Sleipner A is a combined accommodations, production and processing offshore platform at the Sleipner East gas field in the Norwegian sector of the North Sea. It is a Condeep-type oil platform, built in Norway by the company Norwegian Contractors for Equinor. It is known for its catastrophic failure on 23 August 1991, due to a design flaw, that resulted from an error caused by unconservative concrete codes and inaccurate finite element analysis modelling of the tricell, which formed part of the ballasting/flotation system. Location Sleipner A is located on the Sleipner East gas field on the North Sea. Also six satellite fields–Gungne, Loke, Alpha North, Sigyn, Volve and Volve South–are tied-back to Sleipner A. In addition to its own operations, the platform is used as a remote operation center for the Sleipner B wellhead platform. The Sleipner B is operated from the Sleipner A via an umbilical cable. In addition, the Sleipner T carbon dioxide treatment platform is linked physically to the Sleipner A platform by a bridge. Design The platform is designed to accommodate roughly 160 people. The platform deck is with height of . The original hull was a gravity base made up of support pilings and concrete ballast chambers from which three or four shafts rise and upon which the deck sits. Once fully ballasted, the hull was to sit on the sea floor. There were 24 chambers, of which four formed the 'legs' supporting the facility on top in the case of the Sleipner A oil rig. The hull was redesigned after the accident and the Sleipner A Platform was successfully completed in June 1993. 1991 accident Collapse The original hull collapsed during the final construction because of a design flaw. It was towed into Gandsfjord where it was to be lowered in the water in a controlled ballasting operation at a rate of 1 meter per 20 minutes. This was necessary for the fitment of the deck platform to the hull. As the hull was lowered to the mark, rumbling noises were heard followed by the sound of water pouring into the unit. A cell wall had failed and a serious crack had developed, and sea water poured in at a rate that was too great for the deballasting pumps to deal with. Within a few minutes the hull began sinking at a rate of 1 meter per minute. As the structure sank deeper into