National Grid 'failed to fix substation fault that shut Heathrow'

The root cause of the substation fire that shut Heathrow was a preventable fault that National Grid knew of seven years ago but had failed to fix, investigators said yesterday.

- Mark Sweney

The final report by the National Energy System Operator (Neso) on the incident said the fire that cut power to the airport on 21 March was "most likely" sparked by moisture entering the insulation on wires. The outage affected more than 1,350 flights, almost 300,000 passengers and cut power to 67,000 homes.

Neso said National Grid, which owns the North Hyde substation, had been aware of the issue in 2018.

"An elevated moisture reading had been detected in oil samples taken in July 2018 but mitigating actions appropriate to its severity were not implemented," the report said. "National Grid has since initiated an end-to-end review of its oil sampling process, with a view to ensuring that it is robust."

The 77-page report catalogued numerous chances to identify issues at the substation but said decisions had been repeatedly made to defer basic maintenance.