(40c) Understanding Potential Process Safety Events Using Dispersion Modelling

During a Process Hazard Analysis (PHA), the team identifies scenarios that could have significant impacts. Some PHA methods, like the Risk Analysis Screening Tool (RAST), can estimate consequences automatically, while others require manual assessment using different tools. It's crucial for the team to understand the anatomy of an event and how various parameters influence the potential consequences. This paper offers insights and considerations to help readers to comprehend the structure of a potential loss of containment event and its possible outcomes when using a dispersion modelling program.

PHAST^TM allows users to model containment loss scenarios and estimate toxic and flammable impacts. The paper includes a review and critique of parameters that enable a team to conduct a sensitivity analysis of the potential impacts.

Elements of a PHA scenario that could influence outcomes include:

• Which key parameters might trigger the event?
• In a reactive situation, which materials could be released?
• Where are personnel located? Are there nearby occupied buildings at risk of toxic infiltration? Are people working on a nearby platform?
• What is the main wind direction?
• Compare the worst case versus the more likely case.

Using worked examples, the reader will get some useful tips on how to improve their dispersion models.