Fire & Brimstone at the Buncefield Oil Depot, Hemel Hempstead

0520 GMT: Cal­cu­la­tions show that Tank 912 would be com­pletely full and start­ing to over­flow. Con­tin­ued pump­ing causes fuel to cas­cade down the side of the tank and through the air, lead­ing to the rap­id form­a­tion of a rich fuel/air mix­ture that col­lects in bund A — the low enclos­ure sur­round­ing 912 and neigh­bour­ing tanks.

0538 to 0546 GMT: CCTV foot­age shows vapour of escaped fuel start to flow out of the north-west corner of the enclos­ure, towards the west. The vapour cloud thick­ens from 1m deep to about 2m deep and soon flows out in all directions.

0550 to 0600 GMT: The pump­ing rate down the pipeline to Tank 912 gradu­ally rises to around 890 cubic metres an hour, and the vapour cloud starts flow­ing off-site.

0601 GMT: The first explo­sion occurs, and fur­ther explo­sions fol­low, even­tu­ally engulf­ing more than 20 large stor­age tanks.