Spare air - or not?

[CaveMD]

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.

Depends entirely on the regulator. My Hogs work well below their rated IP, they don't even develop a noticable change in breathing difficulty until I probably have 3 breath's or so left at around 40'( I tested them in jackson blue this last weekend on my stage bottles) You can't even tell the tank is low till the pressure gauge isn't even registering anymore.

 

[Lobzilla]

Depends entirely on the regulator. My Hogs work well below their rated IP, they don't even develop a noticable change in breathing difficulty until I probably have 3 breath's or so left at around 40'( I tested them in jackson blue this last weekend) You can't even tell the tank is low till the pressure gauge isn't even registering anymore.

Three to five breaths from first, clearly noticeable problem to no more gas sounds about right. I depends a little bit on the regulator and the size of the tank. As boulderjohn pointed out, you will get a couple more breaths when you ascend. While this is certainly tight, it is in my observation enough to make a normal ascent IF you act calmly but expediently.

This should be a purely hypothetical scenario as we always plan our gas reserves diligently and conservatively (are we?), frequently monitor our gas supply (are we?), have good team/buddy skills (do we?) and dive with people who have the training and mental composure to be of help in an emergency (do they?).

PS: The questions in parentheses were not directed at CaveMD but at those who want to justify the need for a Spare Air in lieu of more effective risk mitigation.

 

[Vassilis Vlachopoulos]

Will some one volunteer to take some spare air bottles to various depths and see how many breaths they get?

@115ft - 35m Spare Air gave me 9 average breaths.
@ 20ft - 6m I was breathing for a duration of 3 min.

 

[Splitlip]

@115ft - 35m Spare Air gave me 9 average breaths.
@ 20ft - 6m I was breathing for a duration of 3 min.

So..if you were to begin your ascent immediately from 115 ft, presumably there would be more than 9 breaths?

 

[WetBoy101]

Thank you Double V !!

 

[Vassilis Vlachopoulos]

So..if you were to begin your ascent immediately from 115 ft, presumably there would be more than 9 breaths?

That is correct because, in fact, I was able to pull the 9 breaths while slowly descending from 115ft to 130ft.

 

[DaleC]

I don't know if its been mentioned but one way to test the feel of an OOA is to use a functioning J valve. The sensation of running up against the reserve is similar.

 

[DevonDiver]

I don't know if its been mentioned but one way to test the feel of an OOA is to use a functioning J valve. The sensation of running up against the reserve is similar.

That gets me thinking. I still think the concept of the J valve is very sound. Whilst not a replacement for a true system of redundancy (neither is Spare Air), the concept of J Valve + SPG does offer a fair solution for ensuring that the diver can make an emergency ascent if their other procedures fail (gas awareness/buddy system etc).

Spare Air really is the preserve of divers who aren't confident that they could apply core scuba procedures with enough certainty to guarantee their survival. It's an emergency ascent system, for shallow recreational dives, rather than true redundancy for specific demands (overhead, deep dives etc). A J Valve could operate the same way - if set to preserve a small amount of gas, which would otherwise be ignored from dive/gas planning. The diver would conduct dives as normal, using their SPG, but in the event of an emergency ascent - could activate the J Valve to access reserved contingency gas for ascent.

To me, it seems that using a J Valve in that manner would be a less bulky, less expensive option to offer the same (minimal) benefits that Spare Air gives.

 

[GrumpyOldGuy]

Following the above logic, using one the the old Scuba Pro regulators that honked at you when you dropped below a preset reserve would also provide the same type of minimal benefits for those who refuse to monitor their gas or have an SPG failure. You could even use these on rental tanks. Sounds great in theory, the market though pretty much reject the idea over 20 years ago for many of the same reasons many reject SA (false sense of security, too small, teaches reliance on gear rather than procedures, reduces the incentive to plan, etc...)

 

[Hatul]

@115ft - 35m Spare Air gave me 9 average breaths.
@ 20ft - 6m I was breathing for a duration of 3 min.

So on a dive to 40 ft (typical of shore dives here in S Calif) if you come up at constant rate that's an average depth of 20 ft, so you get 3 mins which is more than enough to make a safe ascent, -- you just won't make your full safety stop. Still a lot better than the guy who has to make an apneic ascent.

Adam