What if... [loss of buoyancy question]

[dumpsterDiver]

I made a post about this years ago.. some interesting discussions

BC Failure

 

[Bennno]

I made a post about this years ago.. some interesting discussions

BC Failure

Just to avoid misunderstanding: The steel tanks in the US are quite a bit heavier than the Euro tanks. A 12l Euro is still ok with a 7 mil wet suit unless you are a very small person.

 

[halocline]

Hello guys,

I was wondering what if your jacket brakes while you are under water? what you are supposed to do then? if it doesn't pump up anymore? you just remove your weights and try to go slowly up?

Thanks!

Hello, there are a couple of things that might help you. First, and most important, you should not be using your jacket (BC) to ascend. You use your BC to maintain neutral buoyancy at depth by compensating for the compression of your wetsuit, and for the loss of air in your cylinder. That's all it's used for. You ascend by swimming up. In fact, you usually need to vent air from your BC as you ascend, not put air in it.

Second, you should never be in a situation where you have so much weight that you cannot swim to the surface under your own power. In warm water, with a thin wetsuit and the right kind of tank this is never a problem unless you are A) very overweighted and/or B) a really weak swimmer. In cold water you wear a thicker wetsuit, which means it loses more buoyancy at depth, and with a very full tank at maximum depth you could be fairly negative. However, you should still be able to swim up enough to allow your suit to regain some of its buoyancy and that makes it easier.

If you really need so much weight that you can't swim to the surface without inflating your BC, something is really wrong with your set up and you should seek the help of an instructor to fix it. Technical divers that have to carry much more gear usually have two sources of buoyancy in case the BC fails.

 

[Storker]

The steel tanks in the US are quite a bit heavier than the Euro tanks. A 12l Euro is still ok with a 7 mil wet suit unless you are a very small person.

How is the weight of the tank relevant? At all?

IMO the tank's buoyancy swing is the only relevant factor here. A "light" Euro 12x232 and a "heavy" US steel 100 have the same buoyancy swing; they both contain some 3000 surface liters / 100 cu.ft. of gas. You just need a little less lead on your belt for the one that's most negative.

 

[Diver0001]

Hello guys,

I was wondering what if your jacket brakes while you are under water? what you are supposed to do then? if it doesn't pump up anymore? you just remove your weights and try to go slowly up?

Thanks!

I've actually had this happen. I pulled the "pull dump" and the entire inflator mechanism broke free of the BCD. The BCD lost all of its air and I sank to the bottom.

Exactly the same thing happened to a buddy of mine several years later (different model BCD) and to a client on a dive I was on in Egypt 6 or 8 years ago. All of these incidents were caused by pulling on a pull-dump.

In each case the solution was different. My solution was to ask my buddy for help and he managed to get the parts back together enough that I could make a normal ascent even though the BCD was leaking badly. We aborted the dive.

My buddy's solution was to "swim" (actually moon-walk) his way across the bottom to shore because we were close to shore. He didn't ascend and he was unable to regain neutral buoyancy but he was able to literally walk out of the water.

The case in Egypt happened in deep water. The diver pulled the pull dump and I saw his BCD lose all of its air. He started sinking, which was a problem because the bottom where we were diving is about 200m deep. After trying to fight it by finning up etc. it was clear that he wasn't going to win against gravity and he threw off his weight belt. This caused an uncontrolled ascent to the surface but that was better than an uncontrolled descent, given the options.

As an aside I am an instructor and I now strongly advise students NOT to use the pull dump!

R..

 

[halocline]

I've actually had this happen. I pulled the "pull dump" and the entire inflator mechanism broke free of the BCD. The BCD lost all of its air and I sank to the bottom.

Exactly the same thing happened to a buddy of mine several years later (different model BCD) and to a client on a dive I was on in Egypt 6 or 8 years ago. All of these incidents were caused by pulling on a pull-dump.

As an aside I am an instructor and I now strongly advise students NOT to use the pull dump!

R..

I also have heard of this happening, and it's just another example of really stupid design for the sake of perceived convenience. Yanking on a weak rubber hose that you are relying on for buoyancy is not a good idea, yet the pull-dump encourages exactly that. You can't even turn upside down and inflate the BC because the pull dump hose is also the inflator.

Anyhow, glad you and your buddies survived. It does reinforce the idea of never being so heavily weighted with a single buoyancy source that you can't swim up. There's always another solution.

 

[Bennno]

How is the weight of the tank relevant? At all?

It's very relevant. When you use a heavy tank that is still negative when empty you have to balance more than just the 'swing'. The 'normal' (konvex 230 bar) Euro don't do that, so for divers in Europe, it's not really an issue.
Many skinny/smaller people and kids are often 'overweight' without using any weights when they dive a wetsuit...iin that case you do have a problem when you rip out your opv.
That's why you're not supposed to use heavy steels in wet suits... look up 'balanced rig' if you wanna learn more about it.

He started sinking, which was a problem because the bottom where we were diving is about 200m deep. After trying to fight it by finning up etc. it was clear that he wasn't going to win against gravity and he threw off his weight belt. This caused an uncontrolled ascent to the surface but that was better than an uncontrolled descent, given the options.

That guy clearly had too much weight on him... or a kid or very skinny.
Unfortunately, these days, many instructors and shops tend to give people to much weight just so they have it easier.

As I said before, I and lots of other people used to dive without a BC and it works just fine as long as you only carry the amount of weight you really need.

 

[Storker]

It's very relevant. When you use a heavy tank that is still negative when empty you have to balance more than just the 'swing'.

If you're supposing that the diver is wearing a thin wetsuit and is inherently overweighted without any lead, you're of course right.

I'm kinda naïve that way: My reasoning presupposes that the diver is able to balance their equipment and avoid being overweighted, because that's what I'd do. If my tank was too negative to enable me to be correctly weighted in the exposure protection I wear, I'd make some changes to my gear. Because that's the only safe thing to do, especially for a "normally" experienced diver. YMMV, of course.

 

[Kevrumbo]

Hello guys,

I was wondering what if your jacket brakes while you are under water? what you are supposed to do then? if it doesn't pump up anymore? you just remove your weights and try to go slowly up?

Thanks!

 

[Dan]

All drysuits have "a layer of" air between the suit and your body. Usually, that air is held in your undergarments. That's what provides insulation. When you descend, that air compresses, and your suit becomes too tight. That's what we call "suit squeeze". If you don't add air to your suit, you might become so shrink-wrapped that you can't reach your inflator. That's bad. So, a drysuit diver gradually adds air to the suit as they descend to avoid squeeze and gradually vents air from the suit as they ascend to keep neutrally buoyant. For a normal single tank rec dive, a properly weigthed diver won't need to add much - or any - air to their BCD as they ascend or descent; the air in the BCD is only needed to offset the weight of the gas you carry, and it's slowly vented during the course of the dive to compensate for your increased buoyancy as you consume the air in your tank.

In any case, since the drysuit is watertight and connected to your gas supply, it can be used for redundant buoyancy in case your BCD malfunctions. I like that; it gives me an extra layer of safety at sites where a sudden loss of buoyancy may have nasty consequences.

You can tell that I don't wear a drysuit. Thanks for the education of using a drysuit. I'll stick with wetsuit & warm weather recreational diving.

I recently had the experience of "suit squeeze" of a different kind, so I understand of what you are talking about. Two weeks ago I was diving & testing soft & hard cases for my PLB1. I used Kona iPhone 5 pouch that is waterproof to 30m as the soft case for the PLB1. It was fine up to 25m depth. However, when I reached 30m, the "suit squeeze" was strong enough to press the red emergency button of the PLB1, as shown in the above picture. So, no more using soft case for the PLB1.