Gas duster
From Wikipedia, the free encyclopedia
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 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.
Contents |
[edit] Applications
[edit] Cleaning
A gas duster is usually used to clean or dust delicate items or reach difficult areas. The dusters are particularly useful on ventilation fans and electronic heat sinks, which collect dust readily, and are otherwise very difficult to clean. The gases used do not leave residues on sensitive equipment. However, they can create static unless a specific ESD safe compound is added.
[edit] Cooling
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.
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.
Because of their strong cooling effects gas dusters can be used to fix dents in cars when the metal is first heated then sprayed with the extremely cold liquid.[citation needed]
[edit] Safety
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 such as nitrous oxide. However, the gases actually used are denser than air, and inhaling can lead to paralysis, serious injury, or death. Recently, in the United States and Canada stores have begun to ask for ID to verify if the customer is 18 years or older (some include Fred Meyer, Office Max, Office Depot, Staples, RadioShack, Walgreens, Canadian Tire, Shopko, Target, and Wal-Mart).
Though not extremely flammable in gaseous form, many dusters use a fluorocarbon which can burn under some conditions, and warn of this on the packaging. When inverted to spray liquid, the boiling fluorocarbon aerosol is easily ignitable, producing a very large blast of flame and extremely toxic hydrogen fluoride as a combustion product.
Use of dusters can produce large clouds of dust, which may directly affect the lungs.
[edit] Environmental Impacts
Difluoroethane (HFC-152a), trifluoroethane (HFC-143a), and tetrafluoroethane (HFC-134a) are potent greenhouse gases. According to the Intergovernmental Panel on Climate Change, the global warming potential (GWP) of HFC-152a, HFC-143a, and HFC-134a are 124, 4,470, and 1,430, respectively.[1] This means that 1 can of HFC-143a has the same global warming impact as 4,470 cans of carbon dioxide.
Most brands now claim to be ozone friendly, a separate issue from the global warming concern.
[edit] Alternatives
An air compressor fitted with a small nozzle (as part of a compressor accessory kit) can be used in lieu for cleaning. This offers a fixed equipment cost, at the expense of portability. Care must be taken however, as water vapor may condense in the tank or at the nozzle.
Portable compressed air canisters are available, which can be filled with a bicycle pump. The same caution about water vapor applies.
Electric dust blowers make for a cheap and portable alternative [2]
