"The California Air Resources Board has adopted a measure developed with representatives of the electrical utilities that will limit and monitor the emissions of the greenhouse gas sulfur hexafluoride, SF6, from high-voltage electrical applications.
Sulfur hexafluoride, SF6, is used by utilities for insulation and current interruption in electric transmission and distribution equipment. Since the 1950s the U.S. electric power industry has used SF6 widely in circuit breakers, gas-insulated substations, and other switchgear to manage the high voltages carried between generating stations and customer load centers.
Sulfur hexafluoride is the most potent greenhouse gas in existence. With a global warming potential 23,900 times greater than carbon dioxide, one pound of SF6 has the same global warming impact of 11 tons of carbon dioxide. It is also very persistent in the atmosphere with a lifetime of 3,200 years."