Ann. occup. Hyg. Vol. 20, pp. 303-304. Pergamon Prcn 1977. Primed ID Great Britain
REVIEW OF POSSIBLE HEALTH HAZARDS ASSOCIATED WITH ULTRASONICS* C. R.
HILL
about the possibility of harmful biological effects of ultrasound goes back to observations made by Langevin in 1917 during his pioneer work on underwater acoustics. Systematic interest in the subject is much more recent however and its main concerns have been with two rather different types of exposure: those due to medical diagnostic applications, particularly in obstetrics, and those due to industrial equipment capable of generating high levels of airborne ultrasound. The subject has been reviewed elsewhere (HILL, 1968; 1973; 1977) and has recently been given detailed consideration by a Working Group of the World Health Organization whose review of the subject is shortly to be published as one section of a WHO Manual on the Health Effects of Non-Ionizing Radiation. The considerable amount of published evidence on biological effects of ultrasound is, to some extent, self contradictory. However, based on findings that have proved capable of independent confirmation, and available information on the physical exposure levels involved in current medical practice, there seems to be no serious reason either to question the safety of existing diagnostic techniques or to believe that undetected damage (e.g. genetic change) may arise as a result of therapeutic or surgical procedures. The same conclusions are probably applicable for occupational exposures although there is a dearth of information on exposure levels in this area, except in the particular and important case of airborne ultrasound, where auditory damage is of specific concern. Exposure criteria have been formulated for this situation (ACTON, 1968; 1975) and seem to be generally accepted. CONCERN
REFERENCES ACTON, W. I. (1968) Ann. occup. Hyg. 11, 227-234. ACTON, W. I. (1975) Ann. occup. Hyg. 18, 267-268. HILL, C. R. (1968) Br. J. Radiol. 41, 561-569. HILL, C. R. (1973) Radiation Hazards. Code of Practice for the Protection of the Staff of Warren Spring Laboratories. (Edited by BAKES, J. M., RAY, D. J. and SANDERS, M. J.), pp. 8.1-8.4. NATOAGARD-LS-78. Warren Spring Laboratories, Stevenage. HILL, C. R. (1977) Ultrasonics in Clinical Diagnosis (Edited by WELLS, P. N. T.) 2nd edn, pp. 171-180. Churchill Livingstone, London. DISCUSSION P. BAYUS (UML Ltd.): On present evidence, should we avoid the use of therapeutic ultrasound? DR HILL : No, there is no evidence that it is harmful in this application, provided that it is properly used. * Summary. 303
Downloaded from http://annhyg.oxfordjournals.org/ at University of California, Santa Barbara on August 26, 2015
Institute of Cancer Research, Royal Marsden Hospital, Sutton, Surrey
304
C. R. HILL
Downloaded from http://annhyg.oxfordjournals.org/ at University of California, Santa Barbara on August 26, 2015
R. J. BLOW (ITT Occupational Health Service): The permissible limits you suggest for ultrasonic exposure (after Acton), which seem to be the limits proposed in the forthcoming WHO document, differ quite widely from the ACGLH figures in the 1976 TLV list, e.g. Acton under 22.5 kHz suggests 75 dB, whereas ACGIH at 20 kHz recommends 105 dB. Can you comment on this difference? It is obviously important to those responsible for the health of employees in industry where ultrasonic washers are in use. D R HILL: In practical terms there is only a minor discrepancy here since ACTON'S (1968; 1975) criterion states: 'the permitted level is 75 dB in the octave band centred on 16 kHz, or in ± octave bands centred on frequencies up to and including 20 kHz, or in narrow bands centred on frequencies up to 22.5 kHz; the permitted level is 110 dB in octave bands centred on frequencies of 32 kHz and above, or in I octave bands centred on frequencies of 25 kHz and above or in narrower bands centred on frequencies of 22.5 kHz and above'. P. BAYUS (UML Ltd): Should therapeutic ultrasound be applied over the site of a fracture? D R HILL : Probably not, and in any case one should avoid heavy irradiations of any bone structure, which may lead to excessive heating.
REVIEW OF POSSIBLE HEALTH HAZARDS ASSOCIATED WITH ULTRASONICS* C. R.
HILL
about the possibility of harmful biological effects of ultrasound goes back to observations made by Langevin in 1917 during his pioneer work on underwater acoustics. Systematic interest in the subject is much more recent however and its main concerns have been with two rather different types of exposure: those due to medical diagnostic applications, particularly in obstetrics, and those due to industrial equipment capable of generating high levels of airborne ultrasound. The subject has been reviewed elsewhere (HILL, 1968; 1973; 1977) and has recently been given detailed consideration by a Working Group of the World Health Organization whose review of the subject is shortly to be published as one section of a WHO Manual on the Health Effects of Non-Ionizing Radiation. The considerable amount of published evidence on biological effects of ultrasound is, to some extent, self contradictory. However, based on findings that have proved capable of independent confirmation, and available information on the physical exposure levels involved in current medical practice, there seems to be no serious reason either to question the safety of existing diagnostic techniques or to believe that undetected damage (e.g. genetic change) may arise as a result of therapeutic or surgical procedures. The same conclusions are probably applicable for occupational exposures although there is a dearth of information on exposure levels in this area, except in the particular and important case of airborne ultrasound, where auditory damage is of specific concern. Exposure criteria have been formulated for this situation (ACTON, 1968; 1975) and seem to be generally accepted. CONCERN
REFERENCES ACTON, W. I. (1968) Ann. occup. Hyg. 11, 227-234. ACTON, W. I. (1975) Ann. occup. Hyg. 18, 267-268. HILL, C. R. (1968) Br. J. Radiol. 41, 561-569. HILL, C. R. (1973) Radiation Hazards. Code of Practice for the Protection of the Staff of Warren Spring Laboratories. (Edited by BAKES, J. M., RAY, D. J. and SANDERS, M. J.), pp. 8.1-8.4. NATOAGARD-LS-78. Warren Spring Laboratories, Stevenage. HILL, C. R. (1977) Ultrasonics in Clinical Diagnosis (Edited by WELLS, P. N. T.) 2nd edn, pp. 171-180. Churchill Livingstone, London. DISCUSSION P. BAYUS (UML Ltd.): On present evidence, should we avoid the use of therapeutic ultrasound? DR HILL : No, there is no evidence that it is harmful in this application, provided that it is properly used. * Summary. 303
Downloaded from http://annhyg.oxfordjournals.org/ at University of California, Santa Barbara on August 26, 2015
Institute of Cancer Research, Royal Marsden Hospital, Sutton, Surrey
304
C. R. HILL
Downloaded from http://annhyg.oxfordjournals.org/ at University of California, Santa Barbara on August 26, 2015
R. J. BLOW (ITT Occupational Health Service): The permissible limits you suggest for ultrasonic exposure (after Acton), which seem to be the limits proposed in the forthcoming WHO document, differ quite widely from the ACGLH figures in the 1976 TLV list, e.g. Acton under 22.5 kHz suggests 75 dB, whereas ACGIH at 20 kHz recommends 105 dB. Can you comment on this difference? It is obviously important to those responsible for the health of employees in industry where ultrasonic washers are in use. D R HILL: In practical terms there is only a minor discrepancy here since ACTON'S (1968; 1975) criterion states: 'the permitted level is 75 dB in the octave band centred on 16 kHz, or in ± octave bands centred on frequencies up to and including 20 kHz, or in narrow bands centred on frequencies up to 22.5 kHz; the permitted level is 110 dB in octave bands centred on frequencies of 32 kHz and above, or in I octave bands centred on frequencies of 25 kHz and above or in narrower bands centred on frequencies of 22.5 kHz and above'. P. BAYUS (UML Ltd): Should therapeutic ultrasound be applied over the site of a fracture? D R HILL : Probably not, and in any case one should avoid heavy irradiations of any bone structure, which may lead to excessive heating.
