Recently, there have been proposals and a law has been enacted in Oklahoma for a variation, so-called nitrogen gas, either by chamber or a mask. It is believed to be less painful and anxious than the method previously used. In the beginning, actually, the idea of a gas chamber was to let the prisoner condemned to death sleep in a cell which would then be exposed to lethal gas during the night, without the prisoner's knowledge. However, because of poor isolation techniques it was too difficult and so the gas chamber was introduced instead. It was introduced in several states, including Mississippi, North Carolina, Missouri, Colorado, California, Arizona and New Mexico, but it never was as popular as the electric chair and later execution by injection. The method is in fact expensive and thought to be painful because the prisoner must breathe deeply to hasten the death, which is difficult when the body wants to reject the fumes. (With nitrogen, it is different because the body doesn't reject it as strange or fatal.) It is also extremely dangerous to the audience and personnel in case there is a leak, and impossible to halt in case there is an attempt to stop the execution, such as in the cases of Caryl Chessman and Burton Abbott. In the case of an electric current or injection the switch can be turned off and the needle ripped out, and while it might not be enough there is no risk for the people trying to save the prisoner. In one case, when the mechanism jammed, the executioner had to drop the pellet into the acid (producing the deadly fumes beneath the chair where the prisoner was sitting) and jump out of the chamber as the warden stood ready to slam the door and tighten it.