Filling a BC manually vs. with tank?

1. How common is it to manually fill your BC underwater by blowing on the inflator vs. using your tank? Are there times when it might not be a good idea to do it by blowing through the inflator?

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?

Thanks.

Don't freak out about holding your breath underwater. A second or two will not hurt you. Problems arise when you hold your breath for long durations and change elevations at the same time. The air expansion inside of you is what causes problems.

It's very uncommon to fill your BC manually. It is an emergency procedure. Most people will never have to do it.

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

I figured if you need to affect your buoyancy and do not want to use your tank, you would do it manually. Does everyone opt to use the tank unless the tank is low?

Thanks!!!!

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:

1. How common is it to manually fill your BC underwater by blowing on the inflator vs. using your tank?

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Rarely. Only if something fails on your gear.

Are there times when it might not be a good idea to do it by blowing through the inflator?

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

How long is it safe to hold your breath while switching back-and-forth?

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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.

I was taught not to hold your breath while switching between the regulator and the inflator but to let a little stream of bubbles out as you switch. Also, it is a more efficient use of air to use the inflator instead of manually inflating your BCD, so unless you were out of air or had an inflator malfunction, I can't see a good reason to manually inflate your BCD while underwater.

stanw:

1. How common is it to manually fill your BC underwater by blowing on the inflator vs. using your tank? Are there times when it might not be a good idea to do it by blowing through the inflator?

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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.

stanw:

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?

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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.

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.

Short answer... It's not very common because it doesn't take much air for most (experienced) divers to neutralize...

... The other short answer... If you are 5' from the surface and completely fill your lungs... Then, hold that breath to the surface, you might over-fill your lungs and then have a problem...

Now...
There are times when I use my own lungs to become neutral at depth. The fact that I dive a HP 100, zero weight and I am negative without a wetsuit (and the fact that I have tested this situation) means I will need two breaths (90') into my bc to become neutral. (NOTE, your setup and issues might/will be different). Does this mean I hold my breath? NO... I breath slower than some divers (comfort level) and faster than other divers...

I feel comfortable either way, and I use what ever I am comfortable with at the time...
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On a separate note... I shoot a lot of pictures underwater... it requires a steady breathing rate, and the ability to adapt to different issues on the fly (that might seem like I am holding my breath), just remember your training (including the depths/pressures for having an issue when holding your breath)

I hope that muddies it up for you (as it should...)

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