Nitrox mixes above 40%?

[mstachowsky]

Howdy,

I'm just taking the SSI nitrox course now and they mention that EAN40 is the highest they will talk about in the rec course. Just wondering, why would a tec diver use more than 40%? Is it just for decompression, or would it be used in, say, a shallow cave dive to increase limits?

MIKE

 

[616fun]

Increased PO2 of the breathing gas changes the partial pressure exerted on other gases (nitrogen) in the body and forces it out of the the tissues more quickly. I tend to use 50% as a deco mix and do my gas switch at 70'. This places my PO2 of 02 at 1.6 and really kicks in the decompression. Others may only use 100% O2 and switch at 20'. The PO2 of 100% O2 at 20' is 1.6 as well.

---------- Post added March 24th, 2013 at 10:51 AM ----------

To answer you question - no - higher O2 would not be used to extend a shallow dive.

 

[rongoodman]

The only reason I've ever heard of is for more efficient decompression. Rather than switching to a non-standard gas to get around NDL limits in a shallow cave, I would just plan on doing the deco at the end if needed.

 

[mstachowsky]

Neat. So I guess the "advanced nitrox" courses (well into my future...far into my future ) are essentially decompression courses?

MIKE

 

[DevonDiver]

It's just for (accelerated) decompression.

 

[616fun]

Neat. So I guess the "advanced nitrox" courses (well into my future...far into my future ) are essentially decompression courses?

MIKE

Correct. Honestly I've never seen rec diving provide a mix beyond 36%. 32% and 36% are considered standards. Some locations may deviate due to standard depths of the wrecks. An example would be Morehead City, NC. Everyone banks 30% as the depths are almost exclusively in the 100-125' range.

 

[SailNaked]

MOD for 40% is 99ft at 1.6 (table on internet). so the course limits to that because limiting a dive under that depth starts to require some thinking.

diving more O2 only increases bottom time on repetitive dives, a tank of air lasts exactly the same as a tank of Nx. when in say Bonaire where you can do 4 dives in 5 hours Nx is the only way but you only need 32%.

 

[Steve_C]

If you have a good SAC rate and/or dive a larger tank then nitrox can buy you a bit more bottom time on the first dive.

Some like to stay below 1.6 for an extra margin of safety.

 

[boulderjohn]

Neat. So I guess the "advanced nitrox" courses (well into my future...far into my future ) are essentially decompression courses?

MIKE

Correct. If you take Advanced Nitrox from TDI for example, you will almost always that the Decompression Procedures course along with it.

 

[iamjblevine]

Is it in the advanced nitrox course as well that using 1.6 instead of 1.4 is taught? I understand that the 1.4 is merely a conservative safety factor on the 1.6. But does it become "common practice" to ignore the 1.4 after "Advanced Nitrox". Or is the 1.4 just a PADI limit?
Thanks!