This Day in History: 1921-09-21

Factory explosion kills 500 in Oppau, Germany. The explosion takes place when workers try to loosen up 4,500 tons of damp amonium nitrate with small charges of dynamite — a process that had been carried out safely in previous years. The explosion ripped roofs off up to 25 km away. In Heidelberg (30 km from Oppau), traffic was stopped by the mass of broken glass on the streets.