jagfish:
Sea Rat
Are you saying that wearing a hood could prevent this reflex? Not being arguementative here, just wonder how much of a real factor that would be in this situation or others like it...
JAG
Jag,
There are several well-known reflexes associated with water.
One is the mammalian diving reflex, which has to do with the face being immersed in water. This reflex tends to slow the heart rate, and is used by breath-hold (apnea) divers.
The other is not so well known in the diving community, because we go to great lengths to provide adequate thermal protection to the diver's head. But this reflex, if my memory serves me correctly, occurs when the back of the neck is exposed to cold water. I experienced that when I tried an ice-water bath during a mountaineering training session. It is a reflex hyperventilation, which is described here:
In human adults and animals, immersion in icy water results in involuntary reflex hyperventilation and a decreased breath holding ability to less than 10 seconds. This may increase the likelihood of aspiration and rebreathing of icy water in some victims.
Cold-water drowning/cerebral protection
Although this article is about the effects of cold-water near drowning and survivability, it does discuss this reflex. It is a dramatic thing (and traumatic too, if immersed) to have happen.
When I was in rescue work, we taught about water rescues. Water Safety Instructiors (WSI), also teach lifeguarding and rescue techniques. One of the things we have taught is that if you are entering the water in a rescue situation, and the water is cold, enter in such a way so that you mouth does not go under water. If you must enter the water suddenly, with your mouth and nose underwater, cover them to preclude the reflexive hyperventilation aspiration of water. So to answer the question, yes; protecting your head thermally can prevent this reflexive hyperventilation.
Last weekend, I dove solo is the Clackamas River at High Rocks, near Portland. It was a pretty chilly water. When I got out, I left my helmet (modified bicycle helmet) and hood on, as well as my mask. I had a twenty-foot rock climb to make to get out of there, and if I slipped, I wanted the helmet/hood in place. This is for head protection, and thermal protection.
While I was writing the above, Uncle Pug wrote:
However the issue of trespassing does have a bearing on this incident. It is the reason that the divers involved were wading back to the point of entry and not walking on the beach. There is no doubt that if they had been walking on the beach the accident would not have unfolded as it did.
In evaluating a generalized version of the accident we must avoid useless speculation about the specifics of this particular case beyond what we know to be the salient facts. And of course we must realize that the greater part of most *news reports* are suspect.
Yes, the trespassing rules played a role. But they were not the only factor. In accident investigation, under the multiple causation theory, it usually is a combination of things that causes the accident. It rarely is a "single-fault" situation; as a matter of fact, the semiconductor industry actively works on products to ensure that there are no single-fault failures that can cause an accident. In this situation, the following have been identified before I posted:
--The no-trespassing rules.
--Poor dive planning.
--Idiosynchracies of the dive site.
--The actual currents at that time.
But none of these produces a fatal accident in and of itself. There must be something else, which was why I asked the questions. To prevent a similar occurance, all the possible factors need to be identified, and corrective actions taken for each.
We can speculate on some of this, as that is how accident potentials are identified. It pays though, to realize that we are dealing with speculation that the actual facts may be decidedly different for someone who is close to the investigation. In accident prevention circles, these are actually called "what if" analyses.
Another, more specific way of analyzing the potential is to do what's called a "Failure Modes and Effects Analysis (FMEA)." We can speculate about a given failure mode, and analyze it's effects. In electrical terms, we can see what happens upstream and downstream of the failure of a component. In an actual accident, we can use similar techniques to develop a logic tree for the different causes that came together to make the accident happen. This was used on both the Columbia and Challenger accidents.
But to focus on one of the causes to the exclusion of the rest of them misses the reason that the accident happened in the first place. It is this sometimes fatal combination of factors that we need to pay attention to. If all of these factors had to come together to make the accident, take any one of them away and you prevent the accident (in Boolean logic, these are "and" gates; this and this and this and this had to happen to cause the accident).
SeaRat
