A gas duster, also known as canned air or compressed air, is a product used for cleaning or dusting electronic equipment and other sensitive devices that cannot be cleaned using water. This type of product is most often packaged as a can that, when a trigger is pressed, blasts a stream of compressed gas through a nozzle at the top. Despite the names "canned air" or "compressed air", the cans do not actually contain air (i.e. do not contain O2 or N2 gases) but rather contain other gases that are compressible into liquids. True liquid air is not practical, as it cannot be stored in metal spray cans due to extreme pressure and temperature requirements. Common duster gases include hydrocarbon alkanes, like butane, propane, and isobutane, and fluorocarbons like 1,1-difluoroethane, 1,1,1-trifluoroethane, or 1,1,1,2-tetrafluoroethane which are used because of their lower flammability. When inhaled, gas duster fumes may produce psychoactive effects and may be harmful to health, sometimes even causing death. History The first patent for a unitary, hand-held compressed air dusting tool was filed in 1930 by E C Brown Co, listing Tappan Dewitt as the product's sole inventor. The patent application describes the product as a Single-unit, i.e. unitary, hand-held apparatus comprising a container and a discharge nozzle attached thereto, in which flow of liquid or other fluent material is produced by the muscular energy of the operator at the moment of use or by an equivalent manipulator independent from the apparatus the spray being effected by a gas or vapour flow from a source where the gas or vapour is not in contact with the liquid or other fluent material to be sprayed, e.g. from a compressible bulb, an air pump or an enclosure surrounding the container designed for spraying particulate material. Uses Canned air can be used for cleaning dust off surfaces such as keyboards, as well as sensitive electronics in which moisture is not desired. When using canned air, it is recommended to not hold the can upside down, as this can result in spraying liquid on to the surface. The liquid, when released from the can, boils at a very low temperature, rapidly cooling any surface it touches. This can cause mild to moderate frostbite on contact with skin, especially if the can is held upside down. Also, the can gets very cold during extended use; holding the can itself can result in cold burns.