|Description: Colour glossy photograph, framed in black showing a very large explosion. The majority of the area in the photo is engulfed by flames. The explosion is probably from one of the tankers during the train derailment in Mississauga.
History: On 10 November 1979 in Mississauga, at the intersection of Mavis Road, at 11:53 p.m., one tanker of a 106 car freight train carrying explosive and poisonous chemicals derailed. Twenty-three other cars followed and some propane cars burst into flames on impact. Other cars containing styrene and toluene were punctured, spilling their chemicals on to track beds. Within a minute, flammable liquids and vapours ignited, causing a massive explosion of a tank car. The yellow-orange fire rose to a height of 4,500 feet (1,500 metres) and could be seen 100 kilometres (60 miles) away. The fire was fed by six dangerous ingredients - 11 tank cars of propane, four with caustic soda, three with styrene, three with toluene, two box cars with fibreglass insulation and one with chlorine. While chlorine is non-combustible in air, most combustible materials will burn in chlorine as they do in oxygen. Liquid propane, styrene, and toluene are flammable while caustic soda is not flammable, but in solid form and in contact with moisture or water, it may generate sufficient heat to ignite combustible materials. The derailment caused the largest peacetime evacuation of an urban area, at that time. More than 200,000 residents were displaced from their homes from two days to up to one week following the incident.
Teams of MDS Sciex scientists were sent out to the streets of Mississauga with mobile mass spectrometers. At first, chlorine was thought to be the major threat (used in gas attacks during WWI). The problem turned out to be more complex. Some chlorine had leaked, but it was not enough to cause the high levels of eye, nose, and throat irritation of those sent out to clean the wreck. A discovery was made soon after. The leaking chlorine was mixing with the leaking styrene in bright sunlight and was producing mace, a major irritant used widely for self-defence. This is what caused the need for evacuation.