Treat every dive like a tech dive

[boulderjohn]

My only experience with being OOA was in OW class where the instructor shuts down your tank valve. Is this truly a realistic simulation of being OOA or would it be more abrupt? For example in the OOA simulation you could feel it was becoming harder to get air when you took that next breath, but you still got air. In a true OOA would it be more abrupt like you take a breath, exhale and then on your next breath you get nothing. If that is the case that could drastically change how the OOA scenario goes down. Since you exhaled and now can't get air I could see a diver becoming panicked and going for whatever they see. Buddy distance could be an issue too because the delayed time and CO2 accumulation would trigger that desperate urge to breath and again go for whatever reg they see first.

I am surprised by what you describe; the situation is normally just the opposite.

In theory, a tank running out of air should be harder to breathe as it nears the end. As I understand things, back when they first started to do this exercise, some decades ago and before my time, shutting off your air in the pool did roughly recreate that actual feeling of running out of air on a dive. When I was both a DM and an assistant instructor, though, I was the one who demoed this drill many times, and whenever I did it, the air shut off suddenly, with no warning whatsoever. That is because modern regulators are way better than the ones from decades ago. Now that I am an instructor doing this drill, I have sometimes tried to recreate a harder to breathe situation by leaving the valve just a hair open. Perhaps your instructor did that for you.

Some people will also say that this sudden loss of air is what happens when you actually run OOA in the deeper water, again because of higher quality regulators, but that is not my experience. In technical diving, I have breathed stage bottles (tanks used to supply additional breathing gas on very long dives) down very near to the end. I have done so using pretty good quality regulators, and I have always felt it getting harder and harder to get air as I neared the end of the tank. (I never actually finished one off.)

What I have finished off on several occasions is decompression bottles, but on the surface. I sometimes have to cross a mountain pass after diving, and I like to play it safe by finishing off an oxygen decompression bottle before I do. I can definitely feel it getting harder to breathe as I get to the last breaths.

 

[CuzzA]

There's a lot to take in during OW training. Drill after new drill. For an instructor I'm sure it's second nature as you're doing it all the time. So you'll have to forgive me if my account of the actual drill is a little off.

Your post jogged my memory a little more and I now recall the drill went something like this.

Instructor, "I'm going to begin shutting down your air supply by closing your valve. When you notice it is becoming harder to breath I want you to signal to me the out of air throat slash and I will open it back up. This will simulate how it will feel as you deplete your air supply." Sound about right?

So, that drill is a "true" simulation. I guess when I think about divers being out of air I envision them being in a panic, which may be true for some, but since it's not abrupt there's really no reason to panic. Stay calm, you'll likely have plenty of air in your lungs to secure your buddy's alternate air source assuming they are within a reasonable distance.

Obviously, barring an equipment failure, I would never allow myself to become OOA, but I do like to know what to expect, especially since diving is typically a social sport and it may be someone else you're dealing with.

 

[boulderjohn]

Instructor, "I'm going to begin shutting down your air supply by closing your valve. When you notice it is becoming harder to breath I want you to signal to me the out of air throat slash and I will open it back up. This will simulate how it will feel as you deplete your air supply." Sound about right?

Yes. It sounds as if he did not just shut your air off but rather closed the valve until it was barely open. It takes a little practice to do this well.

I guess when I think about divers being out of air I envision them being in a panic, which may be true for some, but since it's not abrupt there's really no reason to panic. Stay calm, you'll likely have plenty of air in your lungs to secure your buddy's alternate air source assuming they are within a reasonable distance.

I tell my students that if never holding your breath is the first rule of scuba, the second is never panicking. You have been taught everything you need to know to get out of any reasonably conceivable OW emergency, assuming you keep your head and follow your training. According to a joint DAN/PADI study, the most common non-medical cause of scuba fatality is an embolism caused by a panicked, breath-holding rush to the surface following an OOA incident. Respond to the incident correctly, and there will be no problem.

But let's say your air does just suddenly shut off, which can happen in shallower depths (which is why it happens in the pool). So what? Stop breathing right now and see how long it takes before things get hairy. You have enough oxygen in your system to keep you going for a minute to a minute and a half. You still have time to get to a reasonably close buddy, and if your buddy is not close, you can still do the CESA as you were taught to do.

When you did the CESA, you started with full lungs, no doubt. You were taught that with the air in your lungs expanding, you can get all the way to the surface exhaling, and you can. But what if your lungs are not full? What if you realized you were OOA as you started to inhale? Well, no one exhales completely--your lungs are probably half full, and that should be enough.

Even if you do exhale it all out on way up, you should still be able to make it to the surface with the oxygen in your system. If you try to inhale as you ascend, one of two things should happen. One is that you won't get anything, which is way better than inhaling water in the event that you had thrown your regulator away. The other thing that could happen is you will get a breath of air. Maybe more. That is because your tank was not empty--it just thought it was. Your regulator has to be able to deliver air to your lungs at a greater pressure than the pressure of the water around you, which is why it gets harder to breathe at the end. As you ascend and the water pressure around you lessens, you should be able to get air from your tank, again assuming you still have that regulator in your mouth.

Just keep your head, and everything will be fine.

 

[huwporter]

Some people will also say that this sudden loss of air is what happens when you actually run OOA in the deeper water, again because of higher quality regulators

I have emptied a stage tank at ~45m (...with 20 BAR or so remaining on the gauge...) and it went from breathing normally to nothing in the space of half an inhale. (For clarity, in this instance it wasn't a big deal since I had a full twinset on my back, a buddy looking at me as I'd just signalled him I was about to switch and my hand already reaching for the clip on my backgas long hose, but still a slightly disconcerting feeling.) Bit of a digression from the training discussion, but the normal > nothing transition can happen.

Cheers,
Huw

 

[boulderjohn]

I have emptied a stage tank at ~45m (...with 20 BAR or so remaining on the gauge...) and it went from breathing normally to nothing in the space of half an inhale. (For clarity, in this instance it wasn't a big deal since I had a full twinset on my back, a buddy looking at me as I'd just signalled him I was about to switch and my hand already reaching for the clip on my backgas long hose, but still a slightly disconcerting feeling.) Bit of a digression from the training discussion, but the normal > nothing transition can happen.

Others have said the same thing. That is why I said what has happened is in my experience. It would be interesting to do some experimentation.

John

 

[uncfnp]

My only experience with being OOA was in OW class where the instructor shuts down your tank valve. Is this truly a realistic simulation of being OOA or would it be more abrupt? For example in the OOA simulation you could feel it was becoming harder to get air when you took that next breath, but you still got air. In a true OOA would it be more abrupt like you take a breath, exhale and then on your next breath you get nothing. If that is the case that could drastically change how the OOA scenario goes down. Since you exhaled and now can't get air I could see a diver becoming panicked and going for whatever they see. Buddy distance could be an issue too because the delayed time and CO2 accumulation would trigger that desperate urge to breath and again go for whatever reg they see first.

CuzzA. There was a recent thread where this was discussed in some detail. If I can find it I will post a link. Basically it was just as you see here. Some can tell a difference, like boulderjohn and myself. Others can not.

Shortly after, someone posted this video. If you haven't seen it you might find it interesting...

https://www.youtube.com/watch?v=XujePQIafRM

 

[CuzzA]

Yes, I've seen that video a few times. In fact I think I've seen just about every scuba accident video on YouTube. Lol. That has been part of my research on scuba diving. I want to learn from others mistakes.

Clearly there were many mistakes on that dive and the most glaring one is the unconscionable failure to monitor your gas.

 

[dumpsterDiver]

Yes. It sounds as if he did not just shut your air off but rather closed the valve until it was barely open. It takes a little practice to do this well.

I tell my students that if never holding your breath is the first rule of scuba, the second is never panicking. You have been taught everything you need to know to get out of any reasonably conceivable OW emergency, assuming you keep your head and follow your training. According to a joint DAN/PADI study, the most common non-medical cause of scuba fatality is an embolism caused by a panicked, breath-holding rush to the surface following an OOA incident. Respond to the incident correctly, and there will be no problem.

But let's say your air does just suddenly shut off, which can happen in shallower depths (which is why it happens in the pool). So what? Stop breathing right now and see how long it takes before things get hairy. You have enough oxygen in your system to keep you going for a minute to a minute and a half. You still have time to get to a reasonably close buddy, and if your buddy is not close, you can still do the CESA as you were taught to do.

When you did the CESA, you started with full lungs, no doubt. You were taught that with the air in your lungs expanding, you can get all the way to the surface exhaling, and you can. But what if your lungs are not full? What if you realized you were OOA as you started to inhale? Well, no one exhales completely--your lungs are probably half full, and that should be enough.

Even if you do exhale it all out on way up, you should still be able to make it to the surface with the oxygen in your system. If you try to inhale as you ascend, one of two things should happen. One is that you won't get anything, which is way better than inhaling water in the event that you had thrown your regulator away. The other thing that could happen is you will get a breath of air. Maybe more. That is because your tank was not empty--it just thought it was. Your regulator has to be able to deliver air to your lungs at a greater pressure than the pressure of the water around you, which is why it gets harder to breathe at the end. As you ascend and the water pressure around you lessens, you should be able to get air from your tank, again assuming you still have that regulator in your mouth.

Just keep your head, and everything will be fine.

"You have a minute or 90 seconds with nothing and you will be fine".

I know this is the party line, but it is not necessarily true at all. If you are scared or working hard and you exhale and get nothing, the carbon dioxide is going to be burning your lungs tremendously within just 20 seconds.. in 40 seconds you are going to be feeling like you are going to die (and you may be close to it). You will NOT be fine.

Don't believe me, try it for yourself. Find a flight of stairs, walk up the first floor at a normal, maybe slightly brisk pace, breath normally. THEN, exhale at the top (most of all of your lung volume) and then just keep walking to the third floor at a good pace.

It is only going to take 20 seconds or less and the first flight of stairs should not have tired you out that much...probably no more than swimming along the bottom- toward the end of the dive.

Maybe I am horribly out of shape, but I know I will not be fine after 60 seconds of nothing (one flight of stairs kicks my butt with no air). I encourage people to experiment and see how it feels for themselves.

It is COMPLETELY different than preparing for it and taking several deep inhalations and holding your lungs full.

 

[NAM001]

I have done the exhale thing for free ascent. You don't have to ho ho ho as hard as yo can. the minimal exhalation is enough o insure the airway is open. expansion will do the rest at the rate that is needed. there will probably be little exhaling at the start but will increase on its own as depth decreases. I have also done the exhale into the bcd/wing when the wing is empty. their are pros and cons to this.

 

[Bigd2722]

Depends on the teammates.

Anyone familiar with Team Diving and who has spent the time and effort to develop qualified team mates knows it's counter productive to ignore team resources.

Tobin

Not suggesting that one should ignore any resource available. To spout the kool aid, solo trained divers make better dive buddies