Gas 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 gases that are much easier to compress into liquids, such as difluoroethane, trifluoroethane, or tetrafluoroethane (the main components of air, which are oxygen or nitrogen, are in fact very rarely used). Hydrocarbons, like butane, were often used in the past, but their flammability forced manufacturers to use fluorocarbons.
Applications
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 themselves do not leave residues on sensitive equipment, however the bitterant added to prevent abuse will leave a residue, making gas dusters an inappropriate choice for cleaning anything users will come into contact with such as keyboards. They can create static unless a specific ESD-safe compound is added.
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; thus, 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. Freeze spray is intended for use as a testing and debugging aid to locate temperature-dependent issues. Because it is non-conductive, it can be used on running electronics.
Alternative to 134a
Many gas dusters contain HFC-134a (trifluoroethane), which is widely used as a propellant and refrigerant. HFC-134a sold for those purposes is often sold at a much higher unit price, which has led to the practice of using gas dusters as a less expensive source of HFCs for those purposes. Adapters have been built for such purposes, though in most cases, use of such adapters will void the warranty on the equipment they are used with. One example of this practice is the case of airsoft gas guns, which use HFC-134a as a source of compressed gas. Several vendors sell "duster adapters" for use with airsoft guns, though it is necessary to add a lubricant when using gas dusters to power airsoft guns.
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 that the customer is 18 years or older (some include Fred Meyer, Office Max, Office Depot, Best Buy, Staples, RadioShack, Walgreens, Canadian Tire, Shopko, Target, Maplin Electronics, CVS, and Wal-Mart)[citation needed].
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 byproducts such as hydrogen fluoride and carbonyl fluoride as a combustion product.
Fluorocarbons, although they replaced the older set of more flammable hydrocarbons, can still combust relatively easily, e.g., by holding a source of fire (such as a match or lighter) to the escaping fluid. They do, however, have a lower chance of exploding in a closed container by means of spontaneous combustion (which is what caused the general switch away from hydrocarbons).
Since gas dusters are often contained in pressure vessels, they are fairly explosively volatile.
Use of dusters can produce large clouds of dust, which may directly affect the lungs.
Environmental Impacts
Difluoroethane (HFC-152a), trifluoroethane (HFC-143a), and completely non-flammable 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, 4470, and 1430, respectively.[1] GWP refers to global warming effect in comparison to CO2 for unit mass. 1kg of HFC-152a is equivalent to 124kg of CO2[2]
Gas dusters sold in many countries are ozone safe as they use zero-ODP gases; however, this is a separate issue from the global warming concern.
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 that can be refilled with a bicycle pump are also an option. The same caution about water vapor applies.
Electric dust blowers offer another alternative.
References
- ^ http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter2.pdf
- ^ http://books.google.com/books?id=U9fMCaiNWkcC&pg=PA477&lpg=PA477&dq=12400+ozone&source=bl&ots=n7TYMwBz8r&sig=HbA9XstcNWLutnSIh7LD_mMJexY&hl=en&ei=LtkES6SzDoKutQOQk9jrDA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CAgQ6AEwAA#v=onepage&q=12400%20ozone&f=false