Out of Air

[limeyx]

Diving thirds is also applicable when you have surfacing obstructions (diving in a channel), or deco to worry about. As I said, the particular gas plan is not the worry here, its the LACK of a gas plan that's the worry. Particularly the lack of a gas plan that assists the buddy.

I dont see why deco requires thirds, unless you leave your deco gas on the upline and that's a whole different discussion...

 

[lamont]

I dont see why deco requires thirds, unless you leave your deco gas on the upline and that's a whole different discussion...

if the plan is to shoot a bag, then you just need your loss-of-one-deco-gas rock bottom reserve in backgas. however, a lot of advanced techdivers will plan big dives so that they're using only Al80 bottom stages, and they hold all their backgas in reserve -- even if they are shooting a bag -- as cluster**** insurance. this is even on dives where there are multiple deco gases carried with the diver, and support divers to deal with the loss-of-deco gas scenario.

 

[Cacia]

I wish I had been diving thirds yesterday.

I did 107, got into 5 minutes of deco. Did it. (last one out)

Was not thinking, was the first in. MD 70 ft. About half way through, I see I have been a little deeper than I realized (saw two very rare fish), and so I start my sloping ascent, planning on diving more shallow than the group, so that we can finish the drift together, etc. Got a reverse block and felt like somebody was stabbing my eye. I did not have enough air to deco and re-descend for the block that was killing me. I could have used .3 more air yesterday, because my SI was insufficient and the squeeze was unplanned. I gave myself a D+.

I shot my bag so that I could steady myself while I died for the time needed. It really sucked. And I am dying today too. I hear if you can descend and then re-ascend slowly, you can deal with it sometimes. I did not have the air needed to do this. "just enough" can screw you.

Thank goodness there was no buddy to screw up.

 

[limeyx]

if the plan is to shoot a bag, then you just need your loss-of-one-deco-gas rock bottom reserve in backgas. however, a lot of advanced techdivers will plan big dives so that they're using only Al80 bottom stages, and they hold all their backgas in reserve -- even if they are shooting a bag -- as cluster**** insurance. this is even on dives where there are multiple deco gases carried with the diver, and support divers to deal with the loss-of-deco gas scenario.

Sure, you can definitely do it that way, but my point was that going into a deco dive doesn't really directly imply you need 1/3's

 

[PerroneFord]

Sure, you can definitely do it that way, but my point was that going into a deco dive doesn't really directly imply you need 1/3's

You are correct.

 

[lamont]

Sure, you can definitely do it that way, but my point was that going into a deco dive doesn't really directly imply you need 1/3's

although since you need to reserve your rockbottom in a loss-of-deco-gas case, you're likely reserving literally a third of your backgas for that. you aren't going to be reserving rockbottom + 1/3rds though.

 

[Arizona]

Good point BrianV! Peitfer handled it well, but should have realized air was consuming at a slow rate. Going 35m the air should go fast so it should have been odd. It is easy to second guess after the fact, but being aware of your average air consumption should be a priority. I find having my Mares Airlab to be really helpful. It shows air consumtion and dive time. As an air hog, I am always on the lookout for my air consumption. I think investing in regs/computer would be well worth it.

 

[limeyx]

although since you need to reserve your rockbottom in a loss-of-deco-gas case, you're likely reserving literally a third of your backgas for that. you aren't going to be reserving rockbottom + 1/3rds though.

True, the numbers do usually end up working out to about 1/3 of a tank for RB for a deco dive.

But if I was doing a 1/3's dive, the 1/3's is *after* Rock bottom has been taken out.

So I'd say "OK, how many PSI do I need to safely ascend from my start point"
subtract that from my total PSI, and then 1/3 the remaining.
And this is of course assuming that my dive doesn't have any deep deco "on the way home" if if does, then I need a different plan.

 

[CrawfishDiver]

bet you watch your consumtion better now. I know I will. good job staying with us. Make sure your new diver friends hear your story

 

[radio flyer]

Great advice. Thanks.