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Some sound advice

23 January 2013

Hearing protection equipment should always be the last resort when managing noise in the workplace but once it is deemed necessary there are a number of points to consider in the selection process, explains Sarah Broadbent

Hearing protection equipment should always be the last resort when managing noise in the workplace but once it is deemed necessary there are a number of points to consider in the selection process, explains Sarah Broadbent

The Control of Noise Regulations details two noise action values and one exposure limit value for noise exposure. If the lower action value of 80dB(A) or 135dB(C) is exceeded, employers must offer HPE upon request.

Where exposure exceeds 85dB(A) or 137dB(C), employers must provide HPE if noise cannot be reduced by other means.

The limit values of 87dB(A) or 140dB(C) must not be exceeded under any circumstances.

Ensuring 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, while external consultancies provide the same service.

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

Attenuation can vary greatly with noise frequency - a product's overall effectiveness depends on the frequency content of incident noise.

Three main methods are used to calculate sound pressure levels at the ear when wearing HPE.

The most accurate is octave band analysis, based on octave band measurements of the noise's sound pressure level.

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

The third is the Single Number Rating (SNR) method requiring measurement of the C-weighted (LC) sound pressure level.

The SNR value (taken from the manufacturer's data) minus the LC value allows calculation of the effective Aweighted sound pressure level.

Not everyone will achieve identical attenuation with an identical item - if HPE is incorrectly fitted, lower protection will be achieved. Protection will also suffer if HPE is dirty or poorly maintained, or if there are compatibility issues with other personal protective equipment (PPE).

"Real world" attenuation For these reasons, the HSE's "Controlling Noise at Work" document suggests a "real world" factor of 4dB be applied, meaning when calculating the actual protection level, 4dB should be deducted from the manufacturer's predicted figure.

Another method is to add 4dB to the calculated sound pressure level (LA) at the ear under the HPE worn.

With the required attenuation level calculated, including the 4dB "real world" allowance, several other selection factors must be considered.

Key factors affecting specification Products must be suitable for the work undertaken - durable enough and not needing regular adjustment. HPE must be compatible with other PPE worn - for example, an operative wearing a welding shield will be unlikely to be able to wear ear muffs underneath. In this instance, ear plugs or banded ear plugs siting under the chin or behind the neck may be more appropriate.

HPE must also account for noise exposure patterns - for example, continuous noise or intermittent loud bangs - and allow for communication if required. Some HPE offers built-in communication radios or level-dependent ear muffs which electronically analyse sound before transmitting to the ear.

Bluetooth can also be built in, offering communication and radio capabilities.

The environment where HPE will be used is a key consideration when choosing between disposable and reusable HPE - products used in dirty or dusty environments are likely to require frequent cleaning and daily visual inspections for wear and damage.

However, for all HPE to remain effective, it is good practice to establish a care and maintenance policy with employees undertaking the simple checks required.

Comfort and user acceptance are vital.

Any usage level under 100 per cent in the exposed area can significantly reduce the HPE's effectiveness. Not wearing HPE for 30 minutes during eight hours' exposure will reduce attenuation to near zero.

The process should also establish whether users have any medical disorder influencing selection, such as earache, ear canal irritation or hearing loss. In this instance, the employer should seek medical advice on the suitability of hearing protection.

Once the decision on HPE is made, training and information must be provided how to fit it, when to put it on, and how to care and maintain it. A health surveillance programme should also be established.

Sarah Broadbent is a technical engineer for occupational health & environmental safety at 3M. See 3M on Sta