Nitrox course. What's the point?

[boulderjohn]

It is true that nitrogen loading is the same whether diving air or nitrox if you go to the NDLs, but it is also true that lots of people diving nitrox do not dive to NDLs. In fact, for lots of diving, it would be very difficult to dive to NDLs while using a rich nitrox mix.

I have many times seen people write as if there were only two choices while diving nitrox--either dive to air tables or dive all the way to nitrox NDLs. I have seen articles in major dive magazine (like Dive Training) that have said precisely that--you can either dive nitrox to air limits for safety, or you can dive to the nitrox limits for extended bottom time. You cannot, the writers insist, have both added safety and extended bottom time.

What such writers seem to be saying is that if you are using 36% nitrox and diving to 80 feet (using PADI tables), you must either end the dive at 30 minutes (air tables) or end the dive at 55 minutes (36% tables). You are absolutely forbidden to dive for 40 minutes to get both safety and extended bottom time! I don't know who is policing you down there, but, dammit, if you go past 30 minutes, you'd better make sure you have enough nitrox in your tank to get all the way to 55, because stopping short of that is not allowed.

 

[Divin'Papaw]

If you stay at depth for the max allowable time for nitrox or air the nitrogen loading is exactly the same. Why do you think you get longer bottom times on nitrox?

Your off gassing on ascent is not identical however. You therefore surface with less nitrogen loading.

 

[Celt]

Your off gassing on ascent is not identical however. You therefore surface with less nitrogen loading.

The computer has calculated the assent to be made also on nitrox,

 

[Gareth J]

If you stay at depth for the max allowable time for nitrox or air the nitrogen loading is exactly the same. Why do you think you get longer bottom times on nitrox?

Did you really mean that last sentence?
Air = 21% O2, 79% Nitrogen
Nitrox 32 = 32% O2, 68% Nitrogen
Nitrox 36 = 36% O2, 64% Nitrogen

Using BSAC tables (sorry can't put my hand on Buhlmann at the moment)

Nitrox 21 (air) = 20 minutes no stop @ 30m
Nitrox 27 = 23 minute no stop @ 30m
Nitrox 32 = 28 minutes no stop @ 30m
Nitrox 36 = 32 minute no stop @ 30m

 

[MichaelMc]

I get cold, short on gas, hungry or bored before NDL kicks in, so Nitrox is safer for me. Maybe you do not get cold, short on gas, hungry or bored first and continue to push whatever ragged edge of NDL your gas allows you, so Nitrox is not safer for you. I hope you do not wind up bent diving that way.

 

[Celt]

It is true that nitrogen loading is the same whether diving air or nitrox if you go to the NDLs, but it is also true that lots of people diving nitrox do not dive to NDLs. In fact, for lots of diving, it would be very difficult to dive to NDLs while using a rich nitrox mix.

I have many times seen people write as if there were only two choices while diving nitrox--either dive to air tables or dive all the way to nitrox NDLs. I have seen articles in major dive magazine (like Dive Training) that have said precisely that--you can either dive nitrox to air limits for safety, or you can dive to the nitrox limits for extended bottom time. You cannot, the writers insist, have both added safety and extended bottom time.

What such writers seem to be saying is that if you are using 36% nitrox and diving to 80 feet (using PADI tables), you must either end the dive at 30 minutes (air tables) or end the dive at 55 minutes (36% tables). You are absolutely forbidden to dive for 40 minutes to get both safety and extended bottom time! I don't know who is policing you down there, but, dammit, if you go past 30 minutes, you'd better make sure you have enough nitrox in your tank to get all the way to 55, because stopping short of that is not allowed.

I get your point, but it should be stressed to new divers which the OP is that if you dive nitrox to its NDL you’re taking the same risk of developing DCS as diving air to its NDL.

 

[Celt]

Did you really mean that last sentence?
Air = 21% O2, 79% Nitrogen
Nitrox 32 = 32% O2, 68% Nitrogen
Nitrox 36 = 36% O2, 64% Nitrogen

Using BSAC tables (sorry can't put my hand on Buhlmann at the moment)

Nitrox 21 (air) = 20 minutes no stop @ 30m
Nitrox 27 = 23 minute no stop @ 30m
Nitrox 32 = 28 minutes no stop @ 30m
Nitrox 36 = 32 minute no stop @ 30m

Yeah longer bottom times on nitrox with no deco

 

[BRT]

Diving nitrox is not safer than air if both are dived to NDL.

Are you sure? If I dive 32% and air to NDL at 100' and then start my ascent I'm betting that if I use the same ascent time and the same safety stop I will have less nitrogen at the surface with the nitrox. What do you think? If you disagree what about dives to 60 feet to NDL's using 50% and air?

 

[Celt]

I get cold, short on gas, hungry or bored before NDL kicks in, so Nitrox is safer for me. Maybe you do not get cold, short on gas, hungry or bored first and continue to push whatever ragged edge of NDL your gas allows you, so Nitrox is not safer for you. I hope you do not wind up bent diving that way.

I’m not advocating diving to NDL I’m pointing out that if you do your taking the same risk no matter what gas you use.

 

[BRT]

If you stay at depth for the max allowable time for nitrox or air the nitrogen loading is exactly the same. Why do you think you get longer bottom times on nitrox?

This would be true if you were magically transported instantly from depth to the surface.