Cave Fills on LP tanks

[rjack321]

But, if you're just beginning technical or cave diving why would they dive 2 bottom stages and an AL40 of O2? Instead of just sticking to backgas and maybe one deco gas? I understand your point, and I dont disagree with your recommendations, but it just seems kind of an apple to orange comparison.

I was just commenting that the "add a stage" logic doesn't really work if you undersize your doubles in the first place. I didn't have much choice cause Al80s were all that I had left in the garage and I figured I needed the practice with 2 stages anyway.

 

[rjack321]

I'm trying to figure out what dive you would do that would require 300 cubic feet of bottom mix and still use only O2 for deco . . .

Plan 60mins at 110ft on 25/25. Not diving thirds, but a padded rock bottom to at least get a bit inshore before ascending. Rock bottom is really about 80cf but we rounded up to 100cf. I think we each used between 180 and 200cf of bottom mix total. 10mins shaped up to 20ft then 15mins on O2 + 5mins up.

95s or 119s (both filled to ~3400) + a stage is a better combo for this dive than multiple bottom stages.

 

[Slamfire]

I bought a (fairly old) set of LP 72s, and everyone uses Aluminium in this part of the world, so whether I like it or not, I get fills to 3,100 psi whenever I take them in.

Haven't blown up yet is all I can say. I kind of like diving "88s".

My Dad has some very old steel 72's. He loves them. He says they are more trust worthy than modern tanks because back in the olden days they didn't have the precision or tolerances that modern manufacturing has. Therefore, they had to overbuild them erring on the safe side. I have no idea where he's getting his info or what kind of "proof" he's got.

... I'd be a lot more reticent about overfilling aluminum tanks than steel ones ... even if they can take it, I doubt they'd survive more than one or two hydro cycles before they ended up as scrap metal ...

... Bob (Grateful Diver)

I've heard that you're fine overfilling steel LP's but that you will reduce their life span, ie. they will fail a hydro sooner than expected. What are your opinions on this? I would think that you'll have to somehow "pay" for your transgression of taking LP's to HP levels. If it is totally fine overfilling LP's then what's the point of labelling them LP? Are there any real world down sides to overfilling them?

 

[Meister481]

Do you actually believe that? (o2 clock that is)

Can you elaborate on that?

Not really the venue.

If I hit around 90% on the O2 clock, I get the chokes and my lungs burn. I guess I'm sensitive to O2. No matter what you believe in or if it differs to how you dive. It works for me. I have to be careful with my O2 consumption. Why carry gas that will cause me to be uncomfortable after the dive. I'll trade a longer deco with extended air breaks for crispy lungs.

 

[LiteHedded]

Not really the venue.

If I hit around 90% on the O2 clock, I get the chokes and my lungs burn. I guess I'm sensitive to O2. No matter what you believe in or if it differs to how you dive. It works for me. I have to be careful with my O2 consumption. Why carry gas that will cause me to be uncomfortable after the dive. I'll trade a longer deco with extended air breaks for crispy lungs.

what ppo2 are you running on the bottom?

 

[Meister481]

what ppo2 are you running on the bottom?

Try to stay between 1- 1.2

Best trade off I have found between deco time and O2 exposure.

 

[JahJahwarrior]

O2 clock or not I have to admit to having a sore throat after a really long hang taking only minimal air breaks. But not enough to make me want to hang longer

 

[LiteHedded]

Try to stay between 1- 1.2

Best trade off I have found between deco time and O2 exposure.

worry less about deco time and more about that o2 exposure.

I've done some fairly long exposures. never had these symptoms. try lowering that bottom ppo2. I find standard gases and backgas breaks help. as well as going to backgas before a switch for a little cleanup.

 

[ucfdiver]

worry less about deco time and more about that o2 exposure.

I've done some fairly long exposures. never had these symptoms. try lowering that bottom ppo2. I find standard gases and backgas breaks help. as well as going to backgas before a switch for a little cleanup.

I wonder how much of this is bottom gas related, and how much is deco gas. If it's CNS clock related, it gets tons worse @ 20ft. The WKPP guys are pushing 1300-1600% or more on the CNS clock, and even at Ginnie I've seen Ainslie push his close to 800%, but I do know he's generous with air breaks during deco.

Think slowing the ascent to give the lungs time to recover on a very low (backgas) ppo2 before hopping right back on the bottle could play into things here? With a short half life, seems 5-10min recovery @ 30ft would do quite a bit to lower CNS.

Meister481, what air breaks are you doing to split up the deco?

 

[LiteHedded]

well IMO it adds up. there's no reason to run a high ppo2 on the bottom other than deco weenery. I don't do it. and the guys at wakulla you're referencing don't do it either

it's necessary on deco. it's not during the working portion of the dive. being generous with backgas breaks on the way up goes a long way. and count the breaks as part of the deco. if you're burning your lungs up something is wrong.

the last trimix dive I did put me at about 160% CNS. no burning throat or lungs.