Abstract A model is presented for assessing the surrounding population's health risk associated with the pollutants released in the atmosphere under the thermic degradation of 20 000 1 of 1,1,1-trichloroethane (TCA) in a fire assuming a temperature of 800 °C. Using literature data on the thermic degradation of that product and the Gaussian plume model, downwind outdoor and indoor concentrations at ground level of released pollutants were estimated in plume's axis up to a distance of 10 km from the source for the most frequent meteorological situation in Montreal and for a thermic inversion scenario. Results show that if such a fire should arise, the surrounding population could be exposed to levels of chlorine, hydrogen chloride and phosgene associated with mucous sensorial irritation, pulmonary inflammation, oedema and even death. Those effects could reach populations up to many kilometres from the fire and the death rate could be high for those in the toxic cloud's axis. The model suggests that, under the most frequent meteorological situation, in-place protection would be effective provided the fire does not extend one hour whereas, under thermic inversion, evacuation of persons up to 2 km from the fire should take place. Because of the various limitations of the model, these evaluations should be used with caution.