The Health and Safety Executive and the Environment Agency this week announced plans to prosecute Total UK, Hertfordshire Oil Storage, British Pipeline Agency, TAV Engineering and Motherwell Control Systems over the blast at the site in Hemel Hempstead in December 2005.
More than 40 people were injured in the incident which damaged thousands of homes and was Britain's biggest peacetime explosion.
The agencies - which are jointly responsible for regulating non-nuclear hazardous industrial sites in the UK - said the criminal proceedings followed a "thorough and complex" investigation.
They declined to comment further.
TAV Engineering is facing one charge of failing to ensure its employees were not exposed to health and safety risks, while Total UK is facing three charges, of failing to ensure the safety of its employees, of failing to ensure the safety of people it did not employ, and of polluting ground water with fuel and firewater chemicals.
Hertfordshire Oil Storage and British Pipeline Agency are both charged with failing to take all the measures necessary to prevent a major accident and with polluting groundwater with fuel and firewater chemicals. Motherwell Control Systems faces one charge of failing to ensure people it did not employ were not put at risk.
The five firms will make their initial appearance at the West Hertfordshire Magistrate's Court in Watford in January.