I can speak with certainty that what caused recent Nanking explosion was VINYL CHLORIDE monomer (gas), and megatons of this nasty chemical have been released into the air.
In terms of acute toxicity, this VCM gas is not the most toxic; but when it comes to chronic toxicity, you can hardly find anything that is nastier than this invisible, explosive, liver-damaging, cancer-causing, evil-human-invented toxic gas.
Many years later, the surrounding areas will see very very high cancer and other disease occurrences that can be traced back to this incident. If you shall witness the future suffering of these innocent people, please tell them they are victims of "Nanking massacre 2010".
VCM - vinyl chloride monomer