Noise induced hearing loss: causes and impacts

November 11, 2015

It is estimated that 18,000 people have noise induced hearing loss (NIHL) caused or made worse by work in the UK. Authors of the research paper Noise-induced hearing loss in the 21st Century from the World Journal of Otorhinolaryngology (WJO) confirm that it is the second most common form of hearing loss, after age-related hearing loss, yet 100% preventable.

Causes of NIHL

Long term exposure to sound above 80dB (A) can cause damage to an individual’s ears. NIHL can be caused by a one-time exposure to an intense “impulse” sound such as an explosion, or by a continuous exposure to loud sounds over an extended period of time, such as noise generated in a woodworking shop.

When we are exposed to potentially harmful noise, sensitive structures in our inner ear can be damaged. These sensitive structures, called hair cells, are small sensory cells that convert sound energy into electrical signals that travel to the brain. Once damaged, our hair cells do not grow back.

So that we can prevent NIHL, it is important to have a basic understanding of:

• Sound
• How sound is measured, and
• What an individual perceives as a change in sound level.

We measure sound levels in decibels (dB). 0dB is the lowest threshold of human hearing, with normal speech having a sound level of approximately 60dB. Sound levels above 120dB can be uncomfortable, with sound levels between 130 to 140 dB being painful.

The meters that we use to measure noise mimic the human ear, which is more sensitive to some sounds than others. Noise measurements at work are usually shown as dB(A), which means they directly relate to what we hear.

The two things that matter are the noise level and how long people are exposed to it. We know that people who are exposed to 80 dB(A) for eight hours a day are likely to suffer harm to their hearing.

You might just notice a 3 dB(A) change in noise levels, because of the way our ears work. Yet every increase of 3 dB(A) doubles the noise level. What seems like small differences in numbers are really big changes in how much noise people are exposed to.

If a noise level is doubled (i.e. the noise level increases by 3 dB), then the same amount of noise exposure occurs in half the time. The following table shows equivalent noise exposures. All of them are the same as being exposed to 80 dB(A) for eight hours.

Equivalent Noise Exposures

The minimum change that a human ear can detect is about 3dB, however, on average a person perceives a change in sound level of about 10dB as a doubling (or halving) of the sounds loudness. A decrease in sound level of 10 dB actually represents a 90% decrease in sound intensity, but only a 50% decrease in perceived loudness because of the nonlinear response of the human ear.

Taking the actual measurement of sound and human perceived loudness into the work environment can have an impact on how we respond to noise as individuals, and would allow a better understanding of the damage that noise may cause to individuals when there are very small increases in noise levels.

Examples of everyday noises that we can expect

Further examples of industrial process associated with high noise levels

Although being aware of decibel levels is an important factor in protecting an individual’s hearing, distance from the source of sound and duration of exposure are equally important.

Impact of NIHL on individuals

The impact of NIHL on individuals is considerable. When a person is exposed to loud noises over a long period of time, symptoms of NIHL will increase gradually. Over time, the sounds a person hears may become distorted, and it may be difficult for the person to understand speech. Someone with NIHL may not even be aware of the loss. Some signs of hearing loss are:

• Muffled hearing
• Temporary hearing loss or ringing ears (tinnitus)
• Struggling to hear a normal conversation or household sounds
• High volume of TV or radio
• Telephone conversations become increasingly difficult
• You cannot hear properly when your back is turned away from the noise.

For some people the problem of loss of hearing is severe enough to impact their everyday life. Many people find that they feel isolated, and frustrated at not being able to be involved in a conversation. There may be a lack of understanding by family, which can result in the family feeling:

• Frustration at not being understood
• Guilt that misunderstandings are their fault
• Embarrassment at others’ misunderstanding
• Irritation at having to repeat a lot
• Anger at the person’s failure to pay attention
• Overwhelmed by the person becoming too dependent.

In a work environment the individual may not be able to hear important information as part of a meeting, and it may cause interpersonal problems that can cause frustration and stress.

What can be done to prevent NIHL?

As we have seen, long term exposure to sounds over 80dB (A) can damage your ears, it is therefore essential that employers comply with the Control of Noise at Work Regulations 2005 in order to protect their workers from NIHL.

The first thing to decide is whether you have a noise problem in your area. This depends on how loud the noise is and how long people are exposed to it. As a simple guide you will probably need to do something about the noise if any of the following apply.

• Is the noise intrusive — like a busy street, a vacuum cleaner or a crowded restaurant — for most of the working day?
• Do your staff have to raise their voices to carry out a normal conversation when about two metres apart for at least part of the day?
• Do your staff use noisy tools or machinery for more than half an hour each day?
• Do you work in a noisy environment, e.g. construction, demolition, engineering?
• Are there noises due to impacts (such as hammering)?

If you think you may have a noise problem, the next stage is to assess the risks. If it is a simple problem, then this may be easy to do. But it is likely that you will need to have the noise levels measured, using a sound meter.

Noise measurements must be made by competent people, who have been trained in the techniques of noise measurement and have experience of assessing noise. They will be able to use the readings to decide whether the noise levels need to be controlled and how.

If noise needs to be controlled, you’ll need to make sure that the controls are put in place and work.

The controls you need will depend on what is producing the noise. Protection is best achieved by controlling the noise at source by following this sequence.

• When purchasing machinery or plant, obtain noise data from the supplier. The noise levels should be relevant to where workers will actually be.
• Move noisy machinery/plant into areas where there are no workers, or few workers (into an outbuilding or dedicated room).
• Where noisy machinery/plant has to remain in the working area, enclose it within a sound-insulating enclosure if possible. Anti-vibration machine mountings may also be required.
• Where enclosure is not possible, reduce noise by other engineering means such as:
  • Lining guards/panels with noise dampening material
  • Providing acoustic screens
  • Lining the inside of hoppers with impact-deadening material
  • Fitting anti-vibration mountings
  • Fitting silencers to exhaust systems
  • Ensuring good maintenance to stop rattles and prevent noise from wear.
• Where noise levels still exceed 85dB (A) ensure workers wear hearing protection (ear plugs or earmuffs) within the designated and clearly marked zones.
• Duration of exposure can be reduced by job rotation or providing a noise refuge.

Where hearing protection is used, it needs to be selected to give enough protection to get below 85dB (A) at the ear. When choosing hearing protection consideration should be given to the comfort and fit for the user, hygiene, and whether the protection has to be worn with other protective equipment. There should be a range of protectors so that employees can choose ones which suit them. Care should be taken to provide protectors that do not cut out too much noise, as this can cause isolation or lead to an unwillingness to wear them.

Do not:

• Make the use of hearing protection compulsory where the law does not require it
• Have a “blanket” approach to hearing protection, it is better to target its use and only encourage people to wear it when they need to.

It is essential that hearing protection works effectively and is maintained in good/clean condition, earmuff seals are undamaged, there are no unofficial modifications, and where compressible earplugs are used, they are soft, pliable and clean.

Impact of NIHL on the UK **Box Out**

NIHL claims are the most abundant of the disease claims received by insurers. Claims cost insurers £70 million per year, however the number of claims has reduced over the last few years. Although, it is thought that the reduction in claims is partly inspired by reform in insurance legislation in 2013 rather than in better controls. There is very little information on the impact of NIHL on the economy, however, the overall impact of hearing loss on the UK economy has been estimated at £25 billion. It is clear that any hearing loss has a massive impact on the quality of life of individuals. Work related hearing loss is entirely preventable, and therefore employers can help themselves in reducing their own costs by putting in place robust noise protective measures, that will prevent their staff from losing their hearing.