Despite its history, the gas chamber was advertised as an efficient and humane form of execution. At least it seemed that way to the observers...
The infamous lime green gas chamber at San Quentin, where all of California's death sentences are carried out. Today the room is used for lethal injections; California abolished execution by poison gas in 1995.
Image courtesy of the California Department of Corrections and Rehabilitation.
History: In 1921, lawmakers in the State of Nevada, horrified by the gruesome electric chair, sought a less violent form of execution. They decided to construct sealed chambers into which prisoners could be locked, chambers that would then be flooded with lethal cyanide gas. Nevada first used the procedure in 1924, and it remained popular for over 50 years, though it has since fallen out of favor due to some unexpected complications (see below). The last gas chamber execution took place in 1999, and only four states still allow it as an option.
Unsavory Overtones: Cyanide gas (Zyklon B) was Nazi Germany's primary means of mass murder during the Holocaust, as it could be used to kill as many as 2,500 people at once.
How It Works: The prisoner is strapped to a chair inside a sealed gas chamber. The executioner (standing outside of the chamber) pulls a lever dropping potassium cyanide pellets into a vat of sulfuric acid, flooding the chamber with lethal hydrogen cyanide gas.
Complications: Death can be extremely slow and painful, as demonstrated in several high-profile executions from the 1980s and 1990s. One of the more infamous was that of Jimmy Lee Gray in 1983, who frantically gasped, moaned, and slammed his head into a steel pipe for ten minutes as the cyanide slowly took effect. In 1996, the 9th Circuit Court of Appeals ruled that execution by poison gas constitutes cruel and unusual punishment.