Likelihood of getting oxygen toxicity at 1.4 PPO

[JVos]

Not sure of the time, but their conclusion was high CO2 in the loop. Nevertheless, they had hits at 1.2...

 

[Germie]

CO2 is no oxygen. High co2 is caused by a bad scrubber, hard working, etc. So was it a normal oxtox? From what i read no.

 

[AdivingBel]

Jeannie doesn’t like to rent me my all 36’s for morning and afternoon dives.

She's just looking out for you. She doesn't want you all hyper at The Pub every night. She wants you safe and sound in your bed by 8 PM.

 

[uncfnp]

She's just looking out for you. She doesn't want you all hyper at The Pub every night. She wants you safe and sound in your bed by 8 PM.

I know. I have tried to convince her that my dive computer and I keep a very close eye on my exposure but she still plays the mother hen.

 

[MrVegas]

I just read through this entire thread. Pretty interesting. As a practical question, for those that have done the Stuart's Cove 2-tank dives in the Bahamas, is there any reason not to use 32% for them? The first dive is advertised as a "wall" dive to about 80 feet with presumably no hard bottom. That depth should be no issue, of course, but I do often use sudafed, and others have written about downcurrents, etc. Probably overthinking this -- my guess is it would make no difference between air and nitrox for those dives either way. (I've used sudafed with nitrox before, but that's only been in quarries where I couldn't get deep enough even by accident to have a problem.)

On a more theoretical level, I think someone had referenced the study involving rats and pseudoephedrine and oxygen toxicity. I actually found and read that study. If I understand it correctly -- not promising that I do -- the rats were given (by body weight) many times (50 to several hunded times?) the pseudoephedrine dose of what a normal human would take and then subjected to 5 atmospheres (132 feet) breathing pure oxygen. The study did find that rats taking the higher doses had seizures faster, so it did have some impact, but the for the rats at the lower (though still very high) doses, it did not seem to have much impact. It did look there was a high level of individual variance in how long it took rats to have the seizures.

 

[Storker]

is there any reason not to use 32% for them? The first dive is advertised as a "wall" dive to about 80 feet with presumably no hard bottom. That depth should be no issue, of course, but I do often use sudafed, and others have written about downcurrents, etc.

I haven't done the Stuart's Cove 2-tank dives in the Bahamas, but I generally prefer air when I don't have a hard bottom at depths even remotely close to 1.6 bar pPO2. It's totally a question of personal risk acceptance, of course, and I'm rather risk-averse. Others may well see it differently.

 

[boulderjohn]

I just read through this entire thread. Pretty interesting. As a practical question, for those that have done the Stuart's Cove 2-tank dives in the Bahamas, is there any reason not to use 32% for them? The first dive is advertised as a "wall" dive to about 80 feet with presumably no hard bottom. That depth should be no issue, of course, but I do often use sudafed, and others have written about downcurrents, etc. Probably overthinking this -- my guess is it would make no difference between air and nitrox for those dives either way. (I've used sudafed with nitrox before, but that's only been in quarries where I couldn't get deep enough even by accident to have a problem.)

On a more theoretical level, I think someone had referenced the study involving rats and pseudoephedrine and oxygen toxicity. I actually found and read that study. If I understand it correctly -- not promising that I do -- the rats were given (by body weight) many times (50 to several hundred times?) the pseudoephedrine dose of what a normal human would take and then subjected to 5 atmospheres (132 feet) breathing pure oxygen. The study did find that rats taking the higher doses had seizures faster, so it did have some impact, but the for the rats at the lower (though still very high) doses, it did not seem to have much impact. It did look there was a high level of individual variance in how long it took rats to have the seizures.

Some things to think about.

I haven't read that study in years, so I am going from memory. The DAN statement on Sudafed and oxygen toxicity that I read back then was pretty funny, because about half the report was telling you why you shouldn't pay any attention to the rest of it. The warning is based on the very flimsiest of evidence possible. The supposed stories of divers who toxed while using Sudafed were even flimsier. No one knows if they actually toxed--they were just a couple of divers who died for some reason, and they were using nitrox and Sudafed when they did. If you read enough fatality reports, you will see that in a fairly large percentage of cases, the actual cause of death is similarly unknown--they just found a deceased diver on the bottom.

The rats were not on Sudafed or pseudoephidrine--they were on something similar.

Over the counter Sudafed contains no pseudoephidrine.

Down currents are rare, and the problem with them is IMO much overstated. I have dived in places that are supposedly famous for them hundreds of times, and I have been in exactly one, and I casually swam out of it--it was like a waterfall.

You do not tox instantly from straying below the MOD for a couple of minutes. You have to be below it for a while. You cannot predict accurately how long that would be, but some people question whether you could stay down that deep that long on an AL 80.

On a dive like that, I would not only have no concerns about using Nitrox, I would be highly upset if they tried to force me to use air.

 

[boulderjohn]

generally prefer air when I don't have a hard bottom at depths even remotely close to 1.6 bar pPO2.

What is "remotely close"? If you dive EANx 32 to 80 feet, you are at 1.1. Is that too close to 1.6 for your tastes?

 

[Storker]

What is "remotely close"? If you dive EANx 32 to 80 feet, you are at 1.1. Is that too close to 1.6 for your tastes?

I don't like that the hard bottom is below the industry's limit for contingency pPO2, so if the hard bottom is deeper than 40m down from the surface, I prefer air over EAN32.

But like I said, I'm certain that others will hold a differing opinion.

 

[MrVegas]

Thanks to both of you for the feedback and the input is helpful. I am usually diving with my teenage son who will also sometimes take sudafed -- the real stuff from behind the counter -- so I probably think about these things a little more than I would otherwise. (My quarry dives and previous Caribbean dives have always had a hard bottom.) I'll probably just stick with the 32% unless the operator recommends not doing that on the "wall" dive. Wonder what the guide uses.

Boulderjohn -- interesting to hear your take on the pseudoephedrine studies, thanks. The recommendations basically seem to be don't go over the recommended dose and don't push the partial pressure limits, neither of which we ever do. We got our nitrox cards right after doing the open water class -- I figured it made sense to get it out of the way. The few nitrox fills I got were really not remotely necessary for the dives I was doing -- however, I will say I felt more awake in the car on the drive home, so I guess you can chalk me up as anecdotal evidence for feeling "better" after the dive. (Note that I always felt fine on air -- the nitrox seemed to leave me a little less sleepy afterwards.)