ExxonMobil Mossmorran plant leaks draw £267,000 fine after five corrosion failures

ExxonMobil‘s Mossmorran plant leaks have resulted in a £267,000 fine for the energy giant, after investigators found five separate releases of highly flammable hydrocarbons at its former ethylene facility in Fife, Scotland. The Health and Safety Executive (HSE), the UK’s workplace safety regulator, said it was only good fortune that none of the incidents ended in catastrophe.

Ethylene is a flammable hydrocarbon gas used in chemical manufacturing. The Fife Ethylene Plant at Mossmorran was classed as an upper tier COMAH (Control of Major Accident Hazards) establishment, meaning it was subject to the strictest possible safety controls because of the volumes of hazardous substances present and the risk they posed to people and the surrounding environment.

How the ExxonMobil Mossmorran plant leaks unfolded

The chain of events began when HSE inspectors visited the plant for a routine inspection on 21 May 2019 and noticed a strong smell of dimethyl sulphide (DMS), a highly flammable liquid that irritates skin and eyes and is harmful if swallowed. That discovery triggered a wider investigation, which uncovered a much longer history of problems.

Inspectors established that a leak had occurred from the same pipe back in February 2018, and that another pipe elsewhere on the site had also leaked in December 2018. Two further leaks followed: one on 29 June 2019 and another in September 2019. All five were caused by corrosion under insulation (CUI), a process that occurs when water penetrates the insulating material wrapped around pipework to prevent freezing, then corrodes the metal beneath.

The scale of those losses was not trivial. According to BBC News, the December 2018 leak alone released an estimated 82 tonnes of hydrocarbons into the atmosphere. HSE inspectors found that two of the five leaks continued for around four months each, while one lasted six weeks and another two weeks. No timeframe was given for the fifth.

HSE concluded that the company’s inspection system was not fit for purpose. ExxonMobil Chemical Limited admitted breaching the Health and Safety at Work Act 1974 and one of the Provision and Use of Work Equipment Regulations 1998 at a hearing at Kirkcaldy Sheriff Court. The £267,000 fine was imposed as a result. Production at the Fife Ethylene Plant ended in February this year.

Regulator says the failure “beggars belief” at a high-hazard site

HSE inspector Lindsey Stein was direct in her assessment. ‘At a site run by one of the biggest energy companies in the world, subject to the strictest controls, and processing high volumes of hazardous material, what our inspectors found beggars belief,’ she said.

Stein added that the failure to properly inspect insulated pipework led to five separate releases of highly flammable hydrocarbons, and that while none of the leaks resulted in a catastrophic event, ‘this was down to good fortune rather than good management.’ She described the corrosion detection and prevention arrangements as ‘woefully inadequate’ and said the measures needed to prevent the leaks ‘were reasonably practicable all along, and they should have been in place long before HSE was forced to intervene.’

On the broader principle, Stein said: ‘Systematic risk management isn’t just best practice, it’s a legal duty, precisely because these are high-hazard operations where the margin for error is minimal. In its simplest terms, process safety is about keeping hazardous substances where they belong: inside the pipes, not in the atmosphere.’

An ExxonMobil Chemical Ltd spokesperson said the company had ‘accepted responsibility and resolved a matter relating to historical corrosion under insulation issues at Fife Ethylene Plant between 2018 and 2019.’ The spokesperson stated that no workers, contractors or members of the public were put at risk, and that ‘the court held that no hazard was created and no actual harm was caused.’

The company said it co-operated fully with HSE throughout the investigation, commissioned an independent assessment, and has since made ‘significant changes’ to how it inspects and manages corrosion risk across its operations. It added that at the time of the incidents, the plant ‘was moving to a revised and improved inspection methodology’, which was subsequently implemented alongside a programme to address what it described as ‘legacy challenges.’

Stein’s remarks suggest the regulator views that explanation with some scepticism. Once HSE stepped in, she noted, the operator was able to identify and fix problems quickly and effectively, suggesting the technical means to prevent the leaks had been available throughout.