Carbon Monoxide (CO): The Invisible Killer Carbon Monoxide, also known as “CO”, is a colorless, odorless and tasteless gas that is a byproduct of incomplete combustion of fuels such as natural gas, propane, wood, coal, gasoline and oil. CO is called the invisible killer because you don’t know it is present and can initially present with flu-like symptoms. Each year, more than 400 Americans die...