Poison gas refers to toxic gases that can cause harm or death when inhaled. These gases can disrupt normal bodily functions, leading to symptoms such as coughing, choking, or even loss of consciousness. Historically, poison gas has been used in warfare, notably during World War I, where it caused significant casualties. Different types of poison gases exist, including chlorine, mustard gas, and nerve agents. Each type has unique properties and effects on the human body. Due to their dangerous nature, the use of poison gas is restricted under international treaties, such as the Chemical Weapons Convention.