Training in the proper use of earplugs: An objective evaluation

1 Introduction

It is known that noise is a main source of environmental pollution [1] and a key risk in the workplace. Occupational noise can cause hearing loss, impaired speech intelligibility and tinnitus and can cause or enhance various other extra-auditory problems, such as sleep disorders, discomfort, stress, fatigue, irritability, increased blood pressure, difficulty working and changes in attention and concentration [1–3].

In occupational health, control measures should be applied in a hierarchical order. Measures that eliminate the source of the noise are thus the most desirable and must be put in place first. During the period before the noise is effectively reduced by implementation of engineering controls, or when engineering or administrative controls are not feasible, then individual measures should be used, i.e., the use of hearing protection devices (HPDs). However, despite there being a general consensus on this matter, strategies to reduce workplace noise are often limited to the provision of HPDs [3–6].

The supply of these devices alone does not guarantee effective hearing protection, as they do not always achieve the required attenuation for a given work situation. Previous studies that quantified the attenuation capacities of various HPDs did not find any correlation between the attenuation provided by the HPDs in the field and values obtained in the laboratory, with the latter exceeding the attenuation values recorded in the field [7–10].

Discrepancies between results obtained in the laboratory and the field are caused by a number of variables associated with the HPD itself, such as its size and material [11], as well as variables pertaining to the user, such as physiological and anatomical factors [12], acceptance (comfort), motivation to use the HPD, proper fit of the device, duration of use [13–15] and the working environment (noise level, activity and environmental conditions) [4, 16–19].

It is important to note that some of the variables mentioned are closely linked with the training provided to HPD users [20, 21]. Previous studies have reported that the use of HPDs in properly implemented hearing conservation programs (HCPs) is associated with reduced hearing loss. However, more consistent evidence is still required regarding other elements of HCPs, including the question of the effect of worker training on the effectiveness of these programs [3, 22].

To monitor the differences between predicted attenuation and the attenuation obtained in the workplace, which can compromise the effectiveness of HCPs, some authors have suggested that individual and objective evaluations of HPDs should be routinely performed [8, 23].

Individual hearing protector fit tests include the field microphone-in-real-ear (F-MIRE) method, in which objective measurements are obtained using two microphones, one located within the external auditory canal (EAC) and the other near the pinna. In addition to its objectivity, another benefit of this method is its speed, as the two microphones simultaneously capture the HPD’s external and internal sound pressure levels, thus providing its attenuation [24–27].

In addition, this method also provides more realistic information on the attenuation of HPDs for workers and employers and can be incorporated into user training for proper fit, allowing anatomical and physiological factors, comfort and convenience, among other factors, to be considered [8, 27].

The aim of this study is therefore to evaluate the effectiveness of an educational intervention for improving the correct use of earplugs as HPDs in workers exposed to occupational noise by using the F-MIRE method and comparing pre- and post-training attenuation values and pass/fail rates.

2 Methods

This study was approved by the Research Ethics Committee under number 858/08 - CAAE 0068.0.198.000-08. This was a cross-sectional study of a convenience sample of 140 (125 male and 15 female, mean age 49) workers at a public university in São Paulo who were exposed to occupational noise. All participants were informed about the study and signed informed consent forms.

3 Results

The aim of this study was to evaluate the effectiveness of an educational intervention on the proper use of two types of earplug HPDs in workers exposed to occupational noise by comparing pre- and post-training attenuation values and pass/fail rates.

The results showed that there was a significant post-training increase in the binaural PAR values for both HPDs. In addition, there was a decrease in the standard deviations of both HPDs, suggesting that the post-training fits were more correct and consistent among the participants and therefore that the educational intervention was effective. These findings corroborate other studies that reported a post-training increase in attenuation values with the use of HPDs [21, 28–30].

The methods used in the above studies [21, 28–30] differ substantially. The study by Williams and Rabinowitz (2012) [29] measured the post-training improvement using Method B of ANSI S12.6-1997. Toivonen et al. (2002) [21] and Samelli et al. (2015) [30] compared trained and untrained subjects using the F-MIRE and REAT (Real Ear At Threshold) methods. Tsukada and Sakakibara (2008) [28] used earplug HPD verification measurements; they compared responses obtained using headphones placed over the ears of subjects with and without HPDs. The number of subjects also varied considerably across these studies, ranging from 15 [29] to 80 subjects [30]. Moreover, the types of HPDs evaluated varied.

Because of this variability in the methods employed, the attenuation values differed greatly. However, all of the cited studies [21, 28–30] agree that training is effective in improving earplug HPD attenuation values, which is in line with our findings.

In regard to the comparison of PAR values between the two HPDs at each stage of the study (the first and second evaluations), there was no statistically significant difference, although in both stages, the attenuation values obtained with the foam HPD were lower than those obtained using the silicone HPD. Neitzel et al. (2006) [7] evaluated the performance of two types of HPDs (foam and custom-molded) and found that the custom-molded protectors achieved higher mean attenuation percentages for noise reduction levels, while the foam HPDs did not achieve satisfactory results. This is in accordance with the values found for the pre-training PARs in this study, suggesting that foam HPDs require greater skill to correctly insert and may, therefore, achieve lower attenuation values. This finding suggests the importance of educational interventions for ensuring that HPDs reach effective attenuation values [7, 31].

A comparison of the percentages of passes pre- and post-training again showed that training in the proper fit of the HPD was effective, as there were increases of 13.5% and 20.2% in the number of individuals who passed for silicone and foam HPDs, respectively; both types had statistically significant differences. These findings are in agreement with those of a previous study in which an increase was observed in the number of workers who achieved sufficient noise attenuation after receiving training in the proper fit of HPDs (46% to 66%) [28].

It is also notable that the increase in “pass” results was greater for the foam HPDs than the silicone HPDs; however, the total “pass” percentage in the post-training evaluation was lower for the foam HPDs. These data can be explained by the greater difficulty in inserting the foam HPD, which requires more steps to achieve a proper fit compared to the silicone one [13, 32], and it is for this reason that this HPD had a greater difference as a result of the training.

An analysis of the foam HPD data at the pre-training stage revealed that almost half of the participants failed, i.e., did not achieve sufficient attenuation. A possible explanation for this result is also related to the difficulty of fitting this type of HPD, as it requires the individual to roll it properly while pulling the pinna in an antero-posterior direction to straighten the ear canal and only then insert it. It must be placed deeply, and then the individual must wait for the material to expand. This is a greater number of steps than what is required for silicone HPDs.

In this regard, Casali and Park (1990 and 1991) [31, 32] showed in their studies that training was more promising for silicone HPDs because individuals better understand the technique for fitting them. They therefore reached greater attenuation values, as was also observed in the present study.

It is important to mention that there was a group of participants (15.8% for the silicone HPD and 23.6% for the foam HPD) who failed in both evaluations for each HPD, even after the completion of training, a result that was also obtained by other authors [33]. In addition, 8.5% of the subjects failed in both evaluations for both HPDs, which may suggest that this group needs additional training or even that for these individuals, an earplug HPD is perhaps not the best option.

This finding indicates that the attenuation provided by HPDs depends on other variables in addition to knowledge about correct usage, such as the shape and geometry of the ear, the mechanical design of the HPD and a low tolerance for discomfort [4, 11–19].

Therefore, in such cases, it is suggested that occupational health teams find alternative hearing protection options for these individuals (for example: custom earplugs, communication earplugs, earmuffs, etc.), thereby ensuring the effectiveness of hearing protection measures.

Another issue to be considered is that there were individuals who passed the pre-training evaluation but failed the post-training evaluation (5.7% for the silicone HPD and 9.3% for the foam HPD), which indicates a need for additional training. Similar results to these were also observed in other noise attenuation evaluation studies; those subjects also had difficulty fitting the HPDs, even after training [21]. For this reason, longitudinal monitoring of HPD fits must be performed, constant training should be provided, and the effectiveness of the attenuation provided by these devices must be maintained.

It is important to stress that the REAT is considered the gold standard for measuring HPD attenuation and that many studies have demonstrated the validity of other HPD fit evaluation methods, such as F-MIRE, although differences in the results obtained by the different methods have been identified [9, 34–37].

However, all of these authors point out that the differences are due to the different methods employed and that each offers advantages and disadvantages depending on its objectives. Regarding HPD fit training, they are unanimous in emphasizing that objective methods, such as F-MIRE, which was used in this study, are more advantageous, as they are faster (even if multiple measurements must be made during training), convenient and easy to use on a daily basis. They allow both the HPD user and the examiner to easily see if the HPD fit is good or bad, incorporating objectivity into the variability inherent in a situation in which human factors are involved [9, 38]. Another advantage of this method, noted by Kabe et al. (2012) [37], is its ability to test HPD attenuation in users with more severe hearing loss, which can be common in a noisy occupational environment and can hinder the performance of the REAT, as it depends on the individual’s subjective response.

The limitations of this study include that it used only two types of HPDs by one specific brand, which means that these results cannot be generalized to the entire range of HPDs on the market. In addition, the post-training evaluation was performed immediately after the educational intervention, which does not provide information regarding long-term training outcomes. We suggest that this should be assessed in future studies.

In terms of the strengths of this study, we would like to highlight the study sample, which was very large compared to the sample sizes of previous studies. In addition, the method used to measure HPD attenuation was an objective method, meaning that the collected data are more reliable.

Finally, in summary, the present study showed the effectiveness of an educational intervention involving the correct use of silicone and foam earplug HPDs in workers exposed to occupational noise, which was demonstrated both by the increase in PARs and by the increase in the number of individuals who achieved sufficient noise attenuation.

The importance of conducting continuing education on hearing health for workers is also emphasized in order to prevent and minimize the effects of noise-induced hearing loss.

In addition, evaluations performed using the F-MIRE method proved effective in determining HPD attenuation levels and objectively assisted in the training of workers for proper HPD fits.

5 Conclusion

This study found a statistically significant increase in PARs and the number of workers passing evaluations after HPD fit training, demonstrating the effectiveness of this educational intervention.

Conflict of interest

None to report.