ATLANTA — How could one fire knock out the main power to the world’s busiest airport and at the same time disable the backup power?

The head of Georgia Power Co. said Monday it’s because power feeds from two sources come together in one place — and he said officials are looking at ways to make sure it doesn’t happen again.

A fire in an underground service tunnel brought Hartsfield-Jackson Atlanta International Airport to a standstill Sunday. Power wasn’t fully restored until about midnight. Thousands of flights were canceled, and thousands of passengers stranded.

Georgia Power believes the failure happened in a switch gear within the service tunnel, the utility’s CEO Paul Bowers told The Associated Press.

“We don’t know what caused the failure, but we do know the failure caused the fire and the fire is what really disrupted the service at the airport,” he said.

According to Bowers, there are two power feeds at the airport from two different substations, and the fire disrupted both feeds. Cables from both substations are mounted on a wall, with the switch at the base of the wall. When the switch ignited, flames went up the wall and set the cables on fire, he said.

He said, it’s too early to say definitively how the power supply setup will be changed, but officials are exploring alternatives.

One possibility: Isolate the switch gear, perhaps in concrete encasement, to retard any fire. Another: Put concrete encasement around the wires on the wall.

He also said it would also be possible to separate power sources for each concourse.