December 2015

Come on feel the noise!

Reuben Ditchburn

Reuben Ditchburn

Noise in the workplace is often seen as the Justin Bieber of safety concerns; whilst most people are now aware of it, the temptation can be to simply stick your fingers in your ears and pretend it doesn’t exist.

Noise Blog Wide

Though it’s nearly ten years since the Control of Noise at Work Regulations (CoNAWR) came into force, many employers still turn to hearing protection first when attempting to protect their workers from the dangers of Noise Induced Hearing Loss (NIHL). This is despite the focus of regulations being clearly shifted to the reduction of noise at source in the latest iteration of the regulations (the addition of “Control of” to the title was no random impulse by the HSE).

The shift was deliberate, and one borne out of reason. Hearing protection, although ostensibly effective, is often not employed correctly. For example, in the past I have seen offshore workers putting ear plugs behind the ears whilst taking a cheerful walk to a helicopter in noise levels in excess of 105 dBA, seemingly unaware of the long term damage they could be inflicting on their hearing. Even variations in peoples’ ear canal size and head shape can drastically reduce the effectiveness of hearing protection. Which is why, in the oil and gas industry for example, there have been a number of claims put in over the years from employees suffering from tinnitus or NIHL, despite the fact that most operators have long held ‘blanket’ hearing protection policies on their sites, requiring it to be worn in all areas.

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 ones surroundings due to high noise also has associated risk, due to a decreased awareness. Noise can also mask important warning alarms and safety messages. It is for this reason that the 2003 EU Directive 2003/10/EC dealing with noise in the workplace (which the CoNAWR implements) put the focus squarely on reducing risk from noise to as low as reasonably practicable (ALARP) before handing out the plugs.

Assessment and mitigation
Following the introduction of the new regulations in 2006, much of the initial focus from industry was on re-evaluating risk assessments in light of the changes to the various 'action values' that had replaced the previous 'action levels' of the 1989 regulations. This reaction had some justification given the shift of the regulatory goal posts as the new action values had been reduced by 5 dBA as compared to their action level counterparts. There has also been the introduction of the new ‘limit value’ above which all work was to cease until such time as the offending exposure could be appropriately mitigated. Therefore, employing companies felt compelled to assess their position before deciding the right course of action.

Furthermore, the regulations called for the risk assessment to be 'reviewed regularly', with the accompanying HSE guidance further defining this as any time that changes occur in the workplace which 'might alter the level of exposure'; even where no change occurred the assessment should be reviewed every two years. This requirement led many companies to become pre-occupied with reviewing and refining the risk assessment to ensure it was representative, rather than implementing controls to reduce the risk. The regulations call for risk assessments and assessment of mitigation to be carried out by 'competent persons'. Whilst, there are many competent assessments of risk undertaken, the subsequent assessment of controls necessary to reduce that risk to ALARP is often either missing entirely, skewed by a desire to sell a product, or based upon a ‘finger in the air’ approach, rather than any sound engineering practice.

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.

Both of these outcomes have a detrimental effect on a company’s future willingness to spend money on reducing risk by engineering means; ultimately, making them more likely to turn to what they see, ironically, as the ‘safer’ (and cheaper) option of hearing protection as first resort.

Sound engineering practice
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.

Any noise risk assessment will essentially look at the measured noise levels around the site in question, and 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. This is not necessarily the noisiest area on a site, but one which 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. Having identified the particular area(s) causing the problem, this process of targeting noise control efforts should continue, and it is at this stage that an engineering approach, backed by proper understanding of acoustics, is required.

If we take the example of a centrifugal compressor, a common source of noise exposure on industrial and process sites, the package itself is made up of a host of component parts with the potential to radiate noise. It might be tempting to think therefore, that a full acoustic enclosure is a reasonable solution. Whilst this may result in a significant reduction in noise, it is also akin to using an extremely expensive sledgehammer to crack a nut. Furthermore, such an enclosure would take up significant amounts of space, and require careful design of the cooling systems and pipework penetrations to be effective.

A far more prudent approach would be to ascertain what the most significant sources of noise are, and to target noise control on those items first. In order to derive a scheme of mitigation that is both effectual and cost-effective, the potential sources of noise need to be rank ordered. This is most usefully done by determining out the sound power level of each constituent source. It will then be possible to determine the contribution each makes to the total noise level in an area. Unlike sound pressure, sound power level cannot be measured directly. It is possible however, to measure sound intensity using a probe attached to a sound level meter with the appropriate software loaded. Whilst a powerful tool, it is not without its limitations: measurements taken in highly reverberant spaces or where there is a considerable amount of extraneous noise present can impact the measurement and reduce the accuracy of the measurement. An alternative to this would be measuring the vibration velocity level.

By using the techniques described above it is possible to determine which of the noise sources on a complex piece of machinery are most responsible for the overall noise level in an area; and tailor the noise control to that individual source, rather than attempting to use a “catch all” method such as an enclosure. When, even after thorough investigation, no practicable engineering noise controls can be found, there are alternatives that can be investigated before hearing protection is issued. Organisational controls that seek to minimise the time workers spend in an area through modification of working practices can be equally as effective in reducing noise exposure on a site as that achieved by noise reduction.

Hearing protection
In contrast to many other safety issues, the effects of noise are rarely felt immediately, but rather creep up over time. Yet the risks are real; if you listen to any testimony from a person suffering sleepless nights from long-term tinnitus, or from one who cannot join in on a conversation in a restaurant due to NIHL, you will know it is not a pleasant experience. Let alone the very real risk to life associated with an inability to hear warnings in a high noise environment.

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. 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 impact gloves next time. 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; and 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 to the risk.