Why don’t they look at a different alternative; inert gas asphyxiation.
“After a number of accidents in which humans suffocated in nitrogen without any warning, the suggestion was made in 1995 that hypoxic atmospheres be used for the humane killing of humans.
Execution by nitrogen asphyxiation was discussed briefly in print as a theoretical method of capital punishment in a National Review article, “Killing with kindness – capital punishment by nitrogen asphyxiation”.
In a televised documentary in 2007, the British political commentator (and former Member of Parliament) Michael Portillo examined execution techniques in use around the world and found them unsatisfactory; his conclusion was that nitrogen asphyxiation would be the best method.
Nitrogen asphyxiation is not currently used by any government as an execution method.”
It’s worth a look, I’d say.
http://en.wikipedia.org/wiki/Inert_gas_asphyxiation#Capital_punishment
Helium asphyxiation would lead to much funnier last words.