The risk of workers suffering hearing damage can be reduced by up to 90 per cent by adopting three key approaches to noise control.
The worldwide flood of personal injury claims for hearing damage due to exposure to harmful levels of noise at work illustrates just how ineffective the current conventional noise risk reduction approaches (dominated by the use of personal hearing protection), have been in managing a health risk that is 100 per cent preventable. This must change.
Businesses need to take account of updated best practice and make three simple changes to the methods they adopt to prevent or reduce workers’ exposure to excessive noise from plant, machinery and tools in various industries and activities. These simple changes can potentially reduce the risk of workers suffering noise-induced hearing loss (NIHL) by 75–90 per cent. Importantly, most organisations can make these changes at a negligible cost compared with the current level of expenditure on noise exposure controls.
There are three (sadly) little understood facts that compromise the efficacy of many current NIHL risk reduction programmes:
- It is virtually impossible to guarantee adequate ‘real-world’ protection using conventional personal hearing protection (personal protective equipment, or PPE), for noise levels above around 90dB(A) – (real-world means the actual level of protection from noise when PPE is worn at work compared to the PPE manufacturer’s data on the noise reduction, or attenuation, provided).
- The risk of suffering hearing damage is directly proportional to the noise dose – so, for example, reducing noise levels from 98dB(A) to 91dB(A) cuts the risk to hearing by 80 per cent; and reducing the noise level from 94dB(A) to 91dB(A) halves the risk.
- Conventional audiometry (the provision of regular hearing checks – health surveillance – for workers at risk of suffering hearing damage due to noise exposure), closes the stable door after the horse has bolted as it cannot detect the early stages of hearing damage.
What hasn’t worked?
- Assuming conventional PPE guarantees adequate hearing protection – it doesn’t. Workers suffer unnecessary damage without knowing it.
- Commissioning noise assessments (such as measurements of noise levels from machines and tools and measurements to try to estimate workers’ personal noise exposure), that generate placebo reports telling you what you already know – that you still have a problem.
- Assuming that noise control (such as modifying the work, process or machine to reduce the noise they produce), is impractical. Knowledge of modern, low-cost engineering noise control techniques is abysmal, and consequently noise levels – and therefore risks – are not reduced.
- Conventional workplace audiometry (health surveillance for hearing damage) provides too little information, too late, to be of use in noise risk management.
PPE: why hasn’t it worked?
Research proving that the real-world attenuation provided by PPE is only a small fraction of the assumed protection has been around for decades. However, most organisations have failed to take this information into account in their hearing conservation programmes, and have instead assumed that the PPE provides sufficient attenuation. Consequently, millions of workers have suffered unnecessary hearing damage. The main reasons for this serious disconnect between theory and reality are:
- Earplugs: these are rarely fitted correctly – you see them dangling from ears like cigarette ends. Incorrect fitting can reduce the attenuation provided from 20dB–30dB to as low as 2dB.
- Earmuffs: although these have less variation in fit compared with earplugs, as a rule of thumb, you should assume a maximum field attenuation (i.e. in actual workplace use) of about 10dB–17dB, whatever the type of protector.
- Wear rate: this should be 100 per cent, but this is almost never achieved for a variety of reasons (for example, because the protectors are uncomfortable to wear, workers lack the motivation to wear them or the employer fails to properly supervise and enforce their use). Removing any PPE for a cumulative 10 minutes a day limits the maximum attenuation to less than 17dB.
The effect of these factors is shown by the graphics below. You must assume that the maximum attenuation achievable from conventional PPE is about 2dB–12dB for earplugs and 5dB–17dB for earmuffs.
It is also important to understand it is virtually impossible to guarantee that PPE will provide adequate protection from harmful levels of noise if the noise is above 90dB(A).
Noise control is misunderstood
The risk of hearing damage is proportional to the noise dose. Every 3dB increase in the noise level doubles the dose and therefore the risk. Although there are dramatic benefits if you can reduce noise to below 80 or 85dB(A). Cutting noise from 97dB(A) to 94dB(A), for instance, halves the risk and reducing the level from 101dB(A) to 95dB(A) provides a 75 per cent risk reduction. Although the provision of PPE to workers is still legally required at 95dB(A), it becomes more effective – and the risk has been reduced by 75 per cent.
What does work?
The following three steps will reduce the risk of hearing damage from noise by 75–90 per cent.
Step 1: update practices around the use of PPE to improve its performance by more than 75 per cent
Measure the wear rate
You must know and record the PPE wear rate – in other words, whether PPE is always worn when required. If, like virtually every organisation, you do not regularly record this parameter, you cannot know whether staff are adequately protected and whether your hearing protection programme is effective. Collecting this data is therefore crucial.
Once you are monitoring this information, you can use the knowledge gained to increase the wear rate and therefore the protection. Increasing the wear rate from seven hours to 7.5 hours a day, for example, doubles the PPE performance. The primary factors that should be considered and modified to improve wear rates are:
- Workers’ personal motivation to wear the PPE and the workplace culture (including enforcement of the rules) – ways of improving these include providing more effective training on how, when and why to correctly wear hearing protection and properly supervising its use.
- Choice of hearing protector, comfort, environmental conditions and compatibility with other protective equipment that is worn – to ensure these are properly addressed you must involve your workers when selecting the hearing protection.
Implement fit testing and field performance
There are several suppliers of fit-test equipment for both earplugs and earmuffs. These can be used to evaluate the attenuation provided by a particular protector for a particular individual when staff are being trained on how to correctly wear that specific model. The test informs you of the attenuation offered for the specific way the employee has fitted the PPE.
The results can then be used to train the user to fit the PPE correctly to improve the level of protection. Earplug fitting is a classic example. Research shows that when these are simply fitted by the user without adequate and suitable training and supervision, they may only provide 5dB attenuation. However, practising correct fitting can increase this figure to 20dB (but only for a 100 per cent wear rate).
However, the drawback to this approach is that the training room is not the workplace. So, while a user may be able to demonstrate 20dB protection during the fit test, there is no way to control the quality of fit once they are back at work. Consequently, even in the unlikely event of a 100 per cent wear rate, the workplace protection will always be an unknown amount and will almost invariably be much lower than the fit-test result.
Switch to using intelligent PPE
New earmuff technology is available that records the actual protection achieved by the user in the workplace. It continuously measures the wear rate, the attenuation provided and the noise to which the user is exposed while working. Consequently, it provides a record of the real-world performance of the hearing protection programme that can be used to provide verifiable evidence that staff are being sufficiently protected.
The earmuffs continuously record external and internal noise levels (plus the location of the user), uploading the data to the cloud. Automated reporting provides evidence of the actual daily noise exposures of users that can be used to track the effects of policy changes and to guide improvements to guarantee no one is under- or over-protected by their PPE. (Over protection is where the protector eliminates more noise than is necessary to protect against hearing damage, and must be avoided as it can make the wearer feel isolated and make communication more difficult.)
As this process is automated, it also saves resources and reduces costs. The noise level versus time versus location data shows exactly where workers are exposed to the highest noise levels and can be used to focus the noise control programme to gain the maximum benefit.
Step 2: how to reduce noise levels (and therefore risk) by 50–80 per cent
The Control of Noise at Work Regulations say: “Hearing protection devices must not be used as an alternative to controlling noise by other technical and organisational means, only for tackling the immediate risk while other control measures are being developed to bring noise exposure to below 85 dB(A).”
The current problems associated with noise control are largely those of attitude and a lack of knowledge of what is possible with current technology. Noise control is an engineering problem, not a safety issue, and should primarily be addressed by low-cost engineering techniques, many of which are self-financing. Compared with conventional palliative noise control measures (such as acoustic enclosures), this approach of low-cost engineering techniques reduces typical noise control project costs by 50–90 per cent. As a result, the cost savings mean it is much more feasible to introduce effective noise control measures.
The key question is therefore: “How do I find the optimum control measures for my noise problems?” There are several options:
- Case studies: the three examples on this page demonstrate the kind of approach that is possible and effective and the gulf between best practice and traditional high-cost palliatives such as acoustic enclosures. For example, on the chopper fan project, the proposed enclosure, silencer and acoustic lagging were replaced with a simple aerodynamic insert inside the fan casing instead.
- Online resources: the online database of engineering noise control best practice case studies on the INVC website is freely available and allows you to search for the best options.
- Remote advice on the control of noise: we offer a free, worldwide remote diagnosis of problem noise sources and a cost/benefit analysis of the most effective noise control options via email, based on you sending us smartphone data. Click here for details.
Step 3: how to make health surveillance useful and effective
The data provided by traditional audiometry is of little use as part of the risk management process as it simply catalogues failures in risk reduction strategies years after the event. While the process itself can be very useful as a motivational exercise to encourage employees to take their hearing seriously, the hearing test results are essentially a tick-box exercise implemented to comply with the regulatory requirement.
Closing the loop with otoacoustic emission (OAE)
Unlike conventional audiometry, the newer OAE hearing tests can detect the onset of damage early enough to be useful as a risk management tool. This is a fast, objective test that requires no action by the person undergoing the test and provides a very easily understood result – the percentage of hearing damage. Consequently, it is an effective tool to evaluate the efficacy of the hearing damage risk management programme, by spotting any increasing levels of hearing damage from year-to-year.
Being able to detect the early stages of damage closes the “how well is our hearing protection programme working” loop. It also provides a valuable education and motivation tool. Think how the warning, “Last year your hearing damage was 10 per cent, this year it is 15 per cent”, would affect the behaviour of a worker.
It’s time to make noise risk management genuinely effective
The current approach to noise risk management is failing to adequately protect workers from noise-induced hearing loss. Consequently, millions have suffered avoidable hearing damage with the attendant serious consequences. In addition to hearing loss and tinnitus (permanent ringing in the ears caused by exposure to loud noise), recent research has discovered that exposure to noise increases the risk of dementia by 9–27 per cent. This perhaps makes noise one of the dementia risk factors we can most easily address and tackle.
Implementing the three simple best practice steps detailed here reduces the risks of hearing damage from noise at work by 75–90 per cent or more at negligible or no cost compared with current practices. It’s time to make that change.
Peter Wilson is Technical Director at INVC
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