Originally Posted by Bettatail
Helium test is for the highly toxic gas service equipment, this standard of leak test is to prevent leak, normally down to molecule level. co2 is not highly toxic gas, and I can't measure how many co2 molecule escape from the system.
the safety issue here is the co2 concentration in enclose environment. the proper operating procedure is pretty much the same as welding shops: "keep the windows open", and co2 concentration can not reach to the level that cause trouble.
I guess I'm confused then because in your first post you said that co2 levels above 5% concentration can be toxic. I have read more than a few threads on this forum where people were having co2 leaks from there system and I don't see how this small amount could pose a problem unless you have your tank setup in a closet that is sealed up with duct tape.