Nitrox Certification?

[RonFrank]

No more bottom time when your SPG hits 500 psi it is still empty.
Biggest advantage is less wait between dives and the unofficial
version it makes you feel better on a three dive day. It doesn't do
anything except limit your depth on a one dive day.

It isn't called geezer gas for nothing. :11ztongue

I don't have dive tables in front of me, but when doing Drift dives on Jupiter (80fsw for all of the dive), everyone but one diver was on Nitrox. That diver got 30 minutes of bottom time. The rest of us were down for 45 minutes with the dives lasting maybe 55 minutes with the safety stop.

So sure, if you suck gas, than Nitrox will not extend bottom time, but I think EVERY diver on this boat saw close to 2h15min of BT on Nitrox over three dives vs. poor Ray, who ended up with 1hr30min total BT. That is 45 minutes more BT, or basically half again the diving he did.

Nitrox is GREAT for that type of diving. Is it worth it?

Well,

Diving Jupiter with tank rental - $90.
Cost of the trip to get there in the first place - $800.
Getting an extra 45 minutes of BT with Nitrox - Priceless!

 

[Charlie99]

Hence my addition - you tend to dive to the limits... when you'r 2 mins away from deco, I dont think it makes much difference whether you're on air on nitrox - you're close to the line !

While diving up to the limits eliminates a lot of the safety factor, being on nitrox in this situation can make a big difference. When doing deep stops and safety stops you offgas signficantly faster when on nitrox, than if you were at the same depth on air.

To put it another way, an nitrox diver at a certain depth and an air diver at the eqivalent air depth could have the same bottom time and would start their ascent equally loaded. After 5 minutes of ascent and stops the nitrox diver would have offgassed more.

 

[Diver0001]

While diving up to the limits eliminates a lot of the safety factor, being on nitrox in this situation can make a big difference. When doing deep stops and safety stops you offgas signficantly faster when on nitrox, than if you were at the same depth on air.

To put it another way, an nitrox diver at a certain depth and an air diver at the eqivalent air depth could have the same bottom time and would start their ascent equally loaded. After 5 minutes of ascent and stops the nitrox diver would have offgassed more.

That's very easy to see if you're decompression diving. If you're making an air dive with decompression on air then the ascent is often something like 25-30% slower than when you're using 50%.

R..

 

[Santa]

- safety is NOT a valid argument - as the book says... air diving is extremely safe today. And I would add: you always dive to the limit.. (till you get no more bottom time) so it eventually makes little difference

Question: I was reading an article by "that ichtyologist guy who introduced deep stops". He found out that If he did not feel as fatigued if he made slow ascents and did several deep stops on the way. The explanation, as I understood it, was that fatigue was partly due to nitrogen micronuclei expanding into bubbles - that was more stressfull on the tissues when ofgassing - than would be the same amount of nitrogen in it's nucleus form. That added stress supposedly makes fatigue a symptom of an increased risk of DCS. Probably for that very reason it's common practice that if you feel fatigued during multiday repetetive diving you take a day off.

So ... if the fatigue that is not just the result of heat loss and exercise can be reduced is it not evidence that nitrox may be safer regarding DCS?

I'm struggling with concepts here so please forgive any bads on my part.

regards

 

[ScubaSixString]

Question: I was reading an article by "that ichtyologist guy who introduced deep stops". He found out that If he did not feel as fatigued if he made slow ascents and did several deep stops on the way. The explanation, as I understood it, was that fatigue was partly due to nitrogen micronuclei expanding into bubbles - that was more stressfull on the tissues when ofgassing - than would be the same amount of nitrogen in it's nucleus form. That added stress supposedly makes fatigue a symptom of an increased risk of DCS. Probably for that very reason it's common practice that if you feel fatigued during multiday repetetive diving you take a day off.

So ... if the fatigue that is not just the result of heat loss and exercise can be reduced is it not evidence that nitrox may be safer regarding DCS?

I'm struggling with concepts here so please forgive any bads on my part.

regards

Pyle stops....Richard Pyle.

Good article and it makes a lot of sense. You're reducing the pressure gradient (130 to 15 feet is a much greater gradient than 130 to 70 to 35 to 15) Makes a lot of sense.

Erics point is if you dive to the limits you dive to the limits. Will there be more offgassing on nitrox? Yes. But within the limits of recreational nitrox (EAN40 and below) the nitrogen gradient (i think thats a reasonable term) between the gas in you and the gas you're breathing isnt enough to make a huge difference. EAN40 still has 60% nitrogen vs 79 in air. Thats why EAN40 isn't typically used as a deco gas (or at least not for long)

But Nitrox CAN provide a safety barrier if you use it for that. And certainly there is some offgassing "credit" but not one you'd want to try to add into your tables (Ie stick with what your computer/tables tell you)

 

[String]

Nitrox is of limited use if you have no idea what sites your diving until the boat is actually on the water and moving as you have no idea what mix is needed.

If your diving is structured, always know the sites in advance and so on i can see a use for it. The way it is here despite lots of us being nitrox qualified its mainly used abroad as its impossible to guess what mix is needed for the dive around here.

 

[Canadian_Diver]

I am seriously thinking of getting my nitrox certification. Could someone please give me some reasons why I should do it. Are the only benefits: slightly more bottom time & maybe feeling better after a dive.

Yup, if you dive it using air tables, it adds in a huge safety margin against DCS, especially doing repetitive dives.

 

[pete340]

Yup, if you dive it using air tables, it adds in a huge safety margin against DCS, especially doing repetitive dives.

Starting to ascend ten or fifteen minutes before you reach the NDL also adds a safety margin against DCS, and has the added advantage that if you need to stay longer you know exactly what your actual margin is. The only reason I can think of for subtracting some unknown amount from the NDL by diving with the wrong tables is that you don't trust your own judgment, and are afraid that you'll push the limits if you know exactly what they are.

 

[jakubson]

Starting to ascend ten or fifteen minutes before you reach the NDL also adds a safety margin against DCS, and has the added advantage that if you need to stay longer you know exactly what your actual margin is. The only reason I can think of for subtracting some unknown amount from the NDL by diving with the wrong tables is that you don't trust your own judgment, and are afraid that you'll push the limits if you know exactly what they are.

Not to be argumentative , but diving the "wrong" tables is actually a more consistent way to provide a safety margin than subtracting 10 to 15 minutes from NDL regardless of depth. When diving with lower EAN tables than your actual mix, you are in essence assuming a constant percentage increase of N2 partial pressure in your tables. This carries through regardless of depth, and can be considered a "constant" safety margin. On the other hand, ascending 10 minutes before the NDL is a lot different safety margin on a 90 fsw dive than it is on a 60 fsw dive.

Just my $.02

 

[pete340]

ascending 10 minutes before the NDL is a lot different safety margin on a 90 fsw dive than it is on a 60 fsw dive.

Which is why I didn't give a specific amount. The point, again, is that applying a known correction makes much better sense than providing an unknown one.