Many flammable products are stored in large tanks at atmospheric pressure. Ignition of a hydrocarbonair mixture in such tanks can lead to an explosion and cause lethal casualties or damage to 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. After giving an overview of past accidents [ 1], this second article focuses on assessment of safety distances using analytical methods available in the open literature. A short theoretical background is first exposed to understand phenomena involved in vented gas explosions. Then, a summary of current methodologies and corresponding assumptions used to evaluate external overpressure in case of a tank explosion is given. (C) 2011 American Institute of Chemical Engineers Process Saf Prog 31: 72-82, 2012