Nitroglycerine has been widely used as an ingredient of explosives and propellants for a long time. It is produced by the glycerine nitration reaction. Many explosions have occurred during handling or storing spent acid after separating nitroglycerine from the reactor in nitroglycerine factories. Safety charts have been constructed by various authors in order to cope with these hazards. In this investigation we construct enthalpy diagrams that correspond with the safety charts produced by earlier researchers. These can be used to evaluate the variation of heat and the safety composition during the handling of spent acid. Furthermore, this study uses practical operating conditions at nitroglycerine factories to evaluate the stability of spent acids in storage. (C) 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.