Filling a BC manually vs. with tank?

[stanw]

Wow! So many great responses in such a short period of time.

My course only covered the general guideline of never holding your breath underwater, though it did not get into any level of detail.

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

2. How much of a depth change are we talking about here?

Thanks everyone!!!!!

The "don't hold your breath" warning applies when you are changing depths.

Since most divers do not know when that is happening, it is likely just a good overall rule of thumb.

If you inflate your BC to conserve the air in your tank, you have many other issues. It is not a viable alternative for that reasoning. It may be good to practice in case of the unlikely loss of inflator operability.

 

[stanw]

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?

Thanks!!!!

Rarely. Only if something fails on your gear.



Removing a regulator from your mouth in very cold water can increase freeflows. Other than that its just easier not to do it.



As long as you want provided you aren't ascending. People get too hung up about the breath holding thing - its not a problem at all unless you are ascending while holding it.

 

[stanw]

My course did not cover blowing tiny bubbles so you don't hold your breath...we just removed the regulator underwater and switched to the inflator.

Good question, Stanw. During my confined water classes we did fin pivots using the BC inflator valve AND fin pivots orally inflating our BD. This knowlege came in handy on a dive where my inflator valve stuck open and I had to disconnect the low pressure hose coupling.

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. Blow a maximum of about 1/2 to 2/3 of a breath into the BC. Firstly, so you have some breath left to blow those bubbles. Secondly, you probably won't need more than that if your weighting and trim are correct.

I sometimes will orally inflate my BC at depth to keep the skill fresh. And if I'm trying to be really stingy on air consumption I'll take a breath, then "recycle" some of it into my BC if needed. To be honest I doubt that giving my BC a toot once in a while does anything to help me conserve air. If I have to hit my purge valve because I didn't plan my breath well enough to clear my reg I've pretty much wasted any air I may have "recycled".

As mentioned here by folks more knowlegable than me, as your bouyancy control improves so will your air consumption.

Steve.

 

[stanw]

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.

"Think about why OW students are taught never to hold their breath.
When is it really unsafe to hold your breath? At such a time, would you want to be adding air to your BC?"

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!

Let me guess. Your newbie air consumption is not so hot...and you'd like to conserve tank air by orally inflating your BC. (Correct me if I'm wrong.)
To answer your question, I'd say it's not that common to fill the BC orally under water instead of using the power inflater. Most divers would probably just use the power inflater since it's more convenient. I guess it depends on your preference.
One of my dive buddies likes to fill his BC orally during the dive as a way to make his tank air do "double duty." I think this is a good skill to practice just in case you have to disconnect a leaky LP inflater hose.
As your buoyancy control improves and you're not doing the yo-yo thing under water, you'll find that you won't be adding/dumping air to your BCD quite as often...so you won't be "wasting" that much tank air by inflating your BCD with the power inflater.
The only time I can think of that it would be a bad idea to inflate the BC orally is if there's something preventing oral inflation, e.g., blocked mouthpiece, etc. String brings up the possibility of reg free-flow in cold water.
Typically, I like to descend fairly quickly, and I'm constantly equalizing on the way down, so it's just more convenient to add air to the BCD with the power inflater.

First of all, it is possible to slooooooowly exhale while switching from reg to BC oral inflation mouthpiece. However, this is a wonderful lead-in to a teaching point...
I think you should ask yourself when you might be adding air to your BC under water. Think about it for a little while...
Under such conditions, is it a problem to be holding your breath?
Think about why OW students are taught never to hold their breath.
When is it really unsafe to hold your breath? At such a time, would you want to be adding air to your BC?
*edited later* I see that String has short-circuited this teaching moment.

Have fun and dive safe.

 

[Nemrod]

I am considering removing the power inflator from my Oxy Mach V wing. I am a minimalist, the original BCs did not have power inflators, it was never a problem to put a puff or two into the BC. Nowadays modern weighting techniques have divers severely over weighted and thus heavily dependent upon power inflated up and down lever air bags.

Getting rid of the power inflator eliminates several failure points and eliminates a hose and complexity and weight from my suitcase and eliminates drag.

N, "N" to zen minimalism

 

[ScubaSteve2000]

Wow! So many great responses in such a short period of time.

My course only covered the general guideline of never holding your breath underwater, though it did not get into any level of detail.

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

2. How much of a depth change are we talking about here?

Thanks everyone!!!!!

Ascending is the problem. Think about it. One atmosphere is 14.7 psi. At 33' of depth we are at two atomospheres. So in 33' you gained an additional 14.7 psi of pressure in your lungs but they are the same size as they were on the surface. (the ol' 2x ata and 1/2 volume thing).

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).

My bouyancy control is less than perfect (a couple orders of magnatude less than perfect actually). I'm happy if I can hold a safety stop within a few feet. I try not to hold my breath.

 

[stanw]

What is the "Essentials video?"

Thanks!

Or, you are diving with a double hose regulator like the Mistral which doesn't have intermediate pressure or you are using one of the AquaMasters that does have IP but you haven't bothered to route it to your BC. This diver might also wear a horse collar rather than a back-inflate device.

If you watch the Essentials video, you will see an air sharing drill and neither diver blows bubbles. Of course, their buoyancy control is PERFECT. They don't appear to move an inch up or down without intending to do so.

Richard

 

[ScubaSteve2000]

My course did not cover blowing tiny bubbles so you don't hold your breath...we just removed the regulator underwater and switched to the inflator.

What about the regulator recovery skills? didn't you have to remove your reg and "throw it away" then do the arm sweep to recover it? We did bubbles. Most of the bubbles were coming from my mouth.

Steve.

 

[grumpymedic]

Stan,
All this is covered during your OW training. Find yourself a good instructor and learn all this in class then apply it in the water. Good luck!

 

[tep]

I use oral inflation as much or more than the power inflator. It's just the way I learned.

Yes, I used to be an air hog, and the tanks were all 72cft or smaller. Now, that's not a problem, but I haven't seen any reason to change my habit. I learned when power inflators were a new-fangled gadget so my instructor thought we shouldn't come to depend on them.

It also has the advantage of NOT changing your buoyancy quite as sharply. You're taking air from your lungs at ambient pressure and transferring it to your BC, also at ambient. If I need a little shot of air, then transferring air already in my lungs to the BC, plus my next breath is often just about right. I don't get the wide buoyancy swings I see some people have who only know to hit the power inflator, until they get really good at just the tiniest shots of high pressure air.

(Yes, I learned to blow a constant stream of bubbles. If the reg isn't in your mouth, you're blowing bubbles.)

It's just another skill to keep in your bag of tricks, like learning to stay horizontal or breathing while you're head-down vertical (lookin' for bug under ledges, or cutting yourself out of fishing line). You don't have to be able to do it, but it doesn't hurt and may even come is useful some day,.