The huge blast at the Buncefield fuel depot in the town was heard as far away as the Netherlands and shrouded much of south-east England in smoke.
It was caused when thousands of gallons of petrol overflowed a storage tank after automatic monitoring systems broke down, an official report found.
A faulty fuel gauge appears to have allowed nearly five swimming pools' worth of petrol to flow into tank 912 at the depot between 3am and 6am that morning.
At the time, the Hertfordshire Oil Storage Terminal - co-owned by Total and Texaco - handled more than two million metric tonnes of fuel each year and was the fifth largest oil products storage depot in the UK.
Today, 15 years on, we look at some of the pictures of the huge blast.
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