Carbon monoxide is a silent killer. Make sure to schedule an annual inspection of heating and venting equipment by a qualified contractor and install a carbon monoxide alarm that meets current standards.
To prevent carbon monoxide from forming, make sure your furnace has adequate ventilation and do not use the furnace closet for storage. Ensure that any space heaters are used properly, installed by a qualified professional and maintained correctly. This includes gasoline , flammable liquids and other combustible materials any from appliances and other sources of ignition.
If you have any of these symptoms after being in an enclosed area get fresh air immediatly and go to a hospital emergency department or call 911