The Risk Analysis Screening Tool (RAST): Part II, using RAST to evaluate the release of ammonia

Abstract This is the second article on the Risk Analysis Screening Tool (RAST). Part I provides an overview of the RAST software and how it can be used when performing a Hazards Identification and Risk Analysis. This article will focus on one piece of equipment: an ammonia storage tank located within a densely populated university campus. For the storage tank, the relief valve vents outdoors at the height of a two‐story building with its release modeled as an outdoor release. The potential failure scenarios proposed by the RAST software confirmed the scenarios generated by the Process Hazards Analysis team. RAST can be used using minimum required inputs and general assumptions and default values within the software. The results are presented in this article along with an additional, similar case study on chlorine. The risk matrix and risk summary tabs give a visual presentation of whether the failure scenarios found by RAST are within an acceptable, tolerable risk. The user or company running the study may change the desired target frequency factor then work to achieve those figures through implementation of protective layers.