The committee was briefed on the incident that took place on 9 February 2011, where the Unit 4 turbo generator at Duvha Power Station destructed during an annual statutory overspeed test. The purpose of the test was to check the integrity of the mechanical trip mechanism which should shut off the steam supply and prevent the turbine exceeding its safe speed limit. The mechanical trip mechanism failed to operate during the test. The electro-hydraulic governor failed to impose the safe speed limit. Due to the rapid acceleration rate allowed by the modification, the operators only had seconds in which to activate the emergency push buttons near the front pedestal and in the control room when the turbine exceeded 3 500 rpm. The unit destructed at about 4 100 rpm. Large parts of the machine such as bearing pedestals, shaft couplings and turbine blades were ejected. There were no physical injuries to staff. A fire broke out in the area between the intermediate pressure (IP) cylinder and the front pedestal, but it was effectively dealt with.