The risk assessment of a marine system is carried out at the early design stages.
It has been identified that a serious hazardous event (top event) arises if
event X happens together with the occurrence of event Y or Z.
Event X occurs when event A or B happens.
Event Y occurs when
(event B happens) or (events B and C occur simultaneously).
Event Z occurs when
(events A, B, C and D happen simultaneously) or (events A, C and D
happen simultaneously).
Events A, B, C and D are independent basic events.
It is assumed that basic events A, B, C and D follow an exponential distribution.
The failure rates for basic events A, B, C and D are 0.0001, 0.0002, 0.0003 and
0.0004 (per hour), respectively.
i) Draw the fault tree for the above top event.
ii) Find the minimal cut sets leading to the top event.
iii) Discuss how the occurrence likelihood of the top event can be
reduced/eliminated.
iv) Calculate the occurrence probability of the top event at t = 1,000 hours.
v) Suppose a particular risk control measure is taken to eliminate the possible
occurrence of basic event B. The elimination of the occurrence of basic
event B does not affect the other three basic events A, C and D in terms
of their failure rates and independence. Calculate the current occurrence
probability of the top event at t = 1,000 hours.
(vi) Suppose event E = A·B·+ B·C + B·D + C·D. Calculate the occurrence
probability of event E at time t = 1,000 hours.