CONSEQUENCE MODELLING OF THE POPULATION RISK EXPOSURE RESULTING FROM AIRBORNE TOXIC MATERIAL RELEASED FROM RAIL CARS WITHIN TORONTO, ONTARIO.

Rail transportation is commonly used to move dangerous goods and hazardous materials throughout Canada. Many of the trains carrying dangerous goods have numerous cars containing toxic-by-inhalation chemicals, including chlorine and anhydrous ammonia, and pass in close proximity to large Canadian population centres. These trains are vulnerable to accidents, sabotage and terrorism, with each scenario resulting in formidable consequences for nearby residents. For example, computer modelling of the airborne concentration distribution of chlorine gas released from a railcar on the Canadian Pacific Rail line reveals that in a ‘worst case’ scenario where chlorine is released in July, approximately 261,590 residents of downtown Toronto would be expected to experience severely irreversible and life-threatening health effects, including death. An event of this magnitude, stemming from a 10 cm diameter puncture hole in the side of the rail car – and could be caused through accidental or intentional means – would cripple the response capacity of nearby hospitals, and unleash a cascading series of effects within the city of Toronto. Further computer models for anhydrous ammonia and chlorine releases reveal that multiple populations would be affected in the event of a release, depending on the weather conditions and timing of the incident, while the characteristics of the chemical throughout the transportation process can play an important mitigation role in population risk exposure. Key Words: toxic inhalation hazard, toxic-by-inhalation, airbourne chemicals, dangerous goods, consequence modelling, Aerial Locations of Hazardous Atmospheres (ALOHA)