IN THE MIX
Rebreather safety
Prevention is the best cure
BSAC ’ s Technical Chief Examiner Dominic Robinson sets out a response to Paul Haynes ’ call for mouthpiece retaining straps to be standardised as a last line defence
Paul Haynes ’ article on the benefits of the Mouthpiece Retaining Strap ( MRS ) is illustrated using a real-world example of a diver who survived Loss of Consciousness ( LoC ) after they became hypoxic at the surface and then sank underwater . The MRS retained the loop in the diver ’ s mouth until the increasing partial pressure of oxygen in the breathing loop reached a level where the very fortunate individual regained consciousness . From this , it is clear that the diver ’ s life was saved by their MRS , so this incident can be seen as a very strong argument in their favour .
Any situation that causes a diver to lose consciousness must be viewed as extremely dangerous . It is possible that an unconscious diver wearing an MRS will regain consciousness as they sink , but this cannot be guaranteed . It is also true that an unconscious CCR diver will have to rely on being rescued before their scrubber expires or oxygen cylinder runs out , as they cannot remain underwater indefinitely . The simple truth is that preventing LoC is far more desirable than mitigating the consequences .
As taught to all CCR divers , the ‘ 3H Hazards ’ of hypoxia , hyperoxia and hypercapnia are the primary mechanisms that can lead to LoC . Although “ all can and do lead to loss of consciousness with little or no warning ” it is also true that all modern eCCRs incorporate multiple monitoring and alarm systems , which are highly effective at notifying the diver well before they suffer LoC . Traditionally , carbon dioxide alarms were the missing link but these are now available for some units , giving the diver time to react before dangerous levels are reached . Based on decades of experience , all BSAC CCR training courses include extensive sessions on how to respond to different scenarios ; divers only receive their qualifications when they have shown competency .
Of course , just because a diver has monitoring systems , alarms and has demonstrated their ability to respond appropriately , it does not mean that they will . For the incident where the diver survived due to their MRS , the cause was explained as ‘ the diver ran out of oxygen and failed to pay attention to his displays and alarms once at the surface ’. It does not explain why they did not check oxygen contents or respond to their alarms , either of which would have almost certainly prevented LoC .
The recent excellent BSAC Human Factors webinar also highlighted a situation where a CCR diver on a training course died after entering the water alone . A multitude of other issues were identified , such as the CCR remaining in pre-dive mode , the oxygen cylinder turned off and the diver being task-loaded with a camera . As in the first incident , the diver became hypoxic , suffered LoC and sank to the bottom . Although the diver ’ s survival chances may have been improved by using an MRS , it is almost guaranteed that
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