Breathing O2 during surface interval

[Ghost95]

I don't know what everyone's opinion of this book is...

Scuba Physiological: Think You Know All About Scuba Medicine? Think again!

but it talks about pre-dive o2 and surface interval o2 as being helpful. Also lots of other interesting info here. Maybe some info has been proven out in trials and some not but it really shows how much we don't know about the magic of decompression science.

 

[tarponchik]

I would. If you're feeling even just a tad bit fatigued, go on O2. Athletes do it all the time after they've exerted themselves. Other than fire, there is no contraindication for using O2 at atmospheric pressures.

Here is some interesting reading for you.

 

[lowwall]

Here is some interesting reading for you.

Read it. This backs up @The Chairman's point. According to this, the tissues most susceptible to oxygen toxicity are the lungs. And "the earliest signs of pulmonary toxicity begin with evidence of tracheobronchitis, or inflammation of the upper airways, after an asymptomatic period between 4 and 22 hours at greater than 95% oxygen, with some studies suggesting symptoms usually begin after approximately 14 hours at this level of oxygen.

In other words, an hour or two of breathing O2 at 1atm isn't going to hurt you.

 

[Hortondon]

@Hortondon I may have missed it but what was your “hit?” What dive computer do you use?

I’m using the Galileo Luna computer.

 

[Hortondon]

Read it. This backs up @The Chairman's point. According to this, the tissues most susceptible to oxygen toxicity are the lungs. And "the earliest signs of pulmonary toxicity begin with evidence of tracheobronchitis, or inflammation of the upper airways, after an asymptomatic period between 4 and 22 hours at greater than 95% oxygen, with some studies suggesting symptoms usually begin after approximately 14 hours at this level of oxygen.

In other words, an hour or two of breathing O2 at 1atm isn't going to hurt you.

That’s very interesting. Thank you for taking the time to post.

 

[Hortondon]

Since you mentioned NDL dives, I ran a 100' dive with 32% through the SAUL probabilistic decompression algorithm and it came up with a 0.169% chance of DCS for a 30 minute dive; 0.047% for a 25 minute dive. So your risk is less than a third if you shorten your dive by 5 minutes. The algorithm does include a 3 minute safety stop. A 30 minute dive is the PADI RDP NDL, and those tables are aggressive compared to what a dive computer may come up with.

These numbers, with your undeserved DCS hit, seem to hint towards increasing the conservatism (shorter dive or longer safety stop, or both) during the dive to avoid the hit altogether, rather than trying to mend it out of water.

If I had the O2 available, it would probably have a bigger impact used underwater rather than at the surface (if feasible of course). You'd get the benefit of the higher ambient pressure keeping the bubble sizes under control, while simultaneously keeping the tissue gradient high (0% N2 in your breathing mix) to offgas quickly. Even just a few extra minutes on O2 or Nitrox underwater might have a bigger impact than at the surface for reducing your risk factors.

Another thing to think about is having to deal with the O2 logistics - if your surface O2 session is say 30 minutes (based upon the prior post) you would probably get 2 sessions out of an AL40 cylinder of O2 depending on fill and type of breathing apparatus.

In a pinch, I might just breathe down the remainder of whatever Nitrox I had left in my cylinder at the surface as that would be better than air.

Your guess in depth and time were close.

Since you mentioned NDL dives, I ran a 100' dive with 32% through the SAUL probabilistic decompression algorithm and it came up with a 0.169% chance of DCS for a 30 minute dive; 0.047% for a 25 minute dive. So your risk is less than a third if you shorten your dive by 5 minutes. The algorithm does include a 3 minute safety stop. A 30 minute dive is the PADI RDP NDL, and those tables are aggressive compared to what a dive computer may come up with.

These numbers, with your undeserved DCS hit, seem to hint towards increasing the conservatism (shorter dive or longer safety stop, or both) during the dive to avoid the hit altogether, rather than trying to mend it out of water.

If I had the O2 available, it would probably have a bigger impact used underwater rather than at the surface (if feasible of course). You'd get the benefit of the higher ambient pressure keeping the bubble sizes under control, while simultaneously keeping the tissue gradient high (0% N2 in your breathing mix) to offgas quickly. Even just a few extra minutes on O2 or Nitrox underwater might have a bigger impact than at the surface for reducing your risk factors.

Another thing to think about is having to deal with the O2 logistics - if your surface O2 session is say 30 minutes (based upon the prior post) you would probably get 2 sessions out of an AL40 cylinder of O2 depending on fill and type of breathing apparatus.

In a pinch, I might just breathe down the remainder of whatever Nitrox I had left in my cylinder at the surface as that would be better than air.

T

 

[Hortondon]

SAUL probabilistic decompression algorithm

Very interesting. Your estimate on my dive profiles are close.

Here are actuals:
Dive 1: 111’ 33 minutes 32% SI 1:27
Dive 2: 108’ 34 minutes 32%

However didn’t experience DSI symptoms until after second day second dive
Dive 1: 105’ 30 minutes Air SI :56
Dive 2: 98’ 32 min Air (this is when DCI symptoms started.)

 

[Hortondon]

@Hortondon I may have missed it but what was your “hit?” What dive computer do you use?

My hit was upper arms, shoulders and neck. Was at hospital under O2 within 4 hours. Spent 3 hours on O2. Felt much better. Next day I had small rash-like bubble bumps on both shoulders. Maybe 40 on each side.

 

[happy-diver]

Been breathing 100% driving home religiously when I remember for decades and there's nothing wrong with me

Amen!


Through a dive reg until my throat gets too cold or I just get sick of it

 

[KenGordon]

My hit was upper arms, shoulders and neck. Was at hospital under O2 within 4 hours. Spent 3 hours on O2. Felt much better. Next day I had small rash-like bubble bumps on both shoulders. Maybe 40 on each side.

If you dive you can get bent. It is not entirely deterministic. Many people get bent within tables or computer limits. You should watch and see if better practice might help, however there is always a chance and perhaps it was your number that came up.

If you are using good practice and still getting bent repeatedly then you might want to get checked for a PFO.

Breathing O2 between dives is not a solution.