‘Only when the tide goes out do you discover who’s been swimming naked.’ – Warren Buffet 27 Mar 2025

Shortly before midnight on Thursday 20^th March a fire at the North Hyde electrical substation in Hayes, west London, knocked out power to 63,000 homes and Heathrow Airport; also affected by the fire were a significant proportion of London’s data centres.

As a result of the fire Heathrow airport was closed for 18 hours affecting over 1350 flights and impacting the travel plans of 200,000 travellers. By comparison no data centres have reported any downtime due to the fire.

So why were the operations of data centres and Heathrow airport impacted so differently?

In short it appears that all the back-up systems and redundancy designed into the data centres worked as expected: UPS (uninterruptible power supply) systems instantly kicked in, meaning no interruption of power to data halls whilst in the background back-up generators fired up and power supplies were switched to alternative substation feeds.

Comparisons between the fifth busiest airport in the world and data centres are slightly unfair and it should be noted that the emergency back-up systems at Heathrow did allow all planes to be safely landed or diverted and the airport to be shut down in a safe manner. That probably provides limited comfort to the affected travellers and airlines.

Whether Heathrow’s back-up plans provided sufficient resilience for this ‘unique event’ will be a key topic for the upcoming NESO (National Energy System Operator) investigation, but I suspect the answer will be no.

Resilience in data centres is already clearly defined, systems are designed, installed and, crucially, tested for this situation. On this occasion, to everyone’s relief it looks like the data centre operators were wearing their bathing suits.

Written by Chris Mason

AP Photo/Kirsty Wigglesworth