Calgary fire fighters respond to a carbon monoxide leak at a downtown building.

A carbon monoxide (CO) leak at a downtown building Saturday morning sent dozens of people out into the frigid cold.  

The problem was discovered around 11:45 a.m at a building located at the 100 Block of 3 Ave. S.E.

Calgary fire crews found a reading of more than 100 parts per million inside the building.

CO levels of 50 parts per million or less is considered safe and anything higher than that is unsafe and the building needs to be evacuated.

Thirty to 40 people were forced from the building and a few took refuge from the cold inside some Calgary transit buses.

There are no reports of any injuries.

Alberta Health Services,  Calgary Hazmat crew and ATCO are all on scene working to determine the cause of the CO leak.