Questions:

1. Develop a Bow Tie Model incorporating Fault Tree & Event Tree for the top event “Pump Fails to Stop” in the pump-tank system below. Describe the preventive and recovery barriers in place. What would be your recommendations on additional barriers.

Fluid from a reservoir (not shown) is pumped into a tank. Switch shown in the pumping circuit is normally closed. Pumping is initiated by an operator who manually re-sets the timer (as given in Operating Manual), upon which the timer contact closes and pumping starts. Before any over pressure condition exists, the timer times out and opens the contact, thereby stopping the pump and preventing tank rupture due to overpressure. If the timer contact does not open with the pump still running, the operator observes reading on Pressure Gauge and opens the manual switch, thereby stopping the pump. If both the timer and operator fail, the relief valve protects the tank from overpressure.