Question 3 (20 marks)

At one nature gas process plant, one 5-inch LPG line operating at 750psi was accidentally cut by a contractor under a routine inspection. LPG vapour was released and covered an area of 50 acres. After around 5 minutes, the vapour cloud was ignited by an unknown ignition source. It was estimated that around 20,000 gal of LPG was lost. Four people died in the accident and eight others were injured. The business was interrupted for 6 six months. In the accident, it took more than 8 hours before the fire was extinguished, and two reasons were found later. One was the failure of the engine-driven fire pumps because the intense heat radiation made its ignition wires damaged. The other one was because the fire broke a fuel gauge, and diesel fuel (to drive the fire pump) was released and ignited, and then the fire pump engine was destroyed.

Based on the accident, please use LPG fire as the main risk and apply the systematic method Bow-tie diagram to analyse the causes and consequences related to the accidents.