Nitrox Rule of Thumb 32 vs 40

[boulderjohn]

Who recommends 100 for recreational divers?

PADI suggests divers increase their depths cautiously, depending upon training and experience. The "and" in that phrase really means "and/or." For divers who get the AOW certification, the suggested limit is AOW, but the actual full suggested recreational limit is 130 with additional training and experience.

 

[tomfcrist]

Who recommends 100 for recreational divers?

The answer to that is a few agencies, although for notably different reasons.

NAUI due to narcosis but implies that it’s acceptable to go to 130 as a contingency. Helitrox is their solution.

PADI was the same back when I did AOW IIRC...minus the helitrox.

GUE takes it a step further and says helium anytime past 100’. My guess as to their reasoning is that nitrox isn’t really reducing narcotic properties of the breathing media (oxygen is narcotic), and the WOB goes up to what they consider an unacceptable level beyond 100’ without helium.

There are more I’m sure...look around.

 

[KeithG]

The answer to that is a few agencies, although for notably different reasons.

NAUI due to narcosis but implies that it’s acceptable to go to 130 as a contingency. Helitrox is their solution.

PADI was the same back when I did AOW IIRC...minus the helitrox.

GUE takes it a step further and says helium anytime past 100’. My guess as to their reasoning is that nitrox isn’t really reducing narcotic properties of the breathing media (oxygen is narcotic), and the WOB goes up to what they consider an unacceptable level beyond 100’ without helium.

There are more I’m sure...look around.

When did PADI go 100? When we got OW way back we were good for 130.

 

[tomfcrist]

When did PADI go 100? When we got OW way back we were good for 130.

IDK...I did my AOW quite a while ago. It was never talked about in class, but was part of the textbook.

FWIW, there is a difference between recommended and maximum. The 130 number is still there.

 

[boulderjohn]

When did PADI go 100? When we got OW way back we were good for 130.

As I said in post #21, for PADI the recreational limit has always been 130. They suggest that you get there incrementally as you gain training and experience. For the AOW class, the limit for the deep die is 100', but that is for that class.

 

[IncreaseMyT]

36 ean should be MOD 90 feet. 1.4 is where we max our ppo2 in my area.

If 1.6 is OK that’s great, but unless we’re talking about repetitive dives I am not sure there is a benefit to going to 1.6 in rec diving

 

[uncfnp]

Hopefully the OP has his answer, that it is based on the MOD for each gas. And I for one have never seen a recreational diver dive 40%. Heck dive shops that don’t know me give me an odd look if I ask for anything past 36.

Only marginally related to the original question but I took nitrox fron TDI and 1.4 was not taught as the gold standard. It wasn’t until I found Scubaboard that I learned I was going to die if my ppo2 hit 1.6.

nitrox isn’t really reducing narcotic properties of the breathing media (oxygen is narcotic),

I never really understood the physiology behind this and apparently its validity has been questioned lately.

 

[The Chairman]

I never really understood the physiology behind this

Oxygen is just as narcotic as nitrogen and probably more so, which is the mechanism of OxTox.

 

[CuzzA]

36 ean should be MOD 90 feet. 1.4 is where we max our ppo2 in my area.

If 1.6 is OK that’s great, but unless we’re talking about repetitive dives I am not sure there is a benefit to going to 1.6 in rec diving

1.4 on 36 is 95 feet.

To your second part, it depends on your profile. Say for example you're diving the Florida Middle Grounds using 32%. These ledges can be 30 feet tall. So you drop down off a 100 ft. ledge to 130ft./1.6ppo2 to grab a fish, lobster or take a pic and then swim back up on the ledge. Even repetitive dives, for 99% of divers, you haven't had enough exposure to cause concern.

 

[uncfnp]

Oxygen is just as narcotic as nitrogen and probably more so, which is the mechanism of OxTox.

Hopefully Dr Mitchell will forgive me for reposting ...

Hello,

To add to the mix, this has just been published.

Objective vs. Subjective Evaluation of Cognitive Performance During 0.4-MPa Dives Breathing Air or Nitrox. - PubMed - NCBI

On balance, I favour the argument that oxygen is less narcotic at the pressures we can safely breathe because there is a substantial gap between inspired and tissue PO2 due to metabolism in the tissues that matter for a narcotic effect. In contrast, the gap between inspired and tissue tensions of nitrogen in the brain is almost zero because the brain is a very fast tissue. Having said that the functional difference in narcotic effect is probably quite small. If we really want to avoid narcosis, then breathing helium is the key.

Simon M