Sulfur hexafluoride
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Sulfur hexafluoride (SF6) is a gas that consists of one part sulfur and six parts fluorine. It is colorless, odorless, non-toxic, and non-flammable. It is soluble in water and some other liquids. It is generally transported as a liquified compressed gas.
SF6 is used by the electricity industry as an insulator for circuit breakers, switch gear, and other electrical equipment, often replacing harmful PCBs. It is used in the semiconductor industry as an etchant. It has been used successfully as a tracer in oceanography to study diapycnal mixing and air-sea gas exchange. It is also emitted during the aluminium smelting process.
According to the Intergovernmental Panel on Climate Change (IPCC), SF6 is the most potent greenhouse gas that it has evaluated, with GWP (global warming potential) of 23,900 (CO2 is 1). However, because its mixing ratio in the atmosphere is low vs. CO2 (ca. 5 ppt vs. 365 ppm), its contribution to global warming is accordingly low.
Sulfur hexafluoride can affect the sound of a persons voice if it is inhaled in small quantities. When SF6 is inhaled, the pitch of a persons voice decreases dramatically because the speed of sound in SF6 is considerably less than it is in air. This is the opposite of what is heard when a person inhales helium.
Although this is a novel amusement, it can be somewhat dangerous as like all gases other than oxygen, the SF6 displaces the oxygen needed for breathing (a phenomenon known as asphyxiation). It is best to inhale only very small quantities at a time, and to allow several minutes of breathing fresh air for every one breath of SF6. Much more dangerous is attempting to inhale SF6 from the pressurised cylinders used for storage. The high flow rate can fatally overpressure the lungs and rupture the alveoli in a fraction of a second, without time to react. It is much safer to fill a small balloon with the gas, and then inhale from there.
External link
High GWP Gases and Climate Change (http://www.epa.gov/highgwp/scientific.html) from the U.S. EPA website.ja:六フッ化硫黄 de:Schwefelhexafluorid