Millions of workers are exposed to noise levels that increase the risk of hearing loss and hearing impairment. In many countries there are mandatory hearing loss prevention programmes (HLPPs), which are considered an effective means to prevent noise induced hearing loss. However, the evidence for this assumption is unclear.
We found one study that showed that noise levels decreased after the implementation of stricter legislation in the mining industry. Even though case studies show that substantial reductions in noise levels in workplaces can be achieved, there were no further reports of controlled studies that this can be implemented and maintained at a larger scale.
In six studies with 188 workers, hearing protection reduced noise exposure of workers about 20 dB(A). However, one high quality study showed that if workers lack proper instructions in the use of earplugs, the attenuation offered is much reduced. Two studies with 3,242 workers evaluated the long-term effect of ear muffs versus ear plugs on noise-exposure and found no significant difference.
We found 15 studies with 79,986 participants that evaluated the long-term effects of protection against noise exposure in hearing loss prevention programmes. The use of hearing protection devices in well-implemented HLPP was associated with less hearing loss but this could not be shown for other elements such as worker training or audiometry alone or noise monitoring. There was one study that showed a possible preventive effect on hearing loss when using personal noise exposure monitoring and worker feedback compared to not using these devices in a hearing loss prevention programme. There was also very low quality evidence in four studies that, compared to non-exposed workers, average hearing loss prevention programmes do not reduce the risk of hearing loss to below a level at least equivalent to that of workers who are exposed to 85 dB(A). Two comparable additional studies showed that the risk of hearing loss is still substantial despite being covered by a hearing loss prevention programme.
Higher quality prevention programmes, better quality of studies especially in the field of engineering controls and better implementation of legislation are needed to better prevent noise-induced hearing loss.
There is low quality evidence that implementation of stricter legislation can reduce noise levels in workplaces. Even though case studies show that substantial reductions in noise levels in the workplace can be achieved, there are no controlled studies of the effectiveness of such measures. The effectiveness of hearing protection devices depends on training and their proper use. There is very low quality evidence that the better use of hearing protection devices as part of HLPPs reduces the risk of hearing loss, whereas for other programme components of HLPPs we did not find such an effect. Better implementation and reinforcement of HLPPs is needed. Better evaluations of technical interventions and long-term effects are needed.
Millions of workers worldwide are exposed to noise levels that increase their risk of hearing impairment. Little is known about the effectiveness of hearing loss prevention interventions.
To assess the effectiveness of non-pharmaceutical interventions for preventing occupational noise exposure or occupational hearing loss compared to no intervention or alternative interventions.
We searched the Cochrane Central Register of Controlled Trials (CENTRAL); PubMed; EMBASE; CINAHL; Web of Science; BIOSIS Previews; Cambridge Scientific Abstracts; and OSH update to 25 January 2012.
We included randomised controlled trials (RCT), controlled before-after studies (CBA) and interrupted time-series (ITS) of non-clinical hearing loss prevention interventions under field conditions among workers exposed to noise.
Two authors independently assessed study eligibility and risk of bias and extracted data.
We included 25 studies. We found no controlled studies on engineering controls for noise exposure but one study evaluated legislation to reduce noise exposure in a 12-year time-series analysis. Eight studies with 3,430 participants evaluated immediate and long-term effects of personal hearing protection devices (HPDs) and sixteen studies with 82,794 participants evaluated short and long-term effects of hearing loss prevention programmes (HLPPs). The overall quality of studies was low to very low.
The one ITS study that evaluated the effect of new legislation in reducing noise exposure found that the median noise level decreased by 27.7 dB(A) (95% confidence interval (CI) -36.1 to -19.3 dB) immediately after the implementation of stricter legislation and that this was associated with a favourable downward trend in time of -2.1 dB per year (95% CI -4.9 to 0.7).
Hearing protection devices attenuated noise with about 20 dB(A) with variation among brands and types but for ear plugs these findings depended almost completely on proper instruction of insertion. Noise attenuation ratings of hearing protection under field conditions were consistently lower than the ratings provided by the manufacturers.
One cluster-RCT compared a three-year information campaign as part of a hearing loss prevention programme for agricultural students to audiometry only with three and 16-year follow-up but there were no significant differences in hearing loss. Another study compared a HLPP, which provided regular personal noise exposure information, to a programme without this information in a CBA design. Exposure information was associated with a favourable but non-significant reduction of the rate of hearing loss of -0.82 dB per year (95% CI -1.86 to 0.22). Another cluster-RCT evaluated the effect of extensive on-site training sessions and the use of personal noise-level indicators versus information only on noise levels but did not find a significant difference after four months follow-up (Mean Difference (MD) -0.30 dB(A) (95%CI -3.95 to 3.35).
There was very low quality evidence in four very long-term studies, that better use of HPDs as part of a HLPP decreased the risk of hearing loss compared to less well used hearing protection in HLPPs. Other aspects of the HLPP such as training and education of workers or engineering controls did not show a similar effect.
In four long-term studies, workers in a HLPP still had a 0.5 dB greater hearing loss at 4 kHz than workers that were not exposed to noise (95% CI -0.5 to 1.7) which is about the level of hearing loss caused by exposure to 85 dB(A). In addition, two other studies showed substantial risk of hearing loss in spite of the protection of a HLPP compared to non-exposed workers.