I have been reading a lot lately about “Deep Water Blackout” of deep Scuba divers, which appears to be a catchall phrase for a largely unexplained phenomenon. I have read hypotheses including oxygen toxicity, nitrogen narcosis, cerebral hypoxia, excessive CO2, and a variety of physiological and psychological factors acting alone and in unison.
Witness accounts range from seeing a breathing non-responsive diver, to seeing them do irrational things before going dark, to sudden disappearance. No doubt it exists, but why isn’t it equally common in surface supplied diving? Actually, it is closer to unheard of.
On one hand, excessive CO2 should be a more common problem for surface supplied working divers because their ill-fitting oral-nasal mask inside the hat has much greater dead space and their work load is generally much higher. Countering this is unlimited gas supply and not being afraid to use it. For all practical purposes, the demand regulator performance is comparable.
I have experienced a near blackout while testing an experimental diving helmet at 190’. I know it was probably exclusively CO2 because I was instrumented in a wet pot. My recollection was nothing like what is attributed to Deep Water Blackout and symptoms were far from sudden or unnoticed.
The physiology is the same for oxygen toxicity and nitrogen narcosis regardless of how the gas is delivered. It also appears that deaths on Trimix have been attributed to Deep Water Blackout where both factors are dramatically reduced.
I doubt that experience or training is the issue because a lot of experienced Scuba divers are listed as “probable victims”. Same for physical condition — military divers keep in great shape but that can’t be said for all commercial divers. Strong and tough sure, great cardio… not so much. One factor stands out, but I doubt that the answer is for deep tech divers to drink more.
For sure, surface supplied commercial and military divers feel much safer. It is highly unlikely we will run out of breathing gas, we can talk to the surface, they can hear us breath, we aren’t going to get lost, and a team of highly trained people worry about our depth, bottom time, mix, and decompression. On top of that, there is a standby diver sitting on a bench that can be in the water in under a minute and find you at the other end of the hose. All that said; if a sense of well-being was the issue, a lot more Deep Water Blackouts would happen more often on high stress dives to newer deep divers. That does not appear to be the case.
Unfortunately, this may be another medical problem that is too rare and expensive to study. Equally unfortunate is post mortem analysis is all too often left with little more than a grossly embolised corpse and eye witness accounts clouded by crisis, low visibility, and narcosis.
I don’t have a theory, but the ones I have heard don’t make sense.
Witness accounts range from seeing a breathing non-responsive diver, to seeing them do irrational things before going dark, to sudden disappearance. No doubt it exists, but why isn’t it equally common in surface supplied diving? Actually, it is closer to unheard of.
On one hand, excessive CO2 should be a more common problem for surface supplied working divers because their ill-fitting oral-nasal mask inside the hat has much greater dead space and their work load is generally much higher. Countering this is unlimited gas supply and not being afraid to use it. For all practical purposes, the demand regulator performance is comparable.
I have experienced a near blackout while testing an experimental diving helmet at 190’. I know it was probably exclusively CO2 because I was instrumented in a wet pot. My recollection was nothing like what is attributed to Deep Water Blackout and symptoms were far from sudden or unnoticed.
The physiology is the same for oxygen toxicity and nitrogen narcosis regardless of how the gas is delivered. It also appears that deaths on Trimix have been attributed to Deep Water Blackout where both factors are dramatically reduced.
I doubt that experience or training is the issue because a lot of experienced Scuba divers are listed as “probable victims”. Same for physical condition — military divers keep in great shape but that can’t be said for all commercial divers. Strong and tough sure, great cardio… not so much. One factor stands out, but I doubt that the answer is for deep tech divers to drink more.
For sure, surface supplied commercial and military divers feel much safer. It is highly unlikely we will run out of breathing gas, we can talk to the surface, they can hear us breath, we aren’t going to get lost, and a team of highly trained people worry about our depth, bottom time, mix, and decompression. On top of that, there is a standby diver sitting on a bench that can be in the water in under a minute and find you at the other end of the hose. All that said; if a sense of well-being was the issue, a lot more Deep Water Blackouts would happen more often on high stress dives to newer deep divers. That does not appear to be the case.
Unfortunately, this may be another medical problem that is too rare and expensive to study. Equally unfortunate is post mortem analysis is all too often left with little more than a grossly embolised corpse and eye witness accounts clouded by crisis, low visibility, and narcosis.
I don’t have a theory, but the ones I have heard don’t make sense.
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