Pony bottle vs. Spare Air?

[peterbj7]

There's an awful lot being said here that's maybe true but off the point and unhelpful. Catastrophic failure of gear is most unusual these days, even supposing routine maintenance hasn't been carried out. What is needed is not a second source of air, but proper management of the first one. Short of catastrophic failure there is NO justification for running out of air. Now, as an instructor I know I'm dealing with people who aren't very experienced so I always ensure I am able to help in such circumstances, but if it ever happens that person isn't going back in the water without a substantial program of re-education.

I've had two incidents in the past few days (more than in the preceding two years). In the first a guest apparently ran out of air and I saw him sharing air with a divemaster. I went over to investigate and handed my own octopus to the OOA diver, to release the DM for his proper duties (he was leading the dive). But as soon as I had handed off my octopus the DM grabbed my primary from my mouth, leaving me with absolutely nothing! It turned out that the DMs octopus, the one he had handed to the OOA diver, was defective and giving 2/3 water. The guest had baulked at it and the DM had given him his primary instead, himself switching to his octopus and then experiencing what the guest had just experienced. Once the DM had found his primary again he gave me back my primary, which was quite nice of him!

Once guest and I were comfortably established, both on my tank, and I was sure he was calm I started investigating. His pressure gauge still showed 1000psi so I tried breathing from his primary. Nothing - about 1/2 breath and the gauge dropped to zero. So I checked his tank valve and lo and behold! - it was about 1/2 turn ON. Almost off. I turned it on properly and immediately the problem was solved. Guest finished his dive on his own tank. Now although we do help guests and watch them while they're kitting up, when we have certified divers I always tell them that they are responsible for their own gear. I also tell them that the last thing they should do before dropping into the water is to take a single deep breath and check that the gauge doesn't move. This guest had gone through the motions (I had watched him) but had stood the "wrong" side of the tank. So when he thought he was turning the tank on he was actually turning it off. He said he hadn't bothered to do the single breath check as with over 100 dives he didn't think it applied to him. But he now knew differently.

The DM and I later had a discussion on his responsibilities and maintenance of his personal dive gear. So everybody was happy.

But the following day we had a similar problem, with another member of the same group. An experienced diver, he and I had been down to maybe 110' during the dive. Later on he came to me and showed me his gauge, which was dropping to zero with each breath and then returning to normal (again around 1000psi). I immediately checked that his tank was fully on, but couldn't turn the valve either way. Locked absolutely solid. We were in around 50' but ended the dive, as neither of us had any confidence in his gear.

Back on the boat we still couldn't budge the valve and of course couldn't remove the regulator as the system was pressurised. Do you know how long it takes to empty a tank just using the purge button, given that the flow of air is restricted because the valve isn't fully on? Absolutely ages. When we were finally able to get the reg off we tested it on another tank and the reg was fine. The tank was rented from a "blue chip" operator here and I had had no reason to suspect there would be anything wrong with it. Still I had to refund the cost of that dive.

The diver said he HAD done the single breath check and that although the gauge had moved it had immediately returned to its previous position, so that was OK, wasn't it? I reminded him that the whole point was that the gauge shouldn't move at all.

So before you strap all sorts of redundant air supplies on, make sure you know how to use the one you've got, and then dive it intelligently.

 

[DandyDon]

I like to do a gear and bubble check on a 15-20 ft stop on descent and make sure our valves are all the way on. All-on or all-off either one is preferable to the false security of 1/4 turn back. I ask the boat mates to not touch my valve as I leave the boat or leave it all the way on, but like to check that again.

As unneeded as a pony should be, Peter, caca happens. If I need it on only 1% of my dives, it was worth it. And I have, after learning to use it correctly...

 

[Web Monkey]

For all of you who say, "if your OOA, your buddy is probably low on air" I just don't get that. I am ending my dive at 700 psi min and that is more than enough air to get me and a buddy to 15 feet and a safety stop.
Bruce

Divers typically dive with others with similar SAC rates (not always, but typically).

This means that if one is OOA, the other one has an excellent chance of being LOA.

Terry

 

[DandyDon]

Divers typically dive with others with similar SAC rates (not always, but typically).

This means that if one is OOA, the other one has an excellent chance of being LOA.

Terry

And you never know for sure unless you're in frequent communication about each other's air, which can be done - but it's distracting to do/request checks every 500 psi.

What I hate is when the other diver needs air, gets on my alternate second stage, and is excited enough to start drawing my back gas down quickly. I invite buddies and other divers to grab either available second stage (not the one in my mouth!) without asking, I'll understand, but if they grab the one to my backgas, I move them to the pony ASAP.

 

[diverDano]

There's an awful lot being said here that's maybe true but off the point and unhelpful. Catastrophic failure of gear is most unusual these days, even supposing routine maintenance hasn't been carried out. What is needed is not a second source of air, but proper management of the first one. Short of catastrophic failure there is NO justification for running out of air. Now, as an instructor I know I'm dealing with people who aren't very experienced so I always ensure I am able to help in such circumstances, but if it ever happens that person isn't going back in the water without a substantial program of re-education.

I've had two incidents in the past few days (more than in the preceding two years). In the first a guest apparently ran out of air and I saw him sharing air with a divemaster. I went over to investigate and handed my own octopus to the OOA diver, to release the DM for his proper duties (he was leading the dive). But as soon as I had handed off my octopus the DM grabbed my primary from my mouth, leaving me with absolutely nothing! It turned out that the DMs octopus, the one he had handed to the OOA diver, was defective and giving 2/3 water. The guest had baulked at it and the DM had given him his primary instead, himself switching to his octopus and then experiencing what the guest had just experienced. Once the DM had found his primary again he gave me back my primary, which was quite nice of him!

Once guest and I were comfortably established, both on my tank, and I was sure he was calm I started investigating. His pressure gauge still showed 1000psi so I tried breathing from his primary. Nothing - about 1/2 breath and the gauge dropped to zero. So I checked his tank valve and lo and behold! - it was about 1/2 turn ON. Almost off. I turned it on properly and immediately the problem was solved. Guest finished his dive on his own tank. Now although we do help guests and watch them while they're kitting up, when we have certified divers I always tell them that they are responsible for their own gear. I also tell them that the last thing they should do before dropping into the water is to take a single deep breath and check that the gauge doesn't move. This guest had gone through the motions (I had watched him) but had stood the "wrong" side of the tank. So when he thought he was turning the tank on he was actually turning it off. He said he hadn't bothered to do the single breath check as with over 100 dives he didn't think it applied to him. But he now knew differently.

The DM and I later had a discussion on his responsibilities and maintenance of his personal dive gear. So everybody was happy.

But the following day we had a similar problem, with another member of the same group. An experienced diver, he and I had been down to maybe 110' during the dive. Later on he came to me and showed me his gauge, which was dropping to zero with each breath and then returning to normal (again around 1000psi). I immediately checked that his tank was fully on, but couldn't turn the valve either way. Locked absolutely solid. We were in around 50' but ended the dive, as neither of us had any confidence in his gear.

Back on the boat we still couldn't budge the valve and of course couldn't remove the regulator as the system was pressurised. Do you know how long it takes to empty a tank just using the purge button, given that the flow of air is restricted because the valve isn't fully on? Absolutely ages. When we were finally able to get the reg off we tested it on another tank and the reg was fine. The tank was rented from a "blue chip" operator here and I had had no reason to suspect there would be anything wrong with it. Still I had to refund the cost of that dive.

The diver said he HAD done the single breath check and that although the gauge had moved it had immediately returned to its previous position, so that was OK, wasn't it? I reminded him that the whole point was that the gauge shouldn't move at all.

So before you strap all sorts of redundant air supplies on, make sure you know how to use the one you've got, and then dive it intelligently.

I'd like re-itereate my previous point, and that is that If a diver feels more comfortable with a completly redundant set of gear, why is he poorley trained???
We all dive diferently, and in differing conditions. If I was diving in belize where the water is 80 degrees, I would feel comfortable without a bailout. But, here in the northwest where the water gets to 40 degrees and we're wearing a ton of neoprene, or undergarment, and thusly a ton of lead, relying on bc's and inflators on our drysuits, there is alot to go wrong, even with the proper amount of gas calculation and dive planning. The bailout is there for emergencies, not a second part of the dive. the divers here keep preaching proper dive planning. The diver in the previous post mentioned a tank failure....oh my god....something that shouldn't have happened...but it did. This is where the bailout is used....not just for more air. they are rarely used, not used all the time.


Skydivers always have a reserve shute........do they always use it?? Do they just show up..pay their money...get on a plane and jump...hoping everything works????
They are highly trained...yet they have a backup, why???For safety...not in lieu of training or planning.

divers can preach all they want about how perfect they dive...all the time...what happenes when something out of their control happens????Only one tank...only one primary??? Try doing that cave diving?????

 

[Katamuki]

After reading ALL 20 pages to this point I am kind of suprised that nobody has used actual math to answer the question of spare air/pony useablity. Hopefully this task isnt beyond me as well.

While RMV and SAC rates arent the usual pre-dive plan for most they will answer air/gas management issues when buying a 2nd air source I think. So... assume a 100 foot dive...

If 100 ft dive (4ata) AND ascent rate = 30ft/min then total ascent time is 3.2 minutes
Add 1 min for 50 foot safety stop (total time is now 4.2 minutes) AND safety stop at 15 ft for three minutes (total time is now 7.2 minutes)

An experienced diver not under tremendous load may have a SAC rate of .5 ft3/min but less ASSUME some stress so the SAC is now 1ft3 (thats supposed to be cubed )

Ascent Requirements: 4.2 min x 2.5ata = 10.8 ft3
PLUS 3 min Safety : 3.0 min x 1.4 ata = 4.2 ft3
Air Needed for 1 Stressed divers: 15 ft3

IF 2 stressed divers then double that to 30ft3
Obviously, if the donor is relaxed and breathing normally at thier .5ft3 rate and so is the parasite then the air requirements are under 8ft3 each to safely ascend.

Therefore... if you need a bottle and you like to go deeper it makes sense to have one large enough to do some good.

 

[ryssyr]

Does your buddy always walk along the bottom like that?

ahh yes. Funny picture. that was at mermaids lair in Belize off of Ambergris Caye. Everyone was fooling around alot on that dive. must have been the location. The photos are very funny, but its the only one with my pony that is clear enough to see.

-R

 

[DandyDon]

Good math, Katamuki - oh, I assume you did it correctly. For me I figured "best laid plans of mice and men oft go awry," got the biggest pony I wanted to mess with on plane trips and recreational diving, never using it as a stage or extended but carrying it just in case - 19 cf, always valve on in the water for anyone who feels the need to grab it. Whether it's more or less than might be planned for each possible situation I might swim into, it's a helluva lot more than most divers on the boats are diving with. I still board boats where SMBs are not common.

Why would I want to allow for 2 divers on my pony, tho? We're going to bail the dive at the first sign of either of us having trouble, and - I only have one second stage on my pony.

 

[peterbj7]

Skydivers always have a reserve shute........do they always use it?? Do they just show up..pay their money...get on a plane and jump...hoping everything works???? They are highly trained...yet they have a backup, why???For safety...not in lieu of training or planning

You've answered your own question. A skydiver plans very thoroughly NOT to use the reserve, and a good scuba diver similarly plans VERY thoroughly not to use his emergency air supply.

The problem here is that many people are counting the emergency supply in with the total air carried and planning their dive based on that larger amount. Either that, or they're using the availability of an indeterminate extra supply of air to obviate careful measurement of their SAC and intelligent application to the dive in question.

When I'm diving in the UK or similar conditions I use either a twinset or a single with a sizeable pony. In such conditions I generally dive to the rule of thirds, even when it's open ocean and there's a clear route to the surface, because I can't remember a dive there that didn't become a deco dive. And I measure my air consumption on most dives so as to refine my SAC, and always do a fairly thorough gas requirements analysis before the dive.

Out here in the warm water of Belize I rarely do a recreational dive with more than just the one air source, because I'm always with other people and rarely use more than half my tank on any dive. A couple of weeks ago I was glad I don't use much air, as I had one person hanging off my octopus and I was buddy breathing with another - at the same time! Made deploying my SMB interesting.

There's no substitute for intelligent planning.

 

[micklock]

A friend's daughter learned to skydive and she was telling us that most of the accidents she heard about was from more experienced skydivers who didn't use a backup chute anymore because they thought they could handle any problems with chutes that became tangled.