There are different options for duster propellant:
HFC-134a: Nonflammable, most common for industrial applications when spraying energized circuits because of the risk of a spark lighting a flammable material. It is under close scrutiny because it has a Global Warming Potential (GWP) of 1400, so 1400 times the impact of CO2.
HFC-152a: Most commonly available duster in consumer retail because it is less expensive than HFC-134a. It is flammable, and will ignite when concentrated (i.e. in liquid form) and exposed to a spark or flame.
HFO-1234ze: This is a newer, nonflammable material introduced in the last 10-years as a very low GWP alternative (<1) to HFC-134a. It is non-flammable and is almost indistinguishable from HFC-134a when sprayed, but unfortunately at a much higher price.