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Sonic boom exposure effects III: Workshop perspective
SONIC BOOM EXPOSUBB EFFECTS:111
SONIC BOOM
EXPOSURE
EFFECTS
541
III: WORKSHOP
PERSPECTIVE E. J. RICHARDS Loughborough University, Loughborough, England AND R. RYLANDER
Department of Environmental Hygiene, National Institute of Public Health, 104 01 Stockholm 60, Sweden
The following interpretive summary of the workshop is an attempt to grasp and co-ordinate some of the more important topics that were raised, with special emphasis on interdisciplinary aspects. The views expressed in this summary do not necessarily reflect the thinking of each individual participant, nor can they be looked upon as a complete survey of all ideas developed during the workshop. Errors or omissions are the sole responsibility of the authors although an attempt has been made to minimize these by circulation of the paper to all participants before publication. Although conclusions and recommendations as reported here thus should represent the foremost in knowledge today, progress is continuously being made and the conclusions drawn in the near future might be different. Such alterations must not be used as foundations for retrospective accusations or criticism of shortsightedness. Such reactions represent too easy an escape from the mentally demanding situation of rethinking which everyone must face as long as scientific knowledge increases. The exposure to sonic booms is a new facet in the environment. Sonic booms may effect structures, terrain and animals as well as humans. The most important reactions in man after exposure to the sonic boom were identified by the workshop as startle, sleep disturbance and annoyance. It was pointed out that there are other stress reactions such as increases in the excretion of stress hormones, cardiovascular, gastrointestinal and central nervous system responses. The lasting effects of such physiological reactions on the health of man cannot be stated at this time. Moreover, data so far accumulated have not indicated such reactions at moderate boom peak overpressures. The commonly used expression “startle” was found to be poorly defined and often confused with orienting responses. It was considered essential to develop criteria to distinguish between startle reflexes and orienting responses, since their effects on performance could be quite different. Minor effects on performance were reported to occur at indoor boom peak overpressures as low as 6 N/m*, but these appeared more likely to have resulted from the orienting response rather than the startle reflex. Momentary impairment of performance on complex perceptual-motor tasks may occur after exposure to booms of moderate peak overpressure, but is less likely to have significant effects on comparatively uncomplicated tasks such as driving. Possible deterioration of the learning process (e.g., in schools with frequent exposure to booms over greater lengths of time) has not been studied. The effect of the sonic boom on sleep was considered to be of great importance. Several studies show that sleep is disturbed at boom overpressures around 30 N/m* under laboratory conditions. Results from a limited field experiment with night exposures in a quiet area show
542
E. J. RICHARDS AND R. RYLANDER
that the awakening frequency is high at boom overpressures around 60 N/m2. Data so far accumulated indicate the presence of groups of high sensitivity or risk in the population, notably elderly people or persons with a neurotic predisposition. Concerning day flights estimates of the number of day sleepers in different communities were considered essential. Even if data exist on the awakening effect both under laboratory conditions and in the community it was pointed out that hardly any data are available concerning the long term effects of sleep disruption. If conventional methods concerning performance are used, effects have been shown only under severe sleep disruption. Primary effects such as startle, performance disruption and sleep interference can result in subjective feelings of annoyance. Annoyance in itself is the result of a variety of environmental factors in which not only the direct effect of boom exposure but also the social surrounding plays a role. A schematic diagram of this complicated reaction picture is given in Figure 1.
Pato-physiological
Figure 1. Interrelationship of various aspects of the environment development of annoyance due to sonic boom exposure.
and pato-physiological
reactions for
In addition to the interrelationships demonstrated in Figure 1 the development of annoyance is also dependent upon other factors. The presence of, or belief in, structural damage or effects on animals, especially pets, will heavily influence the development of annoyance. The relationship between presence of annoyance in the community and number of complaints was discussed in terms of a basis for the establishment of exposure effect criteria for annoyance. It was emphasized that the number of complaints is a result of a complex interaction of factors, many of which are not related to the exposure itself. The number of complaints can thus not be considered as a reliable indicator of the annoyance level in the population. Concerning the exposure in general it was pointed out that in the nominal peak boom overpressure range of 60-100 N/m2 the individuals might hear fewer booms than they are exposed to. Booms may be masked by background noise or decrease below perceptible levels when penetrating through structures. The booms heard could then be those that deviate from the nominal value or occur at a time when the ordinary community background noise is low (e.g., in the evening or in areas for relaxation such as national parks). Consequently, the judgements made by individuals, especially concerning the degree of annoyance, could be based upon booms that attain levels above the nominal value or occur at certain times. The animal reactions encountered after exposure to sonic booms seem to be limited to short periods of alerting and orienting responses. The workshop agreed that results from studies on domestic or semi-domesticated animals were relatively conclusive but additional studies would be required. Additional pertinent information should be obtained from studies on wild animals, especially during sensitive periods such as mating and whelping. The difficulty for the general public to differentiate sonic booms from noise from low altitude
SONIC BOOM EXPOSURE EFFECTS:
III
543
subsonic jet overflights and other intluences from the environment may explain why certain effects on animals have been attributed to the sonic boom. A general conclusion reached by the group working on structures was that damage to primary structures in buildingsin good condition is not to be expected. The type of damage that occurs is mostly superficial and often connected to already existing strains in the structure itself. The term “cosmetic damage” was considered appropriate for this type of damage although the expression was not ultimately accepted, because of its psychological implications. Although the damage in itself is technically unimportant, its psychological consequences in terms of a criterion for annoyance reactions should not be underestimated. It was thought, however, that exaggerated reactions could be avoided if sufficient information concerning the risk of and reasons for structural damage was made available to the general public. Statistical estimates of the probability of failure of a group of structural elements can be made, but knowledge concerning isolated events is insufficient for prediction of the risk of an effect. By examining different areas and conditions of structures therein, picked at random, a good estimate for an expected damage frequency and severity could be obtained. These calculations could then be checked in actual overflights at varying boom peak overpressures. Criteria for various land areas could then be developed and, when combined with effects on humans and animals, form an area criterion for total effects. Based upon the available information on boom effects in the different areas of concern in the workshop the following suggestion for general sonic boom exposure criteria for outdoor reactions has been compiled (see Table 1). TABLE
1
General sonic boom criteria for outdoor reactions
Level no.
Description and effects Likened to distant thunder-might susceptible individuals probably occurs
Approximate outdoor nominal peak overpressure (N/m*)
cause startle reflex in especially
or awaken
light sleepers, habituation
Likened to moderate thunder-startle reflex present among persons exposed outdoors in quiet areas, awakening of sleepers in quiet areas Slight cracking sound, penetrates background noise-windows may rattle, causes startle and orienting response, wakes heavy sleepers Loud cracking sound, clearly audible above background noisestartle reflex and orientation response common outdoors, windows rattle, weak structures vibrate, feeding animals look up, show orienting response Strong cracking thunder-windows rattle, structures vibrate, windows or plaster might break although this is rare, startle or fright among majority of exposed outdoors, majority of sleepers awaken
20 50 100
200
500
Although the arrangement into these different levels is by no means complete and exceptions are common, this type of review can be of help when establishing research priorities. Special caution should be exercised concerning the exact classification of startle because this reaction has shortcomings in terms of definition.
544
E. J. RICHARDS AND R. RYLANDER
Concerning the sonic boom effects in general there was sound discussion about a unit for describing the sonic boom which could be meaningful to all investigators regardless of their specific area of concern. The conclusion was that whereas the nominal peak overpressure would be adequate for certain types of responses, the pressure rise time, the dB(A) fast level or other technical parameters might be more suitable for other types of effects. The importance of vibration especially when the boom was heard indoors had not been sufficiently explored in scientifically well-designed experiments. It was emphasized in the discussions that all units to measure the sonic boom need to be standardized and that the units used should have maximum significance. This becomes especially important when the dose-response relationship is to be established, either as an increased dose at one single exposure or as successive doses over longer periods. In order to facilitate the comparison between results from different research projects the need for a common reference noise signature was expressed. This could be in the form of either a burst of white noise or some other sound and should be included in all human experiments. However, apart from the sleep effect group, no specific recommendation was made concerning the characteristics of this reference noise. The nature of the vibrations of loose objects, particularly the secondary response, and the method by which such response creates sound from shelves, tables, etc., should be examined. It would also be very useful to carry out further work on the visual stimuli associated with such movements and with reflections from the windows arising from their movements. There is some evidence that aural stimuli supported by visual stimulifor example, amplified apparent movements by window reflections-can create fear and annoyance. Another general conclusion was that both laboratory experiments and field studies were necessary in future work. Laboratory studies were considered to be of importance especially to determine effect thresholds and the importance of certain technical parameters for specific effects. Attention was drawn to the fact that results from laboratory experiments have limitations in their application as the exposure in different conditions and the number of test persons is usually rather limited. Concerning field studies, the opportunity should be taken to perform studies in areas where sonic booms occur regularly and are experienced as part of normal daily life. The workshop further expressed the need for making full use of material already available at different research centres. The establishment of a reference centre with a data bank was discussed but no definite plans were made. The sonic boom is only one example of several noises characterized by sudden wavefronts that occur in the environment. Studies on sonic boom exposure effects have a general relevance to these other noises and further research should be designed, whenever possible, to include observations from which more general conclusions concerning these types of sound can be drawn. A problem deliberately avoided during the discussions was how scientific information concerning sonic boom effects should be conveyed to the decisionmakers in society. The formation of representative groups with sufficient technical expertise may provide an alternative to the situation in which scientists feed information into a bureaucracy which processes data and forms decisions by its own unknown standards.
SONIC BOOM
EXPOSURE
EFFECTS
541
III: WORKSHOP
PERSPECTIVE E. J. RICHARDS Loughborough University, Loughborough, England AND R. RYLANDER
Department of Environmental Hygiene, National Institute of Public Health, 104 01 Stockholm 60, Sweden
The following interpretive summary of the workshop is an attempt to grasp and co-ordinate some of the more important topics that were raised, with special emphasis on interdisciplinary aspects. The views expressed in this summary do not necessarily reflect the thinking of each individual participant, nor can they be looked upon as a complete survey of all ideas developed during the workshop. Errors or omissions are the sole responsibility of the authors although an attempt has been made to minimize these by circulation of the paper to all participants before publication. Although conclusions and recommendations as reported here thus should represent the foremost in knowledge today, progress is continuously being made and the conclusions drawn in the near future might be different. Such alterations must not be used as foundations for retrospective accusations or criticism of shortsightedness. Such reactions represent too easy an escape from the mentally demanding situation of rethinking which everyone must face as long as scientific knowledge increases. The exposure to sonic booms is a new facet in the environment. Sonic booms may effect structures, terrain and animals as well as humans. The most important reactions in man after exposure to the sonic boom were identified by the workshop as startle, sleep disturbance and annoyance. It was pointed out that there are other stress reactions such as increases in the excretion of stress hormones, cardiovascular, gastrointestinal and central nervous system responses. The lasting effects of such physiological reactions on the health of man cannot be stated at this time. Moreover, data so far accumulated have not indicated such reactions at moderate boom peak overpressures. The commonly used expression “startle” was found to be poorly defined and often confused with orienting responses. It was considered essential to develop criteria to distinguish between startle reflexes and orienting responses, since their effects on performance could be quite different. Minor effects on performance were reported to occur at indoor boom peak overpressures as low as 6 N/m*, but these appeared more likely to have resulted from the orienting response rather than the startle reflex. Momentary impairment of performance on complex perceptual-motor tasks may occur after exposure to booms of moderate peak overpressure, but is less likely to have significant effects on comparatively uncomplicated tasks such as driving. Possible deterioration of the learning process (e.g., in schools with frequent exposure to booms over greater lengths of time) has not been studied. The effect of the sonic boom on sleep was considered to be of great importance. Several studies show that sleep is disturbed at boom overpressures around 30 N/m* under laboratory conditions. Results from a limited field experiment with night exposures in a quiet area show
542
E. J. RICHARDS AND R. RYLANDER
that the awakening frequency is high at boom overpressures around 60 N/m2. Data so far accumulated indicate the presence of groups of high sensitivity or risk in the population, notably elderly people or persons with a neurotic predisposition. Concerning day flights estimates of the number of day sleepers in different communities were considered essential. Even if data exist on the awakening effect both under laboratory conditions and in the community it was pointed out that hardly any data are available concerning the long term effects of sleep disruption. If conventional methods concerning performance are used, effects have been shown only under severe sleep disruption. Primary effects such as startle, performance disruption and sleep interference can result in subjective feelings of annoyance. Annoyance in itself is the result of a variety of environmental factors in which not only the direct effect of boom exposure but also the social surrounding plays a role. A schematic diagram of this complicated reaction picture is given in Figure 1.
Pato-physiological
Figure 1. Interrelationship of various aspects of the environment development of annoyance due to sonic boom exposure.
and pato-physiological
reactions for
In addition to the interrelationships demonstrated in Figure 1 the development of annoyance is also dependent upon other factors. The presence of, or belief in, structural damage or effects on animals, especially pets, will heavily influence the development of annoyance. The relationship between presence of annoyance in the community and number of complaints was discussed in terms of a basis for the establishment of exposure effect criteria for annoyance. It was emphasized that the number of complaints is a result of a complex interaction of factors, many of which are not related to the exposure itself. The number of complaints can thus not be considered as a reliable indicator of the annoyance level in the population. Concerning the exposure in general it was pointed out that in the nominal peak boom overpressure range of 60-100 N/m2 the individuals might hear fewer booms than they are exposed to. Booms may be masked by background noise or decrease below perceptible levels when penetrating through structures. The booms heard could then be those that deviate from the nominal value or occur at a time when the ordinary community background noise is low (e.g., in the evening or in areas for relaxation such as national parks). Consequently, the judgements made by individuals, especially concerning the degree of annoyance, could be based upon booms that attain levels above the nominal value or occur at certain times. The animal reactions encountered after exposure to sonic booms seem to be limited to short periods of alerting and orienting responses. The workshop agreed that results from studies on domestic or semi-domesticated animals were relatively conclusive but additional studies would be required. Additional pertinent information should be obtained from studies on wild animals, especially during sensitive periods such as mating and whelping. The difficulty for the general public to differentiate sonic booms from noise from low altitude
SONIC BOOM EXPOSURE EFFECTS:
III
543
subsonic jet overflights and other intluences from the environment may explain why certain effects on animals have been attributed to the sonic boom. A general conclusion reached by the group working on structures was that damage to primary structures in buildingsin good condition is not to be expected. The type of damage that occurs is mostly superficial and often connected to already existing strains in the structure itself. The term “cosmetic damage” was considered appropriate for this type of damage although the expression was not ultimately accepted, because of its psychological implications. Although the damage in itself is technically unimportant, its psychological consequences in terms of a criterion for annoyance reactions should not be underestimated. It was thought, however, that exaggerated reactions could be avoided if sufficient information concerning the risk of and reasons for structural damage was made available to the general public. Statistical estimates of the probability of failure of a group of structural elements can be made, but knowledge concerning isolated events is insufficient for prediction of the risk of an effect. By examining different areas and conditions of structures therein, picked at random, a good estimate for an expected damage frequency and severity could be obtained. These calculations could then be checked in actual overflights at varying boom peak overpressures. Criteria for various land areas could then be developed and, when combined with effects on humans and animals, form an area criterion for total effects. Based upon the available information on boom effects in the different areas of concern in the workshop the following suggestion for general sonic boom exposure criteria for outdoor reactions has been compiled (see Table 1). TABLE
1
General sonic boom criteria for outdoor reactions
Level no.
Description and effects Likened to distant thunder-might susceptible individuals probably occurs
Approximate outdoor nominal peak overpressure (N/m*)
cause startle reflex in especially
or awaken
light sleepers, habituation
Likened to moderate thunder-startle reflex present among persons exposed outdoors in quiet areas, awakening of sleepers in quiet areas Slight cracking sound, penetrates background noise-windows may rattle, causes startle and orienting response, wakes heavy sleepers Loud cracking sound, clearly audible above background noisestartle reflex and orientation response common outdoors, windows rattle, weak structures vibrate, feeding animals look up, show orienting response Strong cracking thunder-windows rattle, structures vibrate, windows or plaster might break although this is rare, startle or fright among majority of exposed outdoors, majority of sleepers awaken
20 50 100
200
500
Although the arrangement into these different levels is by no means complete and exceptions are common, this type of review can be of help when establishing research priorities. Special caution should be exercised concerning the exact classification of startle because this reaction has shortcomings in terms of definition.
544
E. J. RICHARDS AND R. RYLANDER
Concerning the sonic boom effects in general there was sound discussion about a unit for describing the sonic boom which could be meaningful to all investigators regardless of their specific area of concern. The conclusion was that whereas the nominal peak overpressure would be adequate for certain types of responses, the pressure rise time, the dB(A) fast level or other technical parameters might be more suitable for other types of effects. The importance of vibration especially when the boom was heard indoors had not been sufficiently explored in scientifically well-designed experiments. It was emphasized in the discussions that all units to measure the sonic boom need to be standardized and that the units used should have maximum significance. This becomes especially important when the dose-response relationship is to be established, either as an increased dose at one single exposure or as successive doses over longer periods. In order to facilitate the comparison between results from different research projects the need for a common reference noise signature was expressed. This could be in the form of either a burst of white noise or some other sound and should be included in all human experiments. However, apart from the sleep effect group, no specific recommendation was made concerning the characteristics of this reference noise. The nature of the vibrations of loose objects, particularly the secondary response, and the method by which such response creates sound from shelves, tables, etc., should be examined. It would also be very useful to carry out further work on the visual stimuli associated with such movements and with reflections from the windows arising from their movements. There is some evidence that aural stimuli supported by visual stimulifor example, amplified apparent movements by window reflections-can create fear and annoyance. Another general conclusion was that both laboratory experiments and field studies were necessary in future work. Laboratory studies were considered to be of importance especially to determine effect thresholds and the importance of certain technical parameters for specific effects. Attention was drawn to the fact that results from laboratory experiments have limitations in their application as the exposure in different conditions and the number of test persons is usually rather limited. Concerning field studies, the opportunity should be taken to perform studies in areas where sonic booms occur regularly and are experienced as part of normal daily life. The workshop further expressed the need for making full use of material already available at different research centres. The establishment of a reference centre with a data bank was discussed but no definite plans were made. The sonic boom is only one example of several noises characterized by sudden wavefronts that occur in the environment. Studies on sonic boom exposure effects have a general relevance to these other noises and further research should be designed, whenever possible, to include observations from which more general conclusions concerning these types of sound can be drawn. A problem deliberately avoided during the discussions was how scientific information concerning sonic boom effects should be conveyed to the decisionmakers in society. The formation of representative groups with sufficient technical expertise may provide an alternative to the situation in which scientists feed information into a bureaucracy which processes data and forms decisions by its own unknown standards.