1837: The American side-wheel steamer Union exploded. The Union operated between Alexandria, Virginia and Prince George's County, Maryland. At around 3p.m. the Union suffered a boiler explosion. Bolts, fragments of steel and other debris was sprayed into the passengers. Three were killed, this included the wife of the engineer. The explosion was caused when material that was used to plug a leak in the boiler fouled the tubes. The material used...horse dung.