Damage to the respiratory tract (i.e., upper airway inflammation and swelling) as a result of inhaling hot gases that may contain toxic substances. Persons exposed to gases produced by burning materials are at risk of developing acute injury to their lungs, and, depending on the composition of the smoke and the duration of the exposure, the combination of heat and gases may be lethal. Firefighters are esp. at risk from this kind of exposure. Construction and decorating materials produce a variety of volatile and irritating substances when burned. Repeated exposure to some of these gases may lead to chronic irritation of the respiratory tract. Firefighters should be aware that the appearance of smoke produced by a fire may not be a true indicator of the amount of toxic substances, including carbon monoxide, in the smoke.