Query almost any experienced open-circuit divemaster working at the dive platform "what is the last thing you do as you put the diver in the water?" and the answer will probably be "I check their tank valve is open." Yet, most boat crew are unfamiliar with closed-circuit diving and, knowing this, most rebreather divers are reluctant to allow others to handle their equipment. Thus vital cross-check challenges are often omitted, perhaps enabling the rebreather diver to enter the water with their oxygen or electronics off. If so, the rebreather loop will become dangerously hypoxic, typically during or a short time after the descent but it has also happened on the surface during entry. Mark, our staff rebreather instructor who is also an experienced rebreather dive accident forensic investigator, has observed this finding surprisingly often in rebreather dive accidents.
After the boat safety briefing, we suggest approaching unfamiliar open-circuit divemasters you encounter to tell them about a safety cross-check alternative for closed-circuit divers. As the divemaster queues up the diver at the platform just prior to putting them in the water, in the case of rebreather divers ask "Is your oxygen on?" rather than touching any valves. The diver should glance at their handset and rock their O2 valve knob to double check then reply with an OK hand signal. (If circumstances permit, Mark also likes to take the loop out for a moment and say "YES and thank you for asking!") The feedback from many long time divemasters on the boats where we dive is this simple reminder immediately before the rebreather diver enters the water has averted several potential dive accidents.
Help promote dive safety, and perhaps save a life, by telling the working divemasters on the boats you dive from about the benefits of asking every rebreather diver immediately before they enter the water...
Is your O2 ON?
One more suggestion... to reinforce the divemaster's new behavior, if they remember to ask you the question then give them an extra generous gratuity and tell them why.
