Spare air - or not?

[Scott L]

Has anyone yet mentioned that the spare air was developed with one use in mind, evacuating from a downed helicopter in water from obviously shallow depths. It was re-marketed to the scuba industry with some success with the aid of uneducated instructors and greedy LDS owners...

 

[doctormike]

Has anyone yet mentioned that the spare air was developed with one use in mind, evacuating from a downed helicopter in water from obviously shallow depths.

Yup. Post #39.

 

[Scott L]

Yup. Post #39.

I guessing Thal. Thanks!

 

[Lobzilla]

It is called HEED (helicopter emergency egress device) in aviation. It has been a couple of year since I did egress training in the "dunker" and the procedures may have changed but we were required to do the majority of egress exercises without using the HEED. If you cannot control panic reactions and cannot methodically work yourself out of the mess, the HEED is not going to save you either. I have the same opinion about the Spare Air.

Edit: I remember one exercise where we were supposed to get out of the dunker with blacked-out goggles and at the opening a safety diver would bear-hug us (to simulate entanglement) while we had to deploy the HEED. The point there was not to learn breathing of the stupid thing but to coolly deploy it when everything else failed.

 

[boulderjohn]

What does it feel like to actually run out of air?

Not sure what agency you did your OW with, but the one I work with has you experience this in the confined water dives. The instructor actually shuts off your gas and you breath it down until you feel the pull and the nothing.

As Andy said, that exercise does not tell you what it is really like. In the shallow water of the pool, it is instantaneous. At depth you have much more of a warning as it becomes harder and harder to pull. The reason is that the first stage regulator has to deliver air at a pressure higher than your ambient pressure. As you start to drop below that, you have to work harder and harder to draw it in. My experience is that you get more of a warning the deeper you are, and the deeper you are the more gas is actually still in your tank when you think you are OOA.

I have actually been at the OOA stage more than a few times, but only at depths beyond recreational levels. Here is what I have experienced.

When I am using a stage bottle as my first breathing source at depth, I watch the gauge on the stage bottle I am breathing, and when it is getting near the end, I get my primary regulator from my doubles ready to make the switch. I switch afterI feel that first tough pull. I have sometimes been pretty casual about it and gone several pulls before actually making the switch.

After a string of local OOG accidents at the beginning of this season I was curious how OOG really manifests itself. So, I closed the isolator valve on my AL80 doubles and breathed of the right tank like every recreational diver would breathe from a single AL80. I went down to 60' and swam around until I felt the breathing resistance increase. I dive Scubapro Mk17 first stages with G250V seconds, which are both balanced and give you less warning about low tank pressure than unbalanced regulators. When I felt the breathing resistance increase, I immediately started my ascent to 30' and stopped at 30' for 1 minute, slowly milking gas out of the regulator. Then I went up to 20', spent another minute there, then to 10' for another minute and finally, slowly to the surface. Since I deliberately took my time ascending I then needed to inflate the BCD/wing orally (which I survived too).

The results do not surprise me at all, and they show once again why feeling that increased resistance in an OOG situation is not a reason to panic.

In the OW class divers are taught the rules for the order of choice in an OOG emergency. Remember what the first choice is? It's a normal ascent. When this was explained to me, the reasoning was exactly what Lobzilla experienced. If you begin an ascent when you feel that first tug, you should be able to reach the surface with a normal breathing ascent. As I said before, the tank has to have more pressure in it than your ambient pressure for the regulator o function, and as you ascend to shallower depths more air will be available to you.

 

[BDSC]

And PLEASE do not start another Spare Air thread.

Sorry, but as long as there is a ScubaBoard, there will be more Spare Air threads. It's as certain as death and taxes!

 

[Max Speed]

Always use one for shallow dives. Use a pony for deeper. Practice with it frequently. Makes it much easier and stress free to get to a buddy or get to the surface.

I've been without air due to simultaneous equipment and buddy failure. Don't want to be there again.

 

[doctormike]

Sorry, but as long as there is a ScubaBoard, there will be more Spare Air threads. It's as certain as death and taxes!

Let's start a thread about whether people who use Spare Air are more likely to prefer a jacket BC or a BP/W...

RJP said it best...

 

[GrumpyOldGuy]

My conclusion is that panic is the real killer, not the OOG situation. (I use the more generic term "Out Of Gas" instead of "Out of Air")

After a string of local OOG accidents at the beginning of this season I was curious how OOG really manifests itself. So, I closed the isolator valve on my AL80 doubles and breathed of the right tank like every recreational diver would breathe from a single AL80. I went down to 60' and swam around until I felt the breathing resistance increase. I dive Scubapro Mk17 first stages with G250V seconds, which are both balanced and give you less warning about low tank pressure than unbalanced regulators. When I felt the breathing resistance increase, I immediately started my ascent to 30' and stopped at 30' for 1 minute, slowly milking gas out of the regulator. Then I went up to 20', spent another minute there, then to 10' for another minute and finally, slowly to the surface. Since I deliberately took my time ascending I then needed to inflate the BCD/wing orally (which I survived too).

Please do not try this at home. Please understand that I had another gas source as a back up during this experiment (isolated left tank with its own regulator set). Do not use my story as a reason to skip proper gas planning or as an excuse for not monitoring your gas consumption during every dive. Running out of gas for real is stupid.

But if you ever run out of gas (unnecessary) without a buddy in sight (imprudent) do not panic. Get your rear end off the bottom FAST, spend as much time as possible in the shallows (above 50% of max depth) where you can suck more gas out of an "empty" tank, and don't hold your breath. Also, practice oral inflation of your BCD with surface air.

And PLEASE do not start another Spare Air thread.

First, congratulations on taking the time to do this experiment.

Second, realize that since you knew you had gas with the twist of the valve, was carefully monitoring for breathing resistance and you planned the experiment, you were able to keep you air consumption low and controlled. In a real OOG situation where a diver finds his buddy out of reach and has no warning, most divers are going to have some level in increased gas consumption even if they are able to mentally keep themselves out of a full blown panic. So their results might need something closer to a CESA.

Lastly, not all shallow dives allow direct ascents. Thick kelp is a big issue and you need to be able to swim out from under it as ascending into it with full gear is asking for entanglement. So you really need to consider your environment.

 

[Lobzilla]

Always use one for shallow dives. Use a pony for deeper. Practice with it frequently. Makes it much easier and stress free to get to a buddy or get to the surface.

I am a big fan of redundant gas supplies but they have to have sufficient capacity to increase safety. Otherwise they just add clutter and more failure points. Double tanks - yes, stage bottles - yes, "pony" - only if it is big enough, Spare Air - utterly pointless.

Getting to your buddy should be a matter of flashing your light or stretching out your arm - in the worst case.
Beyond that you are diving solo and need a completely different attitude about training and equipment.

I've been without air due to simultaneous equipment and buddy failure. Don't want to be there again.

How about addressing the root causes of getting into this pickle?