Dynamic Risk Assessment of an Ammonia Storage Tank Based on Bow-Tie and Bayesian Approaches

The leakage of ammonia from the ammonia storage tank can cause harmful effects to human beings due to the toxic and flammable nature of the chemical. The ammonia leakage can result in the fire of various kinds such as flash fire, vapour cloud explosion, jet fire, and pool fire and causes harm to human health and environment due to toxic gas dispersion. An effective risk analysis is needed to prevent and mitigate such possible incidents. In this study, a bow-tie diagram is developed from the identified causes that can lead to leakage of the ammonia storage tank and its possible consequences. The prior failure probability data for all the basic events are identified, and updated failure frequency data are collected from the industry based on the practical component failure per year. The bow-tie model is further mapped to a Bayesian network for validating the results obtained from the bow-tie analysis using the forward prediction technique. The occurrence probability of the outcome (consequence) events obtained through the bow-tie analysis and the outcome event probability results from the Bayesian network (forward prediction technique) are similar, and hence, the results can be validated. The analysis is carried out on a 500 tonnes capacity ammonia storage unit of a fertilizer industry located in Kerala, India