A methodology to model causal relationships on offshore safety assessment focusing on human and organisational factors 1 A methodology to model causal relationships on offshore safety assessment focusing on human and organisational factors

Focusing on the human beings and the organisations, this paper aims to contribute to offshore safety assessment by proposing a methodology to model causal relationships. The methodology is proposed in a general sense that it will be capable of accommodating modelling of multiple risk factors considered in offshore operations and will have ability to deal with different types of data which may come from different resources. Reason’s “Swiss cheese” model is used to form a generic offshore safety assessment framework and Bayesian Network (BN) is tailored to fit into the framework to construct a causal relationship model. The proposed framework uses a five-level-structure model to address latent failures within the causal sequence of events. The five levels include Root causes level, Trigger events level, Incidents level, Accidents level and Consequences level. To analyse and model a specified offshore installation safety, a BN model will be established following the guideline of the proposed five-level framework. A range of events will be specified, and the related prior and conditional probabilities regarding the BN model will be assigned based on the inherent characteristics of each event. This paper shows that James Reason’s “Swiss cheese” model and BN can be jointly used in offshore safety assessment. On the one hand, the five-level conceptual model is enhanced by BNs that are capable of providing graphical demonstration of interrelationships as well as calculating numerical values of occurrence likelihood for each failure event. Bayesian inference mechanism also makes it possible to monitor how safety situation changes when information flows travel forwards and backwards within the networks. On the other hand, BN modelling is heavily relied on experts’ personal experiences and is therefore highly domain specific. “Swiss cheese” model is such a theoretic framework that it is based on solid behavioural theory and therefore can be used to provide roadmap for BN modelling. A case study of the collision risk between a Floating Production, Storage and Offloading (FPSO) unit and authorised vessels caused by human and organisational factors (HOFs) during operations is used to illustrate the application of the proposed methodology.

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