(53b) A Quantitative Individual Risk Assessment Method in Process Facilities with Toxic Gas Release Hazards: A Scenario Library and CFD Combined Approach

People working in process facilities containing toxic gases may face a risk of gas release and poisoning. Many studies on Individual Risk (IR) have been carried out on a worst scenario basis. However, the worst scenarios-based approach cannot represent the real release risks and may overestimate the IR. In this study, an approach based on gas release scenario library and Computational Fluid Dynamics (CFD) is proposed to quantitatively assess IR in process facilities. By combining gas leakage probability and joint distribution probability of wind direction and speed, the release scenario library can be built. CFD method has been used to predict the concentration field of gas release and dispersion. And then the toxic gas concentration can be converted to poisoning fatality probabilities according to the dose-response model. A virtualized IR contour can finally be defined by the accumulative assessment of all release scenarios. A case study of the IR area classification in a natural gas process and carbon dioxide recycle terminal contains an ammonia refrigeration system has also been conducted. With the proposed methodology, the quantitatively classified IR level in process facilities can provide scientific references for safety decision-makers.

Key words：scenario library, Computational Fluid Dynamics, toxic gas, individual risk, dose-response model, ammonia poisoning