Risk assessment of liquefied petroleum gas (LPG) storage tanks in the process industries using the Bowtie technique

LPG storage tanks contain of large volumes of flammable and pressurized gases. Release of these fluids can lead to disastrous accidents such BLEVE, fiery explosion. Therefore, identifying the causes, consequences, probabilities and scenarios of accidents using Bowtie technique, that is combination of Fault Tree Analyses (FTA) and Event Tree Analyses (ETA), is imperative and the purpose of this study.
The hazards of the mentioned in Tehran Refinery LPG tanks were identified by Fault Tree Analyses and the consequences of the top event were predicted by Event Tree Analyses. Then probabilities of the events were calculated and the accident route, from causes phase to consequences phase, was drawn by Bowtie diagram.
In total, 21 events and 11 minimal cut sets with their occurrence probabilities and importance measure were determined at the left side of the Bowtie diagram. Also 9 consequences and scenarios of the top event were determined at the right side of the diagram. The occurrence probability of the top event (LPG release of spherical tanks) was calculated 3.45×10-2.
All factors involved in the occurrence of accidents and their consequences are showed in the Bowtie diagram. According to the obtained data, failure of cathodic protection systems and instrumentation, and overflow of tanks are included as important defects of the LPG tanks. Due to the high probability of the consequences, preventing systems such as cooling systems and Fire stop systems are required for installing in the studied unit to reduce the consequences of accidents.