Fire officials say flames and smoke raced up the first-floor stairwell and went through the whole building.
PHILADELPHIA (WPVI) -- The ATF is now investigating after three residents and a firefighter were injured in a suspicious fire at an apartment building in Northeast Philadelphia.
The two-alarm blaze broke out on the 8200 block of Frankford Avenue at about 3 a.m. Monday.
Fire officials say flames and smoke raced up the first-floor stairwell and went through the whole building.
The flames displaced 30 occupants of the building.
A SEPTA bus was called to the scene to provide a warm space for residents.
The victims include two men, a woman, and one firefighter.
There is no word on their conditions, but officials said they suffered minor injuries.
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