In another thread there has been brief discussion of reports of the tragic death of a fellow boater who, according to one report, dove on his anchor to free it, as it evidently had become fouled on something. The depth of the water was not mentioned. But regardless of the full set of circumstances leading to the above-mentioned tragedy it has occurred to me that while people don't much think about it, breath-hold diving can be a dangerous activity, especially in cold water. People trained in SCUBA diving are given some instruction, but since most recreational SCUBA divers are trained by instructors of sport shops looking to expand the sport (and sales), training in breath-hold diving is not a priority item. Even among some types of professional diver training, it's not emphasized.
The principal cause of drowning while breath-hold diving among "fit", even fairly athletic, individuals is from passing out under water-- i.e., hypoxic blackout. Essentially, at some point during the activity, there's not enough oxygen reaching the brain. I would expect this to be accelerated in someone doing "work" (as in trying to free or move an anchor) on a breath-hold dive. Hypoxic blackout can come on without warning, even at shallow depths, and may occur on the ascent from a relatively deep dive. In people, the impulse to take a breath is driven by the build-up of carbon dioxide in the blood, rather than by depletion of oxygen there. So, it's possible for the blood to become dangerously low in oxygen (hypoxic) before the impulse to breathe becomes critical if there is hyperventilation, which rids the blood of carbon dioxide, before a dive.
Can find more information at the link below, but FYI:
Hypoxic Blackout - Prevention
1. Do not hyperventilate before breath-holding
2. Do not dive deep
3. Avoid excessive exercise
4. Avoid competitive behaviour resulting in the above activities
5. Ensure buoyancy near the surface
6. Dive with a buddy or have a safety observer/rescuer
7. Educate breath-hold divers of this hazard
http://www.divingmedicine.info/Ch 04 SM10C.pdf
The principal cause of drowning while breath-hold diving among "fit", even fairly athletic, individuals is from passing out under water-- i.e., hypoxic blackout. Essentially, at some point during the activity, there's not enough oxygen reaching the brain. I would expect this to be accelerated in someone doing "work" (as in trying to free or move an anchor) on a breath-hold dive. Hypoxic blackout can come on without warning, even at shallow depths, and may occur on the ascent from a relatively deep dive. In people, the impulse to take a breath is driven by the build-up of carbon dioxide in the blood, rather than by depletion of oxygen there. So, it's possible for the blood to become dangerously low in oxygen (hypoxic) before the impulse to breathe becomes critical if there is hyperventilation, which rids the blood of carbon dioxide, before a dive.
Can find more information at the link below, but FYI:
Hypoxic Blackout - Prevention
1. Do not hyperventilate before breath-holding
2. Do not dive deep
3. Avoid excessive exercise
4. Avoid competitive behaviour resulting in the above activities
5. Ensure buoyancy near the surface
6. Dive with a buddy or have a safety observer/rescuer
7. Educate breath-hold divers of this hazard
http://www.divingmedicine.info/Ch 04 SM10C.pdf
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