Nessun dorma

Environmental aspects of the 51m consultation response, part 20

In this blog I will continue the review of the potential impact of night-time noise caused by HS2 that I began in Silent night? (posted 3 Dec).

In view of its pedigree, it is to be hoped that the World Health Organisation (WHO) document Night Noise Guidelines for Europe (available here) is on the reading list of HS2 Ltd, but the existence of this document is not acknowledged in the AoS. This document has, however, been cited in the Southdowns report.

The WHO document defines noise nuisance levels by the parameter Lnight, outside, which may sound unfamiliar but is just another name for the equivalent continuous noise level over the eight hour night period. The “outside” label is attached to clarify that the noise level is outside the dwelling, as the impact on the sleeper will be from the noise level within the bedroom, which will be attenuated below the outside level by the building fabric.

The WHO document causes some confusion by referring to Lnight, outside as the level at the most exposed façade of the building. My understanding is that this does not imply that it is a “façade” measurement (which I explained in Adding to the confusion, posted 1 Nov), since a footnote on page xvii of the WHO document makes clear that it is the “incident sound” that should be considered, which indicates a free-field measurement. This interpretation is reinforced by confirmation in the WHO document that the definition of Lnight, outside should be as in EU Directive 2002/49/EC (available here), which clearly states that “the incident sound is considered, which means that no account is taken of the sound that is reflected at the façade of the dwelling under consideration”.

The WHO document recommends that “for the primary prevention of subclinical adverse health effects relating to night noise in the population … the population should not be exposed to night noise levels greater than 40 dB of Lnight,outside during the part of the night when most people are in bed”. It identifies this threshold as the NNG (night noise guideline). The document adds that “An interim target (IT) of 55 dB Lnight,outside is recommended in the situations where the achievement of NNG is not feasible in the short run for various reasons”.

The WHO is clearly not content that the IT should be accepted as a long-term target and comments that:

“IT is not a health-based limit value by itself. Vulnerable groups cannot be protected at this level. Therefore, IT should be considered only as a feasibility-based intermediate target which can be temporarily considered by policy-makers for exceptional local situations.”

The importance of IT and NNG in assessing the likely impacts of a project on the health of the affected population may be gauged from Table 5.4 on page 108 of the WHO document. This characterises the health effects of exposure to noise levels between 40 dB and 55 dB Lnight,outside as being:

“Adverse health effects are observed among the exposed population. Many people have to adapt their lives to cope with the noise at night. Vulnerable groups are more severely affected.”

For levels above 55 dB Lnight,outside the verdict is:

“The situation is considered increasingly dangerous for public health. Adverse health effects occur frequently, a sizeable proportion of the population is highly annoyed and sleep-disturbed. There is evidence that the risk of cardiovascular disease increases.”

The Southdowns report points out that the IT “has since been adopted elsewhere as an appropriate criterion level for the evaluation of night-time noise impacts” and also that it has “been acknowledged by the Highways Agency and the upper noise category of adverse night-time effects has been incorporated into a revised standard for noise and vibration assessment of road projects”. The implication of these remarks is that Southdowns considers that HS2 Ltd should employ IT, at least, as the night-time criterion for the assessment of HS2 noise nuisance. HS2 Ltd should, surely, also clarify its position regarding NNG.

As we have already seen a noise level of 55 dB Lnight,outside will be exceeded at any location where LAeq, 18hr is in excess of 60 dB and 40 dB Lnight,outside corresponds to 45 dB LAeq, 18hr. These noise exposures are, for the most part, within the grey dot classification of noise nuisance, leading Southdowns to comment that “the numbers of dwellings exposed to night-time train noise levels above 55 dB LAeq,8hr will be higher than the numbers of dwellings that exceed HS2 daytime trigger levels for ‘High Noise Levels’ and noise insulation”.

In other words, the excuse given in the AoS for not considering night-time noise is plainly invalid. HS2 Ltd has a clear duty to public health here and cannot ignore this matter. As it says in the Foreword to the Night Noise Guidelines for Europe:

“WHO defines health as a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity, and recognizes the enjoyment of the highest attainable standard of health as one of the fundamental rights of every human being. Environmental noise is a threat to public health, having negative impacts on human health and well-being.”

So what about our “fundamental rights”, HS2 Ltd?


One response to this post.

  1. Posted by Roger Waller on December 7, 2011 at 11:41 am

    Some very very pertinent points raised here Peter. Mind you I have always found it strange that constructors seem to assume we will always spend all our time indoors. Perhaps it’s a City thing when one is surrounded by noise, my garden average when last measured was 38db. It’s probably noisier indoors!!!


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