LONDON — An electrical substation fire that shut down Heathrow Airport, canceling more than 1,300 flights, was caused by a preventable technical fault identified almost seven years earlier, a report found Wednesday.
Europe's busiest air hub shut for about 18 hours in March after a fire knocked out one of the three electrical substations that supply Heathrow with power. More than 270,000 passengers had journeys disrupted.
Counterterrorism police initially led the investigation into the fire, which came as authorities across Europe girded against sabotage backed by Russia.
Though authorities quickly ruled out vandalism or sabotage, the fire's huge impact raised concern about the resilience of Britain's energy system to accidents, natural disasters or attacks.
The government ordered an investigation into ''any wider lessons to be learned on energy resilience for critical national infrastructure.''
The report by the National Energy System Operator said that an ''elevated moisture reading'' had been found in oil samples at the substation in west London in July 2018, but action wasn't taken to replace electrical insulators known as bushings.
It said that the March 20 blaze was caused by a ''catastrophic failure'' in one of the transformers, ''most likely caused by moisture entering the bushing causing a short circuit'' that ignited the oil.
The report also said Heathrow underestimated the likelihood of losing one of its three power sources, and as a result, ''its internal electrical distribution network was not designed or configured to take advantage of having multiple supply points to provide quick recovery following such a loss.''
