From reading online on an older forum, related to brewpubs, taverns, etc. The Super Moderator posted this as his bottom line: "Bottom line, don't bother looking for food grade co2. Anyone charging extra for it is simply making a few extra bucks. There are tens of thousands of kegerator owners getting their co2 from industrial welding suppliers and paintball stores for 20+ years. If it were a health issue, the FDA would have been all over it long ago. "
Think about it and all the regulations we have in America. It's easier for Airgas, and other, to simply make it as pure as possible for the 98% of their customer base, and if their main customers are welders, and some restaurant, wineries (we use it constantly) or breweries, they just make it 99.99+% and don't have to worry about special tanks.
I also looked on Airgas website and saw the above. Even their "REFRIGERANT" grade is 99.99% pure. Don't Worry, Have A Home Brew.