A pressurised vessel containing ethylene is instrumented with two sets each of Pressure Switches (PS1 & PS2) and Temperature Switches (TS1 & TS2) which upon activation sound an alarm and to automatically terminate the ethylene feed into the vessel by closing an emergency shutdown valve. The same vessel is also instrumented with a spring-loaded Pressure Safety Relief Valve (PSRV) which upon over-pressurisation automatically opens to relive the pressure by discharging the excess ethylene into a buffer reservoir. Assuming that as a back-up, an operator manually operates the emergency shutdown valve to terminate the feed flow upon hearing the alarm,

a) draw the corresponding fault tree diagram with the top event representing the rupture of vessel resulting in the release of ethylene into the atmosphere

b) calculate the overall probability of system failure resulting in the release of ethylene into the atmosphere using the following data

Buffer reservoir failure probability, PRES=0.1

PSRV failure probability, PPSRV= 0.2 TS1 failure probability, PTS1= 0.1 TS2 failure probability, PTS2= 0.1

PS1 failure probability, PPS1= 0.1 PS2 failure probability, PPS2= 0.1 Alarm failure probability, PALARM= 0.05 ESDV failure probability, PESDV= 0.2 Probability of operator not hearing the alarm, POP=0.1