1) Construct a Hierarchical Task Analysis (HTA) diagram for the industrial operations described below.

Liquid hydrocarbon storage tank system shown in figure 1 consists of two tanks which are filled from a single pressurized line outfitted with a Pressure Indicator (PI). The liquid hydrocarbon is withdrawn or drained under gravity flow via a second line connected to each storage tank. The tank space for Tank 1 and Tank 2 is checked firstly before tank filling operation. Thereafter, Tank 1 and Tank 2 is purged individually for 15 minutes with nitrogen through their pressure control control valves (PIC) E and F respectively, and any gases are vented to the atmosphere by opening vent valves G and H. The operation to follow consists of sequential filling of Tank 1 and Tank 2 via inlet valves A and B respectively. Liquid draining operation is the next step whereby, liquid is supplied to the downstream process via Tnak 2 firstly and then Tank 1 via outlet valves D and C respectively. During liquid draining, valve E and F are opened to allow nitrogen ton purge and pressurize the vapour space in the tanks. The liquid levels in Tank 1 and Tank 2 are monitored during filling and draining operations via their Level Indicator (LI). At the end of the liquid draining, close valves E and F thena close Tank 2 and Tank 1 outlet valves.