The following is a simplification of the hydrogen risk assessment method (Advances in Hydrogen Energy, Kluwer Academic Publishers, Plenum Press, Dordrecht, New York. p. 163-173. Proceedings of an American Chemical Society Symposium On Hydrogen Production, Storage and Utilization, August 22-26, New Orleans, Louisiana, 1999; Chemical Health and Safety 6 (3) (1999) 28.) previously developed at the University of Miami. It has been determined that in simple geometric enclosures, hydrogen leaks can be simulated using helium to predict the concentrations of the gas found near the ceiling after the initial transients disappear. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.