Damselfish
Contributor
If you don't extend your bottom time as long as possible, which would be pretty hard sometimes anyway, you can have some of each. I don't think of it as either/or.StSomewhere:
Which expert is right? re:Nitrox on air tables
- Thread starter del_mo
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Damselfish:
Example:
On an 80 foot dive I can extend my bottom time using 36% to 60% greater than on air and still only reach 73% of my NDL. I think that is called having your cake and eating it too.
Air 25 minute NDL
36% 55 minute NDL
so at 40 minutes on 36% I have better bottom time and lower nitrogen exposure.
StSomewhere
Contributor
Sure, but my point is that at some degree you are "spending" (for lack of a better word) the safety factor by extending the NDL. Like all things in life its a trade off, but in this case a pretty good one. Still better than air, IMO.
grf88:
I like this explanation...
A couple of things that we should mention, is that it is not disolved nitrogen that gives us decompression, it is bubbles and bubbles alone.
that lack of fatigue or freshness that has been mentioned is the lack of "fatigue" as a symptom. Fatigue is a symptom of DCS as we all know, now in mild cases, fatigue is all you may feel. However, no matter how you look at it, if you feel fatigued, then you have DCS.
Perhaps some of the readers of this thread should research how to avoid "asymptomatic DCS" and how to avoid that. You will find there is some interesting new ideas about it.. Much of it focusses less on how much nitrogen loading you have, and far more on avoiding gas phase in the body.
Del_Mo go for it .... Using nitrox as air will only benifit you.. as long as you track the O2.
StSomewhere:
By extending my bottom time I am spending some of the safety benefit but I am still keeping 27% in the bank for safety as compared to diving air.
MookieMoose
Guest
However, no matter how you look at it, if you feel fatigued, then you have DCS.
This statement is ridiculous on it's face. I'm not trying to slam you, but stop and think for a minute. A day of carrying heavy equipment punctuated by periods of exercise in a medium 800 times denser than the environment we as humans normally operate in can leave anyone feeling fatigued without DCS being a problem. I work in DCS research and would like to know where you're getting your information that fatigue=DCS?
Cam
This statement is ridiculous on it's face. I'm not trying to slam you, but stop and think for a minute. A day of carrying heavy equipment punctuated by periods of exercise in a medium 800 times denser than the environment we as humans normally operate in can leave anyone feeling fatigued without DCS being a problem. I work in DCS research and would like to know where you're getting your information that fatigue=DCS?
Cam
MSilvia
Contributor
The way I look at it, if I haven't been diving in a month feeling fatigued doesn't automatically imply DCS. Since that's true, feeling fatigued when I have been diving recently doesn't automatically imply DCS either. It's a possible symptom, but not rock-hard evidence.cancun mark:
RonFrank
Contributor
I just finished my Nitrox classroom, so the stuff is fresh in my mind.
PADI indicates that diving Nitrox does NOT provide additional safety, however this is NOT based on anything but incidents of DCS in air vs. Nitrox. Both are low, and as the numbers are simply a good guess comparing the number of dives vs. DCS incidents, and they do not take into account individual profiles or multiple dives, I'm not sure if the conclusion is valid (in fact I think it is not, and most instructors I've discussed this with including our Enriched Air instructor agree).
Take a look at Nitrogen intake. Using the PADI RDP for air, after a 60 ft dive for 39 minutes one is in the pressure group of P and it would require a SI of 2:28 to get back to an A pressure group. Using EANx32 doing the same dive one is in a pressure group of K and an SI of 2:05 to get back to A. The NDL for a 60ft dive is 55 minutes on air, and 90 minutes on EANx32.
It would seem to me that if one absorbs less Nitrogen during a dive, there is less chance of DCS, and the numbers and limits when comparing air vs. Nitrox make a very compelling argument. If one were to push the NDL on air, and hit a 60ft dive for 55 minutes you are pushing the limit. If one were to dive the same profile on EANx32 one ends up in pressure group P which is conservitive. How is that not MUCH safer?
I realize that there have been no studies done (for obvious reasons) on DCS doing air vs. enriched air. However I can not see how anyone can ignore the fact that diving enriched air is not MUCH safer. The bottom line is that on EANx32, most dives will NEVER hit their NDL with any sized tank because they will run out of air long before hitting the NDL. With Air, that is just not the case.
As for the P02 limits, once one starts doing the math, it becomes clear that it is next to impossible to hit the limit during even a five dive day. For example if all dives are done to 60 feet max with a PP of .9 ata, one would have to do 360 minutes or SIX HOURS of diving on EANx32 to hit the exposure limit.
The only real risk is O2 toxicity, so just don't dive deeper than the mix allows, and all is well.
For $100, IMO it's worth getting the certification, and as I am doing exactly that, my money is firmly where my mouth is. The air fills are also more expensive, so many divers choose to do Nitrox on deeper dives, and go to air on the second.
PADI indicates that diving Nitrox does NOT provide additional safety, however this is NOT based on anything but incidents of DCS in air vs. Nitrox. Both are low, and as the numbers are simply a good guess comparing the number of dives vs. DCS incidents, and they do not take into account individual profiles or multiple dives, I'm not sure if the conclusion is valid (in fact I think it is not, and most instructors I've discussed this with including our Enriched Air instructor agree).
Take a look at Nitrogen intake. Using the PADI RDP for air, after a 60 ft dive for 39 minutes one is in the pressure group of P and it would require a SI of 2:28 to get back to an A pressure group. Using EANx32 doing the same dive one is in a pressure group of K and an SI of 2:05 to get back to A. The NDL for a 60ft dive is 55 minutes on air, and 90 minutes on EANx32.
It would seem to me that if one absorbs less Nitrogen during a dive, there is less chance of DCS, and the numbers and limits when comparing air vs. Nitrox make a very compelling argument. If one were to push the NDL on air, and hit a 60ft dive for 55 minutes you are pushing the limit. If one were to dive the same profile on EANx32 one ends up in pressure group P which is conservitive. How is that not MUCH safer?
I realize that there have been no studies done (for obvious reasons) on DCS doing air vs. enriched air. However I can not see how anyone can ignore the fact that diving enriched air is not MUCH safer. The bottom line is that on EANx32, most dives will NEVER hit their NDL with any sized tank because they will run out of air long before hitting the NDL. With Air, that is just not the case.
As for the P02 limits, once one starts doing the math, it becomes clear that it is next to impossible to hit the limit during even a five dive day. For example if all dives are done to 60 feet max with a PP of .9 ata, one would have to do 360 minutes or SIX HOURS of diving on EANx32 to hit the exposure limit.
The only real risk is O2 toxicity, so just don't dive deeper than the mix allows, and all is well.
For $100, IMO it's worth getting the certification, and as I am doing exactly that, my money is firmly where my mouth is. The air fills are also more expensive, so many divers choose to do Nitrox on deeper dives, and go to air on the second.
RonFrank
Contributor
DA Aquamaster:
You can make the "NOT OVER 40" claim for the one day you hit fourty.... but after that, you have joined us!!
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