A more sophisticated target-hardening approach must consider industrial and other critical industrial infrastructure that could be attacked . Terrorists need not import chemical weapons if they can cause a major industrial accident such as the Bhopal disaster or the Halifax Explosion . Industrial chemicals in manufacturing , shipping , and storage need greater protection , and some efforts are in progress . To put this risk into perspective , the first major lethal chemical attack in WWI used 160 tons of chlorine . Industrial shipments of chlorine , widely used in water purification and the chemical industry , travel in 90 or 55 ton tank cars
Bhopal disaster
Bhopal disaster
Counter-terrorism