I have been using a CO2 tank for airbrushing since college with a set
of gauges that were orignially used for draining beer kegs. The tank
pressure gage gives you an idea of when the tank is about to run out.
The line pressure gauge sets the pressure delivered to the airbrush by
turning the screw on the diaphragm. Experience (from college) shows
that when the tank gauge starts to get close to 500 psi, its time to
get it refilled (tank pressure begins to rapidly decline). I own my
tank and get it hydrostatically tested every five years as required
and it cost about $15. Refills are about the same cost and the tank
lasts each time about four or five years. I use a badger in line
moisture filter. The fittings are pretty easy to find in brass.

I ran the numbers on what it would take to create a hazardous level of
CO2 in a room. This hazard is often seen when CO2 is used as a fire
suppression agent. Taking the low end lethal concentration of 100,000
ppm as a starting point, one would have to rapidly discharge the 20
pounds in a full cylinder into a room about 10 by 20 to create a
lethal environment. (my office right now has a concentration of about
650ppm CO2 which shows good fresh air input, and ASHRAE recommends
levels be below 1200 ppm) This would assume that fresh air is not
being introduced, as in a sealed room. I think someone else pointed
out another major hazard with any compressed gas cylinder and that is
knocking it over and cracking off the valve leading to a rapid
discharge in a rocket like manner. Even if you don't knock the valve
off, a falling cylinder can hurt if it lands on your foot, so keep an
compressed cylinder securely fastened in place.

Regards,
Bruce D. Griffin
Summerfield, NC

--- In STMFC@..., "Michael Mang" <mnmang@...> wrote:

CO2 is a great propellant- just remember that leaks can create a

potentially

hazardous situation in a confined space. You can't breathe for very

long in

a carbon dioxide atmosphere, and you may not even know you are in

one until

it's too late.

Michael "Not wanting to sound like a zealot promoting safety" Mang



I don't wish to sound like a zealot promoting CO2 tanks, but I do
wish to add one comment. Compressed air is still air, it is not a

liquid.

CO2 however is in a liquid state in the bottle, and thus has a very

large

amount of CO2 gas to give off as it is drawn down. A CO2 bottle will

supply

much more air volume than simple compressed air. I haven't carved

notches on

my tank to count the number of uses, but Charles Given's account of more
than 50 paint jobs per bottle fill seems reasonable to me.
-Andy Carlson
Ojai CA