I googled it. Tetrachloroethylene is the one to watch out for, if it's exposed to argon and the heat from welding it forms phosgene gas which apparently was a chemical weapon used in WWI. 4ppm is enough to fuck you up. Lucky for me, I'm a cheapass who hasn't run out of the 10# roll of flux core wire I bought with my welder years ago. So it sounds then like non-chlorinated would be OK, or maybe just makes you grown another arm instead of dying or something. Apparently this was also published in an AI magazine back in 2009.