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The fire that closed Heathrow airport in March was caused by problems at an electricity substation which National Grid first identified seven years ago but failed to fix, an official review has found.
The government-owned National Energy System Operator said in a report released on Wednesday that the fire in March was caused by a โcatastrophic failureโ at the North Hyde substation in Hayes, west London, after moisture got into the โbushingโ equipment, through which current flows in and out of the transformer.
The report said that National Gridโs electricity transmission division had identified high moisture readings in oil at the substation as far back as 2018, but did not address the problem.
It said the readings indicated an โimminent faultโ which required the bushing to be replaced, but โmitigations appropriate to its severity were not actionedโ.
โThe controls in place were not effectiveโ.โ.โ.โThis review finds that there were other opportunities which, had they been pursued, could have caught the issue. Instead, the elevated moisture reading went unaddressed,โ the report added.
The blaze destroyed the substation, triggering power outages for about 70,000 customers in the region including Heathrow airport, Europeโs busiest airport.ย
The closure of Heathrow led to the cancellation of more than 1,300 flights and raised widespread questions about the resilience of critical national infrastructure.ย
Britainโs energy regulator said it has opened an investigation into National Grid Electricity Transmission.
โIt has been established that the root cause of the fire was a preventable, technical fault,โ Ofgem said in a statement.
Ed Miliband, the energy secretary, added the review was โdeeply concerning, because known risks were not addressed by the National Grid Electricity Transmissionโ.
In a statement, National Grid said it has โa comprehensive asset inspection and maintenance programme in placeโ.
โWe have taken further action since the fire. This includes an end-to-end review of our oil sampling process and results, further enhancement of fire risk assessments at all operational sites and retesting the resilience of substations that serve strategic infrastructure,โ it added.
Heathrow, which has faced criticism for its decision to close for a full day following the blaze, said the incident โhighlights clear shortcomings in National Gridโs asset management and outdated safety standardsโ.
