Fundamental to the creation of a hydrogen economy is a viable, safe and affordable hydrogen-energy-system. Examining carefully some of the key properties of hydrogen that are related to fire and explosion, it is found that hydrogen is combustible over a wide range of concentrations. At atmospheric pressure, it is combustible at concentrations from 4% to 74.2% by volume. It has the highest flame velocity of any gas and its ignition energy is very low, which is 32% less than methane gas. In this paper, the problem of "safe hydrogen" is tackled using a new theoretical approach. Hydrogen is mixed with predetermined amounts of methane gas and to be sold as "Hydrothane". The properties of this mixture-most important are the flame speed, lower explosion limit (LEL) and upper explosion limit (UEL) are to be developed as a function of the ratio of the hydrogen-methane. The maximum flame speed, cm/s, for a selected number of hydrocarbons along with the corresponding volume percentage of combustible mixture (fuel in air) are used in the proposed analysis. In addition, Le Chatelier's law is used to predict limits of flammability of the Hydrothane. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.