Carbon monoxide, a colorless, odorless, and non-irritating gas, is produced by the incomplete combustion of organic matter. Carbon monoxide poisoning is the leading cause of accidental death from toxic exposure in France: each year, this "silent killer" poisons between four thousand and six thousand people and causes approximately three hundred deaths, of which 45% are due to accidental poisoning unrelated to fires, 29% to fumes from fires, and 26% to intentional poisoning. The density of carbon monoxide is close to that of air, so it mixes perfectly with it. When inhaled, it displaces oxygen in the blood and causes tissue asphyxia. At low exposure levels, symptoms are nonspecific (headaches, dizziness, nausea, etc.) and resemble those of “common” winter illnesses: clinical diagnosis is therefore difficult to establish. While boilers and water heaters are the primary source of carbon monoxide poisoning in the home, cars in the garage, smoking indoors, fires, or the influx of polluted outdoor air are all potential causes of carbon monoxide emissions. The presence of carbon monoxide is most often due to poor maintenance of combustion appliances, inadequate exhaust ventilation, or "inappropriate" use of certain appliances (prolonged use of space heaters, generators operating indoors, etc.). This is exacerbated by insufficient ventilation in homes. Carbon monoxide poisoning follows a seasonal pattern: 80% of poisoning cases in homes are recorded between November and March, during the period when heating appliances are first turned on.[excerpt from chapter]