A fire at Heathrow which left 200,000 passengers stranded in a major shutdown was most likely caused by a problem which had been known about since 2018, a report has found.
Fire at an electrical substation led to the UK’s busiest airport being shut down for almost an entire day earlier this year, with over 1,300 flights grounded.
A review by the National Energy System Operator (Neso) has found it was most likely caused by moisture present in a transformer since 2018, which went ‘unaddressed’.
The report said moisture had been detected in oil samples at the North Hyde site seven years previously, but action was not taken to replace electrical insulators known as bushings.
No flights operated at the west London airport until about 6pm on March 21 because of the blaze, which started late the previous night.
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The final report by Neso said there was a ‘catastrophic failure’ in one of the transformers, ‘most likely caused by moisture entering the bushing causing a short circuit’, which ignited the oil. The report said: ‘An elevated moisture reading in one of SGT3’s (the transformer’s) bushings had been detected in oil samples taken in July 2018.
‘According to National Grid Electricity Transmission’s relevant guidance, such readings indicate ‘an imminent fault and that the bushing should be replaced’.
‘While the reading was recorded in National Grid Electricity Transmission’s online system, the mitigations appropriate to its severity were not actioned.
‘The controls in place were not effective and failed to identify subsequently that action had not been taken in relation to the elevated moisture reading. This includes an opportunity in 2022 when a decision was taken to defer basic maintenance on SGT3. The issue therefore went unaddressed.’
A spokesperson for Heathrow said the National Grid’s ‘failure to maintain its infrastructure’ led to the power outage.
The spokesperson said: ‘Heathrow welcomes this report, which sheds further light on the external power supply failure that forced the airport’s closure on March 21.
‘A combination of outdated regulation, inadequate safety mechanisms, and National Grid’s failure to maintain its infrastructure led to this catastrophic power outage.
‘We expect National Grid to be carefully considering what steps they can take to ensure this isn’t repeated.
‘Our own review, led by former Cabinet minister Ruth Kelly, identified key areas for improvement and work is already under way to implement all 28 recommendations.’
Energy Secretary Ed Miliband said: ‘The report is deeply concerning, because known risks were not addressed by the National Grid Electricity Transmission, and Ofgem has now opened an official enforcement investigation to consider any possible licence breaches relating to the development and maintenance of its electricity system at North Hyde.
‘There are wider lessons to be learned from this incident. My department, working across government, will urgently consider the findings and recommendations set out by NESO and publish a response to the report in due course.’
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