lermontov
Contributor
What is the physiology regarding off gassing at deco stops when sharing deco gas? is there a rule of thumb regarding extended time for reduced off gassing due to irregular breathing?
Gas sharing at deco stops
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Are you referring to buddy breathing off one deco reg?
I'm interested what the experienced divers post regarding this topic. Strikes me as a situation that should be rare enough there is not a rule of thumb for it.
When doing deco under stress I'll extend my stop until the risk of being in the water outweighs the possible DCS risks.
Careful mental effort to calm and regulate breathing should be possible and is one of my priorities during deco.
Adding an arbitrary fudge factor to the deco obligation is a shot in the dark.
Regards,
Cameron
I'm interested what the experienced divers post regarding this topic. Strikes me as a situation that should be rare enough there is not a rule of thumb for it.
When doing deco under stress I'll extend my stop until the risk of being in the water outweighs the possible DCS risks.
Careful mental effort to calm and regulate breathing should be possible and is one of my priorities during deco.
Adding an arbitrary fudge factor to the deco obligation is a shot in the dark.
Regards,
Cameron
Last edited:
OP
lermontov
Contributor
yes
Skilled buddy breathing is entirely comfortable and a normal breathing pattern can be maintained easily with practice. Should not be irregular.
Regards,
Cameron
OP
lermontov
Contributor
I guess if you can maintain that inhale while buddy exhales and recipricate then yes
Correct. Box breathing for example. Though I tend to personal have a faster inhale and a slower exhale.
If it's a likely enough scenario for you to be planning for, I'd recommend practicing extensively so it isn't a stressors. One way without harassing a buddy (provided they are ok with your practice) is stimulate buddy breathing by watching your buddy's bubbles and removing your reg every time he is not exhaling. A more challenging 'buddy breath' because he isn't thinking of sharing and being mindful of giving you your fair share of reg time.
Hopefully someone will jump in and address your initial question more directly.
Regards,
Cameron
jfe
Contributor
What I have been trained in, and practiced, is that one will carry say 50% O2 and it will be shared on the 6m stop. Deco time 6m. One will stay on back gas while the other one breaths 50% for 3 min then switch back to back gas and the buddy take over the 50% for the next 3 min. Both assent to top on back gas. Full 6m deco duration is observed.
I've been taught this will then be more of a save guard than shorter deco times as it gets into difficulties calculating the spilt, but you can configure your dive planning to include the split, deco programs will allow that. In and OOA situation, normal buddy breathing techniques apply, goes without saying.
I've been taught this will then be more of a save guard than shorter deco times as it gets into difficulties calculating the spilt, but you can configure your dive planning to include the split, deco programs will allow that. In and OOA situation, normal buddy breathing techniques apply, goes without saying.
I'd say either do twice the deco, with one half each on the deco tank (ie quite a fair bit safer than required by the algorithms), or do something like "150% of deco time on the stop, and half the time on backgas, half on deco gas"
Why would one "buddy breathe" a deco reg?
Why would one "buddy breathe" a deco reg?
If you are only using one deco gas (for example 50%)
You switch on every stop during the ascend from 21-6M and do 1.5x time at 6M
You switch on every stop during the ascend from 21-6M and do 1.5x time at 6M
I'm pretty sure that the OP is not referring to scenarios mentioned in technical training, where two ascending divers have gas to breathe, but one of them has lost their deco gas. Of course, there should have been a lost gas scenario calculated so that each diver could complete a (longer) decompression on their backgas, but protocols do exist for sharing a rich deco mix to accelerate their overall decompression.
The referenced situation is that for some reason divers with a deco obligation are sharing a single gas source, and have to "buddy breath". This would be a two-failure scenario (i.e. one diver has lost their back gas and deco gas), so not usually something planned for.
I'm not an expert in decompression physiology, but I'm pretty sure that offgassing is more limited by perfusion than by ventilation. That is, increasing or decreasing your gas exchange rate by hyperventilating or by buddy breathing wouldn't actually change your rate of offgassing. Offgassing happens because of the pressure gradient between the inert gas pressure in the tissues /venous blood and the ambient breathing gas. I suppose in a lab if you reduced ventilation enough, eventually that would be a limiting factor in gas washout too, but that would probably be below the amount of ventilation necessary to sustain life. But I could be wrong..!
The referenced situation is that for some reason divers with a deco obligation are sharing a single gas source, and have to "buddy breath". This would be a two-failure scenario (i.e. one diver has lost their back gas and deco gas), so not usually something planned for.
I'm not an expert in decompression physiology, but I'm pretty sure that offgassing is more limited by perfusion than by ventilation. That is, increasing or decreasing your gas exchange rate by hyperventilating or by buddy breathing wouldn't actually change your rate of offgassing. Offgassing happens because of the pressure gradient between the inert gas pressure in the tissues /venous blood and the ambient breathing gas. I suppose in a lab if you reduced ventilation enough, eventually that would be a limiting factor in gas washout too, but that would probably be below the amount of ventilation necessary to sustain life. But I could be wrong..!
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