Phosphorus is a highly reactive substance and numerous accidents have been reported due to phosphorus reactions with diverse chemicals. Yet, it has generally been considered that phosphorus does not explode when O-2 (or air) is the only available reaction partner. A chemical explosion requires that a bulk volume of reactant be available to react abruptly. Thus, a substance which is highly reactive is likely to participate in an explosion only if rapid, local consumption of reactant can be avoided and a sizable volume becomes capable of reacting precipitously. Since reactions of P with O-2 are rapid, explosions have rarely been encountered and most chemical safety treatises warn of explosive P reactions only in connection with substances other than air. Despite this background, a series of P explosions is described which occurred in molecular beam epitaxy equipment. Earlier known incidents are also discussed. In each case, the details of the environment allowing precipitous reaction of a sizable volume of P have not been well understood, and additional research is warranted. Reference works should make clear that explosions in the system P + O-2 are possible, and that neither additional reactants nor elevated temperatures are required for this. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.