When to donate air?

[johndiver999]

Low on air = close to reserve amount in tank = the amount required to head up to the surface.

That will vary based on depth. If you're at 100', the reserve might be 1000 psi, whereas at 30' the reserve could be 500 psi. So if one buddy has a lot more gas than the other, it makes sense to switch prior to the low on air buddy to hit their reserve supply. So they can go back to it when the dive is over.

I usually carry a 30cf pony bottle. On an interesting dive, that I want to extend, when my main tank gets close to between 500-1000 psi (depending on depth), I switch to the pony, and draw it down close to 200 psi then go back to my main tank. In this example, the pony is my gas sharing buddy.

The equation you provided is clearly incorrect. The reserve amount in the tank is enough to get BOTH divers to the surface sharing one air supply. The amount for one diver to actually reach the surface safely is less than half that amount, particularly if they are reasonably calm (and the reserve amount was calculated based on two hyped up divers).

 

[Oldbear]

To answer the OP’s question on “When” to donate gas for a LOA, here is my take.

1) Try to avoid a LOA, but, things happen

2) Donate before LOA becomes an OOA scenario…stress levels are lower at the LOA stage

3) If I have the opportunity, I prefer to share gas before the ascent, then let the diver use their own back gas to the ascent, safety stop and exit…again less stress. I dive with a long hose, so when donating gas, we aren’t do the Spawning Salmon Mumbo while swimming.

 

[lermontov]

2) Donate before LOA becomes an OOA scenario…stress levels are lower at the LOA stage

^ this is the most practical option

Tech diving plans for these scenarios because dives are often with an overhead so less of a stress once you have gone through the exercise in training and have the understanding and knowledge in regard to redundancy-
Deco procedures course as a starting point is perfect to help manage this and to extend new boundaries

 

[grantmac]

I've donated many times (sidemount or BM long hose) to get a buddy back to a convenient ascent point with plenty of their own gas remaining. I'd far rather donate early when the stress is low rather than having someone come at me after sucking a tank empty.

 

[TMHeimer]

I've donated many times (sidemount or BM long hose) to get a buddy back to a convenient ascent point with plenty of their own gas remaining. I'd far rather donate early when the stress is low rather than having someone come at me after sucking a tank empty.

Is this with various buddies over time or one that needs to shape up?

 

[Nemrod]

When to donate air?​

When they are purple in the face and their eyes are bulging out on stems ? Okay, okay, maybe just a little before .

Kind of like the Seinfeld episode in which the lady could not spare a square of tp to Elaine, nope, no air for you, I cannot spare a cf. Next time watch your dive plan and air supply a little closer.

 

[Still Kicking]

Let me repeat myself, using gas sharing simply to extend a dive is bad practice, IMO.

I think too many issues can arise when you have two divers on one gas supply (separation during ascent, miscommunication, third party OOA etc.) Plus, even if the donor has a long hose, is anyone really having fun swimming around in lock-step?

If you need to share gas in order to make it back to a safe ascent point (boat traffic or something) that's one thing, but just swimming around "enjoying" a longer dive does not seem to be a great idea to me.

If you are going to use this argument, why not have the diver with the highest SAC share gas at the beginning of the dive so they will have more left later?

Instead, I would suggest using a bigger tank, planning shorter shallower dives until SAC improves etc. If using a pony tank allows you to extend a solo dive safely, so be it. It's your reserve .... use it as you see fit.

 

[BRT]

Let me repeat myself, using gas sharing simply to extend a dive is bad practice, IMO.

I think too many issues can arise when you have two divers on one gas supply (separation, miscommunication, third party OOA etc.) Plus, even if the donor has a long hose, is anyone really having fun swimming around in lock-step?

If you need to share gas in order to make it back to a safe exit point (boat traffic or something) that's one thing, but just swimming around "enjoying" a longer dive does not seem to be a great idea to me.

If you are going to use this argument, why not have the diver with the highest SAC share gas at the beginning of the dive so they will have more left later?

Instead, I would suggest using a bigger tank, planning shorter shallower dives until SAC improves etc. If using a pony tank allows you to extend a solo dive safely, so be it. It's your reserve .... use it as you see fit.

I agree, you don't want to wait too long. Leave the big gas user with plenty of air to finish the dive.

 

[grantmac]

Is this with various buddies over time or one that needs to shape up?

Various. Almost always when they likely could make the exit point but why add that stress when I have an entire redundant gas system designed to be shared?

 

[sinidive]

Gas sharing is a needed skill for emergencies.

Practicing skills in safe environments makes them easier if an actual OOA happens.