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navyhmc
12-30-2007, 22:35
Okay, so I am finally making the leap into Voodoo gas and will be taking my class soon-PADI EAN. Since I have it available, I have already bought the book and gone through it at least 3 times-I like to be thorough.

Here's the question: Does Nitrox use decrease one's resp rate and thus SAC times? I've been thinking that the oxygen needs don't necessarily go up with Nitrox and the O2 concentration is up so the number of breaths per minute should go down. I am keeping in mind the CO2 exchange needs as well. At least that's what my paramedic training leads me to hypothesize.

The course material doesn't go into this at all, so what about the real world experience from folks here.

FishFood
12-30-2007, 22:40
Even at 21% you have a large amount of o2 leaving as you exhale. Nitrox doesn't affect my rates, and judging from past threads on this subject, anyone elses' either.

EDIT:

Although, breathing is a mental game... If you were to train your self to breath in a way that would take advantage of the extra o2 (MUCH slower for example), then maybe you could improve SAC rates? Im grasping here....

texdiveguy
12-30-2007, 23:45
Here's the question: Does Nitrox use decrease one's resp rate and thus SAC times?

Breathing of nitrox while diving will not change your respiration rate or effect your SAC rate directly.

CODMAN
12-31-2007, 08:01
Yup, as the others said, it's shouldn't/ won't improve your air consumption. I believe (correct me if I'm wrong) that your vetilatory rate (breathing rate) is controled by CO2 levels, and that won't change by using Nitrox.

So no, you won't get a air consumption benefit. But there are plenty of other benefits which make it worthwhile in my oppinion! way to go for taking the course!:smiley20:

Jay_SMART_Diver
12-31-2007, 08:15
Nitrox's primary benefit is less Nitrogen loading for repetitive dives, for longer bottom times on those repetitive dives. Definitely worth it if you're diving 4-5 dives a day, like on a live-aboard or unlimited shore diving trip (Bonaire, Roatan, etc.). Not worth the cost if you're just doing a couple lake dives, IMO.

CompuDude
12-31-2007, 20:38
Nitrox's primary benefit is less Nitrogen loading for repetitive dives, for longer bottom times on those repetitive dives. Definitely worth it if you're diving 4-5 dives a day, like on a live-aboard or unlimited shore diving trip (Bonaire, Roatan, etc.). Not worth the cost if you're just doing a couple lake dives, IMO.

Cost is relative, since if those few lake dives are the last dives you'll be doing for 6 months, and they lie right in the Nitrox sweet spot where you really gain the most extra BT, a few extra bucks for the dives may well be worth it.

But you're right, other than that. The extra o2 gets breathed out just like the extra o2 in regular air, so there's no real affect on respiration rates. The advantage is the extra o2 displaces nitrogen, so you don't absorb as much during your dives.

Same theory applies for trimix. Keep the o2 percentage normal, and replace Nitrogen with Helium, that way you can get more BT with less Nitrogen absorption... because there's simple less Nitrogen to absorb. (There are other complexities, of course, but this aspect illustrates my point.)