The official investigation of the loss of the Alexander Kielland rig in the
Norwegian sector of the North Sea in 1980 correctly established many
causes, but others were not disclosed until other countries that operate
similar rigs carried out further investigations3.
The rig was semi-submersible. In use the pontoons (Figure 28.2)
were full of water and the rig was partly submersed in the water for
maximum stability. When being moved the pontoons were pumped out
and the rig rose 21 m higher. Though designed as a drilling rig it was
being used only for accommodation. During a heavy storm in March
1980 column D, like the others 8.5 m diameter, broke and the rig
turned upside down. There were 212 men on the rig at the time; 123
of them died.