Cyanide Gas Kills By Blocking Body’s Ability to Use Oxygen


Hydrogen cyanide gas, the lethal agent that will be used for the scheduled April 21 execution of murderer Robert Alton Harris, is one of the most rapidly acting of all poisons.

Cyanide kills by blocking the body’s ability to use oxygen. Specifically, cyanide interferes with an enzyme in human cells known as cytochrome oxidase. The enzyme helps to transfer oxygen from the blood to cells and tissues.

People who inhale significant concentrations of cyanide gas “are dead within minutes . . . basically, the person internally suffocates,” said Dr. Marc Bayer, chief of toxicology at Olive View Medical Center in Sylmar.


Bayer said that within a short time of breathing large amounts of the gas, “the person should be rendered unconscious.”

Hydrogen cyanide gas can take longer to work on an adult such as Harris than an elderly person or an infant. It also takes time for the concentration of the gas to build up in a chamber. In Arizona this week, it took 10 minutes, 31 seconds to put to death a 43-year-old man convicted of killing three businessmen.

The organs most sensitive to cyanide are those with the greatest need for oxygen--the brain and heart, said Bayer, who is on the UCLA School of Medicine faculty. Oxygen deprivation causes potentially painful muscle contractions, convulsions and abnormal heart rhythms, all of which may develop before the cessation of breathing and death.

When Caryl Chessman was executed at San Quentin in 1960, he told reporters he would nod if his death was painful. He nodded his head for 15 seconds before he lapsed into unconsciousness and died.

The protracted convulsions and apparent agony of inmates being gassed has caused lethal injection to become a more common execution method. Only California, Arizona, Mississippi, North Carolina and Maryland have gas chambers.

In lethal injection, a combination of fatal drugs is usually employed. Commonly, a barbiturate, which can cause coma, is combined with curare, a chemical that paralyzes the breathing muscles, and potassium, which can stop the heart from beating.