Nitrox course

[Wijbrandus]

My wife and I are working through our NAUI Nitrox manuals this week. We take our class Monday night. I have a question though, because something doesn't make sense.

One of the listed advantages of Nitrox is shorter surface intervals. Yet later on, the manual says that 1 hour SIs are recommended for Nitrox diving. My PADI OW manual says that 1 hour SIs are recommended as well. To my way of thinking, Nitrox, if you follow the manual's recommendations, does not in fact give you any advantage on the SI. Or am I reading this wrong? Am I reading too much into this?

I've never had a 1 hour SI on any of my trips. 30 minutes is typical, with an occasional 45 minute one if we've had a larger group. This has been diving on air, of course.

 

[Diver0001]

Am I reading too much into this?

They probably mean to say that on the same dive with Nitrox you will have a lower PG at the end of the dive. That translates into less RNT time for the same surface interval and therefore longer bottom times on subsequent dives given the same surface interval when compared to air. Conversely, to get to the same RNT value you need less surface time..... ie "shorter surface intervals". The point, however, is that RNT is less.

R..

 

[Rick Murchison]

My wife and I are working through our NAUI Nitrox manuals this week. We take our class Monday night. I have a question though, because something doesn't make sense.

One of the listed advantages of Nitrox is shorter surface intervals. Yet later on, the manual says that 1 hour SIs are recommended for Nitrox diving. My PADI OW manual says that 1 hour SIs are recommended as well. To my way of thinking, Nitrox, if you follow the manual's recommendations, does not in fact give you any advantage on the SI. Or am I reading this wrong? Am I reading too much into this?

I've never had a 1 hour SI on any of my trips. 30 minutes is typical, with an occasional 45 minute one if we've had a larger group. This has been diving on air, of course.

The recommendation is for a one hour surface interval minimum, even when the requirement is for less.
To better illustrate the SI point, run a series of dives to 60' for 40 min on air and on EAN32. The "reduced SI" will become apparent.
S

 

[Wijbrandus]

I did run the numbers. EAN32 vs. Air, in the mid-range, really makes a huge difference.

Ok, I won't worry too much about it. It seems to be one of those "You should always take an hour break" kind of legalese things they put in training manuals.

I shall allow the tables and my own sense of self-preservation to rule the dive.

 

[MB]

...It seems to be one of those "You should always take an hour break" kind of legalese things they put in training manuals.

I shall allow the tables and my own sense of self-preservation to rule the dive.

For the record, NAUI standards do indeed recommend SIs of an hour or more. That's not just legal mumbo-jumbo; it allows a nice offgassing before you re-stock your tissues with the evil N2! Doesn't matter if you're breathing 21% or 40%, the less N2 you start with on repetitive dives, the better.

That's not just theory, its the real deal. But agency recommendations frequently do not reflect common practice. On any given pair of dives, you'll earn more allowable dive tme on the 2d (or 3d or 4th) dive if you take up less N2 on your 1st dive. So... breathing nitrox results in less N2 uptake on Dive #1, and so subsequent SIs and repetitive dives benefit from that decreased N2 uptake. Your table exercises showed you that.

The cool thing about diving with nitrox is that you can juggle the benefits to match your dive conditions. Bad sea conditions? Reduce the SI so you don't have to endure mal de mer between dives. Repetitive dives? Use Nitrox but use an air profile to increase your margin of safety. Its all good.