WD-40 uses CO₂ as a propellant, which is a non-flammable propellant, safer for aerosols. The CO₂ also allows 97% of the liquid out, so you get the most out of your WD-40 cans as opposed to hydrocarbon-based products. Be sure to point the spray nozzle toward the dot on the top of the can to ensure that the can fully empties.