Firefighters were called to a row house on the 1600 block of North 20th Street just before 6:00 a.m.
They were told someone was trapped on the third floor.
Despite the flames and heavy smoke, three firefighters charged up the stairs.
They didn't find anyone, but before they could get back down, the fire flashed over and they were trapped.
Other firefighters got ladders extended to the third floor.
Two of the firefighters were able to get down safely.
But, the last out, Lt. Marvin Melvin, was badly burned and fell from the third floor. He was rushed to the Temple University Hospital in critical condition. He has since been upgraded to good.
The two other firefighters were also sent to the hospital but have been able to go home after treatment of relatively minor injuries.
Three adults and two children managed to escape the house.
But two of them, a 27-year-old woman and her 4-day-old baby were hospitalized in stable condition.
Fire Commissioner Lloyd Ayers says they're lucky they didn't lose the three firefighters trapped on the third floor.
He says there are strong indications the fire was deliberately set.
The fire marshal is now investigating.
Fortunately, the house did have functioning smoke detectors or the four occupants may not have had time to get out.
Commissioner Ayers says Lt. Melvin is expected to make a full recovery.
