The Buncefield depot is one of the largest oil storage and transfer sites in the UK, handling refined petroleum products and additives before distribution to other facilities. On Sunday 11 December 2005, over-filling of tank 912 with unleaded car fuel resulted in spillage of 300 tonnes of petrol around the tank and formation of a vapour cloud. This ignited at 06:01 hours, producing an explosion and fire that burned for five days, by which time 23 tanks of diesel, kerosene and aviation fuel had been destroyed. The fire plume was dispersed widely above a temperature inversion layer, limiting the ground level plume deposition and resulting health hazards. This chapter describes the circumstances of the event and the Health Protection Agency public health response. Aspects covered include estimation of emissions and pollutants, public health response, environmental impact findings (including atmospheric and plume dispersion modelling, air quality monitoring and international impact) and health impact findings (including emergency department case note review, an occupational health surveillance register, and the Buncefield follow up population survey). The significance of the findings and public health lessons identified are discussed, including consideration of potential health outcomes for different meteorological scenarios that had occurred on other days during 2005.