The sudden collapse of a tower crane on a building site resulted in severe injuries to the driver. Failure took place at the upper portion of the foundation or lowermost section. The mast sections were constructed from four main corner angles welded to end frames also made from angle sections which were gusseted and fitted with additional doubling plates in the corners where the jointing bolts were fitted. It was evident that the collapse was due to failure of the welds attaching the corner angles to an end frame. Many of the welds at the locations where failure occurred were of poor quality. The corner angles appeared to have been cut slightly shorter than the required dimensions. This was compensated in one case by the use of a weld build-up and in the other three by make-up pieces attached by welds of insignificant dimensions.