[30 points] In the water pumping system below, the operation of the pump is automatically controlled via a timing contact. The timer is set to automatically open the contact (and, therefore, disconnect the pump from its power supply) 10 min. after the switch is closed. If the timer fails, the operator is expected to intervene if he/she notices an overpressure alarm. Contact Switch Power supply Operator Pump Timer coil Emergency valve Alarm Tank To perform Human Reliability Analysis (HRA) for this operator's intervention, task analysis has been conducted and the following tasks for the operator to carry out have been identified: Task 1. Upon noticing the alarm, correctly select a gauge for the tank pressure. Task 2. Read the pressure gauge to check if the pressure level inside the tank exceeds a setpoint value. Task 3. Manually turn off the switch (from the "closed" position to the "open" position) to stop the pump (disconnect the pump from its power supply). Task 4. If the pump cannot be turned off, open the emergency valve by turning the rotary control in the correct direction (from "closed" to "open") to open the emergency valve. 1 Given that the actual pressure inside the tank exceeds the setpoint value, the operator is required to turn off the pump or open the emergency valve (if the pump cannot be turned off). There is a high-level dependency between Tasks 3 and 4. No dependency is considered for other tasks. The pressure gauge is a digital display located on a display panel with displays that appear similar and are grouped based on their functions. The switch is a manual two-position switch that is located on a panel with an array of similar-appearing controls identified by labels. Human factor analysis has shown that the designs of the switch and the rotary control associated with the pumping system have no violation of populational stereotypes. Suppose that the hardware systems (e.g., alarm, electrical circuit, pump, and valve) are 100% reliable. a. [5 points] Develop the HRA Event Tree for this problem. b. [25 points] Suppose that the operator is well trained for this accident scenario, but due to a high level of concern with the severe consequences that can be potentially caused by a tank rupture, the operator is under moderately high stress. Calculate the failure probability of this operator's intervention using the THERP technique. You can refer to the tables attached at the end of this HW (Appendix I).