Nitrogen absorption in pool/confined dives?

[cashew]

Does anyone have any information regarding what the nitrogen absorption profiles look like for pool/confined dives? The dive tables start at 35 feet, and the pools around me top out at like 15 feet max depth.

Also, does the normal "12 hours for single dive; 18 hours for multi-dives" waiting period on flying still apply if you are only doing pool work? Presumably, the concerns about nitrogen absorption are still there, but I'm wondering how much of that risk is mitigated by the fact you are staying extremely shallow.

 

[Lorenzoid]

At 15 feet, your entire dive is basically a safety stop. Think about it.

 

[Phil_C]

I would say that normally this is a non-issue.

For an extremely long submersion then yes, theoretically there would be a nitrogen absorption issue, but that would take a submersion measured in hours, not minutes.

If you remember back to those slides about partial pressure and gas absorption from the OW course he two factors are pressure and time. At 15 foot in a pool the atmospheric pressure has only increased to 1.457, compared to 1 at the surface, so you are only marginally absorbing more nitrogen (partial pressure 1.15 rather than 0.79) than at the surface if you stay at the bottom all the time.

It will take a long time to reach tissue saturation like that so tables and pressure really don't come into it at that depth.

As for flying after a pool dive, well again unless it was a really long dive (as in hours long) and you stayed at the bottom the whole time, then you are not really going to have absorbed enough nitrogen for it to be a problem, but if you give it 12 hours then you are playing on the safe side.

I think my computer gives me a 6 hour no fly time if I have spent a two hour session in our 5m/17 foot pool.

Best - Phil

 

[elgoog]

The SSI dive tables have entries for 10ft onwards, in 5ft increments for the shallower depths. If you do an image search for them, a bunch of results pop up and you'll get the actual values and group designations.
For time to fly, I'd imagine it's like a single dive since you're breathing compressed air at higher than 1ata (not much higher, but still ...). If you're looking for what a dive computer will tell you, I have a pool dive this week to test out a new drysuit. I can update this thread then with what a Zoop and Tec2G think the no-fly time is.

 

[cashew]

The SSI dive tables have entries for 10ft onwards, in 5ft increments for the shallower depths. If you do an image search for them, a bunch of results pop up and you'll get the actual values and group designations.
For time to fly, I'd imagine it's like a single dive since you're breathing compressed air at higher than 1ata (not much higher, but still ...). If you're looking for what a dive computer will tell you, I have a pool dive this week to test out a new drysuit. I can update this thread then with what a Zoop and Tec2G think the no-fly time is.

Thanks! I didn't realize that the SSI dive tables started at 10 feet so I will check that out.

 

[rhwestfall]

SSI: 300 min (that's 5 hours) @ 10' puts you as a "D", a 1:10 SI= C, 2:39 = "B", beyond 5:49 is "A"

 

[tbone1004]

At 15 feet, your entire dive is basically a safety stop. Think about it.

but you are still ongassing....

At 15' I wouldn't worry about it, it's only a 0.5ata increase and you aren't going to be in there long enough for it to really matter for FAD.

 

[TMHeimer]

I recall reading that somewhere between 18 and 22 feet is the depth you could stay down indefinitely and ascend directly to the surface. Am I correct?

 

[Lorenzoid]

but you are still ongassing....

At 15' I wouldn't worry about it, it's only a 0.5ata increase and you aren't going to be in there long enough for it to really matter for FAD.

Of course you are ongassing somewhat. But wouldn't the dive have to be far longer than a normal dive for you to on-gas enough for it to matter? One hour at 15 feet isn't going to matter for any practical purpose, such as flying after diving. Am I wrong?

 

[dmaziuk]

Does anyone have any information regarding what the nitrogen absorption profiles look like for pool/confined dives? The dive tables start at 35 feet, and the pools around me top out at like 15 feet max depth. Also, does the normal "12 hours for single dive; 18 hours for multi-dives" waiting period on flying still apply if you are only doing pool work? Presumably, the concerns about nitrogen absorption are still there, but I'm wondering how much of that risk is mitigated by the fact you are staying extremely shallow.

Haldane's conclusion was 2 atm (33 feet) indefinitely, Workman has later adjusted it to %N2 and I forget what else and arrived at 1.58:1 instead of 2:1. So according to the theory down to about 20 feet there isn't pressure differential to cause bubbles. Ever. As long as you don't fly or climb mountains straight out of the pool.