The jury in the trial of three firms accused over the explosion at a Hertfordshire oil depot in 2005 has retired to consider its verdict.
The blast at the Buncefield depot caused widespread damage and injured 43 people, St Albans Crown Court heard.
Hertfordshire Oil Storage Ltd (HOSL), TAV Engineering Ltd and Motherwell Control Systems 2003 Ltd deny health and safety breaches.
Homes and businesses were destroyed in the UK's biggest peacetime blaze.
The explosion, which measured 2.4 on the Richter scale and could be heard 125 miles away, happened after a massive vapour cloud ignited when 250,000 litres of petrol leaked from one of its tanks, the court heard
Hertfordshire Oil Storage Limited, known as HOSL, of Clarendon Road, Watford, denies failing to prevent a major accident.
TAV engineering of Sydenham Road, Guildford, denies failing to ensure employees were not exposed to risks.
Motherwell Control Systems 2003, of Castle Street, Liverpool, denies failing to ensure employees were not exposed to risks. The company, which is in voluntary liquidation, was not represented.
The jury was told Total UK and the British Pipelines Agency Limited had already pleaded guilty to offences under the Health and Safety at Work Act.