Filling a BC manually vs. with tank?

[LarryHinDC]

1. Can you develop an air embolism if you either ascend or descend while holding your breath or does it only happen when ascending?

It's on the ascent only. Whenever you freedive, you'll be descending while holding your breath, so you know that doesn't cause problems. And ascending while freediving doesn't cause problems because you aren't ascending to a point where the surrounding pressure is less than where you filled your lungs.

I tend to fill my BC orally before getting in the water. And since I've gotten myself properly weighted and have worked on my buoyancy contol, I find that I only rarely have to adjust the air in my BC at depth.

 

[BHB ScubaTroll]

Interesting, 3 pages and no one mentioned the main reason I don't manually inflate in the water very often.

Hint- I dive mostly salt water.


With each breath into the BC underwater you'll also push a small amount of water into the BC. With salt water you need to be a bit more "thorough" in rinsing out the inside of the BC if you've been doing manual inflation.

Hey TC, good to see ya... It's also true that each time you let air out of your BC, you let a small amount of water into the BC under water. I would think a thorough rinsing would be in order after all salt water dives

 

[skippy31]

The only time I every manually inflate my BC/wing is when I'm diving in ice water. By ice water I mean in a river under the ice where water is freezing temp top to bottom. This does not include a lake or quarry where ice water is only present for the top few feet.

When your diving in ice water the risk of an inflator free flow is much higher and as a result I disconnect the inflator in this situation and use oral inflation. An inflator free flow can cause a rapid uncontrolled ascent and possible embolism.

Any other time I use my power inflator normally. Obviously the situation described above is really outside the realm of sport diving and is getting into the technical diving realm.

Mat.

 

[Thalassamania]

The only time I every manually inflate my BC/wing is when I'm diving in ice water. By ice water I mean in a river under the ice where water is freezing temp top to bottom. This does not include a lake or quarry where ice water is only present for the top few feet.

When your diving in ice water the risk of an inflator free flow is much higher and as a result I disconnect the inflator in this situation and use oral inflation. An inflator free flow can cause a rapid uncontrolled ascent and possible embolism.

Any other time I use my power inflator normally. Obviously the situation described above is really outside the realm of sport diving and is getting into the technical diving realm.

Mat.

An inflator free flow due to cold? Never heard of such a thing and we dive somewhat colder water (e.g., arctic under the ice which can get down to -2 C). I have heard of first stage freeze that has resulted in free flow of the primary regulator, the auxiliary regulator, even (in one case) both regulators ... but never the power inflator, which has a much stronger spring holding it's downstream valve closed.

 

[skippy31]

Don't believe it? BTW we're not talking about spontaneous free flow but rather free flow and locking on after you operate the inflator to add gas.

We had a death up here a few years back for exactly that reason. Inflator free flowed and diver hit the ice from 90ft. I've also seen it happen to a number of people but usually at the very beginning of the dive causing an aborted dive. Again this normally occurs in ice water.

Something to keep in mind if your dive in ice water.


Mat.

 

[Eric Sedletzky]

Very reasonable questions if he is currently in OW class, or about to start class.

Very troubling questions if he is already certified.

stanw: Fire away with the questions, you'll get some good answers here (for the most part ); but if you are already certified (and from your posts it sounds like you are already diving), this is pretty basic information you should already "own" for your safety.

This is what I was wondering.
Because, if he's been through open water already this is the most basic stuff (and the most critical) and it should have been covered. Even if someone just read the book with no instruction they would have read a detailed description and known the answers to what he's asking.
That's why I'm wondering what's up with the instruction and the agency he went through. Did they not provide all the course material? Unless this is how far down instruction has fallen. Good god, I hope not!
He says he has 0-24 dives and he's posting in the general discussion forum and not the "not certified yet" forum so I'm assuming he's newly certified.

Unless this is some sort of game?

 

[Thalassamania]

Don't believe it? BTW we're not talking about spontaneous free flow but rather free flow and locking on after you operate the inflator to add gas.

We had a death up here a few years back for exactly that reason. Inflator free flowed and diver hit the ice from 90ft. I've also seen it happen to a number of people but usually at the very beginning of the dive causing an aborted dive. Again this normally occurs in ice water.

Something to keep in mind if your dive in ice water.

Mat.

Please keep in mind that I usually add to my BC by mouth ... so we're not arguing technique preference here.

People die in diving accidents and the reasons given often stretch into Urban Myth ... If anyone should know that, it's me, I worked for many years investigating diving accidents and determining their cause.

I don't buy it. I'm open to the concept, but a rather trivial engineering analysis of the problem casts grave doubts on the idea that you present.

Here are the facts as I understand them, please sharpen my understanding of the facts or fit them together in a way that your diagnosis makes sense.

1. A reduction in air pressure results in cooling of the air and thence the regulator or inflator valve.
2. The greater the drop in pressure the greater the cooling.
3. Scuba regulator first stages drop the pressure from about 3,000 psi down to about 130 to 150 psi above ambient.
4. Scuba regulator second stages drop the pressure about 130 to 150 psi.
5. Adiabatic cooling resulting from a less than 150 PSI drop is almost negligible when compared to the drop more than 2,500 psi drop at the first stage at the start of a dive.
6. I there was sufficient cooling to result in a power inflator icing failure, the first stage would have frozen up long before.
7. Lots of power inflators fail open, without freezing, witness the Halcyon problems of a few years ago.
8. With an only modest increase in IP a scuba regulator second stage will blow open and free flow.
9. Most scuba regulators have two second stages attached, both of which may be blown open by a moderate rise in IP.
10. BC inflators have a downstream valve that can be blow open by an increase in the IP, but doing so will require a significantly larger rise in the IP than will be required to blow open a second stage.
11. The failure mode of most regulator freezing is free flow, ice forms in the ambient pressure chamber, the first stage valve is forced open, this flows air through the regulator cooling it further and exacerbating the problem in what is now a positive feedback loop that can only be stopped by closing the supply valve, otherwise the IP rises until gas can escape or the IP is equal to the supply pressure.
12. Unless the supply pressure is very low, the IP hose will rupture at about 300 PSI above ambient, but the IP does not reach that level because the downstream valve of the two second stages act as relief valves and freeflow.
13. Two freeflowing second stages will vent enough gas to prevent much rise in the IP thus it is rather doubtful that the BC inflator will come into the equation.

I just tried this with my Mares Abyss. I put it on a tank, opened the valve and slowly cranked the IP up. One second stage blew open and that was it. The other second stage (slightly de-tuned) and the BC's power inflator were unaffected. I continued to crank a bit, but I knew that would not really make any difference, I stopped and returned the screw to it's normal position.

The only way I could see the incidents that you describe having occurred in the way in which you describe them occurring, is if the diver(s) were using upstream second stages, and we haven't seem them in many a year or (and this is what I believe) failure of the power inflator that had nothing what-so-ever to do with icing or cold.

 

[highlandfarmwv]

I was diving with a friend who had a freeflow via her BC inflator tubing connector. If shse had left it on the dives would have been scrapped. Instead, she disconnected m we dived and she orally inflated when necessary.

 

[Ed L.]

If it hasnt been said. ABout the only time I manually inflate my BC is before a dive getting into the water. That couple of extra pounds of air is a couple of more breaths under water!

 

[Alex777]

I don't usually wear a BC or wing but, if I do, and need to inflate it for some reason, I do it manually. None of my regs have inflator hoses. "Manually" (orally?) inflating is no big deal.