Fire at a generator of a power plant

The incident occurred at the hydrogen coolant circuit, when purging the hydrogen with carbon dioxide and air, aiming at finding a leak. The explosion caused great damage to the turbine-generator unit and was felt by that residents 10km was misunderstood for an earthquake.
Following a preliminary investigation, the power plant company explained that hydrogen was still present when air was injected, creating the condition for the formation of an explosive mixture.

The INITIATING cause of the explosion was probably an inadequate purge procedure performed by injection of CO2 into the the hydrogel coolant system, followed by opening it to air. In presence of rest of hydrogen, air created the condition for an explosion. According to one of the sources, the internal pressure developed by the explosion could have been in the 5 to 10 MPa range. This assessment is based on the diameter and the tensile load of the bolts which failed.

Sources suggested that the explosion occurred due to deviation from the prescribed procedure. If confirmed, the root cause could be related to a human error or errors during the communication of the instructions. However, at 5 years from the explosion, there is no publicly available report providing a root case, which therefore remains unknown.

hydrogen cooling system, turbine, generator

The plant was a new coal-fired power station with a nominal powerof 4.8GW.
At the moment of the incident, only few units were already in function. The unit affected, of approximately 800 MW, was on a short-term outage.

No injuries have been reported. Emergency services attended to seven workers requiring treatment for shock.
The turbine hall and surrounding structures were affected: doors and windows of multiple structures were damaged, the roof sheeting blew off leaving the entire turbine hall area of the affected unit, as well as sections of other two units exposed to the elements. The damage to the generator was extensive (though not quanitfied by the owner).
Various sources estiamted the the costs ranging between 1.5 bn and 2.5 bn of rands (rough estimations not based on real damage assessment).