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Hearing Protection

Published: 10th Jul 2006

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Employer's obligation to protect their workforce

Noise induced hearing loss

Millions of employees throughout Europe are exposed to levels of noise which put their hearing at risk. Hearing loss caused by exposure to noise at work continues to be a significant occupational disease. Deafness, tinnitus or other ear conditions can be a result of exposure to excessive noise. A single, very loud sound such as an explosion can cause NIHL, but most people get it from regular exposure to sounds of 85 dB and above. Whether noise is encountered on the job or in the community, most people are at risk of NIHL if they don't take precautions.

How does noise damage the ear?

The answer to this is not completely known. However we do know that the damage is caused to the sensitive cells in the cochlea. For reasons which are not entirely clear some of the cells part of the way along the sensory organ in the cochlea are more sensitive than others. Hence noise induced hearing loss (NIHL) will begin to affect hearing of certain frequencies.

High noise levels damage the hair cells of the organ of Corti, affecting first those in the basal part of the cochlea concerned with reception of the higher frequency sounds (though not necessarily the highest) and progressing through to those receiving lower frequencies. This is reflected in audiometric changes which show loss of sound perception first in the 4-5 kilohertz (kHz) range, progressing both in severity and into lower frequency ranges.

The first symptom of noise-induced hearing loss is usually difficulty hearing a conversation against a noisy background. The sufferer comes to dislike gatherings of people where everyone is apparently chattering away happily, yet he or she hears just a jumble of noise. Consonants seem to be lost first. Often he or she will mention intermittent high-pitched ringing in the ears, though this is rarely sufficient to be more than an irritant. By the time these symptoms have become sufficient to prompt medical consultation, the damage as measured by audiometry will be severe and, even with cessation of noise exposure, progressive.

When hearing is reduced at 3kHz and below, conversation is significantly interfered with.

What circumstances may lead to Noise Induced Hearing Loss (NIHL)?

Workers at special risk of hearing damage (industrial deafness) are usually those in heavy productive industry, such as metal work, drilling and quarrying, stone cutting, or the use of noisy machinery, as in textiles, printing, wood cutting, transportation and agriculture. Noises above 90 dB, as measured with special instruments that are electronically weighted to mimic loudness functions of the human ear, are likely to cause damage to a proportion of the exposed population with continued exposure. Very high levels may cause damage after relatively short periods, even when the noise is intermittent. This may be illustrated by the frequent finding of hearing loss in people who have fired guns as an occasional hobby, as well as in people who are exposed to noise of lower levels but more constantly, such as those working on construction sites or in other industrial locations such as mines.

Tinnitus is only one of the symptoms of NIHL. Other symptoms include a gradual decrease in sound or a growing distortion, particularly of speech comprehension. Because it comes on slowly, a person with NIHL may not be aware of the impairment at first. He or she may even be unconsciously compensating for the loss by reading. Unlike many injuries or illnesses, hearing loss is permanent and irreversible.

The problem of noise in the workplace isn't new. For example, the problem of 'blacksmith's deafness,' from the continual clanging of metal on metal, dates back hundreds of years. But since World War II - when noise-induced hearing loss began attracting serious attention as soldiers returned from battle with hearing problems - there's little question workplaces have become louder.

From airports to construction sites, street repairs to landscaping - workers face a continual barrage of noise. Belt sanders (93 dB), bulldozers (105 dB), chain saws (110 dB), and pneumatic drills (119 dB) are just some of the offenders.

The 2006 Noise at Work regulations

Work-related noise is a growing concern across Europe as it directly affects millions of workers not only in heavy industry but also in growth sectors such as services, education and entertainment. One third of Europe's workers are exposed to high levels of noise for more than a quarter of their working time.

To protect workers, the 2003 EU directive that came into force in all Member States in 2006, has set a daily noise exposure limit of 87dB(A) and requires that 'the risks arising from exposure to noise shall be eliminated at their source or reduced to a minimum'

Employers have a legal duty to protect the hearing of their employees. Damage to hearing from exposure to loud noise at work is preventable. The risks can be controlled by good management. If people have to shout or have difficulty being heard clearly by someone about 2 metres away there may well be a noise problem at work.

Employers have to reduce risk of damage to employees' hearing and take specific actions where the noise exposure of their employees is likely to be at or above any of three 'action levels'.

What are the changes to the noise decibel levels?

Previously (under the Noise at Work Regulations 1989) the first action level was a daily personal noise exposure of 85 dB(A), the second action level was a daily personal noise exposure of 90 dB(A), and the peak action level was a peak sound pressure of 200 pascals.

With the implementation of the Physical Agents (Noise) Directive regulations in early 2006, the first action level is 80 dB(A) and a peak value of 112 pascals, the second action level is 85 dB(A) and 140 pascals, and there will is a limit value of 87 dB(A) and a peak action level of 200 pascals for exposures to high level noise of short duration, such as cartridge operated tools. This identifies the risks of exposure to impulsive noise as opposed to continuous noise exposure. Employers are required to take specific measures at these levels, including: carrying out noise assessments, reducing exposure, providing information and training for employees issuing personal hearing protection.

Hearing protection

Given the scale of the Noise Induced Hearing Loss problem, combined with the more stringent regulatory environment, clearly employers have an increasing obligation to take measures to protect their workforce.

Several measures can and should be taken in a hierarchical order: Assessment of exposure, using tools and equipment which generate a lower level of noise, segregation and insulation, appropriate work practices and personal protection such as ear muffs and ear plugs. As well as steps to protect workers from noise, many companies now carry out regular audiometry.

  • The most reasonable way to protect the ears is to generate less noise in the first place, by better design of machinery and equipment
  • Secondly steps should be taken to insulate the machinery to reduce the noise that it emits and to segregate people from it
  • People should work in areas where they are not exposed to high levels of noise
  • Remember the 'two metre rule' - if you find it difficult to communicate with a workmate at this distance because of noise, then probably the intensity is high enough to damage your hearing

At a personal level it is possible to protect the ears with ear muffs and/or ear plugs. If you must work in an excessively noisy environment, you should wear protectors. You should also wear them when you are using power tools, noisy yard equipment, or firearms.

Broadly speaking there are three types of hearing protection devices:

  • Muffs
  • Disposable earplugs
  • Custom made ear plugs

Ear muffs

Ear muffs fit over and around the outer ear. They need to be appropriately fitted with correct headband tension, and avoiding glasses or hair which will impair the seal and hence the protection.

Disposable ear plugs

Disposable ear plugs are small, often torpedo nose shaped or indeed with two or three flanges, synthetic inserts, that are fitted inside the outer ear (canal).

There are many types of such earplugs, with a wide range of pricing and noise reduction properties. For them to work properly they should be of the appropriate shape, and correctly inserted. They may cause irritation especially if dirty. They are usually disposable and will not fit properly if repeatedly re-used.

Unfortunately, hearing protection devices have one big drawback: no matter how effective the device, it only works if the wearer fits it correctly and uses it when necessary.

The UK Health and Safety Executive sponsored a research project... to establish the level of protection actually achieved by workers wearing such protectors in industry and to compare these 'real world' results with the test data.'

'The testing of hearing protection in laboratory conditions tends to give an unrealistically high estimate of their performance as, the subjects are usually familiar with the objectives of the test and are given precise instructions on the fitting of the device. Also the protector is usually new, and the subjects do not wear spectacles, and care is taken to ensure that beards or long hair do not impair the effectiveness of the device.'

A number of muffs and disposable ear plugs were tested and 'in general, there is a degradation in mean attenuation and an increase in the standard deviation associated with all the protectors when the 'field' data is compared with that quoted by the manufacturers.'

The report concluded that for muffs 'the degradation in performance is slightly more severe at the higher frequencies and that the average overall reduction is about 5 dB(A),' and that 'for plugs the degradation in performance is more uniform across the whole range of frequencies giving a reduction in overall attenuation of approximately 7-15 dB(A).'

Custom made earplugs

Custom made earplugs tend to be personally moulded and vented. They are a silicone rubber moulding which is moulded to each individual concha bowl and ear canal. The plug incorporates a central drilled channel in which a filter is placed which allows pressure equalisation but presents a finite impedance to the passage of audio frequency sounds.

The acoustic filter attenuates all sounds going to the ear but attenuates more in the mid-band range (approximately 1kHZ-6kHZ). Because of the through hole in the 'ear plug' a person is not completely isolated from his surroundings and conversations and warning signals may be heard.

Because custom moulded earplugs made from a soft rubber are a perfect fit to each ear, there should not be any problems of poor fitting or discomfort and therefore they tend to give laboratory attenuation in the 'real world.' They can also be comfortably worn under helmets or breathing apparatus. With a long life expectancy and no moving parts to wear out, such products are very cost effective over time. ?

Author Details:

Emtec Laboratories is based in Shropshire, England. For the last twenty-five years Emtec has been a market leader in custom made hearing protection manufacture. Emtec Laboratories is responsible not only for manufacturing, but also, direct marketing, aided by a network of agents, nationwide and international. Emtec manufacture the Noisebreaker, a custom made, soft rubber ear defender, which is extremely comfortable and therefore ideal for day-long wear.

Downton Stables, Downton, Shrewsbury, SY4 4PL, ENGLAND

Tel + 44 (0)1743 709480

email: info@noisebreaker.co.ukwww.noisebreaker.co.uk

For more information on hearing protection please visit http://www.osedirectory.com/product.php?type=health&product_id=6

Published: 10th Jul 2006 in Health and Safety International

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