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While hearing protection is the ‘last line of defence’, it remains a critical way in which the residual risk from noise exposure is managed. Getting hearing protection right should be an important part of any effective noise management system to protect workers from the dangers of Noise Induced Hearing Loss (NIHL).
NIHL hearing loss and tinnitus are not the only risks associated with excessive noise.
Exposure to high levels of noise has been linked to increased stress levels, harmful effects on the cardiovascular system and sleep deprivation.
A feeling of isolation from one’s surroundings due to high noise also has associated risk due to a decreased awareness, while noise can also mask important warning alarms and safety messages.
Getting the policy right
Getting it right starts with having a clear enough understanding of both the noise environment and the resultant personnel exposures. Finding ways to eliminate exposure to noise is always going to be preferable to relying upon hearing protection.
Having determined that hearing protection is necessary we need to look at not just the type of hearing protection, but also the way in which we implement its use. A clear policy and supporting guidance should be a priority. For example, the demarcation of areas requiring the use of hearing protection (mandatory hearing protection zones) should eliminate any conflict or confusion. One of the policy aims should be maintaining a clear link between hazard and use of PPE; onerous or unrealistic expectations such as the constant removal and replacement of hearing protection will ultimately lead to poor hearing protection use.
Proper specification of noise control on complex industrial sites requires a detailed understanding of acoustics in order to understand how and where the noise is generated and how it is being transmitted to the area. Specifying controls without that knowledge can often lead to measures being implemented that are either ineffective, or grossly over engineered so that far more money is spent than is strictly necessary.
So how should one approach the specification of noise control that is both appropriate and effective?
The first stage is to ensure that efforts are targeted in the right areas; it is at this stage that a properly conducted risk assessment can be of great benefit.
Any noise risk assessment will essentially look at two key factors:
- The measured noise levels around the site in question
- Where on the site employees spend their time in typical working day
Analysis of this information can not only reveal who is most at risk from noise exposure but, crucially, which areas contribute most to that exposure. It is important to note that this is not necessarily the noisiest area on a site, but one that couples high levels of noise with high levels of occupation. There is little point in spending a lot of time and money on reducing noise in an area in which workers spend little to no time during their working day.
By analysing the results of the initial risk assessment it allows efforts to be targeted in the areas it will have most impact in terms of risk reduction.
Getting the people right
The most overlooked aspect of hearing protection use is end user. A properly engaged and knowledgeable workforce will not only build the culture to a point where hearing protection use becomes the norm, but also leads to the workforce becoming self-policing. Building a strong culture requires:
- Clear policy and guidance
- Appropriate information, instruction and training
- Supervision and feedback
We need to take into account human nature. Annoyances, for example due to poor comfort, can quickly lead to poor fitting or even non-use. The biggest factor in determining the performance of hearing protection is not the device itself, but the user. Effective training in the correct fitting of hearing protection should be considered a life lesson – once properly learned the person can choose to protect themselves fully for the rest of their working life. Figure 1 shows how the different depths of fitting an earplug result in substantial differences in performance.
Practical demonstration is the most effective way to teach the correct use of hearing protection. Training should highlight the following points when fitting earplugs:
- Tight rolling of the earplug – a tighter roll makes it easier to fully insert a plug into the ear canal
- Keep the earplug tightly compressed between the fore finger and thumb of the hand on the same side as the ear into which the plug is being inserted
- Use the ‘off’ hand stretched over the head to pull the pinna (ear) upwards to straighten the ear canal
- Rapid insertion of the earplug (while still tightly compressed)
- Keep a finger placed over the end of the earplug during expansion
- Ear canals vary in size, shape and orientation – ‘wiggling’ of the earplug during insertion may help the plug find its way down the ear canal. Personnel should also be warned that when first installing plugs correctly they may initially feel some discomfort (and a coughing reflex) as the plug enters the sensitive ear canal. This sensation should quickly subside as the plug expands
Personnel should be able to check the quality of ear plug fitting. The two following tests are simple ways to check fit:
- Visual depth check – when viewing the face from the front (either via a mirror or a colleague) the plugs should not be visible. Correctly fitted plugs will be obscured by the small flap of skin (tragus) to the front of the ear canal.
- Sound check – when in a noisy area cup a hand and place over the ear. If there is a noticeable change in noise level or character, then the earplug is not correctly fitted.
Any site safety observation systems should be used as a way of checking fit and promoting awareness.
Getting the PPE right
It is common to see employers offering hearing protection with the highest possible attenuation values in the belief that this better avoids the risk of NIHL and potential compensation claims. This approach is overly simplistic and can often be counterproductive.
Hearing protection will always have a central role to play in protecting people against the harmful effects of noise; clearly when used properly it provides a high degree of personal protection. Moreover, it is important to note that on a large number of industrial sites reducing noise to as low as is reasonably practicable will not constitute reducing it to a level at which it is safe to be exposed for long periods. Therefore, even where properly specified noise control has been implemented, hearing protection may still be required to mitigate the residual risk.
When assessing and approving hearing protection devices it is important to balance attenuation with the hazard created by isolating workers from their environment. Very high attenuation hearing protection, in protecting against high noise can also inhibit the ability to hear instructions, alarms or other warning signs. As a result, high attenuation devices are more likely to be removed to facilitate communication – thereby greatly reducing their effectiveness. Figure 2 shows that even removing hearing protection for short periods while in a noisy environment dramatically reduces performance.
Additionally, personnel wearing high attenuation hearing protection can suffer from fatigue due to the extra concentration required to compensate for this isolation.
Before committing to the use of very high attenuation devices it is important to ensure that it will be used correctly; a lower attenuation device that is used correctly can easily outperform a very high performance device that is not used fully.
When selecting hearing protection, it is important to choose solutions that offer adequate protection without over protecting, i.e. target a protected noise level between 70-80 dBA.
Assessing the hearing defender
First, it is important to understand the performance figures supplied by earplug and defender manufacturers. When working in European countries we should be looking for attenuation data measured against BS EN 352 (parts 1 through 8 dependent upon type). Standardised attenuation data is not a guarantee of a certain level of protection, but is instead a value that statistically should be achieved by just over two thirds of the population (84%), assuming it is fitted in accordance with the manufacturers’ instructions.
Attenuation data can be provided in three different ways as a single number rating (SNR), three frequency dependant values (H-M-L) and a more detailed frequency rating (Octave bands). Assessments using the three ratings increase in complexity from SNR to Octave band, with a corresponding increase in accuracy.
Using the more accurate octave band method allows more careful selection of hearing protection based upon the actual frequency composition of the noise environment.
Figure 3 shows the HSE calculation tool in use. In recognising the difficulties with getting a correct fit, whether due to the use of safety glasses, long hair or even head shape, the HSE recommends a 4 dB correction to account for typical issues.
The correct selection of hearing protection in an oil and gas environment can be demonstrated. Comparison of the protected noise levels from a diesel power generator (dominated by low frequencies) and a gas turbine (dominated by higher frequencies) for one particular high performance disposable earplug and a certain hearing defender shows the disposable earplugs, in this instance, to be the better solution for these noise environments.
The SNR and HML make assumptions about the frequency composition of the noise, which as shown by the more accurate Octave band method, are not always accurate. Table 1 shows that there can be significant differences in calculated levels – there is a 4 dB difference between the SNR and Octave band calculations for the disposable earplugs in the diesel generator room. In this instance, the less accurate SNR underestimates the protection afforded. In comparison, the assessment of the hearing defender adjacent to a gas turbine has the SNR overestimating protection by 4 dB. Noting these inaccuracies, if Octave band data is available this should be used to assess hearing protection.
Using the correct solution
Advances in technology mean that we now have access to options beyond the standard earplug and defender. Custom moulded earplugs have the potential of providing reliable attenuation due to consistency of fit. Furthermore, filters can be used to tailor the level of protection afforded to the environment. Filters can also be chosen to allow more of the speech frequencies, thereby improving communication. Lower attenuation filtered earplugs are common with the offshore oil and gas drilling community – plugs can be worn throughout the working day without compromising the need for reliable communication. When excessive noise levels (110 dB) are present high attenuation hearing defenders can be worn over the earplugs.
Modern custom moulds can be 3D printed, be wired to radios to allow communication, have methods of testing their true attenuation and even active noise control built into them.
Level dependent or ‘tactical’ hearing defenders are similarly increasing in popularity. Tactical hearing defenders employ electronics to monitor the noise environment. When noise levels are low, noise is permitted to pass through to the wearer (or even amplified if desired). However, as soon as noise levels increase the electronics stop the transmission of the noise, effectively reverting them to standard ‘passive’ hearing defenders. Tactical defenders are therefore ideally suited to workers travelling from across different locations and sites, who are routinely exposed to changing noise environments. Tactical defenders are also ideally suited to workplaces with intermittent and unpredictable noise sources. For example, workshops where colleagues can start using tools without warning.
It is important to remember that technology should be an enabler – making its use easier and performance more reliable. Solutions which are cumbersome, uncomfortable or difficult to use will ultimately fall out of use or cause more issues than they solve.
Checking the system works
Having carefully created a system that properly assesses the noise environment, sets a clear policy, educates personnel and provides the best suited hearing protection, it is important to check that everything works.
Case study 1
Offshore drilling contractor – developing clear policy, selecting optimal hearing protection and effective roll out
While undertaking noise exposure management reviews on a number of drilling rigs it became clear that there were variations in the way hearing protection use was implemented. Different sites had different policies (some blanket, others targeted), and different levels at which hearing protection was required with various hearing protection devices available.
Xodus developed an effective and standardised approach for the client. The need to maintain communications was rated very highly so any solution had to minimise the risk of over protection and isolation. With a travelling workforce it was also decided that hearing protection had to be comfortable for use for a full working day. The final policy resulted in employees being issued with custom moulded earplugs; the plugs were filtered and provided relatively low but reliable attenuation (SNR 25 dB). The policy required that ear plugs were worn in demarcated areas. Areas with noise levels in excess of 100 dB, such as engine rooms and on the helideck, required a high attenuation hearing defender to be worn over the plugs. New site maps were prepared clearly showing the areas requiring hearing protection use (single and dual). Acoustic consultants from the company also provided guidance on rolling out the new policy, with the maps being displayed in key locations and policy discussed during inductions, safety meetings and toolbox talks.
Case study 2
Production Platform Operator – Fitting instruction and education
A common finding when assessing the effectiveness of noise management systems is that hearing protection use can be improved. It is commonplace to see proportions of the workforce not using hearing protection to maximum effect. For example, with earplugs, users typically fail to fit the plugs deep enough into the ear canal.
The client acted upon Xodus’ recommendation to provide improved training in the fitting of hearing protection. Posters showing the steps required to correctly fit earplugs, featuring real-life examples of fittings, were developed and displayed on the client’s assets. The company also developed additional guides showing how to perform checks on hearing defenders.
Case study 3
Production Platform Operator – Clarifying and setting appropriate policy
The client identified inconsistencies in the way hearing protection was used at heliports. In Aberdeen, UK, personnel were required to fit earplugs before boarding the helicopter, with hearing defenders being worn over the top (dual hearing protection) during the flight. In Norwich, UK, passengers boarded helicopters without hearing protection but then wore earplugs and hearing defenders during the flight.
Xodus’ investigation into the different site operations, helicopter types and hearing protection devices revealed differences that justified the different approach to hearing protection when boarding flights. The defining factor was that Aberdeen passengers board with engines running, i.e. rotors turning, while Norwich passengers board with the engines off. Both systems, however, ended up with passengers wearing both ear plugs and hearing defenders (dual hearing protection).
The resulting assessment of hearing protection, both during boarding and flights, confirmed that the sole use of either the supplied ear plugs or hearing defender provided adequate protection. The use of dual hearing protection (plug plus defender) was not necessary. The investigation highlighted that two separate parties were providing hearing protection in support of their compliance with the Control of Noise at Work Regulations – leading to passengers wearing dual hearing protection. Xodus developed a fresh policy and supporting posters for roll out at the two airports.
Conclusion
Ultimately, the job of the acoustic consultant is certainly not to blind the client with science. Quite the opposite, noise control options should be presented in a clear, uncluttered way, providing all the information for detailed cost-benefit analysis to be undertaken. But the science has to be there to provide substance to that information.
Even if after all the diagnostic work has been carried out and the cost-benefit analysis undertaken, the control options presented are rejected, at least those decisions will have been based on sound advice.
However, as with any other health and safety concern, personal protective equipment (PPE) should not be the first recourse to risk. It is perhaps the gradual, cumulative nature of noise exposure effects which make people more susceptible to lapses in vigilance with regards the use of PPE. It is not so much that people just have a cavalier attitude; it is simply that the consequences of not wearing hearing protection are often not immediately felt.
Hitting your finger with a hammer is a stark and painful reminder to wear gloves next time, which lingers long in the memory. This is not necessarily the case in forgetting to wear ear plugs. By the time you feel the effects, it is probably too late to do anything about it. Ultimately it is for this reason, rather than concerns over regulatory compliance, that where possible we should look to reduce noise, rather than simply covering our ears.
