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Tackling Noise Conference 2003 Paper produced by Hazel Guest Definitions Before launching into a talk about low frequency noise (LFN) and infrasound it would be a good idea to start by defining what they are.
Figure 1 (above) shows the lower half of a piano keyboard, from the lowest note (which is an A) up as far as middle C. The numbers represent frequency of vibration measured in cycles per second. For each octave descended the frequency is halved. Low frequency is roughly defined as anything below about 150 cycles per second. Infrasound is defined more specifically, and consists of all frequencies below 20. This means that infrasound is off the keyboard to the left. Many people are misled by the term ‘infrasound’ into believing that frequencies below 20 are inaudible to the human ear. In fact they can be heard if loud enough. In this paper I shall be mainly concerned with frequencies below about 50-60 including infrasound, since this is the range which seems to be causing the most intractable problems for the public. Problems Associated with Very Low Frequencies Many modern sounds have very low frequency (VLF) components, for example: · road and air traffic · industrial and commercial machinery · air-conditioners, central heating · amplified bass music These sources are proliferating and are likely to continue doing so for the foreseeable future. VLF’s are different from higher frequencies in certain respects which make them particularly distressing to those people on whom they are inflicted: |
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1. They travel further than higher frequencies and therefore affect a much bigger area. For example thunder sounds much more like a deep rumble from a distance than it does close up. 2. They penetrate through substances which act as sound barriers to other noises. For example, when one is disturbed by a neighbour’s amplified music it is the bass and percussion which are heard most strongly. 3. Unlike sounds of a higher pitch, one cannot habituate to them. People say you can get used to any noise after a while. This is not true of VLF. So, if your complaint is not successfully dealt with by the local authorities then you are doomed to protracted misery. 4. One person may be seriously disturbed by a certain VLF while another, who has perfectly good hearing, cannot even hear it. This is because the lower audibility threshold varies enormously from one individual to another. It often happens that someone complains to the local Environmental Health Officer (EHO) about a certain noise and the Officer cannot hear it, with the result that the complaint is dismissed and the problem remains. This can be devastating for the complainant. 5. VLF’s can cause extreme discomfort even when only just audible, and a slight increase in volume may reach the pain threshold. 6. VLF’s, especially infrasound, are capable of causing a range of symptoms which are known to include: loss of concentration, a sensation of pressure inside the ears, pain at the base of the skull, nausea, and hallucinations. It is not necessary to be able to hear the sound in the normal sense for these symptoms to be experienced. From my own experience I can add to this known list two further symptoms: a very unpleasant sensation as if the brain were vibrating inside the skull, and after long-term exposure a lowering of the lower audibility threshold to the point at which one can hear the background infrasound vibrations in most buildings. 7. On top of the symptoms listed above, after prolonged exposure plus failure to get the authorities to do anything about it, people may suffer psychological damage, and several suicides have been reported in the press. 8. Very little funding for research into the harmful physiological and psychological effects of VLF has been made available to the scientific and academic communities. All I have been able to find so far is a team based in Portugal that has carried out research into the effects on rodents, but not on humans. Forced Vibrations In recent years there have been hundreds of complaints to local authorities in the UK and other countries, from people who are disturbed by low hums or rumbles inside their homes but which cannot be heard outdoors. What is happening? The answer is ‘forced vibrations’. Vibrations from a variety of sources such as traffic, air-conditioners, refrigeration plant and so on, can set a nearby building into vibration. A person inside that building is surrounded by six surfaces (four walls, ceiling and floor) all vibrating at close quarters within a closed environment, and all six surfaces are producing sound waves. Consequently someone indoors experiences a considerably magnified effect compared with someone outside near just one vibrating wall. The volume of sound outdoors may be below the person’s hearing threshold, with the result that the sound is heard indoors but seems to stop as soon as one goes outside. One would think this is a fairly obvious phenomenon, especially as it has been reported by hundreds of complainants. Professor Gavreau described his own experience of this phenomenon way back in 1968 in a paper published in Science Journal. Yet, since then the phenomenon seems to have been ignored. Earlier this year a Report on published LFN research was issued by DEFRA, yet it contains no mention of forced vibrations in homes. Nor is the phenomenon mentioned at LFN conferences. This is a widespread problem which is not even officially recognised, let alone addressed. The result is many highly distressed individuals who live inside homes which have been turned into hell. They are unable to sell and move away, because who will buy the property? I have known of a person who used to drive several miles each night in order to sleep in his caravan. Another complainant resorted to working and sleeping on her balcony during the summer when it was warm enough, and ear-defenders and sleeping pills for the rest of the year. Environmental Health Officers At this point it must be emphasised that this next section of my paper is a criticism, not of individual Environmental Health Officers, but rather of the system which expects them to deal with issues which are the province of acoustic specialists but without giving them either the necessary training or appropriate guidance. How do Officers deal with complaints of VLF? They have three standard responses: · The A-weighted decibel reading falls below the official guidelines for Statutory Nuisance. · I cannot hear it so you must have tinnitus. · You have abnormal hearing, and the law applies only to people with normal hearing. In the second of these responses they appear to be ignorant of the wide differences in lower audibility threshold from one person to another, which I have already mentioned. EHO’s who use this response are unaware that their own lower audibility threshold may be much higher than that of the complainant. They are also making diagnoses for which they are not qualified. The first response, namely that the decibel reading falls below the standard for Statutory Nuisance, is based on a misuse of weighting. Weighting is a device for reconciling measured decibels with the ear’s ability to hear. It involves subtracting a certain number from the decibel reading obtained with a sound-level meter. Figure 2 shows the amount that is deducted for various frequencies (Hz) under two different methods of weighting, A and C. At the lowest frequencies the amount deducted under A-weighting is so enormous that it pretty well eliminates all VLF’s.
A-weighting was designed many years ago and in the scientific world has now been replaced by alternatives, usually C-weighting, for dealing with LF. However EHO’s normally take their initial decibel readings with a sound-level-meter which has A-weighting built into it. Consequently the VLF components of a noise get automatically eliminated from the start. Moreover all the official guidelines issued to EHO’s for determining Statutory Nuisance from noise, still give rules of thumb in terms of A-weighting. Unfortunately A-weighting subtracts so much from VLF’s that the resultant decibel values are rarely high enough to constitute a Statutory Nuisance, no matter how loud and devastating is the noise to the complainant. Even those EHO’s who are knowledgeable about C-weighting, are unable to apply that knowledge because they have to follow the official guidelines regarding Statutory Nuisance which are all framed in terms of A-weighting. The net result is that complaints of VLFN are doomed to being dismissed because the method of measuring the volume of noise automatically eliminates LF components. The extent of the problem became apparent last year when I sent out questionnaires to all EHO’s in the UK. Their replies revealed enormous inconsistencies across the UK, both in their understanding of acoustics and in how they handled LFN complaints. A third of those who responded did not even have access to a frequency analyser, even though their own guidelines state that this is the correct instrument to use. Of those who replied to my question about weighting, a third stated categorically that they would use A-weighting for all LFN complaints including infrasound. This is in spite of the fact that leading scientists have been condemning the use of A-weighting for VLF’s for at least two decades, and the World Health Organisation has published a document which makes the same point. The obvious conclusions to be drawn from this survey are: · The system across the UK is totally inconsistent. · Many EHO’s have inadequate training in the basic physics of LFN. · Their official guidelines are hopelessly out of date. The errors and misapplications of science revealed by this survey, indicate that they are widespread within the profession of environmental health. This is high-lighted by the fact that a spokesperson for the profession’s chartered institute recently confirmed in a letter that A-weighting is used in all cases including infrasound, and dismissed C-weighting as irrelevant. In other words these errors have become institutionalised. Magistrates The third standard response from EHO’s when receiving a LFN complaint, is: You have abnormal hearing, and the law applies only to people with normal hearing. This is rubbish! A search through the relevant laws has not revealed any requirement that complainants must be capable of passing a hearing test in order to qualify for protection under the law. This would be both discriminatory and contrary to the so-called ‘thin skull principle’, which states that if A hits B over the head and B dies because he happens to have a thin skull, then A is still guilty of manslaughter. The fact that B had a thin skull is no defence. Surely this principle means that individuals who have a lower than usual audibility threshold so that they can hear lower frequencies than their Environmental Health Officer, should, if anything, have more protection under the law, and certainly not suffer discrimination simply because of their unusual physiology. Unfortunately magistrates are not usually acousticians or structural engineers and they rely upon EHO’s as expert witnesses when complaints of noise come to court, little knowing that the EHO may be ignorant both of the physics of LFN and of this particular aspect of the law on noise. Some Speculations When my own block of flats was subjected to forced infrasound vibrations caused by neighbouring machinery, my observations led me to a number of conclusions. These are only speculations and therefore need to be confirmed by proper scientific research. They include: · If a VLF is just below audibility, it is nevertheless registered by the brain at an unconscious level. If the stimulus persists, then after some time the brain will begin to perceive it consciously. · After temporary absence from the stimulus, on returning there is a delay before the brain again begins to register it consciously. · After continuous stimulus for a long period of time, there is a permanent lowering of the audibility threshold. Research needs to be carried out to confirm these hypotheses. If proved to be true, then many of the laboratory tests upon which were based our current standards for Statutory Nuisance, will have been shown to be invalid or incomplete. This should radically affect the ways in which research into the effects of VLF’s on the human organism, and audibility thresholds in particular, are carried out in future. Conclusions The system in which are vested the authority and the power to deal with this kind of problem, is riddled with ignorance at every level from junior local Officers right up to Government itself. Much of this ignorance has become institutionalised in the form of pseudo-science and pseudo-law. The following changes are urgently needed: · The phenomenon of forced vibrations in domestic buildings must be recognised. · VLF’s should not be treated under the same regulations as normal noise. They should be recognised as having unique characteristics, and separate laws and guidelines drawn up. · There needs to be a national team of expert acousticians and structural engineers, on whose expertise local Environmental Officers can call whenever they have to deal with a complaint of VLF. · The training of EHO’s needs to include a sufficient understanding of VLF’s such that they are aware when the advice of an expert should be sought. · Magistrates need to become aware that the usual training of EHO’s does not normally equip them as experts in the specialised field of VLF, and that the law on noise does not discriminate against people who do not have normal hearing. · There is a need for research into the effects of infrasound on the brain and on the whole organism, both in the short term and after long-term exposure, whether or not it can be heard. References Centre for Human Performance, Portugal. mariana.pereira@oninet.pt <mailto:mariana.pereira@oninet.pt> Environmental Protection Act 1990, Chapter 43, sections 79-83. Gavreau,V (1968), ‘Infrasound’. Science Journal, vol.4 (January 1968), 33-37. Guest,H (2003), ‘Inadequate standards currently applied by local authorities to determine Statutory Nuisance from LF and infrasound’. Journal of Low Frequency Noise, Vibration and Active Control, vol.22, no.1, 1-7. Leventhall,G (2003), ‘A Review of Published Research on Low Frequency Noise and Its Effects: Report for DEFRA’. Noise and Nuisance Policy, Air and Environmental Quality Division, DEFRA. World Health Organisation (2000), ‘Guidelines for Community Noise’ ed. by Berglund, Lindvall, Schwela and Goh. Published by the Institute of Environmental Epidemiology, Singapore. |
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Tackling Low Frequency Noise |
