Five firms have been fined a total of almost £10m for their part in the Buncefield oil depot explosion in December 2005.
French energy giant Total was fined £6.2m for failing to protect workers and the public while Hertfordshire Oil Storage Limited (HOSL) was fined £2.4m.
British Pipeline Agency Ltd was fined £780,000 at St Albans Crown Court.
TAV Engineering Ltd and Motherwell Control Systems have been fined a combined £15,000.
HOSL was found guilty of failing to prevent major accidents. Total UK admitted failing to ensure the safety of workers and members of the public.
British Pipeline Ltd also admitted two charges in connection with the explosion, failing to prevent major accidents and limit their effects, and causing pollution to enter controlled waters.
The blast injured 43 people and homes and businesses were destroyed.
Commenting HCCI Chief Executive, Tim Hutchings said, "There will be some that think these fines are too lenient but our main concern is to see that any outstanding claims are dealt with as quickly as possible. I would also like to pay tribute to the resilience of the businesses who were caught up in this dreadful event",.