Gas sharing at deco stops

[rhwestfall]

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.

^ +1

 

[Freewillow]

I agree with you Doctormike. No change + Probability for occurence very very close to zéro.

When it comes to tek dives and the sharing of a single deco bottle, I do practice this with my buddy wife. She does not like to carry an extra deco bottle. So when we are planning a deco dive and we know that we will make a deco along a buooy line - a wreck for example -, I have equipped my deco bottle with 2 second stages. No fuzz, very easy, as long as you have enough travel gas to finish your deco in case of failure of the deco bottle

 

[Patoux01]

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..!

Sure, I agree with that. But on the other hand, how would we handle deco if we were diving on Mars? See why we're not answering the exact question? It's simply a matter of "it doesn't happen, we don't care". Had it been phrased "what happens if I breathe with a poor breathing pattern on the deco stop?", then yes, I agree with your answer. But the phrasing does feel like there's something off, so if our questions "but why would it happen?" can help avoid this needlessly complicated solution, I guess it's worth wasting some electrons to ask.
OTOH, some decompression "experts" keep explaining that "it's obvious you need to focus on breathing out when you're at your deco stop, how else are you gonna remove N2 from your body?", which makes you wonder if they really believe they are largely increasing the amount of N2 in the air they expell.


Plus, you need a serious amount of failures before reaching that stage, draining 2 sets of backgas + 1 of the deco tanks is way beyond reasonable.

 

[kensuf]

Buddy breathing deco gas is stupid. I'm required to teach it, but I explain that skills that are not regularly practiced degrade and RARELY does anyone actually practice buddy breathing. Buddy breathing a deco gas if you haven't practiced the skill opens divers up to making other mistakes, such as blowing a deco stop (either up or down) due to task loading.

The best answer is to never be in this situation to begin with by properly maintaining your gear, but if one buddy runs out of deco gas for some reason, the next best option is for one diver to deco on the richer gas while the other is using the richest "lean mix" to continue off-gassing while waiting for the first diver to clear the stop, then diver B goes on the rich mix.

 

[doctormike]

But the phrasing does feel like there's something off, so if our questions "but why would it happen?" can help avoid this needlessly complicated solution, I guess it's worth wasting some electrons to ask.

Absolutely! We have plenty of electrons, I really like it when these discussions range far and wide. Especially in a case like this when the answer to the OPs exact question is less likely to be useful to other readers than answers to more common scenarios.

As I always say, this is a discussion, not a legal deposition.

 

[PfcAJ]

Extend the stops by 50%, alternate who's breathing the deco gas.

Keep it simple.

Fwiw I've actually had to share oxygen with my buddy before. 'Twas no big deal.

 

[victorzamora]

Extend the stops by 50%, alternate who's breathing the deco gas.

Keep it simple.

Fwiw I've actually had to share oxygen with my buddy before. 'Twas no big deal.

Buddy-breathing, or something like X-minute intervals alternating between deco gas and backgas (or next richest deco gas)?

 

[PfcAJ]

Buddy-breathing, or something like X-minute intervals alternating between deco gas and backgas (or next richest deco gas)?

Not buddy breathing if you mean "I take a breath and you take a breath". That's silly and there's no reason for that. You certainly have other gas to breath on your person, no sense in not using it.

Intervals like "you breath for 5mins, then I breath it for 5mins" is the move. Depending on length of deco stops you could even alternate stops.

 

[boulderjohn]

Not buddy breathing if you mean "I take a breath and you take a breath". That's silly and there's no reason for that. You certainly have other gas to breath on your person, no sense in not using it.

Intervals like "you breath for 5mins, then I breath it for 5mins" is the move. Depending on length of deco stops you could even alternate stops.

I fully agree with everyone who has said something to this effect. There is no reason to do this.

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

this is correct. If you were ever to get to the incredibly unlikely scenario that you had to do this, it would make no difference in deco time.

 

[victorzamora]

Not buddy breathing if you mean "I take a breath and you take a breath". That's silly and there's no reason for that. You certainly have other gas to breath on your person, no sense in not using it.

Intervals like "you breath for 5mins, then I breath it for 5mins" is the move. Depending on length of deco stops you could even alternate stops.

That's what I was hoping you meant.