Duster

Gas duster, also known as canned air, is a product used to clean electronic equipment and other sensitive devices that cannot be cleaned using water. The can comes with a straw to direct the forceful wind that it can produce. The gases inside the can have been compressed to the point that they have become liquid, and they evaporate before leaving the can since the valve draws from the top (unlike most aerosol cans which have a straw that draws from the bottom of the can). Despite the name "canned air," the cans actually contain inert gases that are much easier to compress into liquids, such as difluoroethane, trifluoroethane, or tetrafluoroethane. Hydrocarbons, like butane, were often used in the past, but their flammability forced manufacturers to use fluorocarbons.

A gas duster is usually used to clean or dust delicate or sensitive items such as electronic components and computer equipment, as the gases used do not leave residues on sensitive equipment. However, they can create static unless a specific ESD safe compound is added. The spray can often reach places where other cleaning implements cannot. When the can is held upright and activated, gas flows out through the nozzle. The pressure inside the can therefore drops, and is no longer sufficient to keep the contents as a liquid; so some of the liquid boils, until the equilibrium pressure is re-established. The vaporization of a liquid is endothermic, so heat is absorbed, and the can becomes cold.

Since gas dusters are one of the many inhalants that can be easily abused, many manufacturers have added a bittering agent to deter people from inhaling the product. Because of the generic name "canned air", some people mistakenly believe that the can only contains normal air or contains a less harmful substance known as nitrous oxide. However, the gas is denser than air. Inhaling the gas can cause death, paralysis, or serious injury. Recently, in the United States and Canada stores have begun to ask for ID to verify if the customer is 18 years or older.

If the can is held upside down, then its contents are expelled as a liquid. This liquid evaporates very quickly at standard temperature and pressure, chilling anything in contact with it. This process can produce very cold temperatures, easily sufficient to cause frostbite. Similar cans with dip tubes are marketed as "freeze spray," and will expel liquid when held right side up. In most cases this application is no longer practical due to the bittering agent. During normal use, newer formulations of duster leave a bitter taste in the gas itself (noticeable, for instance, if the gas is inhaled through the mouth), and a bitter residue on surfaces that are sprayed, which can persist for days.