The incident happened at 24th Street and Snyder Avenue shortly after 6:30 p.m. Wednesday.
The truck was responding to a call when a 40-year-old male firefighter leaned against a door which apparently wasn't closed.
Medics rushed the man to the Hospital of the University of Pennsylvania for treatment.
He was showing stable vital signs while en route to the hospital.
There is no word on where his fire unit was responding to when the incident occurred.