Police say Amanda Gessner touched off 7 blazes in trash and brush between 3 a.m. and 5:45 a.m. Tuesday within blocks of where she lives in Upper Darby Township.
Officials say Gessner was witnessed earlier in the evening at a local convenience store singing the ditty about the fire department. Her tune was caught on the store's surveillance camera.
One fire damaged a home where a family of four was sleeping. They escaped without injury.
Gessner is being held on $100,000 bail, charged with arson and related offenses.
Authorities say they have no reason to believe she is connected to the recent arsons in Coatesville, a few miles away.
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