Fire investigators believe a spectacular two-alarm blaze at a city school happened after roofing workers took a smoke break.

Thursday afternoon's fire at East Middle School on East Frederick Street generated a giant plume of dark black smoke that was visible for miles. Firefighters brought the blaze under control after about 20 minutes.

The fire has been ruled accidental. A city fire investigator said the blaze likely was the result of "reckless disposal of smoking material."

Many cigarette butts were found on the roof. All of the workers who were involved in a roofing project at the time the fire erupted were interviewed by investigators, as were most of the school employees who had been in the building.

Investigators eliminated all other probable causes in making their determination.

There was minimal damage to the school. Water caused some damage to three classrooms and two bathrooms on the fourth floor.

Most of the fire damage was confined to the roof - which was being replaced - and to the roofing materials being used for the project.

Work on the roof resumed the day after the fire.

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