This paper describes a procedure to include into the quantitative risk assessment (and namely in the construction and solution of the Fault Trees) the Safety Management System (SMS) aspects. The parameters used for probabilistic assessment of the Expected Number of Failures (ENF) of a Top Event are parameterised depending on: 1. a weight assigned to each SMS section with reference to the parameter; 2. a judgment about the correct application of the same SMS section. Each probabilistic parameter (e.g. failure rates, mean time to repair, and so on) is thus modified using a mathematical algorithm, where an overall parameter including all the SMS sections influencing each single parameter is defined. The application of the procedure to a formaldehyde plant allowed the validation of the method and is here entirely reported. (c) 2005 Elsevier Ltd. All rights reserved.