Carbon monoxide is slightly lighter than air and quickly spreads throughout an entire house.
These deaths and injuries are typically caused by improperly used or malfunctioning equipment aggravated by improvements in building construction which limit the amount of fresh air flowing in to homes and other structures. A faulty chimney or heat exchanger can lead to deadly carbon monoxide exposure. The Department of Energy is concerned about CO levels indoors, because its weatherization programs to save energy can tighten houses and other buildings enough to increase CO concentrations. Any appliance or implement which burns a fossil fuel. Carbon monoxide gas is produced when fossil fuel burns incompletely because of insufficient oxygen.