The Thermal Index for Assessing Diver Exposure Risk to Ultrasonic Sonars


  1. Kessel, R.
Corporate Authors
Defence Research and Development Canada, Atlantic Research Centre, Halifax NS (CAN);Maritime Way Scientific Ltd., Ottawa ON (CAN)
Divers can be exposed to ultrasonic fields from hand-held imaging sonars (used to navigate and search in turbid waters, typically 300 KHz to 1.5 MHz) and from diver detection sonars (large area, underwater surveillance in maritime security, typically 70 KHz to 100 kHz). No reports of harm have been reported by divers exposed to these sonars or by the manufacturers of the sonars. Nevertheless, the question of ultrasonic exposure safety and recommendations regarding safe use have apparently never been addressed. One established ultrasonic safety metric is the thermal index (TI) used by the medical diagnostic community. Modern diagnostic equipment provides its operator with several versions of TI, depending on the diagnostic objectives and scanning methodology. TI can be applied in other applications provided that an appropriate model of ultrasonic heating can be developed for the exposure faced. A new heating model is especially required given the departures in diver sonar exposures from the controlled and very focused diagnostic conditions assumed in medicine require a different thermal model as the basis for TI. A very conservative thermal model for diver exposure to ultrasonic sonar is developed here for underwater exposure conditions that are largely uncontrolled, unpredictable, and incidental to other mission objectives. The resulting thermal index and its implications for safe sonar use are illustrated for two diver hand-held imaging sonars and for a diver detection sonar
Ultrasonic sonar;Safe exposure levels;military diving
Report Number
DRDC-RDDC-2017-C088 — Contract Report
Date of publication
01 Mar 2017
Number of Pages
Electronic Document(PDF)

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