Generally, the term disaster means sudden great misfortune and it is a destructive event that results in the need for a wide range of an emergency resources. Occurrence of disasters invariably has profound implication for public health. Disasters may be classified into natural, as floods and earthquakes, technological which are associated with industries and conflict-related disaster which are, usually, related to wars and revolutions. In this article we are essentially concerned with chemical disasters, although other causes are important. We may discuss such causes in other articles.
The chemical disasters may occur suddenly or gradually according to their results or events. There is a surprising fact that about 50% of acute disasters are due to unplanned transportation of chemicals.The worst of acute chemical disasters happened in Bhopal, India (1984) where more than 2500 died and more than 250000 suffered due to the exposure of the people of Bhopal to the released methyl isocyanate pesticide. Another sudden episode occurred in Seveso, Italy (1976) where about 37000 persons were injured due to exposure to polychlorinated dibenzo-p-dioxin. There were many gradual or insidious episodes, but we shall choose the most famous ones according to their place of occurrence, for example, Karkola, Finland (1930), Japan (two episodes,1939 and 1953) ,Turkey (1956), Iraq (1971), Love Canal, New
York (1976) and Spain (1981). Other worldwide occurrence of medical problems for example, acute air pollution episodes, polychlorinated biphenyls and their dangerous effects will be discussed.