Residents of a Royal Oak complex in the 8800 block of Royal Birch Boulevard were evacuated this morning after carbon monoxide alarms went off in the building.
Fire crews arrived at the building and found carbon dioxide levels between 50 and 400 parts per million in the building.
The quickly evacuated residents going door to door to make sure everyone got out of the building safely.
Calgary transit provided buses as temporary shelters for the evacuated residents.
Fire officials were eventually lead to the roof where they found the vents that cycle the air were blocked by ice build up.
Crews fixed the blockage an the allowed the ventilation system to reset and residents were allowed back into the building.
The Calgary Fire Department wants to remind Calgarians of the importance of working carbon monoxide alarms.
For more information go to www.calgary.ca/fire.