Much CO comes from vehicle exhaust. Other industrial sources are small engines, such as fork lifts, and small engine powered tools like pressure washers and some welders. CO can also come from poorly working or exhausted furnaces and water heaters, blast furnaces, boiler rooms, and environmental tobacco smoke.
The more carbon monoxide there is in the air and the longer a person is exposed to it, the greater the danger from CO poisoning. Exposure to carbon monoxide can result in: