‘Yo-yo’ diving in the aquaculture industry

Smart DR, Van den Broek C, Nishi R, Cooper PD, Eastman D. Field validation of Tasmania’s aquaculture industry bounce-diving schedules using Doppler analysis of decompression stress. Diving and Hyperbaric Medicine. 2014 September:44(3):124-136.) Introduction: Tasmania’s aquaculture industry produces over 40,000 tonnes of fish annually, valued at over AUD500M. Aquaculture divers perform repetitive, short-duration bounce dives in fish pens to depths up to 21 metres’ sea water (msw). Past high levels of decompression illness (DCI) may have resulted from these ‘yo-yo’ dives. This study aimed to assess working divers, using Doppler ultrasonic bubble detection, to determine if yo-yo diving was a risk factor for DCI, determine dive profiles with acceptable risk and investigate productivity improvement. Methods: Field data were collected from working divers during bounce diving at marine farms near Hobart, Australia. Ascent rates were less than 18 m∙min-1, with routine safety stops (3 min at 3 msw) during the final ascent. The KismanMasurel method was used to grade bubbling post dive as a means of assessing decompression stress. In accordance with Defence Research and Development Canada Toronto practice, dives were rejected as excessive risk if more than 50% of scores were over Grade 2. Results: From 2002 to 2008, Doppler data were collected from 150 bounce-dive series (55 divers, 1,110 bounces). Three series of bounce profiles, characterized by in-water times, were validated: 13–15 msw, 10 bounces inside 75 min; 16–18 msw, six bounces inside 50 min; and 19–21 msw, four bounces inside 35 min. All had median bubble grades of 0. Further evaluation validated two successive series of bounces. Bubble grades were consistent with low-stress dive profiles. Bubble grades did not correlate with the number of bounces, but did correlate with ascent rate and in-water time. Conclusions: These data suggest bounce diving was not a major factor causing DCI in Tasmanian aquaculture divers. Analysis of field data has improved industry productivity by increasing the permissible number of bounces, compared to earlier empirically-derived tables, without compromising safety. The recommended Tasmanian Bounce Diving Tables provide guidance for bounce diving to a depth of 21 msw, and two successive bounce dive series in a day’s diving.