The first jolt is followed by several lesser 'doses' in power. In an execution using lethal gas, the prisoner is restrained and sealed in an airtight steel chamber. When the execution proscess begins, the executioner opens a valve that allows hydrochloric acid flow into a pan that is underneath the prisoner's chair. This produces hydrocyanic gas. The hydrocyanic gas destroy's the body's ability to process blood hemoglobin.
Unconsciousness occurs within seconds if the prisoner takes a deep breath.
Death is usually pronounced within 6 to 18 minutes. After death has been declared, the chamber is evacuated through carbon and neutralizing filters. The body it 'outgassed' before being released from the chamber. Several States use this form of execution. Essentially, the prisoner's weight is divided into 1260 to arrive at a drop in feet.