Structural collapse caused the release of around 2,400kg of highly flammable liquid petroleum gas.
HSE investigation found that long-standing corrosion of the steel tower was not dealt with.
Workers exposed to the risk of serious injury and burns in a major incident.
The refinery has been fined £1 million after a major gas leak following an investigation and subsequent prosecution by the Health & Safety Executive.
On 8 November 2022, a partial collapse of a large steel tower caused the structure to slew and rupture pipework, resulting in the uncontrolled release of liquefied petroleum gas (LPG).
The incident led to the loss of approximately 2,400kg (5,300 pounds) of LPG over a 33-hour period. It took just over 30 minutes for around 400kg (~900 pounds) of the gas to be released following the collapse.