Aerosol cans contain both a payload and a propellant. The payload is the substance that the can distributes, such as insecticide, paint, or olive oil. The propellant is a pressurized gas that allows the payload into the air. In previous decades, the propellant was commonly chlorofluorocarbons (CFCs) which have been since banned due the damage they do to the ozone layer. They have been usually replaced by propane, butane, or isobutane, but some contain carbon dioxide, or nitrogen gas.
Empty aerosol cans usually can be safely recycled, but discarded non-empty aerosol cans should be treated as hazardous waste. This is because propellants are dangerous, often flammable, and under pressure. (In addition to their uses as aerosol propellants, propane, butane, and isobutane are all highly flammable and used as fuels.) Damaged or overheated aerosol cans can explode, causing a danger to life and property.
The other major hazard caused by aerosols is the product within the can. Insecticides, paint, and solvents may be dangerous to life and limb, and workers should take the necessary precautions associated with the product as well.