Surface oxygen and CNS O2 toxicity

[Duke Dive Medicine]

Did either of these two gentlemen have any decompression training? Did they have any understanding ... other than just following the numbers on their computer ... of what their dive profiles were doing to their bodies?

Diver number 1 stated that he violated the ascent rate on his second dive. Well ... duh! How did he conclude this had anything to do with his PO2?

I don't think these accidents are symptomatic of a knowledge deficit so much as an indication of divers ignoring their training ... or simply diving beyond it.


This information is clearly covered in the existing nitrox training materials. In other words, if there's a deficit in knowledge, it's because these two gentlemen didn't benefit from the training they received ... assuming they weren't out using nitrox without getting the training in the first place.

Sometimes you can't fix stupid ... except, perhaps, by making it hurt ...

... Bob (Grateful Diver)

The air diver was trained by TDI. I don't know what the N2O2 diver's training was. I put the dive histories in as background, but the decompression illness and violation of the ascent rate in one case wasn't really the point. The fact that two divers in a row, from two separate areas of the country, had the same misconception about receiving surface oxygen is what made us sit up and take notice. Thanks for your comment.

 

[Duke Dive Medicine]

Who recommends a limit of 1.2? 1.4 seems to be pretty much the standard MAXIMUM for bottom gas.

Sorry. Typo. We go by the Navy Diving Manual, which says that working dives with a pO2 greater than 1.4 are not permitted. Thanks for catching that.

 

[tstormdiver]

Sorry. Typo. We go by the Navy Diving Manual, which says that working dives with a pO2 greater than 1.4 are not permitted. Thanks for catching that.

I sort of wondered about that, thinking something might have changed since my Adv. Nitrox/ Deco training. From that class I was taught a PPO of 1.4 max for bottom gas,.... 1.3 if under a heavy workload & 1.6 maximum for decompression, being at rest.

 

[waterpirate]

It is more widely accepted by deep hunters/spear that 1.2 is max for bottom mix or you wind up being talked about here.
Eric

 

[dschonbrun]

The Max PPO2 values have gradually decreased since the Navy Diving tables came out over 40 years ago. I've seen literature with 2.0, then years later with 1.8, 1.6 etc... now it's 1.2 (good reason).

If diving on Air, you reach PP02 of 1.2 ATA at 47 meters = 155 ft, beyond recreational limits. If you're diving Nitrox, one hopes you know a bit more about PPO2, and have a depth floor at PPO2 = 1.2 ATA marked on your tanks, and established in your dive plan.

 

[snowmaker]

I think NC is more likely looking at the profiles. Venice is very shallow diving with NC shark tooth diving is right around 110'.

 

[snowmaker]

Venice Fossil Divers - ScubaBoard

I think NC is more likely looking at the profiles. Venice is very shallow diving with NC shark tooth diving is right around 110'.

 

[dumpsterDiver]

I remember when nitrox was first being introduced to the rec community and there was a lot of resistance. I remember reading that one of the very serious drawbacks associated with nitrox use was that if you ever did get bent, it would be too dangerous to treat you in a chamber (and use oxygen) because you would be more likely to have an oxygen hit in the chamber. I remember reading that some chambers were reported refusing ANY diver who used nitrox.

With this kind of background information, it is no wonder that some old school divers may have some completely incorrect assumptions about oxygen.

 

[lowviz]

I remember when nitrox was first being introduced to the rec community and there was a lot of resistance. I remember reading that one of the very serious drawbacks associated with nitrox use was that if you ever did get bent, it would be too dangerous to treat you in a chamber (and use oxygen) because you would be more likely to have an oxygen hit in the chamber. I remember reading that some chambers were reported refusing ANY diver who used nitrox.

With this kind of background information, it is no wonder that some old school divers may have some completely incorrect assumptions about oxygen.

Thanks for bringing this up, maybe Duke Dive Medicine will comment on the far less serious consequenses of taking a 'hit' in a chamber.

 

[rjack321]

Thanks for bringing this up, maybe Duke Dive Medicine will comment on the far less serious consequenses of taking a 'hit' in a chamber.

I have had CNS symptoms in a chamber about 4 yrs ago. Nausea and vomiting weren't very pleasant but better than residual damage.

This was in a major regional multi-place chamber which treats alot of divers. The attendant did not recognize them as CNS toxicity at all. In fact he continued to deny they were related to O2 exposure at all despite the fact that the nausea slowly built over each O2 breathing period to the point where I knew within ~2 minutes of where I was timewise. I was able to control the vomit until the hood was removed. At which point I had an air break and the nausea subsided until the next O2 session. (I was on a Table 6 extended). Repeat about 6 times.

The attendant (also a commercial diver) in there with me had no idea what ConVENTID was or that nausea was even a symptom of CNS toxicity. He actually thought O2 "calms" the stomach. Just goes to show you the educational distance still to go.