Carbon monoxide gas chambers—a euthanasia method used since World War II—are routinely used in animal shelters throughout the country, including Rhode Island, Ohio, Texas, and Virginia.
The American Veterinary Medical Association—whose euthanasia guidelines are widely followed—considers carbon monoxide gassing an acceptable method when done in a properly manufactured and equipped chamber. Many animal-welfare advocates, though, say the method is inhumane.
"It's America's dirty little secret," said Grim, who has written the book Miracle Dog: How Quentin Survived the Gas Chamber to Speak for Animals on Death Row （Alpine Publishing）. "If people actually saw the gas chamber working, they would sign a petition tomorrow to ban it." Due to Grim's fundraising and lobbying efforts, the St. Louis gas chamber shut down in January of this year.
From start to finish, the process of gassing an animal takes about 25 minutes. One or more animals are placed in an airtight chamber, and a high concentration of bottled carbon monoxide gas is released. Cats and dogs are rendered unconscious within a minute, then eventually die from lack of oxygen.