Investigation Reveals Preventable Causes of Heathrow Substation Fire

A recent investigation has revealed that the catastrophic fire at Heathrow Airport's North Hyde substation, which occurred on March 21, 2025, was primarily due to a preventable technical fault that the National Grid had been aware of for seven years. The National Energy System Operator (Neso) published its final report, detailing that moisture had infiltrated the insulation around electrical wires, leading to a significant power outage that disrupted over 1,350 flights and affected nearly 300,000 passengers, while also cutting power to 67,000 homes.

The Neso's report indicates that National Grid had detected elevated moisture levels in oil samples as far back as July 2018, yet failed to implement adequate mitigation measures. According to the report, “An elevated moisture reading… had been detected in oil samples taken in July 2018 but mitigating actions appropriate to its severity were not implemented.”

This oversight appears to have been compounded by a series of maintenance failures at the substation. The 77-page investigation revealed multiple opportunities for identifying the issue, with decisions made to defer essential maintenance. A review conducted by National Grid in 2022 highlighted that fire suppression systems at the site were inoperable, and a fire risk assessment in July 2024 indicated that if a fire broke out in any of the three supergrid transformers, it would not be adequately suppressed. Despite the identification of these risks, the necessary actions to rectify the issues remained outstanding at the time of the incident.

In response to these findings, the Office of Gas and Electricity Markets (Ofgem) has initiated an investigation into National Grid to determine whether it complied with legislation and license conditions regarding the maintenance of the electricity system. Ofgem's Director General for Infrastructure, Akshay Kaul, emphasized the importance of maintaining energy infrastructure, stating, “We expect energy companies to properly maintain their equipment and networks to prevent events like this happening. Where there is evidence that they have not, we will take action and hold companies fully to account.”

The forensic analysis conducted by Neso, in collaboration with the London Fire Brigade, uncovered a “catastrophic failure” of one of the transformer's high-voltage bushings, which serve to insulate electrical currents. The failure of this component ultimately led to the fire that resulted in an extensive outage at Europe’s largest airport. The airport's internal estimates suggest that reconfiguring its electrical network after such an outage typically takes between 10 and 12 hours, a fact not widely known outside the technical teams at Heathrow.

Despite the severe disruptions caused by the fire, three data centers connected to the airport's power supply were able to continue operations using backup generators. The Neso report noted that energy network operators generally lack awareness of whether their customers are classified as critical national infrastructure, highlighting a significant gap in operational communication.

Fintan Slye, the Chief Executive of Neso, acknowledged the professionalism of all parties involved in managing the crisis, despite its severe impact. However, the incident has been particularly damaging for Thomas Woldbye, the Chief Executive of Heathrow Airport, who publicly expressed regret for being uncontactable during the emergency. He reportedly slept through multiple emergency calls, raising concerns about the airport's crisis management protocols.

In light of the findings, the Energy Secretary Ed Miliband stated that the report is “deeply concerning” and indicated that the government will urgently review the recommendations outlined by Neso. The ongoing investigation by Ofgem aims to determine whether the failures observed are indicative of a broader systemic issue within National Grid’s operations.

This incident serves as a crucial reminder of the importance of maintaining infrastructure integrity, particularly in sectors critical to national and international operations. The implications of the report extend beyond Heathrow, prompting discussions about infrastructure reliability, regulatory oversight, and the potential need for reforms in energy management practices moving forward.