A transient two-dimensional mathematical model for the heat and water vapor transport over the respiratory tract of human body was established and applied to predict the thermal impact of inhaled hot air during the early stage of fires. Influences of individual's physiological status and environment variables were comprehensively investigated. Burn evaluation was performed using the classical Henriques model to predict the time for thermal injury. It was shown that decreasing the air velocity and increasing the respiratory rate is helpful to minimize the thermal injury in the respiratory tract. The effect of relative humidity of surrounding dry hot air could be ignored in predicting the burn injuries for short duration exposures. Due to evaporation cooling on the mucousal membrane, the burn injury often occurs at certain positions underneath the skin of the tract near the inlet of the respiratory tract. Most of the tissues near the surface suffer injury immediately after exposure, while in the deeper tissues, serious damage occurs after a relatively longer time period. The method presented in this paper may suggest a valuable approach to theoretically evaluating the injury of hot air to the human respiratory tract under various fire situations.

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This is partially supported by the National Natural Science Foundation of China under grant 50325622.