What kind of profiles are requiring a 80cf of o2? And..

[211ratsbud]

How close must your gas requirements be to your capacity to consider the jump? We practiced like 4ths to 6ths in deco procedures. Plenty safe but say I'm planning a dive that requires 15-20cf of o2. That's nearly half and makes no contingency for both +time/depth and buddy gas. Just want to get a feel for what others practice.

Thx!

 

[tbone1004]

@DanaHunt are you talking about when to choose an al40 vs an al80?

You have to choose your bottle sized based on the gas you need. What those requirements are is up to you. Single dive requiring 20cf of gas? That's a real short deco.
20cf assuming my bottles are actually filled to 3000psi, would get an AL40. Gives half if you are doing half and half deco with a buddy, but are you really planning on violating depth/time and a buddies deco bottle kicking the bucket? How much back gas reserves do you have in backgas to complete an extended deco? Too complicated to answer.

20 minutes at 150ft on 21/35 with 100% deco, 50/80GF's. You have 11 minutes on 100%. Go to 160ft for 20 minutes and it's 12 minutes of deco. That's irrelevant.
30 minutes because you screwed up on time and it's 18 minutes on 100%. Not enough for you to do half and half with a buddy, but what are the odds? Up to you to figure out the risk:reward.

AL80's aren't hard to carry, so if you think it's high risk, then bring the 80.

 

[PfcAJ]

You need 1.5x your planned required deco gas amount.

More than about 40-50mins at 20ft gets an al80.

 

[211ratsbud]

Yea I thought the odds were low or even negligible. I felt pretty comfortable considering as low as 2x but better planning 3rds on deco gas.

I had been surfing the web and I came across a few pics of 80cf bottles stuffed with o2. My alarm went off and said well they're probably using a third of that or so and was really curious what contingencies are common among a greater group.

I have an 80 of 50% that I have dove with a few times. Doesnt bother me at all.

 

[PfcAJ]

Yea I thought the odds were low or even negligible. I felt pretty comfortable considering as low as 2x but better planning 3rds on deco gas.

I had been surfing the web and I came across a few pics of 80cf bottles stuffed with o2. My alarm went off and said well they're probably using a third of that or so and was really curious what contingencies are common among a greater group.

I have an 80 of 50% that I have dove with a few times. Doesnt bother me at all.

Reserving 2/3 of a bottle as reserve makes no sense.

Reserving 1/3 does.

 

[Foothills]

While I find a 40 cf is much more pleasant to slog to & from the shore, I would much rather have excess deco gas, and often carry an 80 cf of O2 rather than a 40 cf cylinder "just because". I like knowing I can "probably" do multiple deco dives off the one cylinder (obviously depends on the dive plans), and having "spare" O2 at a dive site (I usually dive at locations a few hours from a hospital) can't hurt if something goes wrong.

 

[211ratsbud]

Reserving 2/3 of a bottle as reserve makes no sense.

Reserving 1/3 does.

Something for me to consider but not how we practiced.

 

[PfcAJ]

Something for me to consider but not how we practiced.

Why did you reserve 2/3? Why that number and not 1/2? Or 3/4? Or 1/3? Or some other number?

 

[stuartv]

Presuming we’re talking about a dive where I’m only carrying 1 deco gas...

If my plan requires up to 20 cu-ft, I’ll carry an AL40. If it requires more, I’ll either shorten my planned bottom time, or carry an 80.

Half my bottle is for me. Half for my buddy, in case he loses his deco gas.

So, half the bottle is contingency gas. Backup contingency plan is remaining back gas.

If **** happens where my buddy and I use ALL our back gas just to get to the gas switch, and one of us has lost our deco gas, and we suck down the deco gas quicker than planned...well then, I guess we are screwed (meaning surfacing with omitted deco).

 

[PfcAJ]

Presuming we’re talking about a dive where I’m only carrying 1 deco gas...

If my plan requires up to 20 cu-ft, I’ll carry an AL40. If it requires more, I’ll either shorten my planned bottom time, or carry an 80.

Half my bottle is for me. Half for my buddy, in case he loses his deco gas.

So, half the bottle is contingency gas. Backup contingency plan is remaining back gas.

If **** happens where my buddy and I use ALL our back gas just to get to the gas switch, and one of us has lost our deco gas, and we suck down the deco gas quicker than planned...well then, I guess we are screwed (meaning surfacing with omitted deco).

But if you’re sharing the deco gas... why do you need to double the stop time? If you aren’t doubling the stop time, why reserve double the gas?

You’re still offgassing when on backgas, just not as fast as with oxygen.