Gas duster

A gas duster can

Gas duster, also mistakenly known as canned air or compressed air, is a product used for cleaning electronic equipment and other sensitive devices that cannot be cleaned using water. Despite the name "canned air," the cans actually contain gases that are much easier to compress into liquids, such as 1,1-difluoroethane, 1,1,1-trifluoroethane, or 1,1,1,2-tetrafluoroethane. Hydrocarbons, like butane, were often used in the past, but their flammable nature forced manufacturers to use fluorocarbons. Referring to the contents as "air", compressed or otherwise, could be dangerously, even fatally misleading, if someone regards the contents as being safe to breathe in concentrated form. Such terms should not be used.

Applications

Cleaning

A gas duster is usually used to clean or dust delicate items or to reach difficult areas. Gas dusters are particularly useful for 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 leaves a residue, making gas dusters an inappropriate choice for cleaning anything users will come into contact with such as keyboards. They can create static electricity^[1] unless a specific ESD-safe compound is added.^{[citation needed]}

The can must be held upright during use. Inverting, tilting or even shaking the can during use may result in the un-evaporated liquid being forced through the nozzle instead of the gas. The liquid will boil away almost instantly outside the can, producing extreme cold in the process. In liquid form, the contents of the can will act as a solvent, causing unwanted damage to surface coatings or labels, this is generally only a problem with optical lens coatings. Side effects of the intense cold can also cause problems due to localized condensation.

Cooling

When the top is pressed down to open the valve, 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, the temperature can reach −50 °C (−58 °F), and the can becomes cold.

Continued use over a short period of time results in the reduction of the can's temperature. As the temperature drops, the vapor pressure of the liquid also drops, resulting in decreasing force of the gas at the nozzle. When the force of the ejected gas at the nozzle is insufficient to accomplish anything useful in terms of dust removal, and the temperature of the can reaches the boiling point of the liquid (that is −25 °C (−13 °F) for difluoroethane), the liquid no longer evaporates into gas in any useful quantity. The can must then return to room temperature before it will again provide sufficient gas flow. Alternating between two cans (allowing one to warm while the other is being used) is one way to work around this problem during an extensive dusting job. Warming the can with a heat source can be dangerous as the can may overheat and explode.

A related category of product has an internal dip tube that reaches to the bottom of the can, so it sprays the liquid. It evaporates very quickly, chilling items it touches in the manner that dry ice (solid CO₂) would. These "chill spray" cans are used to troubleshoot malfunctioning electronic equipment.

Safety

Since gas dusters are one of the many inhalants that can be easily abused,^[2] many manufacturers have added a bittering agent to deter people from inhaling the product. (That reference misuses, or did misuse "air" in its summary description), 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.^{[citation needed]}

Though not extremely flammable in gaseous form, many dusters use a fluorocarbon that can burn under some conditions. As such, there is also a warning label present on some gas dusters. 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.

The liquid, when released from the can, boils at a very low temperature, rapidly cooling any surface it touches. This can cause frostbite on contact with skin. As the can gets very cold during extended use, holding the can itself can result in frostbite.

Since gas dusters are often contained in pressure vessels, they are considered explosively volatile.

Environmental impacts

Global warming: 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 (IPCC), the global warming potential (GWP) of HFC-152a, HFC-143a, and HFC-134a are 124, 4470, and 1430, respectively.^[3] GWP refers to global warming effect in comparison to CO₂ for unit mass. 1 kg of HFC-152a is equivalent to 124 kg of CO₂^[4]

Ozone layer depletion: Gas dusters sold in many countries are ozone safe as they use "zero ODP" (zero ozone depletion potential) gases; tetrafluoroethane, for example, has insignificant ODP. This is a separate issue from the global warming concern.

Off Label Uses

Many gas dusters contain HFC-134a (tetrafluoroethane), 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 the 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.

Alternatives

True "air dusters" using ordinary air are also available in the market. These typically have much shorter run times than a chemical duster, but are readily refillable. Both hand pump and electric compressor models have been marketed.

See also

• Inhalant abuse

References