Phosphorus explosions

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 O2 (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 O2 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 + O2 are possible, and that neither additional reactants nor elevated temperatures are required for this.