Out of Air! Could you...

[jonnythan]

Thanks, DA, but I'm pretty familiar with the physiology. What worries me is an OW diver who wants air while kicking up from 70 feet inhaling enough on the BC, particularly as he gets more shallow, to cause an embolism shortly thereafter. It would be easy enough to pause out of panic at the top of the breath before exhaling and close the air passages long enough to do this.

IMNMD[non-MD]O, this is not a good option at all. I believe the focus should be on exhaling and keeping the airway open, not complicating things by trying to hold your breath and find your inflator while you're kicking upward. Totally OOA at depth sans buddy is probably the most stressful thing a diver can encounter, and at that point you need to get to the surface and keep your airway open - adding another couple of things to do at that point is not necessary.

 

[DA Aquamaster]

My NMD understanding is that an inhalation or two (or even the attempt to inhale actually helps open up spaces in the lung and can help prevent a lung expansion injury. This, along with more air becoming available in the tank on the way up, is I believe one of the major reasons that most agencies teach that an ESA should be done with the reg in the mouth and to make a couple of attempts to inhale on the way up.

I have had only one OOA experience (do to extreme stupidity on my part) and what I discovered is that after exhaling nearly completely prior to taking a breath is that I got absolutely nothing from the reg for that anticipated next breath. It was a little disconcerting to say the least and occurred during some very strenuous activity. Most people are not going to be very comfortable going without air for more than about 15 seconds in that situation.

In that case I think breathing on the BC is a better option than a potentially panicked ascent to the surface by a diver who is feeling extremely starved for air. A breath or two from the BC in that situation could buy you time to make a planned and controlled ascent. In my case I had a 30 cu ft pony, so it was a moot issue.

 

[DA Aquamaster]

No SPG's ???? How on earth did you know how much gas you had left ? (I think I took up diving at the right time) lol

One day I am going to research back in time to see how gear has changed over the years. There went as many divers then as there are now. I wonder what the accident and fatality rate was 30 yrs ago. Interesting research.

When I started diving, SPG's were still optional but stongly recommended. Due to college induced budget limitations, an SPG was pretty far down the list of dive gear to be purchased.

Most tanks were equipped with J valves and when the reg started to breath hard, you pulled the rod attached to the to J valve to access a 300 to 500 psi reserve. Of course, there was inevitably a time where you reached back and pulled the rod, only to discover it had snagged on something during the dive and had already been pulled, which meant you had already used the reserve. ESA's were not just a theoretical "if" kind of thing, but rather more of a practical "when" kind of thing. This was reflected in OW training where actual ESA's were performed from 30-40 ft.

Another difference was that regs commonly used an unbalanced first and second stage. This meant that you could feel the breathing resistance gradually increase as the tank pressure dropped and with some experience you could feel when you were low on air before it became a critical issue. At the time I started diving, it was pretty much accepted that you could get by without an SPG with an unbalanced reg but really needed to have one if you were diving with a balanced reg as they gave little or no warning that you were low on air.

Air planning and gas laws in general were stressed to a far greater degree in OW and AOW training than they are now. And gas planning and air consumption calculations were something that had a practical application on every dive, not just deep ones, if you were diving without an SPG. Good math skills and some ability to do some basic math in your head were required diving skills.

I don't remember ever being particularly worried about not having an SPG in my first year or two diving, but then I was young and invincible. Now I don't even like to dive shallow with my double hose reg without an SPG even though I still have a J-valve and a pretty good idea of dive time, air consumption and what I should have left in the tank. Fortunately I recently acquired a banjo fitting for my double hose reg and I will be able to take a vintage sea view pressure gauge along with me.

 

[DORSETBOY]

As a part of my training I was asked to remove my regulator and then perform a controlled ascent from 30m to 10m. To my surprise there was plenty air in my lungs to do the 2 minute ascent, even while exhaling all the way up.

Now I wouldn't try such a stunt again just for the h*** of it, but as a result of the excercise I'm confident that in case of a catastrophic equipment failure a trained diver can reach the surface without expansion injury or drowning. Of course you would still have to worry about DCS ...

Most western navy sub crews are trained to do an equivalent of a cesa, I think from 30m, in a tank environment. Wouldn't fancy trying it myself but it certainly seems to work ok.

 

[gsxr1997]

take advanced rescue - you will try breathing from your bc inflator -doesnt work as well as you might think . -first thing to come out of bc and into your mouth/lungs will be water

 

[Cudabait]

If you've just taken your last breath, you have a full set of lungs, No need to play with the BC, CESA.....

Probability is that an average diver is not going to have a lung full of air. Some degree of air starvation is more likely. Problem becomes the ability to handle task loading under increasing stress. So here we go....I'm gonna agree with Walter on this one. And yes, this can be done, easily, if the diver is in control of him/herself. And no, you will not immediately become negative by taking air from the BCD UNTIL IT IS EXHALED. All the more reasons to be in control and able to handle the extra task loading under stress. Personally, I would probably start a CESA immediately from any depth......however, I would certainly be mindful that a little air was available in the BCD if I felt I was approaching blackout. Blackout = drowning. Again, it is possible, even feasible, and it is not taught for obvious reasons.

Regards,

 

[pete340]

you will not immediately become negative by taking air from the BCD UNTIL IT IS EXHALED.

And that "exhaled" means contracting the chest, not just allowing air to vent out in response to reduced external pressure. In the latter case you're still displacing the same amount of water, so you're still buoyed up by the same force.

 

[wedivebc]

Someone recommended having to estimate how much air to breathe so that you did not become too negative. That is not an issue, as you inhale from the bag into your lungs and the volume is constant. You can also exhale back into the bag as your expired air still has about 16% O2. It also contains CO2 as well, but for a short ascent to the surface CO2 buildup in the air in the BC is not as large a problem as it would be simply doing an ESA. And on the way up as you need to vent air, just exhale it into the water to avoid putting more CO2 back into the bag.

I'm with DA Aquamaster but one point I would like to make. Assuming the bcd is filled with air then the expired air will have a higher po2 than .16 (16%) it will of course be decreasing as you approach the surface but the diver performing this will probably get enough O2 to survive the trip to the surface, will have kept his airway open by continually breathing and will probably end up with a massive CO2 headache but live to tell about it.

 

[Diver0001]

Completely hypothetical situation:

You are neutrally buoyant at about 40' (i.e. there is some air in your BC). Then you take the last breath off your tank and your buddy is nowhere to be found. So you now have to make it to the surface.

Couldn't you, in theory, suck some air from your BC during your ascent? You have to deflate as the air expands anyway on the way up, why not breathe some of that air?

Granted, through good buddies and air management, you should never encounter this, so it is more food for thought.

Purely hypothetical, yes. In practice I think it might actually increase your chances of drowning.

R..