One week after a catastrophic fire at the North Hyde electrical substation plunged the UK’s flagship Heathrow Airport into chaos, questions are mounting about what went wrong—and what the incident reveals about the vulnerabilities in Britain’s aging power infrastructure.
A massive explosion and fire that erupted around 8:20 p.m., on Thursday, March 20, at the North Hyde electrical substation near the international airport caused widespread power outages across West London and prompted the temporary closure of Heathrow Terminals 2 and 4. The airport faced significant disruptions, forced to cancel over 1,300 flights—outages that affected more than 290,000 passengers.
At its peak, the fire knocked out power to an estimated 67,000 households and businesses. The London Metropolitan Police declared a major incident at 12:42 a.m. on March 21. With more than 70 London Fire Brigade personnel on the scene, crews worked to evacuate residents and contain the blaze.
“The fire involved a transformer comprising 25,000 liters of cooling oil fully alight,” said London Fire Brigade Deputy Commissioner Jonathan Smith during a press briefing. “This created a major hazard due to the still live high-voltage equipment and the nature of the oil-fueled fire.” Firefighters worked in what Smith described as “very hazardous conditions,” establishing a 200-meter exclusion zone while coordinating with “specialist power network engineers” from National Grid, which owns the substation, to work toward restoring power.
Power supplies were ultimately restored to all customers connected to the North Hyde substation at 6 a.m. on March 22, National Grid reported, following a grid reconfiguration in partnership with local grid operator SSEN Distribution as an interim solution.
While the blaze was brought under control early on Friday, March 21, the fire was not fully extinguished until Thursday, March 27—seven days after it began—owing to residual hotspots within the oil-filled transformer. Firefighters used bulk foam, indirect misting techniques, and drone-based thermal imaging to monitor and suppress the blaze, eventually cutting through the steel casing once the equipment cooled. LFB noted it initiated a more aggressive response once oil levels dropped significantly. A waste management company is working alongside partners to dispose of oil and water to minimize environmental impacts.
The cause of the fire remains under investigation. LFB is leading a fire investigation focused on the substation’s electrical equipment, conducted under the authority of the Regulatory Reform (Fire Safety) Order 2005. The Metropolitan Police have confirmed they are not treating the fire as “suspicious.”
Separately, on March 22, UK Energy Secretary Ed Miliband used new Energy Act powers to commission the independent National Energy System Operator (NESO) to investigate the power outage that impacted Heathrow’s Terminals 2 and 4 and surrounding areas. The probe—launched in coordination with the Office of Gas and Electricity Markets (Ofgem)—will seek to uncover both the immediate cause of the disruption and any broader risks to energy resilience across critical national infrastructure. “We are determined to properly understand what happened and what lessons need to be learned,” Miliband said.
Ofgem Director General for Infrastructure Akshay Kaul said the entity will work with the government and NESO to ensure the “review goes as far as possible to ensure steps are put in place to avoid any repeat of an incident of this scale in the future.” If “the review finds any breaches of standards or license obligations, we will not hesitate to take action,” he said.
Early Forensics: What Might Have Gone Wrong
However, experts from across the industry have speculated that the fire may have stemmed from a failure within an oil-filled power transformer at the 275-kV North Hyde Substation. This is consistent with incident footage showing large flames and heavy black smoke at the substation.
National Grid owns the 1960-built North Hyde Substation, one of several substations that feed into the North Hyde Grid Supply Point (GSP)—a critical electricity interface owned and operated by Scottish and Southern Electricity Networks (SSEN). SSEN transforms high-voltage transmission power into lower-voltage electricity for local distribution in West London as one of the UK’s two primary distribution network operators. The North Hyde GSP encompasses a network of 66-kV, 22-kV, 11-kV, 6.6-kV, and low-voltage circuits and serves about 64,000 customers. SSEN confirms that two of its distribution network sites within the GSP directly supply Heathrow Airport, while other substations and GSPs also provide dedicated power to different parts of the airport campus
SSEN notes that, as part of a broader strategic reinforcement plan, North Hyde Substation was slated to replace its three existing transformers with new 60 MVA 66/11kV units and install a new 11-kV switchboard by 2028 to support projected demand through 2050. The strategic plan rolled out last year notably seeks to address rapid load growth and capacity constraints driven by new housing, commercial development, and data center connections in West London along with addressing aging infrastructure. Given that the North Hyde Substation forms part of Britain’s original 275kV supergrid commissioned in the 1950s and 60s, some of the site’s infrastructure, including its large power transformers (LPTs) may date back more than 60 years. Current records indicate that the substation serves approximately 64,000 customers with a 2023/24 peak recorded demand of 169.44 MVA.
“The initial press reports suggest that the fire is due to an electrical fault that developed within an oil-filled transformer at the substation. Such a failure would have caused severe and widespread electrical arcing activity–‘sparking’–which would have ignited the oil as it was ejected forcefully from the transformer. This would have resulted in a large fire that was difficult to extinguish,” Stuart Mortimore, a fellow of the Institution of Engineering and Technology and a fire and forensic investigations expert, said in a statement on March 21.
“The damage caused makes it unlikely that much useful physical evidence will remain. The investigation is therefore likely to concentrate on the operation of the transformer and its maintenance. Specifically, if it had an on-load tap changer—a complicated switch that can automatically change the output voltage while supplying electricity—that was operating at the time of the fire, this could point to a fault with the switch,” he added.
“While transformer failures do occur 2.4–4% over a 40-year lifespan, fires causing mass outages are rare,” noted noted Dr. Conor Murphy, vice president of Engineering at NovoGrid, an Irish company specializing in grid analytics software. “However, the oil-cooled equipment in substations poses inherent fire risks, particularly from aging infrastructure or overloaded systems. While not common, they are planned for, there is typically a concrete blast wall surrounding transformers at this voltage level.”
“Common causes of substation fires include transformer overloads, insulation failures, arc flashes from faulty wiring or maintenance errors, and voltage surges or equipment degradation. The exact cause of the Heathrow fire remains under investigation, with no confirmed details yet available. I’d speculate it was an aged asset in this case, but have limited knowledge of the equipment specifics,” he added.
Murphy, however, also pointed to more extensive damage. “From the footage, I have seen, it looks like the air-insulated switchgear may have sustained significant damage from being in the vicinity of the fire. Damage to these components would disrupt power routing and safety mechanisms, so they will need to be made good again prior to energizing the site,” he said.
Transformer Fire Risk and Protection StrategiesWhile the Heathrow incident underscores the real-world risk of transformer fires, transformer safety is a well-studied area where industry knowledge—and practical protection strategies—are highly developed. In a December 2024 POWER feature, John Sinisi and Montgomery Sinisi of Sinisi Solutions—a New Jersey-based firm specializing in designing and deploying innovative fire and ballistic barrier solutions to protect critical infrastructure from hazards—outline some best practices for minimizing the risk of catastrophic transformer failures. “Substations and electrical switchyards are vital nodes within the power grid, facilitating electricity conversion from high-voltage transmission lines to lower-voltage distribution networks,” they write. “Transformers, the cornerstone of these facilities, are highly susceptible to explosion and fire hazards due to high-energy electrical environments and flammable insulating materials, such as oil. Environmental factors, such as lightning strikes or equipment failure, can further escalate the risks of explosions and fires.” The experts recommend passive fire barriers as a vital safety measure to physically isolate transformer fires, minimizing the spread of flames, heat, and smoke. Barriers provide continuous, no-activation-needed protection (unlike sprinkler or foam systems) and require minimal maintenance. Beyond mitigating damage, they help utilities comply with NFPA, IEEE, and FERC safety regulations while shielding nearby control buildings and sensitive infrastructure. Barrier design should also account for transformer spacing (such as the 50-foot rule), wind and seismic conditions, and environmental risks like water contamination. Custom-built barriers, they note, can be deployed even in tight substations or retrofitted into existing facilities to strengthen fire resilience, they said. Read the full article here: Transformer Safety: Fire Barriers as Essential Protection for Electrical Infrastructure |
Grid Weaknesses and Lack of Redundancy
For now, questions are also swirling around the resiliency and redundancy of the UK’s grid.
National Grid CEO John Pettigrew earlier this week suggested to The Financial Times that there should have been enough power for Heathrow to remain open during the debacle, noting two other substations serving the airport were working. UK Transport Secretary Heidi Alexander later reportedly told Sky News that the airport’s decision to close the terminals was a precautionary measure prompted by the need to fully shut down and restart critical systems in certain terminals.
Even so, the incident underscores a significant weakness in the UK’s grid infrastructure, experts said. “The scale, that is the impact from a single point of failure, is extremely high because of its impact on Heathrow Airport,” Murphy said. “To me the event is unprecedented owing to its impact on critical infrastructure impact. Complete airport shutdowns due to power failure is extremely rare. This suggests a simultaneous loss of primary, standby and local backup power sources, which is unusual.” Redundancy is typically built into grids, he noted.
That lack of resilience, some experts argued, is partly structural. Prof. Martin Kuball, a Royal Academy of Engineering Chair in Emerging Technologies at the University of Bristol, said the National Grid lacks built-in resilience “because we still rely on old technology in sub-stations that use copper windings to distribute power rather than new technology, so-called solid state transformers.” He added: “Due to this, there is currently still a rather sparse distribution of these substations rather than a more resilient network.” However, solid-state transformer technology remains “five to ten” years from full deployment, he noted.
While the UK—like many countries—recognizes the urgency of grid modernization, it faces formidable challenges, particularly a global supply chain crunch for critical components. In a February 2025 report, the International Energy Agency (IEA) warned that it now takes two to three years to procure cables and up to four years to secure LPTs. In addition, “The results of our survey suggest that prices for cables have nearly doubled since 2019, and the price of power transformers rose by around 75%,” it notes. As POWER has reported in great detail, a shortfall in specialized labor is just one concern among other substantial hurdles.
Manufacturers have responded by ramping up transformer production, but major suppliers like HD Hyundai Electric and Hyosung Heavy Industries reported a combined order backlog exceeding $10 billion by Q3 2024, while Hitachi Energy’s backlog has more than tripled in four years to surpass $30 billion, the IEA noted.
The strain poses a significant challenge for National Grid as it embarks on “The Great Grid Upgrade,” a comprehensive initiative to modernize and expand the UK’s transmission and distribution network to support the nation’s decarbonization goals. National Grid in December rolled out plans to invest approximately £35 billion in its transmission business over the five years leading up to March 2031. This investment includes over £11 billion dedicated to maintaining and upgrading existing transmission networks, as well as constructing three Accelerated Strategic Transmission Investment (ASTI) projects designed to connect 50 GW of offshore wind energy by 2030. Overall, the strategy encompasses an estimated £60 billion investment over a five-year period to upgrade the energy system.
“Lessons will be learned,” said Prof. David Flynn of the University of Glasgow. But what is immediately clear is that Britain must invest in dedicated R&D to address the vulnerabilities exposed by this incident—especially at the nexus of energy and transportation. That includes important research from national initiatives like the Data and Resilience Hub and the Transport Systems Integration for Transition program, which are “integral to how we advance practices, understanding and enabling technologies towards improving the resilience of our increasingly interconnected transport and energy infrastructure and services.”
—Sonal Patel is a POWER senior editor (@sonalcpatel, @POWERmagazine).
Editor’s Note (Updated March 29): This story has been updated to reflect new details from the London Fire Brigade indicating that the fire at the North Hyde substation was fully extinguished on March 28.
