The S210-25 Smoke Emitter Provides an Inexpensive Method of Generating Swirling Smoke. This is a Great Product for Testing of all High, Medium, and Low Pressure Ductwork Systems and also for Air Balancing. The Smoke Emitted does not Contain Oil nor Zinc and will not leave any Residue. It is Non-Toxic and has the same Density as Air, so that is is Possible to Observe True Air Movements without the Complicating Factor of having to Allow for the Natural Rise or Fall of the Smoke