What caused the fire that shut down London’s Heathrow Airport?

LONDON – Investigators combed through the burned-out remains of a power substation near London’s Heathrow Airport on March 21, seeking the cause of a spectacular blaze that shuttered Europe’s busiest travel hub for much of a day and raised broader questions about Britain’s energy infrastructure.

Officials and energy experts said a fault in a transformer with 275,000 volts running through it probably sparked a massive, oil-fuelled fire that severed the airport and tens of thousands of nearby homes from the power grid. Systems designed to prevent such a fire apparently failed, and the size of the blaze appeared to keep a second, nearby transformer from restoring electricity.

But the mystery of what caused that fault in the first place remained far from solved by the end of the day on March 21, even as

flights resumed at Heathrow.

The Metropolitan Police in London said that counter-terrorism specialists had taken charge of the investigation, “given the location of the substation and the impact this incident has had on critical national infrastructure”. At the same time, political leaders and industry experts said it appeared most likely that the fire was an accident.

Both possibilities left residents of Britain and global travellers rattled.

If a malicious adversary can so dramatically disrupt worldwide travel by causing a fire in a neighbourhood power station, it raises new concerns about the ability of open societies like Britain’s to guard against such non-traditional attacks.

And if the fire was the result of an undetected weakness in the basic infrastructure of Britain’s power grid, the scope of the chaos that was unleashed could undermine confidence in the nation’s ability to fix crumbling systems at a time when finances are strained.

Prime Minister Keir Starmer and Mr Sadiq Khan, the Mayor of London, sought to reassure residents and travellers on March 21, with Mr Khan telling Sky News in an interview that despite the involvement of counter-terrorism officers in the investigation, there was “no reason at all for anyone to be concerned or alarmed”.

Still, neither the Prime Minister nor the Mayor offered answers to some of the urgent questions being asked by frustrated travellers, nervous neighbours of the airport and political officials across the country.

Why didn’t the airport have sufficient power backups? Did the electric utility not plan for the possibility of such a fire, either from sabotage or technical malfunction? Do major airports usually have backup systems that can power the entire operation, or do they rely on one main source of energy?

Mr John McDonnell, a lawmaker who represents Hayes, the area where the fire broke out, said that any investigation undertaken in the days ahead would need to look at “why backup arrangements have not worked”.

“There are lessons that have got to be learnt here,” he told reporters on March 21 afternoon.

By early afternoon on March 21, Britain’s National Grid said the network of the North Hyde substation, where the fire happened, had been reconfigured to restore power to the airport and neighbourhood, calling it an “interim solution” while repairs get under way. Officials with National Grid did not respond to an e-mail requesting information about the incident.

That announcement paved the way for a partial opening of the airport, where the first flights began landing again by evening.

“We will now work with the airlines on repatriating the passengers who were diverted to other airports in Europe,” airport officials said in a statement. “We hope to run a full operation tomorrow.”

But even as Heathrow attempts to return to normal operations, a sense of uncertainty remains.

Mr Ed Miliband, Britain’s Energy Secretary, said in an interview early on March 21 with Sky News that the fire at the electrical substation that crippled Heathrow Airport also took out at least one of the main backup systems designed to keep the power running.

“There was a backup generator, but that was also affected by the fire, which gives a sense of how unusual, unprecedented it was,” Mr Miliband said.

Transformers convert current from one voltage to another, and are often filled with oil that acts as both an insulator and a coolant. The types of oil used can withstand high temperatures, but they can ignite if they get hot enough.

In the case of the transformer near Heathrow, experts said it would have been turning 275,000 volts into 66,000 volts when it apparently failed.

Mr Jonathan Smith, the deputy commissioner for the London Fire Brigade, said the blaze involved “a transformer comprising 25,000 litres of cooling oil that was fully alight” at the substation.

The failure of at least one backup system to quickly restore power after such a major outage is likely to be at the centre of questions about the reliability of Britain’s infrastructure in the aftermath of the fire and airport closure.

In a statement, Heathrow Airport said that the facility had “multiple sources of energy” but that there was no backup that would supply enough power to operate the entire airport, which it said “uses as much energy as a small city”.

The statement said that backup diesel generators and uninterruptible power supplies did kick in that would have allowed planes to land and passengers to disembark. But they would not have been enough to allow the airport to operate fully.

Mr Simon Gallagher, a former senior executive at Britain’s largest power provider, said he believed the substation near Heathrow had been designed so that if the first transformer had a problem, a second one could kick in quickly.

“Basically, we designed things so that something can fail”, and the system can still continue working, he said.

But, he said, a number of things must have gone wrong, seemingly allowing the fire to rage through the prevention systems and damage both transformers. That is highly unusual, said Mr Gallagher, who is now the managing director at UK Networks Services, which advises clients on the resilience of their electricity networks. NYTIMES