Thick, black smoke could be seen coming from a building at 12th and Sansom streets during the noon hour Monday.
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Video shows explosion during fire on top of Center City high-rise
A second alarm was called around 1 p.m., and the fire was declared under control a short time later.
The Philadelphia Fire Department said the building is a high-rise residence that is under construction.
The fire involved roofing materials, insulation and propane tanks.
Video from Action News viewer Kelsey Lock shows the fire from across the street.
It shows the smoke rising into the air for a few moments before a propane tank on the roof explodes.
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The Philadelphia Fire Department says about 100 firefighters responded to the scene.