Re-using air from BCD in dire emergency?

[Teamcasa]

Yes, it does.

How does a submarine maintain 1 ATM, no matter the depth?

 

[The Kraken]

Codyjp,

"So what would be gain be on a spare air during an ascent from 100'? "

Waaaaaaaaay tooooooo funny ! ! ! !

the K

 

[*dave*]

How does a submarine maintain 1 ATM, no matter the depth?

With a thick ass bulkhead that resists ambient pressure. They don't escape the law, they manage it.

Are you suggesting that submarine and a scuba cylinder aren't subject to Boyle's law? They are... Poke a hole in either one and you'll get different results, depending on depth. What happens when a burst disc lets go on the surface? What would happen if the disc magically disappeared at... 2000' depth? In one case, there would be a rather loud release of the tanks contents. In the other, water would rush into the tank as though it were a vacuum.

What law would you use to describe the different effects?

 

[Atomic_Diver]

would you rather be awake to expierence your self drown, or passed out, and wouldn't even know it?

 

[*dave*]

So what would be gain be on a spare air during an ascent from 100'?

3ft3/3000psi=.001ft3/psi
100'=4ata(3ata ascent)
3ata+14.7psi=44.1psi
44.1*.001=.04ft3

Plenty, if you have really small lungs.

 

[diverdoug1]

However, if I were 100 feet from the exit to the cave and completely out of gas, I'd try it. I'd try anything; wouldn't you? And if I made it out, I'd sell all my gear because I was clearly much too stupid to continue to dive, for having gotten myself into that bad a situation.

TSandM, I have to say that I have given your post alot of thought today. Your posts have ALWAYS been well reasoned and informative, but I feel I must take issue with this one. Any properly trained cave diver (as I know you are) knows that cave diving is an exercise in risk management/avoidance. They also know that there is a degree of risk DESPITE superb training/inellligence/maturity/preparation. I have had the misfortune of losing 2 friends while they were cave diving. Both were evidently gas management failures. Both were VERY experienced and well trained (one of them was my cave instructor, and renowned in the cave diving community for his extensive cartography). My point is that it is important to accept that there is a finite risk for cave diving, even if you are not a "stroke" (ie ; careless , stupid, or poorly trained). I have and still know of many cavers who feel they are "bullet-proof" because they are so carefull, and follow their training. It is not true. To truly make an informed decision about risk accaeptance, you must truly appreciate that there is a risk (even though it is made much smaller with proper training). Many people state that the car ride to the cave is the most dangerous part. Not true. The mortality risk per hour of activity among trained cavers is estimated to be slightly higher than general aviation (which is slightly higher than riding a street motorcycle). I am not trying to discourage any of these activities. I cave dive, and I have driven my motorcycle to the airport to fly my plane. I have flown my plane to cave dive. Anyway, I just wanted to put in my 2 cents that it's not just the stupid that can get themselves into bad or deadly situations (although I'll bet in the ER it sometimes seems that way)

 

[boulderjohn]

The issue is more the lowered ambient pressure during ascent. Your regulator needs help from the PSI to match the ambient pressure at depth. As you ascend, the amount of PSI present is enough to let things flow.

I once demonstrated to students how simply cracking the valve open on your tank will allow you to breathe freely on the surface, but it would not function at depth, even though the tank was full. I hate to admit it, but after doing that demonstration, I got distracted long enough that I forgot what I had done and then entered the pool with my valve still only cracked. It had breathed freely on the surface, but once I reached only 10 feet of depth in the pool, I was acutely aware of the problem.

 

[TSandM]

DiverDoug1, I did not mean to insult or disparage your friends.

I dive in a team of three, and we do careful gas planning, and I dive conservative limits. For me to end up having to breathe the air in my wing, I'd have to have gotten very stuck or very lost, AND lost my buddies or delayed them as well, until we had used our reserves. I don't know what it would take to get that screwed up -- I am not an explorer, and have no intention of going to sidemount and trying to crawl through tiny tunnels. There is plenty of cave that's easily backmount diveable to keep me busy for the rest of my reasonable cave diving career. If I had an event like that and lived through it, I think I'd quit cave diving, because I would either have had to make a serious error in judgment or a very serious error in technique.

 

[diverdoug1]

DiverDoug1, I did not mean to insult or disparage your friends.

I dive in a team of three, and we do careful gas planning, and I dive conservative limits. For me to end up having to breathe the air in my wing, I'd have to have gotten very stuck or very lost, AND lost my buddies or delayed them as well, until we had used our reserves. I don't know what it would take to get that screwed up -- I am not an explorer, and have no intention of going to sidemount and trying to crawl through tiny tunnels. There is plenty of cave that's easily backmount diveable to keep me busy for the rest of my reasonable cave diving career. If I had an event like that and lived through it, I think I'd quit cave diving, because I would either have had to make a serious error in judgment or a very serious error in technique.

I understand no insult was made or intended, I just want you to understand the risk you are accepting. A 3 buddy team that is doing conservative cave dives is relatively low risk, BUT there is an inherent risk of the overhead environment (no matter how conservative your dive planning is). NEVER think you are diving SAFE (just safer). Plan your dive knowing that the last thing you know in your life might be (AND COULD BE) clawing your fingers to the bone on limestone, and it will be much less likely to happen. I am in the caves at least once a week for the past 14 years, and I still have to give myself a slap in the face once in a while to keep up my "fear edge". I have had my share of "OH SJIT" moments in my cave diving career. Serious errors in technique and judgement can happen to the best of us. Keep sharp, and keep smart. No caver is safe or bullet-proof

 

[Codyjp]

TSandM, I have to say that I have given your post alot of thought today. Your posts have ALWAYS been well reasoned and informative, but I feel I must take issue with this one. Any properly trained cave diver (as I know you are) knows that cave diving is an exercise in risk management/avoidance. They also know that there is a degree of risk DESPITE superb training/inellligence/maturity/preparation. I have had the misfortune of losing 2 friends while they were cave diving. Both were evidently gas management failures. Both were VERY experienced and well trained (one of them was my cave instructor, and renowned in the cave diving community for his extensive cartography). My point is that it is important to accept that there is a finite risk for cave diving, even if you are not a stroke (ie ; careless , stupid, or poorly trained). I have and still know of many cavers who feel they are "bullet-proof" because they are so carefull, and follow their training. It is not true. To truly make an informed decision about risk accaeptance, you must truly appreciate that there is a risk (even though it is made much smaller with proper training). Many people state that the car ride to the cave is the most dangerous part. Not true. The mortality risk per hour of activity among trained cavers is estimated to be slightly higher than general aviation (which is slightly higher than riding a street motorcycle). I am not trying to discourage any of these activities. I cave dive, and I have driven my motorcycle to the airport to fly my plane. I have flown my plane to cave dive. Anyway, I just wanted to put in my 2 cents that it's not just the stupid that can get themselves into bad or deadly situations (although I'll bet in the ER it sometimes seems that way)

Could you please give is the source for this data? I've always wondered if these calcs have been made and how different activities all size up. Thank!