The Delaware County Daily Times (http://bit.ly/Msx8Ky ) says the blaze broke out shortly before 4 p.m. Friday in Upper Darby.
Mayor Thomas Micozzie said the blaze was declared under control within 20 minutes.
He says the firefighters were in the living room checking for hot spots that might rekindle the flames when the plaster ceiling fell on them.
One firefighter was admitted to the Hospital of the University of Pennsylvania for observation. Two others were treated at Delaware County Memorial Hospital and released.
The blaze gutted the first floor of the residence, displacing seven people as well as four people in an adjoining unit. The cause is under investigation.
Information from: Delaware County Daily Times, http://www.delcotimes.com