Exactly. At this point, we have a very few known facts and some items that have been reported in posts on this thread which may be true or may be simple hearsay. At this point I'm choosing to go with a null hypothesis of proper dive planning being followed rather than assuming the deceased pushed the limits in one or more ways. Given what has been stated about him in this thread and elsewhere, the former seems more likely than the latter.
What happens in a lot of these A&I threads, as boulderjohn posted earlier, is the desire to find some clear root cause of the accident. . .
A lot of the posts in this thread seem to assume that something had to have gone wrong in order for this event to happen - exhaustion, exceeding MOD, bad dive planning, etc. So if we're going to discuss those, why not lay out what would have had to happen before any of those scenarios came into play? Then we'll at least know what information is needed to support a particular hypothesis rather than blindly speculating - for example, whether or not the deceased had done both prior dives or whether there was heavy current that day.
Again and yet again, based on what scant published and third party information there is,
the best non-trivial hypothesis is the one that has the fewest assumptions. A "null hypothesis" is obviously a
trivial reductio ad absurdum statement and does nothing to help make sense of this accident, along with useless admonitions on speculation.
Again. . .There is a common experience for all SoCal oil rig divers of a live boat drop-off and surface fin-kick swim to get inside the structure's boundary, in that you have physical activity with a natural physiological tachypneic (increased breathing rate) response even before the descent to depth. Potential compounding issues are the victim's fitness level and any underlying relevant medical history -and therein lies your root "factors",
@HalcyonDaze and
@boulderjohn, factors that are presently unknown at this time as well. Therefore Rule Out
CO2 Toxicity/
Hypercapnia in Scuba Diving activity as the precipitating event to the primary Cause of Death by Drowning. . . (This differential diagnosis of Hypercapnia is supported by the research referenced in
post #133 and the video in
post #139).
See also this lecture on Respiratory Physiology with regard to Carbon Dioxide starting at the 4:00 minute mark:
What we as Oil Rig Divers can learn from this, is to take a few minutes to recover and regain a normal relaxed breathing rate -without the work-of-breathing of the regulator in mouth- on the surface, before beginning a descent to depth. If you cannot, and especially if there are equipment problems or water conditions turn out to be too rough for your ability, abort and signal the Diveboat for pick-up.
I just want to add a generic dive safety comment, since we don’t know what Henry had in his tank. Personally I don’t use Nitrox on dives that have no bottom such as this blue water dive or wall dives.
On a deep dive at Punta Sur in Cozumel (but still less than the MOD of EAN32) I noticed the dive guide also used air, and when I asked him about it he said It’s in case he may need to chase after someone deep and exceed the MOD.
I also recall reading a case report of a diver having a seizure on Nitrox at around 1.4 atm O2 partial pressure. In Cozumel I use air for the first deep dive and EAN36 for the second shallow dive.
On Oil Rig Dives, I always use Air and a DPV/Scooter to provide mobility at all phases of the dive -including the surface swim for both drop-off and pick-up. If going far below the second horizontal crossbeam framework (36m/120') down to the third & fourth tiers for significant minutes of bottom time, I usually breathe an appropriate Helium mix in a twinset together with 50% & 100% O2 deco gases.
Another Lesson Learned from this Accident: The most important factors to consider when using any recreational Oxygen-Nitrogen gas mixture are gas density/work-of-breathing, ppO2, and narcosis. Physical activity at deeper depth together with increasing gas density eliciting the effects of work-of-breathing and spiraling CO2 retention, adds to the anesthetic effect of Nitogen Narcosis, along with elevated ppO2 levels which in turn increases the chances of Oxygen Toxicity Syndrome.
The critical gas density point for Air (and for EANx32 & 36) is right at 40m/130' -which just happens to be the maximum recommended recreational depth limit. That the surviving diver reportedly tried to rescue the deceased by going down to a depth of 50m/167' (with whatever remaining tank pressure) is commendable. Amazing and fortunate that other than a CO2 headache, this diver did not go hypercapnic into unconsciousness; Oxtox seizure; or on the ascent, run out of breathing gas and develop acute DCI.
and waiting for any official news. My guess is that I will be finished with it before that time 
