If the inflation bottle is mounted inverted along the edge of the backplate, it's pretty easy to reach the valve to shut it off in the event the first stage freezes open or the inflator sticks. In the case of a frozen first stage, it will thaw in a few minutes and if the inflator stays stuck you can add air to the suit by manipulating the tank valve as needed.
You can also set the intermediate pressure of this first stage much lower than the 120 to 145 psi that your breathing regulators will be running at. This slows the flow rate which reduces problems in the event something sticks (first stage or inflator valve) and reduces the potential for either of the above problems to occur.
As for the air vs argon thing there are strong supporters on both sides of the issue. I used to be an Argon believer but my experience and a double blind study has not supported any real operational advantage with Argon. It is theoretically about 1/3 less efficient in conducting heat than air, but to get full benefit requires fully purging the air out of the suit and that takes a couple of dives or a few full inflation and dumps (which still will not get the air out of the insulating fibers as efficiently as diving the suit). So at best if you are using argon you probably want really comfortable seals and a pee valve as well so you can just leave the suit on all day long to derive maximum benefit.
Both air or argon however will keep you much warmer than helium, so a separate inflation tank is par for the course for cold water tri-mix divers.
You can also set the intermediate pressure of this first stage much lower than the 120 to 145 psi that your breathing regulators will be running at. This slows the flow rate which reduces problems in the event something sticks (first stage or inflator valve) and reduces the potential for either of the above problems to occur.
As for the air vs argon thing there are strong supporters on both sides of the issue. I used to be an Argon believer but my experience and a double blind study has not supported any real operational advantage with Argon. It is theoretically about 1/3 less efficient in conducting heat than air, but to get full benefit requires fully purging the air out of the suit and that takes a couple of dives or a few full inflation and dumps (which still will not get the air out of the insulating fibers as efficiently as diving the suit). So at best if you are using argon you probably want really comfortable seals and a pee valve as well so you can just leave the suit on all day long to derive maximum benefit.
Both air or argon however will keep you much warmer than helium, so a separate inflation tank is par for the course for cold water tri-mix divers.
