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Hearing protection in the workplace

Author : David Leonard of Howard Leight by Sperian

12 January 2010

It will not come as news to anyone that due to its insidious nature occupational hearing damage continues to be an enormous problem across every sector of the UK working population, including oil & gas and petrochemical industries. The potential for permanent noise induced hearing loss is a constant danger.

Hearing protection in the workplace
Hearing protection in the workplace

In the hazardous area a high standard of hearing is required to perform jobs while the inability to hear warning and safety signals endangers the person in question and others.

Deaf and hard of hearing people number 8.7 million people in the UK. Indeed, in the USA the circumstances are no better with work related hearing loss reported as one of the most common occupational diseases. It is estimated that over 30 million workers are exposed to hazardous noise on a daily basis and more than 10 million workers suffer from noise induced hearing loss.
There are a number of factors suggesting these trends will be replicated in Europe, as with the enforcement of EU legislation and the lowering of action levels, more workers are covered by noise regulations.

A report issued in 2009 by the HSE entitled ‘Real world use and performance of hearing protection’ gave a positive indication about the availability of appropriate Hearing Protection Devices (HPDs) in the UK. However, it also reported that “possibly only 60% of workers supposedly using hearing protection are in fact protected.”  So if HPDs are available, why does hearing protection fail in the real world? One of the major reasons why it fails, and this applies particularly to ear plugs, is that it is incorrectly fitted. Other elements that contribute to the failure of hearing protection in the real world include lack of compatibility with other personal protective equipment, deterioration of products and abuse.

A second major reason for hearing protection failing is that it simply isn’t used. Common objections are that the HPD is ‘uncomfortable’ or that communication with fellow workers is hindered or that the HPDs in some way inhibit the ability to work safely in a hazardous environment. One reason, commonly given in industry, is that “my machine sounds different,” and this indeed is true.  But, after only seven days a typical machine operator will adjust to the new sounds and can carry on, only now with protected hearing. There are, of course, the more frivolous objections which I repeat here, if only to highlight and debunk a couple of myths, amongst which are: ‘I don’t need an HPD, I am used to the noise;’ ‘I have already lost some of my hearing. Why should I wear them?’ ‘I think I will hurt my ear drums if I insert a plug too deeply’; ‘I don’t want an ear infection’. All nonsense.

The way in which to address the above issues is to implement a hearing conservation programme.  But, implementing such a programme is not as straight forward as it should be due to the problems associated with the single number rating (SNR) system, de-rating schemes for HPDs, HPD fitting and the delivery of effective training.

SNR was adopted by International Organisation for Standardisation (ISO) in 1994 as a simple method for estimating the attenuation of hearing protectors. But, the SNR is simply an estimate of the protection an HPD can offer based upon population averages, not a measurement of actual protection. SNR is therefore a theoretical number and how much protection an individual worker will achieve with a particular earplug in the field remains unknown, especially given the problems with incorrectly fitted HPDs already outlined.

The weakness of the theoretical nature of the SNR is a recognised problem and, as a consequence, many countries have devised their own HPD de-rating recommendations, but again these rules apply generally to a population and not an individual person. In Germany, for example, the BG Technical Committee recommends subtracting 3dB from the ‘advertised’ attenuation rating for custom moulded earplugs, 5dB from earmuffs and 9dB from all other earplugs. Some experts in the UK advise that practitioners should subtract 4dB from the SNR while in the U.S.A. 7dB is a common de-rating. But, once again the problems surrounding the correct fitting of HPDs in the field render de-rating largely meaningless in practice.

It is possible using field verification systems to eliminate the infinite variability which SNR and de-rating introduce as a field attenuation study conducted by the Howard Leight Acoustical Laboratory showed. The study, which used Howard Leight by Sperian’s VeriPRO earplug fit testing technology, showed that one-third of workers achieve attenuation higher than published attenuation ratings for their earplugs: the amount of protection received by the wearer is better than ‘advertised’. Another third of the test group achieved attenuation within 5dB of the advertised ratings and were achieving adequate protection. The remaining third had attenuation that was more than 5dB below the published attenuation rating and were not being protected adequately for the environment within which they work.
This study reinforces the fact that no generalised rating scheme for hearing protectors can be effective without knowing how much attenuation individual workers actually attain in the real world.  If, a safety professional were to supply earplugs based on the assumption that all earplugs only achieve 50% of their published SNR in the field, then two-thirds of the workers in this study would be seriously over-protected, since they are achieving much higher protection than 50%. As a general guideline, hearing protection should bring Protected Exposure Levels (the noise level under the earplugs) to between 70-85dB (from ISO Guideline EN-458) and therefore if a person is over-protected verbal communication may be hindered, warning alarms might not be heard and in certain hearing critical jobs over-protection might be just as hazardous as under protection.

The study highlighted that the level of training had a strong correlation to good earplug fit and therefore good attenuation in use. More precisely that is, the more often a worker had received one-to-one training in the proper use of HPDs, the higher the chance of a good fit was, the same could not be said of group training.

Hearing conservation training, be it group training or one-to-one, typically involves a presentation which reinforces the dangers and the consequences of hearing loss and then moves on to correct HPD selection and fitting training. However, any sort of hearing conservation training must address the individual challenges that the workers’ environment presents. Within the same site different job functions may require different HPDs, reusable as opposed to disposable roll down earplugs for example, and this can often be the main problem if a ‘controlling mind’ selects a single HPD product to cover an entire site. The HPD may adequately protect some but will under-protect or over-protect others and some it will just not suit at all and therefore they will not use it. It is these types of issues that are more easily addressed in a one-to-one training session and can therefore be attributed to their success.

Why the study referenced is so interesting is because it provides evidence that a field-deployable test is able to bridge the gap between laboratory estimates of attenuation (SNR) and the real world attenuation achieved by workers as they normally wear their HPDs (PAR). This point about bridging the gap between the lab and the field, and the difficulty in doing so, is highlighted in the HSE study ‘Real world use and performance of hearing protection’. The measurements used in the HSE study were made in an artificial ear simulator in a laboratory, yet, as the study concedes, “the attenuation of an earplug in an ear simulator often exceeds the performance achieved by human subjects as the earplug is fitted into a smooth cylindrical ear canal simulator.”

Information on PARs arms the safety professional with greater amounts of hard information with which they can construct an effective hearing conservation programme. The key elements to setting up a successful hearing conservation programme are: the provision of a number of different types of potentially effective HPDs; one-to-one training; strict enforcement of the hearing protection policy and; continuing communications and education.

As an aside, one idea which many people have when considering the above, is that by using the PAR information the ‘fit-testing’ of HPDs is now possible. Like a respirator test, field verification of hearing protectors can indeed provide valuable information – but it also has its limits. Fit testing, whether for respirators or HPDs, only verifies the capability of a piece of equipment in the hands of the user. It can only provide a snapshot of attenuation at the time of the test; it does not reveal the noise exposure for the worker a day later, or even an hour later. The question of whether the fit testing of HPDs should be governed by legislation is one for the future but with apocryphal tales of mandatory compensation pay-outs for hearing loss and the consequent hike in insurance premiums, it is perhaps a move which would benefit employers and employees alike.

Only action from government, in terms of education and consumer legislation, can address the threat that the growth in modern technology poses to our hearing. However, within the working world it could be said that the gap between the laboratory and the field has effectively been bridged, allowing safety professionals to discard theoretical data and to base their hearing conservation initiatives firmly in reality.

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