Optimal nitrox mix the devils throat

[kwinter]

This entire thread shows lack of understanding of dive physiology. I will not encourage anyone who doesn't understand to breathe something potentially toxic.

Someone please point out to me the paragraph in any nitrox training manual that speaks about reducing narcosis with any scientific data to back it up. Adding 11% to the oxygen constant would reduce the nitrogen content to 68%. That would barely be a perceptible difference from air. Enhancing the oxygen content is used to decrease decompression or extend NDL by increasing offgassing. Nitrox is therefore considered a shallow gas, although 32% could still be used on a 132 ft/40 meter dive at a max pO2 of 1.6 for a short time.

Adding helium to your breathing mix is the answer to reducing narcosis. Get some advanced nitrox, decompression, and trimix training. Learn the correct physiology and you won't be spouting garbage for others to pounce on.

I'm feeling rather surly this morning.

 

[Candiru]

This entire thread shows lack of understanding of dive physiology. I will not encourage anyone who doesn't understand to breathe something potentially toxic.

Someone please point out to me the paragraph in any nitrox training manual that speaks about reducing narcosis with any scientific data to back it up. Adding 11% to the oxygen constant would reduce the nitrogen content to 68%. That would barely be a perceptible difference from air. Enhancing the oxygen content is used to decrease decompression or extend NDL by increasing offgassing. Nitrox is therefore considered a shallow gas, although 32% could still be used on a 132 ft/40 meter dive at a max pO2 of 1.6 for a short time.

Adding helium to your breathing mix is the answer to reducing narcosis. Get some advanced nitrox, decompression, and trimix training. Learn the correct physiology and you won't be spouting garbage for others to pounce on.

I'm feeling rather surly this morning.

good advice

 

[fdog]

I hate "trust me" dives...


The OP certainly presented as an experienced diver, who has multiple dives at this location, and would know depths expected as well as the profile. Thus all that was needed was the best mix.

Just as I would decline to offer an answer to someone posting "I've never done deco. What would be the schedule for this 200' dive on air?", I would likewise defer coughing up a mix for this dive.



There's so many factors to be considered in generating a mix, all of which are covered in a Nitrox syllabus. For example, typical recreational MOD's are built around a ppO2 of 1.4; yet, the OP mentions a concern about running into deco. In this case, it would be prudent to back off of 1.4, to say, 1.3, to reduce chances of a tox episode. Toxing while under a bit of obligation just makes the situation worse for both victim and rescuer.

Most classes mention the situations that (may) potentiate a tox episode: cold, dark, claustrophobia, workload. In determining a mix, you take these into account when determining what ppO2 you are willing to tolerate.



Every Nitrox class that I know of covers best mix calculations. Sadly, I have seen some classes lately where apparently all that's taught is some rudimentary theory, and here's how you analyze, refer to this chart, and don't go deeper than that...bam, you're done. Hence the prod to look to your class materials and instructor. It's a brutal statement, but if you can't calculate the best mix, then maybe you shouldn't be breathing nitrox on the dive.



Asking someone to blindly give you a mix for a deepish dive is, absolutely, a "trust me" dive. They don't know your tolerance(s)...they don't know your workload...and you don't know what ppO2 they are calculating for!

Nitrox diving is mixed gas diving. There's more to it than analyze & write on the tape.


All the best, James

 

[Candiru]

Point well taken. I should ask max depth punta sur and not mention nitrox. My logs show a discrepancy, what are peoples max depth at the exit of the throat.

 

[Beyond_Diving]

As far as I can remember, you come out at around 135'

 

[fishi]

Candiru, the first exit is at 110 and the lower exit is at 124. I shot this with a gopro last month.
[video=vimeo;56259469]http://vimeo.com/56259469[/video]
Click HD for best picture

 

[Jim Lapenta]

What's worse are the classes that teach you how to set your nitrox computer and little else. Garbage in, garbage out.

 

[Kevrumbo]

Ideally for me, 25/25 trimix in double 11L backmount cylinders (or double 11L sidemount), with Oxygen for short deco profile using a small 4L tank --might be a tight squeeze through the restrictions in "The Throat" though IIRC. Warm tropical water, and hopefully no down-currents to battle at max depth 40m, do-able in Eanx28 doubles backmount or sidemount and deco profile on just backgas, ascending up immediately after egress to a "clear-headed" depth above 30m.

Use straight/no EAD for conservatism, Ratio Deco/Min Deco algorithm, depth ave 21m to 24m for 20min to 30min bottom time --most of the time drifting along with the current looking at the marine life & deep reef scene after traversing through the Throat. . .

 

[Candiru]

Candiru, the first exit is at 110 and the lower exit is at 124. I shot this with a gopro last month.
[video=vimeo;56259469]http://vimeo.com/56259469[/video]
Click HD for best picture

link?

 

[fishi]

The Devil's Throat on Vimeo