A fire at a Lawrenceville barbecue restaurant that surprised employees and threatened power lines was caused by a lightning strike, Gwinnett County fire officials said Wednesday.

No one was injured in Tuesday’s fire at Sonny’s BBQ at 660 Duluth Highway, Gwinnett fire spokesman Capt. Ryan McGiboney said. The restaurant’s manager called 911 after a customer in the drive-thru told employees she could see smoke coming from an exterior wall.

Soon after the manager was told about the fire, employees began to see smoke and flames inside the building and evacuated, McGiboney said. Firefighters arrived about five minutes after the 911 call and began battling the flames from ladder trucks out of safety concerns over the power lines around the building.

Once the fire was knocked down, firefighters searched the building and confirmed no one was inside, McGiboney said. Crews stayed in the building to monitor for airborne chemicals while utility workers secured services like natural gas and electricity. The fire was extinguished about 22 minutes after the initial 911 call.

Because the fire was caused by a lightning strike, investigators deemed it accidental, McGiboney said.