attenuation in the long term (MD 0.15 dB, 95% CI ‐3.44 to 3.74; 1 study, 103 participants; moderate‐certainty evidence).

Fit testing of premoulded earplugs with extensive instructions on the fit of the earplugs may improve their noise attenuation at the immediate retest when compared to fit testing without instructions (MD 8.34 dB, 95% CI 7.32 to 9.36; 1 study, 100 participants; low‐certainty evidence).

Effects of fit testing of HPDs with extensive instructions versus fit testing of HPDs with simple instructions

Fit testing of foam earplugs with extensive instructions probably improves their attenuation (MD 8.62 dB, 95% CI 6.31 to 10.93; 1 study, 321 participants; moderate‐certainty evidence) and also the pass rate of sufficient attenuation (risk ratio (RR) 1.75, 95% CI 1.44 to 2.11; 1 study, 321 participants; moderate‐certainty evidence) when compared to fit testing with simple instructions immediately after the test. This is significant because every 3 dB decrease in noise exposure level halves the sound energy entering the ear.

No RCTs reported on the long‐term effectiveness of the HPD fit testing with extensive instructions.

Authors' conclusions

HPD fit testing accompanied by simple instructions probably does not improve noise attenuation from foam and premoulded earplugs. Testing the fit of foam and premoulded earplugs with extensive instructions probably improves attenuation and PAR pass rate immediately after the test. The effects of fit testing associated with training to improve attenuation may vary with types of HPDs and training methods. Better‐designed trials with larger sample sizes are required to increase the certainty of the evidence.

Author(s)

Thais C Morata, Wei Gong, Christina Tikka, Alessandra G Samelli, Jos H Verbeek

Abstract

Plain language summary

Do earplug fit tests plus training on how to fit earplugs help people who work in noisy environments?

Key messages

• Earplug fit testing paired with simple instructions for properly fitting earplugs probably does not improve noise reduction.

• Earplug fit testing paired with extensive instructions probably improves protection against noise compared to receiving no instructions or simple instructions.

Why are noisy work environments a problem?

Noise exposure at work is associated with serious health conditions, from hearing loss and tinnitus (ringing or buzzing sounds in the ears without an external source), to injuries and heart/blood vessel problems. Hearing protection devices (HPDs) – such as earplugs and earmuffs – are commonly used to reduce people’s noise exposure at work. Especially for earplugs, it is well‐known that many workers struggle to insert them properly into the ear canal. Ill‐fitting earplugs will not protect one's hearing sufficiently.

What are hearing protection fit‐test systems?

Hearing protection fit‐test systems are technologies that measure the extent to which noise is reduced (attenuated) at the ear for a person wearing earplugs or another hearing protection device.

What did we want to find out?

We wanted to find out if hearing protection fit testing plus training to wear earplugs (or other protection devices) properly is effective at reducing noise experienced by workers, and whether they continued to wear earplugs consistently. We also wanted to find out if people’s age, gender, earplug type, and experience of using hearing protection devices made any differences to the effectiveness of fit testing and training.

What did we find?

We found 3 studies involving 756 participants. They examined the effects of giving people simple or extensive instructions for fitting their hearing protection devices (all the studies used foam or premoulded earplugs) together with fit tests that measured how much noise was reduced. We did not find any studies that examined whether fit testing and training promoted consistent hearing protection use, nor any studies that examined whether age, gender, or hearing protection experience influenced noise reduction.

Main results

• Earplug fit testing accompanied by simple instructions probably does not improve personal attenuation ratings (PAR) from foam and premoulded earplugs compared to no instructions.

• Fit testing with extensive instructions probably improves workers’ protection against noise, measured immediately after the test and training, compared to having no or simple instructions. An increase in protection of about 3 dB will halve the sound's power at the ear, increasing the protective effect of earplugs.

• The effects of fit testing may depend on the type of hearing protection device and training methods.

• None of the included studies measured or reported harmful effects from fit testing and training, and we did not think it was likely we would find any.

What are the limitations of the evidence?

We have moderate to low confidence in the evidence. Our confidence was reduced because the studies were small, and we had concerns about how participants were allocated to groups.

How up‐to‐date is the evidence?

The evidence is current to February 2024.

Author(s)

Thais C Morata, Wei Gong, Christina Tikka, Alessandra G Samelli, Jos H Verbeek

Reviewer's Conclusions

Authors' conclusions 

Implications for practice 

We found that hearing protection device (HPD) fit testing associated with simple instructions probably does not improve the personal attenuation rating (PAR) for foam and premoulded earplugs in the short and long terms, compared to no instructions. Therefore, in the workplace, simply providing HPDs with no or with simple instructions probably does not ensure that noise‐exposed workers achieve the needed levels of protection from the HPDs they wear.

Fit testing earplugs accompanied by extensive instructions probably improves the PAR values from foam and premoulded earplugs by 8.6 decibels (dB) (95% confidence interval 6.3 to 10.9 dB) compared to no instructions at immediate follow‐up. This is a relevant increase in protection: every 3 dB decrease in noise exposure level halves the energy entering the ear. Workers who are using foam and premoulded earplugs whose fit is insufficient probably need extensive instructions on how to wear their earplugs correctly to achieve sufficient noise reduction from the earplugs they wear.

There were no studies that evaluated workers' adherence to wearing HPDs, and there was no evidence on how often the test and training would need to be repeated to maintain the results.

Implications for research 

To increase the certainty of the evidence, more randomised controlled trials (RCTs) of fit testing HPDs with instructions on how to improve their fit are needed. Preferably, first the fit test should be performed, and then workers who have insufficient attenuation should be randomised to receive simple instruction, extensive instruction, or no instruction. This will avoid a ceiling effect from workers who already have sufficient attenuation, as noted in one of the included RCTs (Murphy 2007). In addition, RCTs that evaluate if and how often fit tests should be repeated are needed. It is conceivable – and supported by uncontrolled studies – that the effect of instructions wears off and should be repeated. This review shows that RCTs are possible and feasible. Given that RCTs have a lower risk of bias than other study designs, updates of the current review should only include RCTs.

Better characterisation of noise exposure conditions of the participants would allow the extrapolation of findings across studies. Noise levels and work tasks can vary widely, which suggests different needs in terms of noise attenuation. Earplugs can become "loose" with time and require periodic re‐inserting (Nélisse 2012), but, so far, few field studies have examined possible fluctuations in PAR values over work shifts (Gong 2023; Nadon 2021; Wu 2016). In theory, current technologies could address this issue by providing continuous monitoring of an individual’s actual noise exposure with HPD. In practice, however, this approach has had limited implementation so far (Voix 2022).

To effectively facilitate the implementation of HPD fit‐testing interventions, studies analysing the cost‐effectiveness of HPD fit testing associated with training, as well as evaluating the HPD fit‐testing integration into hearing loss prevention programmes are especially needed. Studies on the effects of fit‐test interventions should not necessarily be restricted to hearing outcomes. One study reported that using three HPD fit‐test frequencies (500, 1000, and 2000 Hz) was sufficient for accurately estimating workers' PAR (Federman 2016), and some studies reported that different PARs were estimated using different test methods (Kabe 2012; Neitzel 2006; Samelli 2015). Therefore, studies examining the specifics and suitability of test protocols are also needed.

Research is needed to address the quality concerns identified in the present review (randomisation, detailed description of the study population, of their exposures, testing procedures, and publication of a protocol before data collection). High‐quality studies would offer greater certainty on implementation strategies that could lead to the protection of workers from noise exposure.

Currently, adverse effects are generally not recorded in the literature. This may be because investigators lack a mechanism to identify them. Future studies should report any adverse effects if they happen.

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