Hurricane Irma has left millions people without electricity, as winds, rain and storm surges have brought down grid infrastructure across Florida and Georgia. Utilities were stuck waiting for safer conditions to assess the damage, before they can even begin to work on what is “likely to be one of the largest industry restoration efforts in U.S. history."

That’s how the Edison Electric Institute (EEI) trade group described the challenge facing utilities in the days and weeks to come. More than 6.1 million utility customers were without power in Florida, Georgia and South Carolina, it reported. 

In response, more than 50,000 workers from the U.S. and Canada have assembled at staging areas across the affected states, EEI wrote. But they face the same downed trees, washed-out bridges and roads, and coastal storm surges and flooding that are preventing emergency responders from getting to the worst-hit areas. 

Even after the storm passed, parts of the grid will “need to be rebuilt completely before power can be restored,” EEI warned. “This will delay restoration times, and customers should be prepared for the possibility of extended power outages.”