Temporary Auditory-Threshold Shifts Induced by Twenty-Five-Minute Continuous Exposures to Intense Tones in Water

Four bare-headed divers were exposed for twenty-five minutes to continuous tones in water at frequencies of 700, 1400, and 5600 hertz at estimated sound pressure levels between 153 and 165 decibels dB above 20 micropascal. Subsequent analyses revealed that the eight ears involved were actually exposed to average sound pressure levels between 143.1 and 165.1 dB. These exposure levels are comparable to those to which divers may be exposed while using some underwater hand-held tools. Temporary auditory-threshold shifts TTS were measured from two minutes to five minutes after the exposure terminated. TTS at two minutes post-exposure was between 23 and 55 dB and recovery times varied from twenty-four hours to more than fifty hours depending on exposure conditions. Nonauditory effects including middle-ear sensations and a reddened ear-drum were also observed. The results indicate that several hand- held tools now in use by military and civilian divers are extremely hazardous to hearing. The results also support the theory that the dynamic range of the water-immersed ear is smaller than the dynamic range of the ear in air.