NOISE INDUCED HEARING LOSS

While many of us take our hearing for granted, people who have worked for many years in noisy industry will attest to the difficulties hearing loss can cause.  In its early stages, many people affected by noise induced hearing loss (NIHL) are unaware they have it.  

However NIHL is insidious in nature; it increases slowly but surely over the years of continued exposure.  Ears do not discriminate when it comes to noise; any loud source of noise is potentially damaging whether it be industrial or recreational.  Are you damaging your hearing through noise exposure?  Do you engage in any of the following?

• Mowing the lawn
• Using power tools
• Motor–bike riding
• Recreational shooting
• Motor car racing (spectator or participant)
• Attending rock concerts (indoors or outdoors)
• Working around noisy machinery

If you answered yes to any of the above you must ensure your hearing is adequately protected.  Consult you hearing health clinician for advice and/or a full diagnostic hearing assessment.

The Hearing Mechanism

Sound enters the ear canal and is transmitted via the middle ear to the inner ear, where there is a very delicate structure containing many millions of “hair cells”. These hair cells contain little hair-like structures called cilia.

Cilia bend and sway in response to vibration caused by sound waves and as a result of this movement the hair cells send messages to the brain to indicate that sounds are present.

Damage to Hair Cells

If we over expose our hair cells to noise they become less able to bend and sway in response to sound vibrations.  This means a response can only be obtained by bigger vibrations caused by louder sounds.  Continued exposure may result in the eventual death of hair cells.  The symptoms of such damage are often experienced in the form of: hearing loss, increased sensitivity to loud sounds, distortion and tinnitus.

Hearing Loss

The decrease in hearing sensitivity caused by noise exposure starts in the high frequencies (high pitches).  This often causes the sufferer to experience difficulties hearing the telephone or door bells, understanding the television at a normal volume or understanding speech in a noisy situation such as a restaurant or shopping centre.  

With additional noise exposure, the hearing loss influences further in the high frequencies, aggravating any existing communication difficulties and then slowly progresses to include the lower frequencies.  By this stage, even face-to-face communication in a relatively quiet situation can become extremely difficult.

Increased Sensitivity to Loud Sounds and Distortion

Many people with NIHL also complain of intolerance to loud noises.  Even some moderate to moderately-loud sounds such as clanking cutlery and crockery may be experienced as unbearably loud.   Distortion is also commonplace and refers to the general lack of clarity of sounds, in particular, speech.  These problems are due to physiological changes that occur in the inner ear as a result of hair cell damage from excessive exposure to noise.  

Tinnitus

One of the most common and often debilitating problems caused by NIHL is tinnitus.  Tinnitus is defined as the presence of any sound in the ear/s or head that is not caused by an external sound source.  In other words, it is a sound generated by the hearing system that only the sufferer can hear.  It is often described as ringing or buzzing in the ears, although descriptions of the reported sound are many and varied.  Tinnitus can often be the first warning sign of damage to the hearing system from excessive noise and often precedes any recordable drop in hearing.  Tinnitus can be temporary or more permanent.  

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Management of NIHL

Hearing loss caused by excessive noise exposure is permanent and can cause the sufferer to feel isolated and cut-off from family and friends.  Recent advances in hearing aid technology have meant that we can help many of these people to reconnect with the hearing world, but even the best hearing aid is not as good as the ears that nature provided us.

Tinnitus caused by excessive noise exposure can be temporary or permanent.  While there is no instant “cure” for tinnitus, there are several methods to help manage the condition.  The best way to treat hearing loss and tinnitus is to avoid getting it in the first place.  The best way to do this is to limit noise exposure and/or wear hearing protection.

How Much Noise is Too Much?

Employers in noisy industry are bound by Occupational Health and Safety regulations to ensure their workers are not exposed to too much noise.  In Victoria, the regulations state that a worker may not be exposed to more than 85 decibels (dB) over an eight hour shift.  

Another way to decide how much noise is too much is the concept of a “noise dose”.  This refers to the relativity of noise levels to time of exposure.  It means that for every 3dB increase in noise level, the time of noise exposure must be halved; this will keep it within safe levels.

Safe Noise Doses 

We also use this as a benchmark to establish safe limits of noise exposure for recreational noise, but many of us are unaware how loud our environment is; this is because we don’t have access to the equipment used to measure noise levels. Some common activities and their average noise levels can be found in the table below.