Several hundred students at the Art Institute of Philadelphia were forced from the 14-story building before dawn Monday after carbon monoxide detectors went off. The dorm is home to about 550 students.
Fire officials say three women had to be taken to hospitals following the evacuation.
School spokeswoman Carise Mitch says about a half-dozen students complained of illness following the evacuation. Two went to hospitals and were later released.
The city ordered the building closed until the source of the gas is found. That could take several days.
Mitch says the students will be housed at hotels until they can return to the dorm.
Two restaurants on the building's ground floor are also shut down.
