No 5 Turbine before
This incident happened Saturday 7th August 1971 without any warning. Luckily it was a weekend because fewer people were around on site. No 5 Turbine was running normally when a loop pipe `Bailey Joint’ by the RHS of the Turbine HP Cylinder failed. The force of the steam was so great that the loop pipe straightened up as shown in the photographs. The loop pipe was only approx. 4m from the `C’ Control Room door and the blast pointed towards No 4 Turbine and `B’ Control Room approx. 40m away.
Steam at 110bar 568degC was blasted down the turbine hall. Luckily no one was in the immediate direction of the blast or they would have been killed or seriously injured. The tremendous noise and the turbine hall filling with steam and dust was so quick and severe that the staff in the `C’ Control Room were shocked, concerned for their own safety and not sure what had happened. The control room rapidly filled with steam and dust making it difficult to even tell which unit the steam was coming from. Several people tried to escape through the back doors of the Control Room.
Frank Stone, the Engineer in `C’ Control Room crawled on his hand and knees to the back door of the Control Room but couldn’t see anything for steam and dust so he crawled back to the turbine panel and hit the No 5 Unit emergency trip button.
The damage caused by the steam blast included:
- Blew all the lagging insulation from everything in its path creating a “dense grey-brown fog and incredible noise” as one witness described. This would have contained asbestos from the damaged insulation.
- Lifted and shattered all the tiles off the turbine hall floor between No 5 and No 4 Turbines and blew them away. Some of these destroyed an air conditioning unit on `B’ Control Room.
- Blew the planks off a nearby scaffold. One scaffold board landed where someone had been working on No 4 feed pump bearings some 12 metres below.
- Moved an access platform in its path with such force that it damaged oil pipes on the next turbine.
No 5 Turbine after.. Photo supplied by Andrew James
- People say an instrument fitter was blown over some distance away and moved along the floor fortunately without injury.
- Lifted the residual dust from any location in its path and made it airborne. Asbestos, coal dust etc. This dust would have been breathed in by anyone in the area during or immediately after this disaster and then settled out along the turbine hall.
- The Crane driver was on the crane catwalk above the turbine when the blast occurred. “He just dropped, face down, and left a perfect outline of his body on the catwalk.” – where the dust had settled around him. There were pictures of this outline in the dust.
No. 5 Turbine after. Photo supplied by Andrew James
- The residual dust (containing asbestos) that lay in many places which were not cleaned would have remained dormant for years until disturbed.
Definitions
Turbine – A steam turbine is a device that extracts thermal energy from pressurised steam and uses it to do mechanical work on a rotating output shaft. In this case the energy produced by the turbine is used to drive an electrical generator. At Castle Donington there were six 100 Megawatt Turbine/Generator units. They were supplied with steam from their associated boilers at 110bar 568degC.
Steam Chest – A steam chest is a high pressure vessel which receives steam from the boiler and feeds it to the turbine via an emergency stop valve and a governor valve which regulates the output of the turbine. At Castle Donington there were two steam chests for each turbine. They were fixed either side of the turbine high pressure cylinder and supplied steam to the turbine via four loop pipes.
Loop Pipe – is one of four pipes in the form of a loop to allow enough flexibility for the turbine to expand and contract as it heats up and cools down. These four loop pipes supply steam from the two steam chests to equal positions around the input nozzles of the high pressure turbine.
Castle Donington Information
