Filling a BC manually vs. with tank?

[eponym]

My air consumption is not too bad, I was just wondering what others do and if it made more sense to try to conserve air by doing it this way. I have not honestly done any sort of tests to determine how much air is actually used when doing this with the tank.

The motions and effort involved in taking a breath, removing the reg, blowing into the inflator assembly, and replacing the reg probably outweigh any small savings you could gain from orally inflating the BC.

Each pound of buoyancy you need in the BC underwater is created with one pint of air at the surface, two pints at 33', etc. A pint is roughly one-sixtieth of a cubic foot. So your BC air use is low unless you're overweighted or very deep.

Good question, though.

-Bryan

 

[bleeb]

2. Which raises another question for me, if you do this manually underwater, aren't you technically holding your breath while you switch from regulator to the BC air inflator? How long is it safe to hold your breath while switching back-and-forth?

Remember the first rule of diving. Never hold your breath. Like any other time you practice regulator removal at depth (OOA drills for example) you should blow tiny bubbles so you don't hold your breath.

I'd suggest that this actually be stated a bit more strongly and that every beginning OW diver should strive for techniques for keeping the airway open like blowing bubbles becoming close to an automatic reflex, and not something they need to remember to do or think about. If they're going off regulator in an emergency, they're liable to be quite task loaded and the consequences of getting this one wrong have a significant chance of being quite severe.

 

[eponym]

Hate to have to ask this, though, what do you mean by "Removing a regulator from your mouth in very cold water can increase freeflows." What are "freeflows?

Hang on--okay, I understand. You've not yet taken the open water diver course. *

Okay--you came to the right place. I was just finishing up an outline on free-flows for new divemasters.

Expanding gas gets cooler, for reasons that IMO need not concern us here. Gas expanding in your first and second stages cools them before it gets to you. The harder you breathe, and the longer you hold that inflate button down, the greater the cooling. There is a point where the mechanism is so cold that water around it can freeze and hold it open, if the ambient water temps are already low. Then you get a constant big loud flood of bubbles. Your course should cover what to do when that happens.

It will not happen (okay, mostly) if you don't take your reg out, don't work too hard underwater, don't lean on the inflate button, and (most important) choose to dive warm water only. It can happen also if the air temps are very low and you breathe off the reg before submerging, in which case you've pre-cooled it.

-Bryan

* Wait, scratch that. Your profile says not certified but your posts say you've taken a "course." So are you the proud owner of a c-card?

 

[bleeb]

I read somewhere (and I bet somebody here will know exactly where to find it) that as little as 2 psi increase when holding your breath can cause damage to the lungs. Just to keep the math simple lets use 30' for 2 ATA and 15 psi per ATA. That's around 6" per psi (or 2 psi per foot).

Vague memories of a posting here on SB citing a medical case study where someone embolized rising 8" in a swimming pool.

IIRC one of the docs once posted somewhere on here that the parts of lung tissue that people should be most worried about have about the strength of wet tissue paper, since some of those membranes are only one or two cells thick.

 

[eponym]

What is the "Essentials video?"

So many questions. Keep 'em coming, never be afraid to ask.

It's a DVD that illustrates key skills needed by those who want to practice a diving discipline known as DIR (doing it right). Redundancy, standardization, and precise control are some ways to characterize it.

For more see the DIR forum here on SB, for example this thread.

-Bryan

 

[Eric Sedletzky]

I'm guessing you are talking about when you are ascending. This is a question I asked in this same thread somewhere (haven't had a chance to read through all the responses)...whether the danger of holding your breath while ascending or descending was also something not covered in my course -- I was just told not to do it.

Thanks!

This has got to be a troll.
Please tell me you're not serious.

 

[tc]

Read back a bit ZKY, he's new.

 

[Lee Taylor]

Just curious, what would be considered a "long duration" when holding your breath?

Thanks!!!!

To your point, "long" is a relative term and needs to be quantified. The post states "A second or two will not hurt you". Therefore, it can be derived that "long duration", in this case and point, would be more than a second or two. The answer is there, just easily overlooked.

 

[tc]

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.

 

[Thalassamania]

I tend to orally inflate most of the time. If for no other reason than your buoyancy does not change until you take your next breath, that helps to keep you nicely in balance.

If you are freaked out removing your regulator from your mouth or have trouble holding your breath for a second while maintaining your position in the water column, I'd suggest that the training that you received was inadequate and it would be a good idea to seek remediation.