Gas generators used during power outages and emergencies cause more than 200 deaths in the United States per year, according to the U.S. Consumer Products Safety Commission. Carbon monoxide is called the "Invisible Killer" because it's a colorless, odorless, poisonous gas. Carbon Monoxide poisoning can also be caused by incorrectly-vented fuel-burning appliances such as furnaces, stoves, water heaters and fireplaces.