Some initial and provisional explanations as to why the design defects came about and why the accident progressed in such a catastrophic manner are presented by the Swiss Federal Nuclear Safety Inspectorate (ENSI) in its reports which examines the circumstances before, during and after the accident. In order to understand the scope and complexity of the event, an interdisciplinary analysis team was formed at ENSI. Its members include (for example) experts in the fields of people and organisation, radiation protection, electrical engineering, mechanical engineering, materials technology and system technology.