A SOUND EAR II - Association of British Orchestras

A SOUND EAR II
Key terms - noise level, average
noise level, exposure and risk
Noise is a fluctuation in air pressure, measured in Watts per square metre. The point of traumatic damage is
100,000,000,000,000 times the quietest sound detectable by a healthy ear. To cope with such large numbers, we count
the noughts - so decibels (dB) are similar to the Richter scale for earthquakes (but with the decimal point shifted one
place to make decibels look substantial). A 10dB change is a ten-fold change. A 3dB change is a doubling or halving.
The 5dB reduction introduced by the new law is a 69% drop.
To take account of the particular sensitivity of the human ear the dB(A) scale gives more or less weighting to certain
frequencies and is used for all risk measurements other than peak exposures.
Noise does not have a unit equivalent to Kilos or Calories – it only has the equivalent of mph. Rarely, a noise source
produces a very steady level. Usually, it fluctuates so we need to know the average level (Leq). Wear and tear on the
ears depends on the average level and the amount of time it lasted – called the exposure. When relating this to work,
we calculate the actual exposure and normalise it to eight hours (a nominal working day) to give the daily personal
noise exposure. Thus if someone does two sessions, their daily personal noise exposure will be lower than the
combined Leqs, because 6 hours’ exposure is averaged over 8. You can download an Excel macro from the Health &
Safety Executive website http://www.hse.gov.uk/noise/calculator which is invaluable in calculating exposures and a
useful educational tool (play around with the level and duration of exposure and see what difference it makes).
Exposure is about the noise level surrounding someone’s head. Where daily personal noise exposure is/will be too high,
people must be protected by wearing ear plugs or ear muffs etc, to reduce the noise entering their ears – ie. the risk.
If an ear splitting sound system is playing in an empty room, the average noise level may be extreme, but nobody is
exposed. If someone runs into the room to switch off the system, their exposure may be low even though the Leq
is high. If someone stays in the room to work on the system, and makes proper use of good ear protection, their
exposure may be very high, but the risk could be low.
What exposure period do you use? If you pay someone for a session, can you average their exposure over eight
hours? We think not. Orchestras of essentially full-time players may be able to average over the day, but in the main
we suggest you should only average over the time you have bought.
What if a player has already used up their exposure for the day when they turn up for your session? You could make
it a condition of booking that they manage their exposure so as to be able to incorporate your session (during which
risks are controlled as necessary).
Most Health & Safety law applies to risks arising out of or in connection with work. In respect of noise, this could
mean that calculations of exposure should include personal practice, since it is necessary for their work. There is
currently no consensus on this issue, and to date all orchestral noise assessments have excluded personal practice.
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Photo - Claire Tregaskis