The warnings to residents in the south-east US came right before Christmas: delay washing clothes or running the dishwasher, and curb hot water use until the bitterly cold temperatures eased up.

It still wasn’t enough for two of the nation’s largest electric utilities.

As temperatures plummeted to 40F (4.4C) in a few hours and gale force winds swept across the region between 23 and 24 December, the pre-holiday preparations were put on pause as Tennessee Valley Authority (TVA) and Duke Energy implemented historic rolling blackouts lasting about 30 minutes to an hour.

By some accounts the utilities’ inability to supply power during the extreme weather almost plunged the entire eastern US into darkness. And in some parts of the country, as much as 63% of the outages came from natural gas plants, according to the PJM Interconnection, an organization that operates the largest regional power grid in the US.