A quick, easy way to test the safety of fume hood exhaust before use. Just a squeeze or two from the plastic bottle dispenses a cloud of ultra-fine, lightweight silica powder, which remains suspended long enough to visually check whether or not fume hood exhaust is functioning properly. It is also useful for detecting drafts, gas leaks, and air currents in rooms, ducts, and exhaust systems. The amorphous silica powder is inert, non-toxic, and non-flammable. 1.5 gm bottle.