Carbon monoxide forced 35 people out of their southeast Calgary homes Friday morning after a fresh air intake vent became plugged with ice.

Firefighters responded around 7:20 a.m. MT to the 15200 block of Bannister Road S.E. after a resident reported the smell of gas on the third floor. Crews told 35 people to leave the 60-unit building and discovered readings of 150 to 310 parts per million of carbon monoxide throughout the building.

The evacuees were able to stay warm in Calgary Transit buses until being allows back inside.

ATCO crews and firefighters found the source of the gas to be a fresh air intake vent on the roof that had become plugged with ice.

Crews are ventilating the building before evacuees will be allowed to return.

One person was assessed by EMS but no other injuries were reported.