Feeling the OOA

[TSandM]

In fact, to your body, it matters very little whether you stop breathing with your lungs empty or full. What determines the length of time you can hold your breath is the CO2 buildup in your blood, and that occurs regardless of the volume in your lungs.

If you honestly can only hold your breath for 25 seconds before your vision blurs, something's not right. Most people can manage at least 30 seconds before they breathe, but it's air hunger and not decreased vision that makes them inhale.

However, it is a very reasonable concern, to think about where your alternate air source is. I did an experiment several years ago in Hawaii, because my husband insisted he could be a long way from me, since we could see so far. I let him get about 25 feet away, and I exhaled and stopped breathing, and began to swim for him. I quickly discovered the swim was harder than I realized, because I was, of course, NEGATIVE with empty lungs, and had to swim up as well as across. When I got to him, he was taking a photograph and not paying any attention to me, so I had to shake his arm to get him to look at me so I could signal him I was OOG. By the time I had a regulator in my mouth, I was NOT a happy diver.

This taught me that 25 feet is the absolute largest distance I ever want between me and something to breathe.

But, as Bob says, being OOG should be a vanishingly rare occurrence. Running out of gas because you've used it all is almost 100% preventable (unless you are unlucky enough to get entanged in something your buddy can't get you out of) by good planning and good diving habits. Equipment problems that result in no access to your gas supply do occur, but they are rare (dip tube occlusions, for example). Nonetheless, since this is truly a life-threatening problem underwater, it is good to keep your skills (air sharing, and air sharing ascents) sharp and well practiced.

 

[rstofer]

That thought, together with the idea that eventually every diver gets an OOA, is pretty scary.

Not scary enough to stop me from entering the diving world, but I hope it's scary enough to make me check the tank thoroughly, every single time.

Every diver does NOT run out of air! I knew from a very early age that I couldn't breathe underwater and that knowledge has caused me to pay a great deal of attention to my SPG.

The SPG does two things: First, it tells you how much air pressure is in your tank. That part is obvious. The second, and more important, thing that it does is display your life expectancy in least usable units. As that needle moves counter-clockwise, your life expectancy decreases. The rate at which the needle moves (psi per minute) is also the rate at which your life expectancy is declining. Simple as that.

Equipment failures are VERY rare. There's no reason to expect a regulator to crap out mid-dive. There is every reason to expect a diver to have made a mistake with not fully opening the tank valve.

As dives get deeper, consider redundancy. There is no way I can dive doubles; I'd never make it from the parking lot to the surf. But I CAN carry a small pony bottle. I have both a 13 cf and 19 cf pony that I am starting to play with.

In my case, the pony isn't strictly for redundancy. I want to dive my Aqua Lung DW Mistral double hose single stage regulator. There is no intermediate pressure for an octo or BC inflator. Hence the pony. Of course, the octo isn't for me. It's for my buddy. I may want to play with obsolete regs but I still have an obligation to my buddy.

Richard

 

[Red_5]

I've had an OOA. Doing an AOW dive, I was at ~80FSW, I got into a really low on air situation (another story in and of itself) and proceeded to the surface, watching my accent rate on my computer. I ran out at 10 FSW, so I was pretty lucky in that respect. breathing became harder till nil shortly thereafter.

A full debrief was had with all concerned.

I won't rehash much of what was already posted above.

 

[rstofer]

Equipment failures are VERY rare. There's no reason to expect a regulator to crap out mid-dive. There is every reason to expect a diver to have made a mistake with not fully opening the tank valve.
/QUOTE]

I guess I should point out that it is entirely possible for a regulator to free-flow. This is NOT a life threatening event if you have a lot of air in the tank or have the presence of mind to crimp the hose. It is also possible for the regulator to freeze up in cold water.

Probably the best way to avoid these situations is to use the proper regulator for the environment, use good cold water practices and have the reg serviced from time to time (I am not necessarily hung up on 1 year or die). Or, dive in south ease Asia; my first choice for a solution!

But there are other equipment problems that MIGHT occur even though they are unlikely. Things like a stuck or leaking inflator valve. A broken inflator elbow. A punctured bladder (the one you are wearing). A lost weight belt. All of these will increase the stress level.

Richard

 

[boulderjohn]

That thought, together with the idea that eventually every diver gets an OOA, is pretty scary.

Not only does every diver no eventually run out of air, it is not even remotely close to being true.

Other than a couple of deliberate out of air scenarios, I have only been near a true OOA emergency once in my life. In that case, a diver on her second dive of the day either forgot to switch tanks or switched to an almost empty tank without checking the gas supply at the beginning of that dive. Contrary to what others routinely predict would happen, she reached for her buddy's alternate and everything was OK. (BTW, I was with a fairly large group of instructors once, and someone asked about their experiences, and in every one of the relatively few cases, the OOA diver went for the alternate.)

In my conversations with other experienced divers, their experiences have been pretty much the same.

If I were to make a prediction based on probability, it would be that you will never run out of air yourself, and you will never be in a group where someone runs out of air.

 

[Andy077]

I had an OOA at 12ft during a dry suit training dive, suit flooded, was having trouble hovering, and burned up a TON on buoyancy.
Anyway, i was watching the gauge and knew it was dropping, and have breathed fire dept SCBA thanks down to zero so i knew that when it became hard to pull air, it was about to be dry.

 

[Paladin]

Another consideration: At depth, your lungs may feel empty but the air still in them will expand as you ascend. This should be kept in mind as well.

 

[JohnQPS122]

During class, in the pool, my wife's instructor came around behind each of us (I was there as a refresher) and shut off our air so we could feel it, and turned it on when we signaled OOA. Loss of air was not immediate, I felt it coming, breathing got slightly harder for several breaths.

Don't let a fear of running out of air (no, it does NOT happen to every diver eventually) stop you from trying scuba. That would be like never driving a car for fear you'll drive it over a cliff and it'll explode in a giant fireball like in the movies.

 

[boulderjohn]

During class, in the pool, my wife's instructor came around behind each of us (I was there as a refresher) and shut off our air so we could feel it, and turned it on when we signaled OOA. Loss of air was not immediate, I felt it coming, breathing got slightly harder for several breaths.

I'm surprised. That is a required drill for PADI, and back when I was an assistant, I had it done to me often. I never felt anything but an instantaneous lack of air.

In theory, that is because of the depth of a pool. With some regulators at depth, you will get that tough-to-breathe feeling before you are OOA, and that is what that drill is supposed to simulate. I have learned as an instructor that I can fake that in the drill by almost shutting off the air until I see the needle bobbing. Perhaps that is what the instructor did.

 

[DevonDiver]

Don't let a fear of running out of air (no, it does NOT happen to every diver eventually) stop you from trying scuba.

If you follow the 'rules' provided on your entry level scuba training (OW course) and subsequent courses, then it is virtually impossible that you could run out of air during a dive.

When divers do run out of air, or have other problems, it is virtually always because they have broken rules, due to complacency, laziness or exceeding their abilities/training/certification.

Basically....

1. Check your air regularly (during the dive...and during pre-dive safety check).
2. Check your buddies air regularly and vice versa (during the dive...and during pre-dive safety check).
3. Strictly maintain an adequate reserve of air.
4. Plan your dives, dive your plan.
5. Maintain appropriate depth/time diving limits.
6. Use properly serviced and functioning equipment.

This is sufficient to keep any diver safe.

With more experience/training, you should aim to refine this by:

7. Establishing an awareness of your air consumption requirements (calculated SAC rates).
8. Including air consumption and gas supply withing your dive plan.
9. Accounting for increased air density/consumption as depth increases.
10. Understanding how physical exertion/panic/stress will effect your air consumption.