DIVE LOG JUNE 2025 issue 412

However, in certain circumstances, this system can fail. For instance, if the diver ascends too fast, the electronics may not have time to pick up the oxygen shortfall and compensate for it. Maybe the rebreather’s oxygen cylinder is empty, or the injector is blocked by corrosion or other debris, in which case, no matter how hard it tries, the electronics can deliver no additional oxygen to the breathing loop. Rebreather divers are taught how to deal with these issues, but if they do not focus on closely monitoring their oxygen level, they will not even know that emergency procedures are required, because, as in free diving, there will be no warning. As soon as the oxygen partial pressure drops below 0.16, they will black out instantly. This phenomenon may lie behind several otherwise unexplained rebreather fatalities in recent years, many of which occurred at the end of a dive when the diver was close to the surface. In some instances, they had already surfaced and waved to the dive boat before sinking suddenly. Safety in the Shallows

attention to wander. After all, in shallower water, we are safer. If something goes wrong, we have more time to fix it because we are consuming less air, and if the issue is something we can’t fix, it’s easier to abort the dive as we are closer to the surface. Most rebreather divers tend to be open-circuit divers first, and they acquired this mindset before they made the switch to closed-circuit. This is a problem because, when you are diving with a rebreather, the danger of hypoxic blackout means that the shallows are not a sanctuary – quite the opposite. It is usually safer for a rebreather diver to stay deep while they work out how to solve a problem, and it can be fatal if you become less vigilant as you make your ascent from a rebreather dive. So, during rebreather training and beyond, divers need to work hard to shed their open-circuit mindset and acquire instead the habit of remaining disciplined and focussed throughout the dive, on their way up, and right up to the point where they are positively buoyant at the surface, with their rebreather mouthpiece closed and breathing fresh air. Not until then are they safe from the dangers of shallow water blackout.

As divers, we tend to relax our vigilance once we begin our ascent. Thinking that the dive is nearly over, we allow our

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DIVE LOG Australasia #412 - April‘25

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