A chemical process takes place in a reactor vessel continuously, but it has to be monitored for abnormal behaviour. The system has two sensors S1 and S2 that can independently detect an abnormal temperature. They pass an electrical signal to an electrical OR-gate A, which passes a signal on to both the protection units P1 and P2 if either sensor gives a signal. The protection units and the OR-gate get electrical power from electric power unit E1, while sensors get power from electric power unit E2. Build a (qualitative) fault tree for the top event "Protection system not available" using failure of the indicated components.

A chemical process takes place in a reactor vessel continuously, but it has to be monitored for abnormal behaviour. The system has two sensors S1 and S2 that can independently detect an abnormal temperature. They pass an electrical signal to an electrical OR-gate A, which passes a signal on to both the protection units P1 and P2 if either sensor gives a signal. The protection units and the OR-gate get electrical power from electric power unit E1, while sensors get power from electric power unit E2. Build a (qualitative) fault tree for the top event "Protection system not available" using failure of the indicated components.