5.3: Interpretation
The most important factor to be borne in mind when interpreting the guideline values given in either of the 1980 or 1995 WHO-inspired noise criteria documents is that neither set actually has any official status. The fact that the guideline values in each case are based on a consensus reached by an invited group of international experts in the field lends them credibility, but, in such a complex field, it is inevitable that individual experts will disagree to some extent. For this reason, any attempt at formal ratification of the guideline values by any form of international voting would probably be doomed to failure. On the other hand, both documents represent a considerable amount of careful and detailed analysis of the available literature and are extremely valuable for that reason alone.
If the basic validity of the guideline values given in the WHO-inspired documents is accepted, and ignoring the minor differences between the 1980 and 1995 versions and any minor controversies raised by differences between individual expert opinions, the next step is to consider how the guidelines might be interpreted in future noise regulations and standards. This is basically quite straightforward, in that apart from the 1980 suggested 'general environmental health goal' of 55 LAeq for daytime outdoor noise levels, virtually all of the guideline values are specified at the lower threshold below which the occurrence rates of any particular effect can be assumed to be negligible. It can be concluded that the guidelines do provide useful guidance as to the lower threshold levels below which residual noise impacts can probably be considered as negligible (threshold X on the curve given in figure 5). They can therefore be considered as 'desirable' and ideal targets.
While in an ideal world it may be desirable for none of these effects to occur, in practice a certain amount of noise is inevitable in any modern industrialised society. Perhaps the main weakness of both WHO-inspired documents is that they fail to consider the practicality of actually being able to achieve any of the stated guideline values.
We know from the most recent national survey of noise exposure carried out in England and Wales (SARGENT 93) that around 56% of the population are exposed to daytime noise levels exceeding 55 LAeq and that around 65% are exposed to night-time noise levels exceeding 45 LAeq (as measured outside the house in each case). The value of 45 LAeq night-time outdoors is equivalent to the 1995 WHO guideline value of 30 LAeq night-time indoors allowing 15 dB attenuation from outdoors to indoors for a partially open window (for free-air ventilation to the bedroom). The percentages exposed above the WHO guideline values could not be significantly reduced without drastic action to virtually eliminate road traffic noise and other forms of transportation noise (including public transport) from the vicinity of houses. The social and economic consequences of such action would be likely to be far greater than any environmental advantages of reducing the proportion of the population annoyed by noise. In addition, there is no evidence that anything other than a small minority of the population exposed at such noise levels find them to be particularly onerous in the context of their daily lives.
In view of the uncertainties involved in setting standards, the WHO guidelines might be considered as a highly precautionary approach if used when setting future noise standards and regulations to protect against possible health effects. While this precautionary approach may be justified by the scientific plausibility of these effects, it is necessary to place these possible effects in proper perspective. An over-precautionary approach to setting future noise standards and regulations at too low levels might lead to unacceptable impacts in other areas.
5.4: Summary
In essence, the WHO guidelines represent a consensus view of international expert opinion on the lowest threshold noise levels below which the occurrence rates of particular effects can be assumed to be negligible. Exceedances of the WHO guideline values do not necessarily imply significant noise impact and indeed, it may be that significant impacts do not occur until much higher degrees of noise exposure are reached. One difficulty here is the true importance of the different noise effects considered when placed in an overall context relating to quality of life, and the extent to which noise control might have excessive consequences in other areas of human experience.
As such, it would be unwise to use the WHO guidelines as targets for any form of strategic assessment, since, given the prevalence of existing noise exposure at higher noise levels, there might be little opportunity for and little real need for any across the board major improvements. On the other hand, the most constructive use for the WHO guidelines will be to set thresholds above which greater attention should be paid to the various possibilities for noise control action when planning new developments. It is important to make clear at this point that exceedances do not necessarily imply an over-riding need for noise control, merely that the relative advantages and disadvantages of noise control action should be weighed in the balance. It is all a question of balance, and mere exceedance of the WHO guidelines just starts to tip the scales.
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Published 12 September 2000
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