A lot of dry ice is simply industrial grade dry ice. There's all sorts of metal filings and other debris in it.
And it can't come into contact with copper. Carbonic Acid (e.g. Seltzer) mixed with copper results in a dangerous poison. Soda fountains always use plastic or Stainless Steel fittings downstream from the carbonator.
Not sure what an enclose space has to do with it. 20 lbs of dry ice in a closet might be dangerous, but a block of it in your living room is negligible....