Sometimes mixing techniques isn’t a good idea

What I mean in my Title is mixing processes
of two different types of diving sometimes
do not blend well together. During my Open
Water training and all training in between
OW and Instructor, I have been taught to
open the valve of the tank all the way, then
approx. 1/4 turn back.

During my Close Circuit Rebreather, CCR
rebreather training, I was taught to open the valves, just until they are open and stop.
The reason for this is in an emergency, if for example the Oxygen begins to freeflow
into the loop, you must address ‘the problem’ and get back on the loop. One way to
stop O2 from free flowing is to turn off the O2.

If you are at 180 feet, you can see the danger of your O2’s PPO spiking UP.
Anyway, if the O2 valve was turned ALL the way Open and 1/4 turn back, the
amount of time it would take to turn off the O2 (when compared to a valve opened
enough to allow O2 out) would be greater than.

The Scenario:
Some friends and I decide to execute a cavern dive.
I figured I would shoot some video while they do what ever it is they came to do.
I turn on my Open Circuit Cylinder by cranking the valve until my hoses charged
and I stopped opening the valve. I test the regulator and all seems fine. I instruct
the folks to give me 5 minutes in the hole before coming in. So enter the shaft to
about 20 feet, then into the cavern I go. I went in to setup myself, my camera and
the lighting. During this I was bumping up against the ceiling
(Still trying to get my bouyancy too), I went to take a breath and NO AIR. Hard as
a rock, like sucking on your wrist. Nothing. So I litterally thought to myself, “Huh?”
and I tried for another breath… Nothing. “What the … Hmm. OK, what do I do?”
Now all these thoughts are occuring in miliseconds. I was not scared, afraid,
anything like that. I remained calm and said “Hey, theres the exit, there’s light” and
I swam for the exit. As I reached the floor below the exit 20 feet above me I look up
and I see the other divers, still on the surface, looking down at me. I give the out of
air sign and head up.

I remember saying to myself, “Exhale.. Exhale..” and the air comes out naturally
(I believe my rebreather training helped my experience this expansion of air –
I’ll explain that in a different post). When I reached the surface, I gobbled up a
lung full of air and orally inflated my BCD.
Discovering my air valve was OFF, we turned it on and I spend the rest of the
dive taking video of the exploration. 

Oh yes, with the valve fully opened and 1/4 turn back

The Lesson:
Mixing techniques from two different types of diving may not blend well together.
In this case, the use of a Closed Circuit Rebreathing System vs. the Open System
of cracking open the valve vs. fully opening the valve. 

Remember, Nothing substitutes for proper training. See your local instructor and
dive shop for professional experience and guidance.

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