In France, carbon monoxide (CO)—an odorless gas produced by the incomplete combustion of carbon-containing materials (gas, coal, wood, fuel oil, etc.)—causes about 100 deaths each year. However, there are regional disparities in the incidence of CO poisoning, with the most densely populated regions being the most affected, such as Nord-Pas-de-Calais, Île-de-France, and Rhône-Alpes.In 2011, just over 1,000 cases of poisoning were reported to the surveillance system (Figure 1), involving nearly 2,400 poisoned individuals: approximately 75% of them were treated in a hospital emergency department, nearly 25% required hospitalization, and hyperbaric oxygen therapy was administered to about 18% of them. For nearly 75% of these cases, an environmental investigation was conducted. The reported cases of CO poisoning are mostly accidental domestic poisonings. The main source of these poisonings is an appliance connected to an individual flue and fueled by mains gas (boiler, water heater, etc.). Nearly one in five poisonings stems from the prolonged, inappropriate use of a portable space heater, the use of a brazier or barbecue inside the home (living room, garage, basement, or cellar), starting a vehicle in an enclosed space such as a garage, or using a generator in a closed space (cellar, basement inside a house under construction). However, more than three-quarters of French people with combustion heaters are unaware that they have devices in their homes capable of emitting CO, according to the Environmental Health Barometer (INPES, 2012).