Nitrox - 1.40 or 1.60 PO2?

[Thalassamania]

The gear that is keeping you at a constant ppO2 is called a CCR.

And the gear that allows you to vary your ppO2 is called O/C.

And as East is east, and West is west, n'ary the twain shall meet.

What is your point?

 

[nereas]

What is your point?

That your point about keeping apples and oranges mixed together is rather illogical.

They may make a great fruit salad. However they make really bad logic.

 

[Anti-Hero]

That your point about keeping apples and oranges mixed together is rather illogical.

They may make a great fruit salad. However they make really bad logic.

This discussion is about p02, and it's safety. Not the method by which you reach that p02. Go away.

 

[Thalassamania]

That your point about keeping apples and oranges mixed together is rather illogical.

They may make a great fruit salad. However they make really bad logic.

Back to the ignore hole for a week or two. You are truly an unbelievable troll.

 

[Charlie99]

Rebreather vs open circuit is relevant only in that a rebreather diver with a setpoint of 1.3ata ppO2 is going to be doing the ENTIRE dive at 1.3ata.

An open circuit diver would have the same sort of oxygen exposure only if he immediately dropped down right to the 1.3ata MOD and stayed there the entire dive.

As Gene Hobbs and others have pointed out, oxygen toxicity is a function of both TIME and ppO2.

If I were doing dives of several hours, then I'd consider 1.4ata ppO2 outrageously high. OTOH, if I'm going to do a dive where I know I'll be at 1.2ata or less, except for a 5 minute drop down to check out the propeller on a wreck, I'd have no problem with 1.4ata and might even consider something as crazy as 1.5ata. But just for that very limited time.

A question each diver should be considering is to what depth/ata ppO2 he would be willing to go to in order to rescue another diver in an emergency. Do you treat the 1.4ata (or 1.2ata or 1.6ata or whatever your "magic number" is) as a solid floor below which you will not descend in even an emergency?

I've looked at the numbers and have come to the conclusion that with EAN32 in an AL80, that my limit in an emergency is available gas, not ppO2. With EAN36, an emergency ppO2 floor of 2.0ata or 150' does become the limiting factor rather than gas during the earlier phases of the dive.

Sometime to think about now, rather than when faced with an emergency.

Charlie Allen

 

[garyfotodiver]

OK, OK, I have my SSI Enriched Air Nitrox DVD (c) 2004 in my computer. Couldn't find the book.

The DVD states that the CNS Oxygen Toxicity threshold appears to be 1.1, and the risk increases above 1.4. So all these technical discussions are very interesting, but I,as a recreational diver, will stay within the limits suggested by my training which is 1.4. As I understand, the OP was speaking of recreational EAN use. So recreational EAN use is germane to the thread. I fear that some of the more intricate points made might have a reverse effect and possibly confuse a diver not as knowledgeable as some of these very intelligent and experienced posters.

That would be sad, as one of us might have to dive after someone, and not with him/her.

 

[hobodiver]

A question each diver should be considering is to what depth/ata ppO2 he would be willing to go to in order to rescue another diver in an emergency. Do you treat the 1.4ata (or 1.2ata or 1.6ata or whatever your "magic number" is) as a solid floor below which you will not descend in even an emergency?

I've looked at the numbers and have come to the conclusion that with EAN32 in an AL80, that my limit in an emergency is available gas, not ppO2. With EAN36, an emergency ppO2 floor of 2.0ata or 150' does become the limiting factor rather than gas during the earlier phases of the dive.

Sometime to think about now, rather than when faced with an emergency.

Charlie Allen

Interesting point. Do you have any links relating to this?

 

[Gene_Hobbs]

Interesting point. Do you have any links relating to this?

The US Navy has published "excursion" limits for oxygen diving (100% O2). It is mentioned on page 13 of the following paper but this is really a great historical review. The US Navy manual will have the most current limits (though I don't remember seeing this as a change in the latest revision).

Butler, FK. Closed-circuit oxygen diving in the U.S. Navy. Undersea Hyperb Med. 2004 Spring;31(1):3-20. RRR ID: 3986

 

[nereas]

...
An open circuit diver would have the same sort of oxygen exposure only if he immediately dropped down right to the 1.3ata MOD and stayed there the entire dive...

AND stayed there, forever, and ever, and ever.

Like a CCR diver can. Forever.

That is why you plan ppO2 exposure for CCRs as well as for O/C twin-tank tech-deco diving.

But alas NOT for NDL recreational.

Alas, Pandora's box, once opened, cannot again be closed.

[I am definitely thinking that logic should have been kept a secret and stayed in Greece.]

 

[nereas]

Back to the ignore hole for a week or two. You are truly an unbelievable troll.

Please understand, oh Ye Mods, that I really love (Platonically) Thalassamania.

Anyone who comes up with a Greek name like that cannot be all bad.

Err, even though his "logic" may not be orthodox Greek, all the time.