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Specifying hearing protection equipment

Author : Sarah Broadbent, Technical Engineer – Occupational Health & Environmental Safety, 3M United Kingdom

15 September 2010

Noise is a fact of life in many working environments. The use of machinery cannot be avoided but it can have a devastating effect on the hearing of operatives if they are not provided with sufficient protection from the noise it creates.

Specifying hearing protection equipment
Specifying hearing protection equipment

Excessive noise affects our ears and our hearing, especially the sensitive inner ear, in particular the cochlea, which is a coiled, fluid-filled structure housing the nerve elements required for hearing. The cochlea receives the energy vibrations caused by noise passing from the eardrum through the middle ear. Around 30,000 tiny hair cells in the cochlea are stimulated by the movement of the fluid. The movements of these hair cells then produce nerve impulses which are transmitted to the brain and are interpreted as sound. It is these hair cells which can be damaged and ultimately destroyed through exposure to excessive noise, causing hearing loss which in some instances is temporary but is often permanent and irreparable.

The extent of the issue was highlighted by Self-reported Work-related Illness (SWI) surveys in 2008/09 which found that 17,000 people employed in the past 12 months in Great Britain are estimated to be suffering from work-related hearing problems.

Current UK law on the issue requires employers to implement a hierarchy of control measures before the use of Hearing Protective Equipment (HPE) is considered. The first is the elimination or substitution of the sources of noise. However, while some processes can be automated, investment in new equipment is an expensive and typically long-term consideration, meaning noisy equipment could remain in situ for months or even years. Meanwhile, the fact remains that many processes require some form of human control or intervention, requiring operatives to be near to the equipment while it is operating.

The second stage is engineering controls, such as using a process which generates less noise or reducing the noise generated by the source, as well as administrative controls such as job rotation or simply increasing the distance between the operator and the source of noise, which can dramatically reduce their exposure. 

Only when these two stages have been thoroughly explored should the supply of HPE be considered.

The Control of Noise Regulations details two noise action values and one exposure limit value for employee exposure to occupational noise. If the lower action value of 80dB(A) or 135dB(C) is exceeded, employers are required to make hearing protection available upon request.

Where exposure exceeds the upper action level of 85dB(A) or 137dB(C), employers must provide personal hearing protectors where noise cannot be reduced by other means.

The limit values of 87dB(A) or 140dB(C) must not be exceeded under any circumstances.
These figures are, in theory, relatively clear, but ensuring the levels are not exceeded requires accurate assessment of the noise type. Specialist equipment is available for use by in-house safety managers to measure noise levels, alternatively the same service can be provided by external consultancies.

British Standard EN458 suggests an exposure level of between 75 and 80dB(A) as being ideal, with 70-75dB(A) and 80-85dB(A) as acceptable. Anything above 85dB(A) is deemed as excessive noise likely to cause hearing damage. Conversely, wearing HPE which reduces noise levels to below 70dB(A) can cause other problems, as the employee may experience difficulties in communication or hearing warning signals and as a result become isolated from their environment.

The attenuation of hearing protection can vary greatly with noise frequency, and the overall effectiveness of a particular ear protection product depends on the frequency content of the incident noise.

There are three main methods that can be used to calculate the sound pressure levels at the ear when wearing hearing protection.

The most accurate method is octave band analysis, which is based on octave band measurements of the sound pressure level of the noise. This, in conjunction with manufacturer’s data on the attenuation provided in each octave band, will result in an accurate assessment of noise at the user’s ear.

The High, Medium, Low (H, M, L) method requires measurement of the A-weighted (LA) and C-weighted (LC) sound pressure levels. The H, M, L values supplied by the ear protection manufacturer can be used to estimate the protection required.

The third is the Single Number Rating (SNR) method which requires measurement of the C-weighted (LC) sound pressure level. The SNR value (taken from the manufacturer’s data) minus the LC value allows the effective A-weighted sound pressure level at the ear to be calculated.
It is essential to recognise and understand that the varying occupational noise hazards and environments will require different types of hearing protection, offering different attenuation levels.

A further main issue here is that not everyone will achieve the same level of attenuation with an identical piece of equipment. If the HPE is not correctly fitted, then a lower level of protection will be achieved. For example, many people do not realise that roll-down earplugs need to be squeezed into as small a cylinder as possible and then pushed well into the ear and held for a few seconds to offer optimal protection.

Protection levels will also suffer if the HPE is dirty or poorly maintained, or if there are compatibility issues with other personal protective equipment (PPE).

For these reasons, the HSE’s “Controlling Noise at Work” document suggests that a “real world” factor of 4dB be applied, meaning that when calculating the actual protection level offered by HPE, 4dB should be deducted from the manufacturer’s own predicted attenuation figure.
Another way of applying “real world” attenuation and derating is to add 4dB to the calculated sound pressure level (LA) at the ear under the HPE worn.

Once the required attenuation level has been calculated, including the 4dB “real world” allowance, there are a number of other factors to be considered in the selection process.

Key factors affecting specification
The products must firstly be suitable for the work being carried out – being durable enough for the environment they are in, and not needing regular adjustment. HPE must be compatible with other PPE being worn – for example, an operative needing to wear a welding shield will be unlikely to be able to wear ear muffs underneath. In this instance, ear plugs or banded ear plugs which sit under the chin or behind the neck may be more appropriate. Alternatively, consideration could be given to a welding shield with approved ear muffs built onto the side.

HPE must also account for the pattern of noise exposure – for example, continuous noise or intermittent loud bangs in foundry environments – while it should allow for communication if required. Some HPE offers communication solutions such as built-in communication radios or level-dependent ear muffs which electronically analyse the sound before transmitting it to the ear. Bluetooth can also be built in within HPE, offering communication and radio capabilities.

The environment in which the product is to be used is another key consideration when choosing between disposable and reusable HPE –  products used in particularly dirty or dusty environments are likely to require regular maintenance in the form of frequent cleaning and daily visual inspections for wear and damage.  However, for all HPE to remain effective, it is good practice to ensure a stringent care and maintenance policy is in place and that employees carry out the simple checks required.

Comfort and user acceptance are vital, and even a small period of non-usage due to discomfort or removing the HPE (for example, to listen to someone talk) will potentially have a significant effect on the protection offered. Any level of usage below 100 per cent in the exposed area is likely to significantly reduce the HPE’s effectiveness. Simply not wearing the HPE for 30 minutes during an eight-hour exposure will reduce the HPE attenuation to near zero.

The selection process should also establish whether the user has any medical disorder that could influence the selection. This can include earache, irritation of the ear canal, discharge, hearing loss, or any type of sensitivity to noise. Where employees have any such medical conditions, the employer should seek medical advice as to the suitability of hearing protection.

Once the decision on HPE has been made, it is not acceptable simply to provide HPE to employees and expect that to be enough. It is a legal requirement that training and information be provided in correctly fitting the HPE and when to put it on, how to care for and maintain the products and ensure that a health surveillance programme is in place.

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