An inquiry into last December's explosions at the Buncefield oil depot in Hemel Hempstead has blamed the failure of mechanical safeguards to detect leaking fuel. BBC News looks at the chronology of events in the run-up to the first explosion.
1900 GMT, 10 DECEMBER 2005
Tank 912 in an enclosure to the west of the main oil depot starts to receive unleaded motor fuel from a pipeline, pumping at about 550 cubic metres an hour.
0000 GMT, 11 DECEMBER
The terminal closes to tankers and a stock check of products is carried out, which reports "no abnormalities".
The level gauge for Tank 912 records an unchanged reading, but filling of Tank 912 continues at a rate of around 550 cubic metres an hour.
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.
The first explosion occurs, and further explosions follow, eventually engulfing more than 20 large storage tanks.
The main explosion is centred on the car parks between the site and the Fuji and Northgate buildings.
The exact ignition points are not certain, but are likely to
have been a generator or the pump house.
At the time of the explosion, the vapour cloud extends almost 300m to the west and north of the tank.