Using the figure to answer the question.

The safety system for the following pressure vessel consists of four valves, which are connected to the tank. The valves will open if the pressure in the tank exceeds a certain level (for example P0). The content in the tank will be released to the environment if both valves Al and A2 on Line-1 or both valves A3 and A4 on Line-2 are open.

a) Construct fault tree analysis for this system, b) Assuming the probability of failure for each valve is 0.01, determine the probability of failure for the top event, c) The reliability of the system.

NB: There is a solution of this question in chegg but this was not correct. So don't copy from that source