Chapter 13: Irritant Gases

Irritant gases are formed in the majority of combustion scenarios and are responsible for the sensory effects encountered during exposure to smoke. The irritant gases evolved and the rate of generation depend upon the temperature and ventilation state of combustion. Combustion derived irritant gases are generally classified either as inorganic acid gases or as organic irritants. The toxicity resulting from exposure to irritant gas is dependent on the chemical, the exposure concentration, the exposure duration and its solubility. The primary effect of irritant gas exposure is likely to be sensory irritation and the severity of irritation is dependent only upon the concentration of the irritant present, and is independent of the exposure duration. The irritant effect of stinging or burning of the eyes and throat may cause exposed individuals to close their eyes and hold their breath to alleviate the irritation, which may hinder their ability to escape from the hazard. Exposure to irritant gases often causes a burning sensation of the mucous membranes of the upper respiratory tract, including the nose, mouth and throat. Pulmonary irritation commonly follows sensory irritation, due to inhalation of the irritant gas into the lungs resulting in bronchoconstriction, coughing and breathing difficulties. Unlike sensory irritation, the severity of pulmonary irritation is dependent upon both the concentration and the duration of exposure. Exposure to high concentrations of irritant gases can potentially be fatal in a period of between 6 and 48 hours after removal from the exposure due to the development of pulmonary oedema. Continued monitoring of exposed individuals is, therefore, important during this period. This chapter reviews aspects of the mechanisms by which combustion products cause irritancy and the effects of a number of specific irritant substances occurring in combustion products.