5 replies to this topic

[Stoo]

I am just back from a week at Turneffe Caye in Belize and while I was there, I became involved in a discussion about the use of Nitrox. It very quickly became apparent that almost without exception, most people understood the advantages of diving Nitrox (increased margin of safety, extended bottom times) but not so much the risks... say, like dieing.

This reminded of a situation we had here in Ontario last summer where three divers (two of whom I know/knew personally) were involved in an incident that ultimately resulted in the fatality of a reasonably experienced diver, who worked part-time at a well-respected shop, and who assisted with teaching. The initiating cause of his death: Acute Oxygen Toxicity.

There is nothing especially earth-shattering about this until you read that his maximum pO2 was "only" 1.49 ata. By most standards, this is only slightly more than the generally accepted level of 1.4 and well below the supposedly "tolerable" level of 1.6.

The reason I mention this here, is that presumably most of us know that there are numerous factors that influence a diver's susceptibility to a possible 02 hit. Of particular interest to photographers, might be the level of exertion...

How many times have you been hanging out on the edge of the wall when a flock of Eagle Rays flies past? We are too savvy to know not to chase them, but we are sure as heck going to try to keep up to grab that shot. And if they head down a little deeper, might you find yourself steaming along at the "acceptable" depth limit for the 32 mix, pushing a camera the size of a lunar lander.... and suddenly you are in trouble. And your non-photographer buddy is about 3 miles back!

Anyway, this isn't a forum to get too involved in safety talk, so let's just call it a friendly reminder... Check your mix... don't take the shop's word that it's ok. Watch your depth. Watch your level of exertion. And keep your butt in decent shape!

Stay safe friends!

The accident report is attached if you are interested in reading it...

Attached Files

•  ouc_report_of_ontario_scuba_diving_incidents_in_2010.pdf   262.51K   54 downloads

Edited by Stoo, 21 March 2012 - 05:09 PM.

[tdpriest]

I am surprised. This tragic death was explicitly linked to signs of panic and CAGE on post-mortem examination. There is little, except for PPO2 measurement, to support the hypothesis that oxygen toxicity was directly to blame. There is a reason that a PPO2 of 1.4 bar is widely accepted: even at 1.6 bar the risk of cerebral oxygen toxicity is low. Yes, hypercapnoea, hyperventilation, rapid increase in PPO2 and stress, both physical and psychological, can increase the risk of seizure, but the evidence here is circumstantial. It looks to me as if someone is making a point.

The report doesn't convince me, as an anaesthetist, occasional hyperbaric physician and diver.

Tim

[diverdad]

Hi all, first I would like to offer my deepest condolencies to the family and friends of the deceased.
I am a little cynical about the high PP02 being the cause of death although possible as everyone has different tollerances. Myself and my dive buddies dive rebreathers and we almost always at the end of a long deep dive flush the unit with 02 and run the last 10-15 mins of decompression at PP02 of 1.6.

I don't want to get into a debate on decompression or diving methods as this is a sensitive topic in light of what has happened and also this is a photography forum.

But I do take your point on educating people on diving Nitrox. I have seen people exceed the MOD on holiday dives.

Education, Education, Education.

Safe diving

Lee

[gina]

I am just back from a week at Turneffe Caye in Belize and while I was there, I became involved in a discussion about the use of Nitrox. It very quickly became apparent that almost without exception, most people understood the advantages of diving Nitrox (increased margin of safety, extended bottom times) but not so much the risks... say, like dieing.

I also want to extend my condolences to the family and friends of the deceased.

I would like to point out, however, that the advantages of Nitrox include EITHER an increased margin of safety (if you dive with enriched air but use air tables/computer settings) OR extended bottom time, but you cannot have both. If people do not understand this they make take extra risks while on Nitrox thinking the non-existent safety margin will cover them.

-Gina

[Stoo]

If people do not understand this they make take extra risks while on Nitrox thinking the non-existent safety margin will cover them...

All valid points and like you, Lee, I routinely "clean up" my dives with a little pure 02 at 20 feet... while at rest. I lie to my computers when I set the second gas at 90% so I don't have to listen to it screaming at me ever time I drop my arm. (A friend of mine dropped a computer set at 50% in 135 feet of water, left it there for three weeks, then recovered it. Now THAT was an unhappy little bit of hardware...)

I don't recall if this was in the report, but it is my understanding that there was a pretty strong current running that day as well which might have been a factor.

The accident made a lot of us scratch our heads. I didn't know Todd well, but he was a good diver, and it's a "routine" dive, if there is such a thing...

Anyway, just wanted to toss this out there.

[vetdiver]

So sad to hear of any diver's death, regardless of cause.

Stoo, thanks for putting this warning out. I do want to just state that relatively low-ppO2 tox hits can and do happen, though there is not that much information out there about them - I had one in January (1.46 ata - and I had matched/exceeded this ppO2 hundreds of times in harsher conditions). This is not the place to go into detail, but the physician I consulted with told me that this ppO2 was absolutely adequate to cause acute O2 toxicity; it was not that difficult to find another diver or two with similar experiences. I urge you all to be careful and conservative.