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Audiometry home
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Audiometry routine & reports
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Types of hearing loss
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Audiometry Q & A
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Noise assessment & training
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Spirometry / lung function
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About
hsmc
testing unit waiting area,
acoustic linings visible
Audiometry booth in
a mobile unit
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Types of hearing loss
Audiometry in the workplace is undertaken to try and
identify any hearing losses which are taking place due to noise exposure,
but why is it such a big deal?
There are two effects of high noise exposure - the hearing loss itself
and Tinnitus.
Tinnitus
This is experienced by many people, most often as a temporary ringing,
whistling or buzzing in the ear, (note: if the noise in the ear is more
like a voice saying "The Pope is an alien who has come to steal all our
pizza" this is probably not tinnitus, but does make you quite scary...). At low levels it is often
ignored but it can become permanent and have a huge impact on the life
of the sufferer.
Temporary tinnitus arising from colds, recent flying, etc. is perfectly normal and fades away again but tinnitus arising by noise is a more serious matter. During
the day this is often swamped by other noises but at night it can keep
sufferers awake which, as you may imagine, going on for month after month
and year after year has enormous impacts on their physical and mental
health. This is not helped that tiredness is also known to cause tinnitus and so a vicious cycle can begin.
Noise Induced Hearing Loss
The second potential effect is a reduction in the individual's ability
to hear, with the greatest losses being suffered at the key frequencies used to give meaning and clarity by the human voice. The loss is caused by the
cells in the ear which detect noise being damaged and ceasing to work.
The loss is permanent and cannot be reversed - the cells will not grow
back or recover.
One effect of this which is worth knowing about is that, certainly in the initial and middle stages of noise induced hearing loss, someone can have a large-ish degree of loss but not be deaf. The simplest way to explain it is that they can hear a car drive past 200 yards away quite easily, but can't follow what someone is saying who is sat next to them if there is a lot of background noise, such as in a pub, etc.
Other causes of hearing loss
The problem of noise induced hearing loss can be that it often does not occur in isolation and is laid on top of other hearing losses, most commonly the natural degredations due to knocking on a bit when hearing naturally gets worse as we get older.
The following are rough and ready charts of hearing loss in ten year increments. These show the lower limits of what would be acceptable hearing with increasing age - ideally hearing would be better than this. (These are the levels beyond which we would refer an idividual if too many results were dropping below the lines).
As a very rough guide at the age of 65 a man may show a loss of up to 70dB at the 4KHz frequency, while a woman may have lost up 58dB at the same point.
This loss in itself is significant and if a younger person was to suddenly go from their normal hearing to the ability of a 65 year old the losses would sound profound.
The basic principle of workplace audiometry is that we use the hearing tests to identify losses before they become a problem and avoid adding further reductions in hearing due to noise to the ageing process.
How this relates to the audiometry reports you will receive
The individual results may be presented graphically or
as tabular data. Graphically, audiometry results are presented for both ears,
in a similar manner to those shown here:
The graph above shows how the audiometry results look, in this case
for someone with a perfectly normal reduction in hearing.
The age-factor is taken into account by the faint red line visible on the audiogram above which
simply put is the lower limit of acceptability (this is not the only determining
factor but it is a key one) and this changes with the age of the employee.
The audiometry chart below is one we are interested in, particularly in workplace audiometry. This chart gives a good
indication that the individual is suffering from a degree of noise induced
hearing loss. This is classically evidenced by the dip seen at around
the 4,000Hz level, followed by a recovery up to 8,000Hz.
Note: audiometry can determine if noise may have played a part in an individual's hearing loss, it cannot:
- Diagnose the exact source of the noise - all noise sources have pretty much the same effect on hearing, irrespective of pitch.
- Tell you when a noise loss ocurred, so if somone worked in Job A for 15 years then Job B for 15 years, you cannot tell from the result which job, if any, caused the damage.
- Say for sure that 'noise caused this loss'. It is often stated that a 4 or 6kHz drop, recovering at the high end - the 'V' shape in the charts above - is proof of noise loss. However, recent studies have shown that 1 in 3 people with no history of noise exposure at all have exactly that same pattern of loss.
All audiometry at this level can do therefore is say that yes, there is a hearing loss, and it may be linked to noise exposure.
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