PHILADELPHIA (CBS) – Some residents living in South Philadelphia had quite a scare Sunday.

According to PGW, a carbon monoxide leak in the 1800 block of Broad Street in South Philadelphia displaced 10 people sending four to the Hospital of the University of Pennsylvania. The four people were conscious upon arrival.

The carbon monoxide leak was on the third floor of the apartment building. The heater was not connected in the basement of the apartment building and the heat on the third floor was on and set to 95 degrees. Because the flue was not connected in the basement, it caused a carbon monoxide leak on the third floor.

PGW has reconnected everything. The six people evacuated and not taken to the hospital have returned to the building.