Int. J. Environment and Pollution, Vol. X, No. X, 199X 1 Copyright © 1998 Inderscience Enterprises Ltd. SMEDIS: Scientific Model Evaluation of Dense Gas Dispersion Models N.C. Daish, R.E. Britter and P.F. Linden Principal Consultant, Cambridge Environmental Research Consultants Ltd., 3, King’s Parade, Cambridge, CB2 1SJ, UK S.F. Jagger Head, Fire Safety Section, Health & Safety Laboratory, Harpur Hill, Buxton, Derbyshire, SK17 9JN, UK B. Carissimo Research Scientist, Electricité de France, Direction des Etudes et Recherches, 6, Quai Watier, 78401 Chatou CEDEX, France Abstract: SMEDIS is a project currently in progress to develop a protocol for the scientific evaluation of dense gas dispersion (DGD) models, with particular emphasis on the complex effects of obstacles, terrain and aerosols often found in real situations, and then to apply this protocol to DGD models currently in use in Europe. This paper describes the general features of a model evaluation project and then outlines the implementation in the specific case of SMEDIS. The paper concludes with some experiences from the project to date. Keywords: dense gas dispersion, model evaluation, model validation, complex effects. Reference to this paper should be made as follows: Daish, N.C., Britter, R.E., Linden, P.F., Jagger, S.F. and Carissimo, B. (2000) ‘SMEDIS: Scientific Model Evaluation of Dense Gas Dispersion Models’, Int. J. Environment and Pollution, Vol. 14, No. 1-6, pp. 39-51. 1 Introduction and context Following a number of major incidents involving the accidental release of hazardous materials, such as those at Flixborough, UK in 1974 and Seveso, Italy in 1976, a regulatory regime has developed, particularly in Europe, which requires operators of chemical and process plant to produce a “safety case” to demonstrate safe operation of their plant. Such a safety case involves identifying possible accident scenarios and calculating the consequences of the hazards associated with those scenarios by use of predictive mathematical models. Users of these models - developers, consultants, safety personnel or regulators - apply them to inform safety-critical decisions and, in doing so, often face questions regarding