Sound Advice

Do you want some?

Often, in the world of health and safety, we concentrate on the obvious hazards within the workplace and forget those aspects that do not immediately present themselves as a risk.

One such aspect is occupational noise. Being subjected to excessive noise over a prolonged period of time can lead to deafness and/or other types of hearing damage. Hearing loss caused by exposure to noise at work continues to be a significant occupational disease. Recent research estimates that 170,000 people in the UK suffer deafness, tinnitus or other hearing related conditions as a result of exposure to noise at work.

We should not forget that we have a legal duty under the current Noise at Work Regulations 1989 to reduce the risk of damage to employees’ hearing whilst at work through engineering or other means.

The current regulations set out actions and guidance for controlling noise through three Action Levels – First, Second and Peak. As with other health-based legislation, personal exposures are based upon an 8-hour working day, with correction factors for those working 12-hour shifts. The stipulation of the Noise at Work Regulations 1989 is that operators should not be subjected to noise doses exceeding 90dB(A) Lep,d (daily noise dose) over a working day. Where the Lep,d falls in between 85dB(A) and 90dB(A) hearing protection is recommended as a result of the increased risk of hearing damage. At 90dB(A) or above the provision of hearing protection becomes mandatory.

The Control of Noise at Work Regulations 2005

A new EC Directive on Noise was formally adopted in November 2002, giving member states 3 years within which to enact the requirements through domestic legislation. The timetable in the UK means that new regulations will be adopted late 2005 with a short transition into early 2006. The existing Noise at Work Regulations 1989 will be repealed and replaced by the Control of Noise at Work Regulations 2005.

There are a number of differences between the old and new legislation. The primary ones are related to new stricter noise exposure standards. There will be a reduction of 5dB(A) to both the Lower and Upper Action level and to 80dB(A) Lep,d and 85dB(A) Lep,d respectively. In addition, the Peak or third Action Level of 140dB(C) will be replaced with 1st and 2nd Peak Action Levels of 135dB(C) and 137dB(C) Peak respectively.

Another major change with the new Control of Noise at Work Regulations 2005, is the introduction of a Maximum Permissible Limit of 87dB(A) and 140dB(C) Peak. This level prohibits anyone being subjected to a daily noise dose greater than 87dB (A) Lep,d . In order to help compliance with this element of the regulations, the use of hearing protection will be accepted.

Much emphasis has been placed on reductions to noise standards but it is important that we do not lose sight of the most fundamental changes – the shift in emphasis from measurement to control. The aim is to encourage employers to assess the likelihood of harm occurring (risk assessment) and implement a control regime that focuses on elimination then engineering control to reduce this risk to acceptable levels. Whilst in many cases the need for noise monitoring will still be required, the new emphasis means that the first step must always be to eliminate as much noise as possible then control any remaining noise at source.

Health effects

Noise induced hearing loss (NIHL) has long been recognised as a common industrial disease. Repeated exposure to high noise levels on a daily basis over a prolonged period of time is known to cause cumulative hearing loss. The loss is due to degeneration of the hair cells within the inner ear, or cochlea. Hearing loss can occur at a range of frequencies, depending on the type of noise, but typically damage resulting in NIHL is caused at 4KHz – one of the most important frequencies within the audible range because of its effect on our ability to hear the spoken word.

NIHL is sometimes confused with ‘natural’ hearing loss that occurs with ageing, known in medical circles as PRESBYCUSIS. Whilst Presbycusis also causes loss at the 4KHz range, the loss is less acute than that associated with exposure to noise at work. Indeed the expert eye can easily differentiate hearing loss caused by exposure to noise at work from that associated with ageing because the level of deafness is far more acute. This can be seen by the acute angle on an audiogram curve. Because of this the condition is also known as the “4KHz dip”.

There are a number of terms relating to hearing damage that are worthy of explanation. SENSORI-NEURAL hearing loss is permanent damage to the auditory nerve stemming from the inner ear or cochlea.

If the hair cells are made to work too hard for too long, they become fatigued or damaged. TEMPORARY THRESHOLD SHIFT (TTS) is one of the first signs of over-exposure to noise. The hearing loss is recovered over a period of hours spent in a quiet environment. If noise exposure at levels high enough to cause TTS is allowed to continue uncontrolled then PERMANENT THRESHOLD SHIFT (PTS) occurs. Here the hair cells are damaged beyond repair and the nerve cells die. Like presbycusis, this creeps up unnoticed, first becoming apparent as a dullness in perceived sound and later in loss of ability to hear normal conversation, particularly when in a social environment such as a pub, where there is a lot of background noise.

Actions to take

Until the Control of Noise at Work Regulations become law, you are obliged to assess and control noise in accordance with current legislation. Thus, as an employer, you have a duty to reduce the risk of hearing damage to employees by controlling exposure to noise. In order to carry out this duty, the first thing you need to know is which employees are considered to be at risk and to what degree. Once you know this you can ascertain the noise sources (machinery and/or activities) that contribute the most noise and determine priority actions.

The key to obtaining this information is the Noise Assessment. The current regulations require an adequate noise assessment, which will facilitate compliance with duties relating to controlling noise exposure, providing suitable hearing protection, marking out hearing protection zones, undertaking audiometry and giving information, instruction and training to employees.

If any of your employees are likely to be exposed to the Second Action or Peak level, you must arrange for a competent person to assess the actual level of noise exposure.

People who work in engineering workshops, sawmills, foundries, bottling plants, discos or textile mills, or who use noisy equipment and machinery on a farm, in forestry, or on a construction site, are just some of those who could be exposed to dangerous noise levels.

As a simple guide you may have a problem if:

• You have to shout to be clearly heard by someone 2m away
• Your employees’ ears are still ringing after leaving the workplace

Controlling exposure

The regulations require that exposure to noise is reduced as far as possible at source before we provide and expect employees to wear ear protection. One of the underlying reasons behind the new legislation and accompanying guidance is that many companies simply do not comply. The provision of hearing protection does not reduce noise at source, yet in many cases simple maintenance techniques can have a significant impact on noise reduction.

There are many ways of reducing noise and noise exposure at source or along the transmission path before the noise reaches the person, but it must be accepted that no single technique will be appropriate for each situation.

In many cases, sufficient noise reduction can only be achieved through adopting a range of different techniques, some simple and cheap and others more complicated and costly. The first step must always be to try to eliminate the noise. After that, consider the many ways and means of controlling it. Consider the following in this order:

Use a different, quieter process or quieter equipment, e.g.:

• Can you do the work in a quieter way?
• Can you replace whatever is causing the noise with something that is less noisy?
• Introduce a low-noise purchasing policy for machinery and equipment

Introduce engineering controls:

• Avoid metal-on-metal impacts, such as the introduction of line chutes with abrasion-resistant rubber and reduce drop heights
• Vibrating machine panels can be a source of noise – add material to reduce vibration (‘damping’)
• Isolate vibrating machinery or components from their surroundings, e.g. with anti-vibration mounts or flexible couplings
• Fit silencers to air exhausts and blowing nozzles

Modify the transmission paths by which the noise travels through the air to the people exposed. For example:

• Erect enclosures around machines to reduce the amount of noise emitted into the workplace or environment
• Use barriers and screens to block the direct path of sound
• Increase the distance between the noise source and the operator

Design and lay out the workplace for low noise emission such as:

• Use absorptive materials within the building to reduce reflected sound, e.g. open cell foam or mineral wool
• Segregate noisy machinery and processes from quieter areas
• Design the workflow to keep noisy machinery out of areas where people spend most of their time
• Limit the time spent in noisy areas
• Maintain noisy equipment and machinery properly and regularly – it will deteriorate with age and can become noisier

Hearing protection

The provision and use of hearing protection should only be considered after sufficient measures have been taken to reduce noise at source, when the noise level remains above the Second Action Level. Ear defenders should be both suitable (i.e. comfortable and suited to the job) and effective (i.e. protect noise level entering the ear down to at least 85dB(A)).

There are 3 main types of ear protectors:

• Ear Plugs
• Ear Muffs
• Semi Inserts

Ear Plugs comprise disposable or reusable compressible material that can be inserted into the ear canal and will conform to the shape of most individuals’ ears without special fitting. They are convenient to use, although good hygiene is required. Disposable plugs should be thrown away at the end of every shift and re-usable plugs washed at the end of each shift and re-used. Ear Plugs are not suitable for those persons suffering from any form of ear disease.

Ear Muffs are the most popular means of re-usable ear protection and comprise hard plastic cups that fit over and surround the ears and are sealed to the head by cushion seats filled with a soft plastic foam and/or viscous liquid. The inner surface of the cups is covered with a sound absorbing material, usually soft plastic foam. Air cool pads are available for use in hot weather or hot environments. Helmet mounted Ear Muffs are available for use when safety helmets are required.

Semi Inserts are pre-moulded ear caps attached to a headband that presses them against the entrance of the ear canal. To make an effective seal the headband needs to press the caps firmly into the ear canals, and some people find the pressure intolerable, especially over long periods. Others find them convenient because they can be slipped off easily in quiet periods.

“if the majority of noise is low frequency (diesel engines, generators, etc) more care will need to be given to the protection provided”

When choosing hearing protection it is vital to ensure it is the correct type for the environment. This is determined through the Assumed Protection Factor (APF) which is supplied with all forms of hearing protection. One assesses the APF against the frequency analyses of the machines/environment. This will provide the information regarding the predominant noise, either high or low frequency. Once that is known, assessing the hearing protection is easy. As a general rule most hearing protection is good at the upper end of the scale, i.e. 500Hz-8KHz, but not so good at the lower end, 63Hz-500Hz. Therefore, if the majority of noise is low frequency (diesel engines, generators etc) more care will need to be given to the protection provided.

Dual protection

Where noise levels exceed approximately 115 dB(A), it is likely that both ear plugs and muffs will need to be worn to achieve the required attenuation. Values of APF for plugs and muffs used together should be obtained from the manufacturers. In practice the combined protection is unlikely to be more than 5dB(A) above the individual protection.

Maintenance and hygiene

The selected ear protection provided will, if worn correctly by the operator, provide a degree of protection against the noise. However, it is not recommended for the long term, because it has been shown that such protection is rarely worn correctly. Thus it is important that operators be trained to ensure that ear plugs are properly inserted or ear muffs correctly fitted around the ear with the seal in contact with the head all round, otherwise the level of protection is dramatically reduced.

To ensure that the ear protection (particularly ear muffs) provided stays in good condition regular checks must be carried out, including inspection of:

• The condition of ear muff seals
• Tension of headbands
• General condition of various parts
• Resilience and softness of ear plugs
• General cleanliness

Conclusion

Introducing a positive purchasing policy could be the single most cost-effective, long-term measure that you take to reduce noise at work. Choosing quieter equipment and machinery from the start can save you the cost of introducing noise-reduction measures once it is installed.

Remember, when the new regulations are implemented in the UK during 2005, they will repeal the existing Noise at Work Regulations 1989 and effectively lower the accepted noise levels within the UK workplace. Be prepared, undertake risk assessments and start to implement engineering controls before carrying out unnecessary noise readings. Follow the basic rule of thumb: If you have to raise your voice to someone who is less than 2 metres away the noise is approximately 80dB(A).

In order to protect your employees and business, understanding noise is vital.

For more information please visit http://www.osedirectory.com

Published: 10th Oct 2004 in Health and Safety International