Nitrox Surface Interval

[artusor]

I just finished my NITROX class, but I had one question that I have not gotten a good answer for. In class I was told that the minimum surface interval when diving Nitrox was one hour. I don't recall any minimum SI when diving air, so my question is, why is there a minimum SI for Nitrox and not air?

If the effectof the SI is to off gas Nitrogen, and Nitrox has less Nitrogen than air, I don't see why there is a min. SI. Is that something that most people follow? Also, is this taught by all of the agencies, or is this just a PADI recommendation?

Thanks in advance for any light you can shed on htis.

 

[Wayward Son]

Incorrect, so far as I know. One hour is a good SI, and usually enough that I'll have more BT than I have gas for, but I can go in sooner. I just won't have as much NDL BT available, same way it works with air.

One nice thing about EAN is that you get more NDL BT available for a give SI. For example, I usually dive EAN32, my wife is still on air. After a 1 fr SI, I'm allowed (rough numbers, not from a table) almost twice the NDL time at a given depth than she is.

Take a look at your nitrox tables. So far as I recall, mine to not have any such SI requirement & I can plan dives with much shorter SI's than one hour.

 

[Rick Murchison]

I just finished my NITROX class, but I had one question that I have not gotten a good answer for. In class I was told that the minimum surface interval when diving Nitrox was one hour. I don't recall any minimum SI when diving air, so my question is, why is there a minimum SI for Nitrox and not air?

If the effectof the SI is to off gas Nitrogen, and Nitrox has less Nitrogen than air, I don't see why there is a min. SI. Is that something that most people follow? Also, is this taught by all of the agencies, or is this just a PADI recommendation?

Thanks in advance for any light you can shed on htis.

The one hour break is a recommended minimum; not on any chart.
As in many things Scuba, rules-of-thumb are there to cover the edges of the envelope. In this case, the hour minimum surface interval is to provide an adequate "air break" between high oxygen exposures.
The charts and tables alone allow "too short" SI's under some circumstances, so the hour minimum was thrown in to cover that.
Rick

 

[Charlie99]

The one hour break is a recommended minimum; not on any chart.

Is this an agency recommendation, or just something one particular instructor came up with?

Which cert agency?

 

[Rick Murchison]

Is this an agency recommendation, or just something one particular instructor came up with?

Which cert agency?

It is an SSI recommendation for sure; I believe it is also recommended by all other Nitrox certifying agencies.
Rick

 

[Toolbox-13]

Yes PADI also recomends 1 hour, it is a good rule of thumb....but its not cut into stone
Enjoy your longer bottom times...

 

[mossym]

yeah, we were told the same thing on a PADI course.

 

[Wayward Son]

I took IANTD, don't recall this suggestion.

I do know that as a practical matter, I usually look for about 1 hr SI anyway, as I see no reason to go back down before I have enough NDL time available to use up my tank. So I generally look for at least 45 minutes or a bit more for that reason.

With my wife diving air, we really need an hour for her any ways. I'll be glad when I can get her into a class and breathing the same gas I do.

 

[Rick Murchison]

I took IANTD, don't recall this suggestion.

I do know that as a practical matter, I usually look for about 1 hr SI anyway, as I see no reason to go back down before I have enough NDL time available to use up my tank. So I generally look for at least 45 minutes or a bit more for that reason.

With my wife diving air, we really need an hour for her any ways. I'll be glad when I can get her into a class and breathing the same gas I do.

When I took the IANTD course (in its infancy) the one hour recommendation was there - I believe its origin is in NOAA's guidelines... I'll check on that this evening and let y'all know.
Rick

 

[Damselfish]

Was definitely in my PADI class too, for the purpose of helping keep O2 exposure down.

Not that I see this rule get followed often (< 1hr intervals on day boats are pretty common no matter what people are diving.) I don't see it as a magic number, but I've often wondered when I see people post here that a benefit of Nitrox is "shorter surface intervals" without mentioning the hour recommendation.