Deco stops

[andibk]

Dr. Deco
When using 02 for decompression how often do you recommend air breaks? Which gas should I do the air breaks on the bottom mix (with or without helium) or another deco gas with a lower f02?

Bruce

 

[raxafarian]

but I say use the gas with the lowest o2 that is not hypoxic.. ie. don't try and breath a bottom mix with 12% o2. In that case, use your lowest deco gas (or travel mix).

 

[Genesis]

12% O2 in your bottom mix is perfectly fine on a 30' Deco stop; the PO2 is ~22%, or a bit above normoxic!

(If you meant "hypoxic at your current depth", I agree with you )

 

[raxafarian]

yes, hypoxic at current depth.

Why are you taking an air break at 30ft? I was thinking 20ft. on 100%.

never mind.... guess you're using 80%.

 

[WreckWriter]

raxafarian once bubbled...
Why are you taking an air break at 30ft? I was thinking 20ft. on 100%.

never mind.... guess you're using 80%.

Some people do their 30' stop on back gas to maximize the O2 gradient when starting the 20' stop, others only break when the 20' stop (or 10' for those that do them) exceeds 12 (or 20) minutes.

My own preference is the second method. If my 20' stop exceeds 12 min I break to back gas for 5 min then switch back to O2.

I NEVER use 80%

WW

 

[Dr Deco]

Dear Readers:

I do not do this type of diving and thus have not opinion or experience.

The other readers have provided some of their own experience here. Possibly we will have more.

Dr Deco
=-)

 

[Diver0001]

Dr Deco once bubbled...
Dear Readers:

I do not do this type of diving and thus have not opinion or experience.

The other readers have provided some of their own experience here. Possibly we will have more.

Dr Deco
=-)

Any idea why an air break would help in decompression?

R..

 

[Dr Deco]

RO:

It is my understanding that the air break is solely for pulmonary toxicity fears. In my researche xperience, I have never seen air accelerate decompression when compared to oxygen.

I have heard of the opposite, where oxygen allows safe decompression even when very, very long air depress results in the bends.

Dr Deco:doctor:

 

[wb416]

Diver0001 once bubbled...


Any idea why an air break would help in decompression?

R..

It's been a while since I read the reason, so I can't give you the specifics, but I'll attempt a layman's overview.

The long duration of breathing high PO2 mixes, generally the result of longer deco times coinciding with the 20ft stop, can result in a loss of "transfer efficiency" in the lungs.

The lungs "deteriorate" to a point where off-gassing efficiency of nitrogen is compromised. This "deterioration" is irreversible in the short-term, but can be "prevented" or "held-off" by breaking to back gas (or lowest non-hypoxic mix) in fixed intervals. The time on back gas is counted towards deco.

I'm sure I don't have all the details "pegged" here, but perhaps it'll give you some food for thought.

 

[wb416]

cwb once bubbled...
I'm sure I don't have all the details "pegged" here, but perhaps it'll give you some food for thought.

Here's another brief explanation from a more "reliable" source than myself.

Lung reaction to high PO2

If the link doesn't take you directly to the text of the page on "Pulmonary Oxygen Toxicity" just click on the link of that page. Text is 2/3rds down the page or so.