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.