Smoke from the Buncefield fire on 11 December 2005 quickly traveled with clouds, winds, to cover much of SE England.

BUNCEFIELD FIRE LIKELY CAUSED WHEN PETROL (GASOLINE) BEING POURED INTO TANK OVERFLOWED, SPARKED
9 May 2006

New report suggests mechanical failure caused gauge reading fuel levels in one tank to "stick", leading to workers filling the tank to be unaware it would shortly overflow. Fuel kept being poured into the tank, allegedly until it somehow caught a spark, causing a massive explosion and the largest fire in Europe since the Second World War.

The fuel tank in question reportedly overflowed for an estimated 40 minutes before the fire. The amount of fuel spilled is not clear, but would have been a significant amount, putting the facility at serious risk for conflagration. There is not considered to be any definitive information at present available as to what sparked the fire or why the fire spread to rapidly and so extensively throughout the entire depot.

One local man whose home was destroyed by fire told BBC News 24 the explosion was "inevitable, really", given the fact that "fumes" were constantly spewing from facility. The comment is clearly anecdotal, and such details have not been not thoroughly investigated.

There is a criminal investigation ongoing to determine wrongdoing and allocate any blame for criminal negligence, if there is any; that investigation is expected to answer many of the outstanding questions about exactly what happened and why the explosion was so massive. Damage to the facilities was so extensive, it is expected to be difficult to determine the precise sequence of events. [s]

BACKGROUND:
OIL DEPOT FIRE LEADS TO SPREADING SMOKE & SOOT CLOUD OVER LONDON
11 December 2005

Today the city of London was obscured by a cloud of black smoke emanating from a massive petroleum fire at the Buncefield fuel depot, in Hertfordshire, near Luton airport, north of London. The fire resulted from at least one severe explosion at the fuel storage facility. The blast occurred just after 6:00 GMT and was reportedly heard up to 100 miles away, including in northern France and the Netherlands. [Full Story]