Because CO 2 is one and one half times as heavy as air it tends to 'pool' in low areas such as basements and underground areas not subject to air movement. As it 'pools,' it displaces the air that includes oxygen.
Carbon dioxide is found in nature.
We exhale CO 2 with every breath. Green plants convert carbon dioxide back to oxygen and other components. It is commonly used to carbonate beverages and in the manufacturing of 'dry' ice and fire extinguishers. Because carbon dioxide displaces oxygen, it is a health risk since we need oxygen to live. CO 2 is an asphyxiant.