"Danny D." wrote:

I made a home-built C02 carbonation machine using a 20 pound carbon
dioxide tank and some pneumatic hoses & couplings, which, along with a
tire valve inserted into a soda-bottle cap, allows me to easily carbonate
water at home, three liters at a time (as shown in this photo below):
http://www1.picturepush.com/photo/a/...g/12065184.jpg

Do you have a certificate of analysis on the CO2?
I worked at a company that hadn't paid much attention
to safety until we had an accident. We then searched
every area for possible hazards, and found dozens of
them. One was the CO2 gas for our laser. I was
thinking that in the course of operation, some of
the CO2 might be converted to carbon monoxide.
It turned out the CO2 as purchased contained a
significant amount of CO. If the valve on the tank
failed, the room where it was used could quickly
fill up with a hazardous level.

I don't know what grades of CO2 are offered, but
I doubt if the grade we were buying would be safe
for consumer use.