Developing a multi-disciplinary approach to risk-based mapping (RBM) in an onshore refinery: A case study on optimal gas detector placement

Abstract

Ensuring fire and explosion safety in petrochemical facilities is a significant challenge due to the complexity of the environment. Input is required from operators, engineers, software developers and standards to guide the work. Risk-based mapping (RBM) provides a holistic approach to developing solutions. In this paper RBM is applied to the problem of gas detector placement in an onshore refinery based on a facility-wide analysis. This is done as an alternative to prescriptive geographic-based detector placement. The inputs from different disciplines are identified and a framework for a multi-disciplinary approach is proposed. The case study considers twenty-six processing units and two tank farms, comprising 1400 pieces of equipment, which were assessed and gas detectors were placed to reduce the risk of undetected gas by 80–90%. Computational Fluid Dynamics (CFD) analyses were incorporated to explicitly consider factors such as leak source location, fluid properties, nature of the release (high pressure or spillage), topography, air movement (wind speed and direction), ambient temperature and obstructions (equipment, buildings and structures). Both the likelihood and consequence of events are considered. A key observation from the RBM study was that for atmospheric storage tank farms, the size of the risk volumes must be carefully considered to allow for the timeous detection of gas clouds. Transient analysis of gas cloud growth up to predefined limits was used for this purpose. The work provides a framework to consider multiple representative loss of containment scenarios and yields quantitative evidence to optimize not only the placement of detectors, but also the layouts and mitigation and emergency response measures.