WetRocks
Contributor
CavernFrog, now you are confusing NDLs and toxicity... Boulderjohn was talking about CNS toxicity not NDLs at a particular depth
First Dive Trip Without Instructor - Need to Rent Gear & Help Planning
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bamafan
Contributor
You don't need nitrox ar Morrison. The vent is the only part that gets that deep. You will get bored of that rather quickly. As far as 32% max depth it is used by spearfishermen in the Gulf to 130' all the time. For a short dive with 25 minutes or so of bottom time I wouldn't be concerned with 32% to 130'. Now long bottom times over 1.4 are idiotic.
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CavernFrog
Contributor
Why does it seem people are saying "you don't need nitrox, it's not that deep" when nitrox isn't for "going deep" but for spending more time underwater? Why would anyone not want to dive nitrox so long as they will not exceed its max depth?
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CavernFrog
Contributor
WetRocks
Contributor
I understand what you are saying. I do not think you understood what boulderjohn was saying. Go back and re-read, he specifically mentions that oxygen toxicity is not a problem at Morrison without a shovel.
That said, I'm with you, I don't dive air...it's 32% or trimix for me. Not because of NDLs because almost all of my dives are beyond that, but to reduce the nitrogen loading and keep dive planning consistent.
Those limits are not for oxygen toxicity. They are for No Decompression Limits.
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CavernFrog
Contributor
Exactly. I thought when you said "all day", you had switched to talking about NDL.
Oxygen toxicity has no time requirement. If you go past the max depth for a particular O2 % you can instantly go into a seizure.
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Oxtox does have a time requirement, it is a duration of exposure to high ppO2 that induces the seizure. Now that is near instant at high ppO2's, but you can still get a oxtox under the right conditions due to the CNS clock.
Now, nitrox does limit your depth, but what the guys are alluding to above is the benefit of nitrox is not valid at shallow depths. What you are doing with nitrox is trying to get as shallow of an equivalent air depth as possible to extend your NDL's *in recreational diving*. If you are doing 40-60ft dives, then the benefit of diving nitrox is pretty insignificant. EAN32 at 60ft has an EAD of 47ft. The NDL's don't change enough to really warrant using it. At 100ft though, the EAD is now 81, and that's a pretty significant bump. If your EAD ends up in a place where you get near unlimited NDL's, then it's not really worth using.
Looking at the PADI tables, if you look at the NDL's, you don't really get any benefit in diving nitrox until you are at at least 60ft, but even then, is your SAC rate good enough and/or are you doing enough bottom time to warrant it? Dive tables can't account for your average depth which the computers will. For 3x 45minute cavern dives, with a computer, you're probably going to be shallow enough to not warrant the nitrox. IMO.
Unfortunately it also appears you didn't get a really robust nitrox course. Not your fault, but too many instructors and agencies are skimping over the hows and the why's and just pushing the what's
bamafan
Contributor
You can dive whatever you want but I assume you will be diving an al80 and I doubt at Morrison you would be able to get into deco with one unless your sac rate is better than I envision. Now if you did 2 or 3 dives back to back it would probably help but honestly unless you are trying to push one of the vents I don't know why anyone would stay down below 90' that long there.
No, it takes time--quite a bit, really, although it cannot be accurately predicted.
I do not know of a single case of confirmed oxygen toxicity in recreational diving. I said that in a thread recently, and someone gave me a case, but the diagnosis looked pretty iffy to me. I know of a number of cases in technical diving, but each one was a serious violation of MOD, and each one still took a while. In one case, a diver was on a wreck that lies between 150-170 feet for over 20 minutes before he toxed. He thought he was diving air, but it was EANx 36.
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