Europe's busiest air hub was shut down for around 18 hours on 21 March after a fire at the North Hyde substation in west London knocked out power to the airport.
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A fire at a power substation that led to the cancellation of more than 1,300 flights at the UK’s Heathrow Airport was caused by a preventable technical fault identified almost seven years earlier, according to a report released on Wednesday.
The report by the National Energy System Operator stated that an "elevated moisture reading" had been detected in oil samples at the substation in west London in July 2018. However, no action was taken to replace the electrical insulators, commonly referred to as bushings.
The March blaze was caused by a "catastrophic failure" in one of the transformers, according to the report's findings, "most likely caused by moisture entering the bushing causing a short circuit" that ignited the oil.
The report also stated that Heathrow underestimated the likelihood of losing one of its three power sources. 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."
Energy Secretary Ed Miliband said that the findings were "deeply concerning".
Energy industry regulator Ofgem had opened an investigation into whether the substation’s operator, National Grid Electricity Transmission, had breached its license condition, Miliband explained.
National Grid said that Britain has "one of the most reliable networks in the world, and events of this nature are rare. National Grid has a comprehensive asset inspection and maintenance program in place, and we have taken further action since the fire."
Europe's busiest air hub was shut down for around 18 hours on 21 March after a fire at the North Hyde substation in west London the previous night knocked out power to the airport.
More than 270,000 passengers had their journeys disrupted.
Counterterrorism police initially led the investigation into the fire, which came as countries across Europe were on high alert against Russian-instigated sabotage.
Although authorities quickly ruled out vandalism or sabotage, the fire’s significant impact raised concerns 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."