On the 14 August 2003, a complex combination of immediate events and longer term vulnerabilities led to a domino effect in which 50 million people had their power supplies interrupted. Consequent losses were between $5–$10 billion. It is, therefore, one of the most serious disruptions to a national power distribution network. The causes included technical issues to do with network capacity and the algorithms used to predict potential distribution problems. It also had managerial and human factors causes; these arguably included an over-reliance on automated monitoring systems. The infrastructure failure also stemmed from governmental and regulatory intervention in the operation of the energy markets. The following paper applies accident investigation techniques to represent and reason about the complex interactions between these causes. In particular, we use Violation and Vulnerability (V2) diagrams to map out arguments for and against market deregulation as a causal factor in engineering failures.