Deco Bottles- 30cf vs 40cf?

[Tortuga68]

If my buddy requires it, fine I'm happy to stay. If he wants to leave me on deco, that's fine too. Don't really care one way or the other. But what you have to understand is that most of my buddies have more big solo dives in caves than most people have dives.... period. They really don't care if you leave them at 10'. Now the flipside of the coin... this isn't my philosophy with all divers, just some divers. Hell, even just a select few divers. I know a girl who has spent the last 20 minutes of a cave exit throwing up over and over again. There's no way I'm going to leave a weak diver in the water, even if they think their okay with it

There's nothing I "have to understand"... you're okay to leave (some) people in the water, based on your assessment of their dive skills/situation - I'm not. Whether they're okay with it or not, or how many millions of dives they have is not a factor. It's not about whether they require it, it's my decision not theirs

 

[Superlyte27]

There's nothing I "have to understand"... you're okay to leave (some) people in the water, based on your assessment of their dive skills/situation - I'm not. Whether they're okay with it or not, or how many millions of dives they have is not a factor. It's not about whether they require it, it's my decision not theirs

Eh, I guess we all have things we do underwater that others would think are downright stupid. It probably is a differing philosophy or I guess maybe what we each perceive differently as real risk or just tempting fate. I guess I could list a couple of examples below:

http://www.scubaboard.com/forums/tek-trip-reports/364710-100m-air-dive-workup-pg.html

http://www.scubaboard.com/forums/advanced-scuba-discussions/345916-85m-air-dive.html



Okay, off to the movies with my 11yr old son. We're seeing Wolverine. Hopefully it doesn't suck.

 

[MalibuJerry]

So, I don't know about the rest of you, but when I learned how to do deep technical dives one of the key elements was gas planning. Have enough gas for yourself and your team mate so that you can BOTH safely get back to the surface doing all your deco even if you need to share gas. And you are team diving, you stay with your team mate unless an emergency requires you to leave him to get assistance.

Moreover, if the decompression algorithm says it takes 30 minutes of normal breathing with 50/0/50 to respirate the inert gases that move out of solution at a stop and you only do 22 1/2 minutes over a 45 minute span you have not respirated the same amount of gas. It is not the same deco "just slower". The way to share gas is for your team mate to be inhaling while you are exhaling so that you both have the normal 30 minutes and you are following your deco schedule. Perhaps what was meant is that you do the same amount of respiration, just over a longer period of time. Fair enough. Do the calculation, you will need twice your requirement of gas, more if your buddy has a higher deco sac rate.

 

[Tortuga68]

Eh, I guess we all have things we do underwater that others would think are downright stupid. It probably is a differing philosophy or I guess maybe what we each perceive differently as real risk or just tempting fate. I guess I could list a couple of examples below:

http://www.scubaboard.com/forums/tek-trip-reports/364710-100m-air-dive-workup-pg.html

http://www.scubaboard.com/forums/advanced-scuba-discussions/345916-85m-air-dive.html

Not really sure what your point is? Thought we were discussing current atitudes, not previous risks taken

Enjoy the movie

 

[PfcAJ]

So, I don't know about the rest of you, but when I learned how to do deep technical dives one of the key elements was gas planning. Have enough gas for yourself and your team mate so that you can BOTH safely get back to the surface doing all your deco even if you need to share gas. And you are team diving, you stay with your team mate unless an emergency requires you to leave him to get assistance.

Moreover, if the decompression algorithm says it takes 30 minutes of normal breathing with 50/0/50 to respirate the inert gases that move out of solution at a stop and you only do 22 1/2 minutes over a 45 minute span you have not respirated the same amount of gas. It is not the same deco "just slower". The way to share gas is for your team mate to be inhaling while you are exhaling so that you both have the normal 30 minutes and you are following your deco schedule. Perhaps what was meant is that you do the same amount of respiration, just over a longer period of time. Fair enough. Do the calculation, you will need twice your requirement of gas, more if your buddy has a higher deco sac rate.

I would agree with you if it worked like that. But it doesn't.

Sure, by extending the stops by 1.5x, you haven't breathed the deco gas the entire time. But you've been decompressing LONGER than what the original schedule called for. That't the trick. If it wasn't, back gas deco would never work. You're offgassing even if you're not on the deco gas, just not as quickly, hence the extended stop times.

Trying to align your respirations with your buddy for 30mins, moving through ascents, isn't going to work, and at worst, lead to co2 buildup and all the associated issues it entails. Certainly not something you want to mess with on a high ppo2 gas.

 

[gekodivebali]

30 or 40? 40 is just more flexible with similar footprint. I'd put a 30 on a breather or for redundancy on no deco dives only

 

[MalibuJerry]

I would agree with you if it worked like that. But it doesn't.

Sure, by extending the stops by 1.5x, you haven't breathed the deco gas the entire time. But you've been decompressing LONGER than what the original schedule called for. That't the trick. If it wasn't, back gas deco would never work. You're offgassing even if you're not on the deco gas, just not as quickly, hence the extended stop times.

Trying to align your respirations with your buddy for 30mins, moving through ascents, isn't going to work, and at worst, lead to co2 buildup and all the associated issues it entails. Certainly not something you want to mess with on a high ppo2 gas.

So you think off-gassing only has to do with inert gas going from solution to bubbles in the blood and the rate and volume of respiration of those bubbles is not important? you are right on one thing, you will have more bubbles in your blood, but unless you can respirate them at a fast enough rate with the reduced volume of gas, they are still going to be there when you ascend to the next stop, just a little bit larger. Okay good luck, I'm outa here

 

[PfcAJ]

Its not quite like that.

Bubbles are present on the venous side during deco, and they're eliminated in the alveolar capillary bed. They don't accumulate in the lungs (if they do, you get the chokes).

When you ascend, the blood becomes over-saturated relative to the gas in the lungs, and gas exchange takes place. After x mins at y depth, its ok to move up to a shallower depth.A deco gas accelerates this process since it has less of whatever inert gas you're trying to get rid of. You're still eliminating inert gas when you're not breathing from your decompression cylinder, just at the original rate. Hence, backgas deco.

Its not like you magically stop offgassing when you're not breathing the deco gas. If that was the case, no one would ever be able to deco on backgas.

Sharing the bottle and extending the time gives both divers access to the deco gas while minimizing the ascent time as much as possible. You end up with extra of 'breaths' (1.5x more), with half of those being on the deco gas. In our 30min on 50% example, you and your buddy don't each need 30mins on 50% since you're still offgassing during the backgas component when you're not sharing the bottle.

Make sense?

 

[Peter69_56]

Its not quite like that.

Bubbles are present on the venous side during deco, and they're eliminated in the alveolar capillary bed. They don't accumulate in the lungs (if they do, you get the chokes).

When you ascend, the blood becomes over-saturated relative to the gas in the lungs, and gas exchange takes place. After x mins at y depth, its ok to move up to a shallower depth.A deco gas accelerates this process since it has less of whatever inert gas you're trying to get rid of. You're still eliminating inert gas when you're not breathing from your decompression cylinder, just at the original rate. Hence, backgas deco.

Its not like you magically stop offgassing when you're not breathing the deco gas. If that was the case, no one would ever be able to deco on backgas.

Sharing the bottle and extending the time gives both divers access to the deco gas while minimizing the ascent time as much as possible. You end up with extra of 'breaths' (1.5x more), with half of those being on the deco gas. In our 30min on 50% example, you and your buddy don't each need 30mins on 50% since you're still offgassing during the backgas component when you're not sharing the bottle.

Make sense?

Nope you lost me after you said "Its not quite like that". Think I must have been narc'd as you explained.

 

[PfcAJ]

lol, sorry man.

Tl;dr: Breath gas, bubbles go away.