Cause of substation fire which knocked out power to Heathrow ‘still unknown’

The cause of an electricity substation fire which triggered the closure of Heathrow for almost a day in March still remains unknown, according to an initial report into the incident.

The airport was shut for the majority of March 21 due to the offsite blaze at the substation near Hayes in west London.

Interim findings into the North Hyde substation outage by the National Energy System Operator (NESO) comes ahead of a final report due to be published in June. 

The NESO found that the resulting outage from the fire led to 66,919 customers losing power, including the complete loss of power to part of Heathrow’s private internal electrical distribution network.

“Heathrow airport took the decision to close due to the disruption caused to operationally critical systems following the power outage,” the interim report said.

“Heathrow airport closed for the majority of Friday 21 March, partially reopening that afternoon. 

“To enable this, Heathrow Airport Limited, utilising its two other electrical connections to SSEN (Scottish and Southern Electricity Networks) Distribution’s system, reconfigured its own internal electrical distribution network to restore power to its terminals and wider airport infrastructure.

“Heathrow airport reopened for business-as-usual operation on Saturday 22 March.

“The root cause of the fire remains unknown whilst forensic fire investigations are ongoing.”

The Metropolitan Police confirmed on March 25 that it had "found no evidence to suggest that the incident was suspicious in nature".

The report added: “Looking ahead, NESO anticipates that the final report will contain findings and recommendations relating to the resilience of energy infrastructure, the response and restoration of energy infrastructure including cross-sector incident management, and the resilience of critical national infrastructure to energy disruption.”

A Heathrow spokesperson said: “Heathrow welcomes the NESO review’s initial report, which raises important questions for National Grid and SSEN that we hope the final report will provide answers to, including the cause of the fire. 

“Further clarity on how the fire started and why two transformers were subsequently impacted can help ensure greater resilience for the UK’s energy grid moving forward.”