The Buncefield Depot is an oil storage facility located near the M1 motorway on the edge of Hemel Hempstead in Hertfordshire, England northwest of London. On Sunday morning December 11, 2005 a large explosion and fire occurred at the Buncefield Depot eventually involving over 20 fuel storage tanks. The explosion measured 2.4 on the Richter scale, caused severe damage to neighboring buildings, and damaged windows over a mile from the site. The incident has been called one of the largest fires in Europe since World War II and caused large smoke plumes over Southern England. Despite the significant damage caused by the event there were no fatalities or serious injuries.
Exponent provided engineering services to evaluate the cause of the explosion. It was determined that the explosion was caused by the overflow of a fuel storage tank. The tank overflowed for about 40 minutes at rates ranging from 2,400 to 3,900 gallons per minute creating a cloud of vapor that was visible on security cameras as it spilled over the bund wall in the northwest corner of the site. The cloud later spread throughout the facility and extended into the parking lot of neighboring facilities before it was ignited.