A 2-man crew of a vacuum truck was carrying out a routine activity of discharging oily sludge at a waste management pit. The inexperienced helper switched the pump to discharge oily waste, and then opened a valve on the discharge line. There was no flow. With the pump still running, the helper tried to unblock the valve by using the stick of a sweeping brush. Whilst trying to unblock the valve, pressure in the tank was building up followed by a pressure surge which blew open the tank rear door and hit the helper in the head throwing him 13 m towards the waste pit. He died immediately .