My sandblasting hood kept fogging up so I had some 1/4" plastic tubing that I hooked a quick connect to on one end. The other end I duct taped to the top of the plastic hard hat and fed the end through a hole I drilled in the front brim, letting it hang down about an inch. When I'm blasting I turn a small regulator up to about 5 psi. It works great keeping the lens from fogging and the positive pressure inside the hood really cuts down on the sand coming inside the hood.
Now if I could only figure out why my photos keep rotating when I post them.