Nitrogen Saturation at low depth question

[Fosters]

I've been looking with interest at the underwater hotel in Keylargo which sits down at 21ft.

If you stay overnight, you will be nitrogen saturated as your 'dive' will be 10+ hours. i understand this. But why don't you need stop on the way back up, even if it is only coming up from 7m/21ft ?

Also why isn't this reflected on dive planners as an unlimited NDL?

 

[Doppler]

I've been looking with interest at the underwater hotel in Keylargo which sits down at 21ft.

If you stay overnight, you will be nitrogen saturated as your 'dive' will be 10+ hours. i understand this. But why don't you need stop on the way back up, even if it is only coming up from 7m/21ft ?

Also why isn't this reflected on dive planners as an unlimited NDL?

Because the difference in ambient pressure between "the dive's max depth/pressure" and the surface (About 0.7 ata) is not sufficient to require stops... i.e. the nitrogen tissue tension (Haldane) or critical bubble radius and population (dual-phase) will be at a level / size that the body can eliminate within a tolerable margin of safety.

 

[StSomewhere]

It also depends on whether the ambient pressure inside is greater than 1 ata or equal to 1 ata.

 

[Sideband]

It also depends on whether the ambient pressure inside is greater than 1 ata or equal to 1 ata.

It has a moon pool so it would have to be greater than 1ata wouldn't it? I liked the other question.
Why, if, "difference in ambient pressure between "the dive's max depth/pressure" and the surface (About 0.7 ata) is not sufficient to require stops", isn't 20' and less listed on any table (that I know of) as unlimited NDL? I'm going to look at the Navy tables tonight and see what they are as I believe they go as low as 10'. Wonder what they say to do for a deco stop if NDLs at that depth are exceeded?

Joe

 

[StSomewhere]

It has a moon pool so it would have to be greater than 1ata wouldn't it?

Yup.

I liked the other question. Why, if, "difference in ambient pressure between "the dive's max depth/pressure" and the surface (About 0.7 ata) is not sufficient to require stops", isn't 20' and less listed on any table (that I know of) as unlimited NDL? I'm going to look at the Navy tables tonight and see what they are as I believe they go as low as 10'. Wonder what they say to do for a deco stop if NDLs at that depth are exceeded?

Great question. My IANTD air table (Buhlmanm) starts at 40' or approx 2.2 ata (btw, 125 minutes). 20' would be something like 1.6 ata IIRC.

 

[Fosters]

Thanks for the responses so far guys.

I think on my next trips i will be doing more TDI gas courses to get a greater knowledge (even though I probably won't dive past recreational limits).

i'd feel a bit safer/more prepared knowing more on this subject

great site btw

 

[rab]

It's not "unlimited" except that the pressure group maxes out. I think it may have been a USNavy table, but it clearly indicated (via footnote) that the pressure group reached a maximum for shallow depths. I'd have to go find it (might be a copy in my log book), but a call to the hotel would probably be the best way to get the answer -- They have to get the question eften enough.

-Rob

 

[Xanthro]

Is the hotel actually pressurized beyond 1ATA?

 

[D_B]

has a Moon pool , think big hole in bottom. Inside pressure must be same as water pressure or water will come in

DB

 

[Xanthro]

has a Moon pool , think big hole in bottom. Inside pressure must be same as water pressure or water will come in

DB

But the moon pool room could very well be a separate compartment and the rest of the hotel not be pressurized.