Many flammable products are stored in large tanks at atmospheric pressure. Ignition of a hydrocarbon-air mixture in such tanks can lead to an explosion and cause lethal casualties or damage the surrounding facilities and buildings. To apprehend this, safety distances for humans, structures and equipments need to be defined. Several simple methodologies have been set up to estimate safety distances in case of an atmospheric storage tank explosion. This first article gives an overview of accident frequencies of atmospheric storage tanks and past accidents described in the open literature, to show the possible accidental sequences, underline the most frequent causes involved in explosions of atmospheric storage tank, and highlight the potential consequences of such accidents. (C) 2011 American Institute of Chemical Engineers Process Saf Prog 30: 381-392, 2011