Investigations of major accidents show that technical, human, operational, as well as organizational factors influence the accident sequences. In spite of these facts, quantitative risk analyses of offshore oil and gas production platforms have focused on technical safety systems. This paper describes an effort to develop further the quantitative risk analysis of the platform specific hydrocarbon release frequency by considering operational barriers in event trees and fault trees, as well as risk influencing factors that determine the basic event probabilities in the fault trees. A generic model based on Risk Influencing Factors has been developed and is adapted to use for specific failure scenarios. The full Bayesian Belief Network (BBN) model is presented, and two alternative implementations are outlined. Human error probabilities are discussed, importance measurement, as well as modelling of common cause and interactions. Use of the model is briefly outlined, but the possible applications are presented more thoroughly in a companion paper. It has been demonstrated that the model is capable of reflecting relative differences between alternative installations with different cultures and implementation of management systems. The model is also useful in demonstrating the importance and effects of improving human and organizational aspects. (C) 2011 Elsevier Ltd. All rights reserved.