The evacuation of inhabitants and an economic loss of at least 2 million Euros in 2004 were the result of a burst in a small water main, located in the dike of an inland canal. This incident was investigated on the highest level by the Dutch Safety Board. Several combining factors like descending of the dike, stress built up in the concrete protection sleeve and corrosion of the main eventually caused the subsidence of the dike. The Board emphasized to the drinking water companies the need of a management system for external safety. To prevent reoccurrence, Vewin, the Association of the Dutch Water Companies, together with the Dutch drinking water companies, have developed a methodology to measure and support the implementation of a safety management system. Furthermore, an approach was developed and implemented to identify external safety risks of mains which cross or lie parallel to primary dikes, primary motorways and railways. On a national level, 3,044 primary locations were identified where potential unsafe situations might exist This article describes the methodologies which are illustrated by the practical experiences of Vitens, the largest drinking water company in the Netherlands.
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