The toxic gases that can be associated with smoke can be grouped into three classes. Asphyxiant gas or narcotic gases deprive the body of oxygen. They are also dose related.The two most important asphyxiants are CO and HCN. Irritants is simply irritant gases that affects the senses. Some of the most important gases of irritant gases is halogen acids and some partially oxidized gases. Sometimes gases can be classified as others this is when small materials generates toxic smoke. 75 words minimum .