INTRODUCTION

Excessive noise in the workplace is a well known cause of deafness, and many thousands of claims for industrially-caused deafness have been successfully fought through the courts. Noise induced hearing loss is the single biggest source of claims for industrial injury in the United Kingdom. The exposure of workers to noise in the workplace is legally controlled in the UK by the Health and Safety at Work Act 1974, and specifically under the Noise At Work Regulations 1989 (1), hereinafter abbreviated to NAWR. The latter have been amended by the issue of a European Community Directive (2)

Noise Does as a limit. The NAWR are based on the concept of a "noise dose" Briefly, this is based on the idea of equal sound energy, that a sound of a given level for a given time is equally hazardous in respect of hearing damages as on of say half of the noise power for twice the time. Two noise dose limits are adopted in the NAWR, of 85 and 90 dB at which different actions are required, but this has now been transcended by European legislation (2) which specifies a single sound dose limit equivalent to 85 dB (A) re 20µPa for a "working day" which is defined as being of eight hours (all levels in this report are referenced to 20µPa Noise doses at a level greater than this have been shown to cause irreversible hearing loss. Where the exposure is for a shorter time than eight hours, the equal energy concept allows an increase of level 2 dB for every halving of time of exposure, for instance, to 88 dB(A) for four hours pr 91dB (A) for two hours. Conversely, where the exposure is over a longer period of the day, as in saturation diving, the noise level must be lower, and over a twenty four hour period a level of about 80dB(A) is the maximum permissible. In practice, the noise levels encountered in the workplace vary during the day, but the equal energy concept is still applied and in practice the dB LAeq- the "averaged" level, or level of a constant noise of equal energy- is calculated, and used in the same way Reference (1) lists the rather involved method by which noise dose may be estimated, and there are now a wide range of sound level meters that provide this function for measurements taken in air.

While there is no physical reason for this scale being adopted, it has been found to relate well to the degree of hearing damage caused in many thousands of cases of industrial deafness and hence it has been universally adopted in legislation at European level.

Categories Of Noise Exposure

There are three main categories of occupational noise exposure to divers

  1. They may be exposed to noise while in transit to the place of work, for example while in flight in a helicopter to a diving platform

  2. They may be exposed to noise on the platform while at atmospheric pressure

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