AccidentsAccidents

Industrial Deafness / Tinnitus

What is Noise-induced Hearing Loss?

Sound reaches our ears as vibrations which are channelled along the ear canal to the eardrum. When the eardrum vibrates, it causes the three little bones of the middle ear to rock back and forth and they in turn pass the vibrations into the inner ear (or cochlea) where they are detected by special cells known as sensory ‘hair’ cells. Hairs on the tips of these cells detect the vibrations, enabling the cells to transmit signals to the brain. As we grow older, hair cells will naturally die off, coinciding with deterioration in our hearing. However, exposure to excessive noise can distort and damage hair cells, making them unable to transmit incoming sound to the brain and resulting in permanent hearing impairment.

Are there Different Types of Noise-induced Hearing Loss?

Noise damage to hearing can, broadly speaking, be divided into two types. Firstly, there is the gradual deterioration in hearing which comes from prolonged exposure to a noisy environment. Secondly, there is the more extreme acoustic trauma, a term used to describe the immediate damage to hearing experienced after exposure to a sudden, exceptional loud noise such as an explosion.

The exact process by which noise-induced hearing loss occurs is not yet fully understood, though scientists believe that the metabolism of the sensory cells is disturbed by the over-stimulation. What is clear is that repeated exposure to high intensity sounds can lead to a weakening of the structure of the sensory cell, leading to its eventual disintegration. This means that, at first, any hearing loss is temporary (a ‘temporary threshold shift’ of hearing). However, if the exposure continues or the ear is not given enough time to recover, the hearing loss becomes permanent and irreversible.

How Loud is too Loud?

Sound is measured in decibels (dB) on a logarithmic scale - this means that an increase or decrease of 3 dB represents a doubling or halving of loudness. So, for example, 73 dB is twice as loud as 70 dB.

An average conversation will reach around 60 dB while a busy street can peak at 80 to 90 dB. By 120 dB, some damage to hair cells will occur and at 140 dB noise causes immediate injury to an unprotected ear.

Although legislation governs levels of noise at work or in children’s toys, it is impossible to set an objective noise level which is safe for all. Provided the ear is allowed to rest, a level of 90 dB might be tolerated for up to 8 hours, but increase that level by just 3 dB and the time is reduced to just 4 hours. By 105 dB the limit is less than 15 minutes.

However, no two people will have an identical tolerance to noise. Research suggests that numerous other factors may have an impact, such as exposure to noise before birth or a genetic predisposition toward hearing loss.

Can Noise at Work Damage Hearing?

Noise-induced hearing loss is by far the most common preventable cause of all hearing loss and industrial noise remains the greatest source of all noise-induced hearing loss in the UK. According to the Health and Safety Executive (HSE), around 1.1 million people are exposed to potentially damaging noise levels in their workplace and a further 170,000 already suffer from deafness, tinnitus or other noise-related ear conditions as a result.

A recent survey found that a third of workers in noisy jobs left work with dull hearing, and a further 20 per cent suffered tinnitus. The report also found that it was not only workers in traditional industries who risked hearing damage - employees in call centres, restaurants, nightclubs, couriers and the police were also at risk. The Government has recently announced that studies are underway to identify health and safety issues, including noise hazards, in call centres and the leisure industry.

Are there any Industrial Noise Regulations?

The Noise at Work Regulations 2005 obliges employers to take specific action when noise reaches the set ‘Action Levels’ of 80 dBA and 85 dBA. These levels represent a worker’s average noise exposure during an eight hour working period and take into account any noise reduction workers gain from wearing ear protection. These specific requirements are in addition to the general duty on employers to minimise risks to employees.

If noise levels reach an Action Level threshold, employers have a specific duty to act to protect their employees' hearing as follows:

If daily noise levels reach 80 dBA

Your employer must:

  • tell you about the risks, and explain how you can protect your ears.
  • provide ear protectors for you to use and keep them in good working order.
  • make every effort to reduce noise levels as far as possible, by modifying or replacing equipment and maintaining it regularly. Noisy machinery may need to be enclosed so that the sound is muffled.

If daily noise levels reach 85 dBA

If you must work somewhere with daily noise levels at or above 85 dBA the law makes the wearing of ear protectors compulsory. So, in addition to the actions listed above, your employer must make sure that you wear them - if they don’t, they can be taken to court. Average daily or weekly exposure levels should never be above 87 dBA and sound levels must never peak above 140 dBC at someone's ear.

Your employer must also clearly mark ear protection zones - areas where you must wear ear protection.

However, the Regulations also require employers to ensure noise levels are minimised before resorting to ear protection, such as installing sound reduction equipment and taking noise levels into account when ordering new machinery.

Assessing the noise levels in your place of work can be complex and, according to the Regulations, should be carried out by a ‘competent person’.

However, the HSE advise that if you are unable to hear someone speaking normally at a distance of two metres, the noise level is likely to exceed 85 dBA. If you are still unable to hear at one metre, the level could be over 90 dBA.

Industrial noise levels vary greatly. Average peak noise levels by occupation include:

Quiet Office40-60 dB
Noisy Restaurant80-90 dB
Process Plant80-90 dB
Lathes90 dB
Can Manufacturing Plant100 dB
Hydraulic Press100 dB
Call Centre*up to 100 dB
Foundry100 dB
Police*up to 100 dB
Motorcycle Courier*up to 100 dB
Pneumatic Drill100 dB
Cinemaup to 110 dB
Chainsaw110 dB
Sandblasting112 dB
Diesel Engine Room120 dB
Riveting130 dB
Nightclub110+ dB

*Using in-the-ear acoustic devices, certain industries may be exempt from the Noise at Work Regulations 2005 and may be covered by specific noise legislation.

How can Hearing Loss from Industrial Noise be Prevented?

  • despite the Regulations outlining employers’ specific responsibilities, it is also the responsibility of all workers to ensure that they take necessary precautions to protect their hearing from noise-induced hearing loss:
  • advise your employer to undergo a full noise assessment.
  • be aware what noises can be damaging to your hearing, and wear ear protection in a noisy environment and in all designated areas - there will, or should, be signs to show you.
  • make sure you fully understand how to use and care for your ear protection.
  • tell your employer if there is a fault with either your own ear protection or the noise control equipment.
  • if you do work in a noisy environment, make sure you have regular hearing tests.
  • suggest to your employer ways of further reducing noise levels in the workplace.

How does Noise Damage Hearing?

Sensorineural hearing loss, the kind of loss experienced by people exposed to excessive noise, primarily affects the inner ear. Typically, someone with a noise induced hearing loss will have a ‘dip’ in hearing at around the 4 kHz frequencies. These frequencies are especially important in speech discrimination which means that, although some sounds will remain reasonably clear, the important speech sounds are unclear or distorted. A person with this type of hearing loss may be able to hear voices but may be less able to distinguish between similar words. Because the high frequencies are the first to be affected, understanding the voices of women and children can prove especially difficult. Understanding speech against a background of noise or other people speaking is also a common problem with this type of hearing loss.

However, it is possible to recognise signs of hearing damage at a far earlier stage. If your ears feel blocked, you have difficulty hearing people or you suffer tinnitus on leaving a noisy environment, your hearing may be damaged. Repeated exposure to noise at a similar level could leave you with permanent tinnitus or a serious hearing loss in later life. If you do suspect your hearing is damaged, make an appointment to see your family doctor immediately. Usually, your doctor will refer you to an audiologist or ENT specialist who will carry out a hearing test.

What Research is being Conducted into Noise-induced Hearing Loss?

Despite the fact that noise-induced hearing loss is permanent, scientists are optimistic that it may eventually be possible to reverse the damage in the ear by repairing or regenerating the sensory hair cells.

When these hair cells are damaged they are not replaced in mammals; however it has been shown that birds possess the ability to replace these damaged hair cells. Research is being undertaken to try and understand why birds are capable of regenerating hair cells, and what prevents this occurring in mammals. This will hopefully lead to the future development of treatments to induce hair cell regeneration in humans in order to restore lost hearing.

Researchers are also looking at identifying the genes involved in the normal development of hair cells. Some of the genes involved in this process have already been identified, and research is continuing with the aim of controlling cell development and looking at ways of triggering the process when damage has occurred to hair cells. The discovery of many of the genes responsible for hereditary deafness is also opening up significant new lines of research, enabling scientists to identify and study the precise role of some of the proteins needed for the development and functioning of healthy hair cells.

Research has been done to help understand the relationship between damage to the ear and tinnitus, and also the molecular basis of tinnitus, which may help in developing therapies to control the condition. Other studies include the effects of tinnitus on the sufferers' ability to concentrate and its interference with mental functions, and also the development of Tinnitus Retraining Therapy which helps to alleviate symptoms for many sufferers. In spite of these developments and the significant progress that has been made in recent years, medical answers for deafness and other hearing problems remain some way off.


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