Accidental DECO and mild panic in a non tech certified diver.

[Bob DBF]

I like the fact that they actual urge caution, because the initial Royal Navy figures where developed whilst they where involved in combat operations, in Alexandria in 1941

I understand he is urging caution, however there are no studies on the actual Nitrox that we are using at depth. So much for caution, or more likely, the extrapolations are safe enough. 1.6 has been the recreational standard, but I understand the society becoming more risk adverse and divers becoming less fit and knowledgable, why the industry would want to lower the limit.


Bob

 

[Dan]

The solution - whilst still involved in combat operations issued in 1943, was to have an absolute limited maximum exposure to a PO2 of 1.76.

I once went to 144’ with 32% Nitrox (PO2 of 1,72) for 2-3 minutes without any problem.

 

[CAPTAIN SINBAD]

I don't believe there are any diving agencies that sanction using 1.6PO2 during the bottom (work) phase of a dive. 1.6 is only allowed during decompression ( zero work).

I've been lucky and never seen anyone fit in the water. One of the teams I dived with came very close to loosing a diver who fitted in the water. Luckily they where on the deco' bar, so there was plenty of help to hand. I have always been very wary of high PO2's ever since.
I've been on one trip when someone was late switching from travel to back gas. He was proper poorly on the boat when we finally surfaced. His buddy brought him straight up. We knew there was something wrong during deco', because there where extra stage cylinders clipped off to the trapeze, where the buddy started dumping kit on the way back up. I don't believe the diver fitted on that occasion, but his exposure was brief.

Talking to one of the chamber operators when I did a chamber experience they said the variability of individuals to high PO2's was quite surprising and alarming at times. One of the reasons we where all on full face mask when we breathing high PO2 was because he can pull it off quickly if we did react badly.

Correct on all accounts. UTD actually limits PPO2 to 1.2 instead of 1.4 for bottom mix because the consequences can be fatal. Some of these deep air divers like Hal Watts have taken almost twice of that and still survived but definitely not recommended.

 

[Gareth J]

I understand he is urging caution, however there are no studies on the actual Nitrox that we are using at depth. So much for caution, or more likely, the extrapolations are safe enough. 1.6 has been the recreational standard, but I understand the society becoming more risk adverse and divers becoming less fit and knowledgable, why the industry would want to lower the limit.


Bob

When I did my Advanced Nitrox training back in the early 90's, the instructor had a US Navy study, which was excellent, if not a little frightening. To be honest, I can't be sure if it was pure O2 at differing depths or Nitrox.

Looking at the DAN document.
The British Navy started with a PO2 of 2.5 in 1941, they reduced it to 1.76 by 1943. We now have an absolute limit of 1.6 PO2, and a recommended diving limit of 1.4 PO2

There is a significant difference between what is acceptable during combat operations, (even during combat operations, too high a loss means you are not militarily effective).

 

[Tribal]

So to summarize. The only example of an 02 hit that comes even close to my stated parameters, is a diver at a P02 of 1.6 under heavy exertion for the entire 40 minutes at EAN40 under what is most likely an artificial, controlled laboratory setting intentionally inducing a heavy workload + an unusually long P02 1.6 level at the highest possible concentration of recreational Nitrox, for the entire dive.

There aren’t many reports of highway accidents caused due to a speed of 200mph either. That doesn’t mean it’s safe to drive that fast.

 

[caruso]

There aren’t many reports of highway accidents caused due to a speed of 200mph either. That doesn’t mean it’s safe to drive that fast.

Irrelevant.

 

[electric_diver]

The decompressing diver is real world. Warm water, drysuit, at rest, 100% O2 on a 6m stop.

I see this fallacy a lot. Deco is not always warm. Deco is not always at rest.

 

[Gareth J]

I see this fallacy a lot. Deco is not always warm. Deco is not always at rest.

You are correct, for some reason, I thought it was the Britannic, but it was actually the Lusitania. So cold water, although in the Gulf Stream.

Why are you working hard on the decompression?
If its tidal you have a trapeze, especially for this type of diving. If it's a short hang then its either Jon lines into the shot or DSMB's and go with the tide.
To be fair, most UK diving is DSMB's and go with the tide. This is OK if your decompression schedules are reasonably short, say under 20 or 30 minutes, that does depend a little on the speed of the water. Beyond that, then I would insist on a trapeze, at least you can keep the team together and have emergency gas on the lower and upper bar's.
With a trapeze the boat can follow it and all of the divers are in one place.

 

[RayfromTX]

---

---

A ScubaBoard Staff Message...

I would like to thank all the members that have taken part in this thread. We have conducted ourselves well and shared important information without excessive rancor. I would especially like to thank Caruso for posting the thread and not getting overly defensive when comments were critical of the actions that led to this near miss.

This post is in the Accidents and Incidents forum. It occurs to me that it is more appropriately located in the near misses forum. A subtle distinction but I will go ahead and move it there. Thanks again for your participation and civility in discussing a topic that has potential for conflict. Y'all make me proud to be a member.

---

 

[johndiver999]

There is a significant difference between what is acceptable during combat operations, (even during combat operations, too high a loss means you are not militarily effective).

What also needs to be considered when the topic of pushing ndl with a rich mix is: what is the benefit? How much less dive time would you have if you backed off the mix 1 or 2 percent? Those numbers seem to be relevant when trying to formulate a “reasonable” dive plan.