An Allegheny Power transformer exploded Tuesday morning, touching off a fire that burned throughout the day, officials said.
Hagerstown Fire Department Battalion Chief Richard Hopkins said firefighters were called to the substation at Wilson Boulevard and Oak Street at about 8:20 a.m.
At one point, officials from the power company tried to put out the fire with a dry chemical, but Hopkins said it kept re-igniting.
"The decision was made to let it burn," he said.
Hopkins said there were about 100 gallons of mineral oil that were burning.
"It's not a real fierce fire. It's just gradually burning itself out," he said.
Debbie Beck, a spokeswoman for Allegheny Power, said the fire started when a metering outfit failed. The device works just like a meter at a private home, she said.