The SCR is actually safer (nitrogen wise) than open circuit

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Posted by Chuck Tribolet on March 21, 2005 at 16:29:09:

In Reply to: back in your SCR days posted by northcoast diver on March 21, 2005 at 13:12:08:

The only reason I haven't been diving the SCR is
that it's had a minor leak I've had trouble
tracking down. I've got all the parts now, and
could just replace them, but this engineer wants
wants to find the real problem,

And you clearly don't understand how an SCR
affects dive profiles. Simply put:

A. The mix in the bottle determines MOD because
the mix in the bag CANNOT exceed what's in the

B. The lowest possible mix in the bag determines
how to set the computer (or tables, or whatever)
There are formula's for calculating it, but just
subtracting .07 from the mix in the bottle is a
a easy and conservative approach. So if I have
40 in the bottle, my MOD is 99 feet (1.6 max
PPO2 for 40 mix), and I set the computer to 33.
But if I'm just paddling around with the camera,
what's actually in the bag is about 37 or 38, so I'm
actually being conservative on the nitrogen loading. The mix in the bag would only drop to
33 if I worked really hard for several minutes,
and even then wouldn't be a problem at 33, because
that's what the computer is set for.


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