Dozens of residents were forced out of their southeast condominiums early Friday morning because of a build up of carbon monoxide inside the building.

Fire crews were called to the complex at 15204 Bannister Road S.E. at about 7:20 a.m. after a resident on the third floor of the building smelled gas.

When crews arrived, they evacuated 35 people from the 60 unit building and Calgary Transit buses were brought in to keep them warm.

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

Firefighters found readings of 150 to 310 parts per million of CO thoughout the building and began ventilating it.

Crews say a fresh air intake on the roof was clogged with ice and was the source of the Carbon Monoxide.

Carol Henke, the public information officer with the Calgary Fire Department, says that carbon monoxide is very deadly. "When you are exposed to carbon monoxide for an extended period of time, it can be deadly. That's why we call carbon monoxide the silent killer. It's odourless, tasteless, non-irritating. So, the only way you would know that carbon monoxide is in your home is either through a carbon monoxide alarm or you can feel the symptoms which can be similar to flu-like symptoms. It can be confusing for people - do I have the flu or do I have carbon monoxide in my home?"

She says the only place the building had carbon monoxide detectors was down in the parkade.

Henke says that carbon monoxide detectors are part of new buildings, but there are no regulations to have them in older buildings. "When new buildings are built and new furnaces installed, it's code to have a carbon monoxide detector on every level outside the sleeping areas. Older buildings don't have that requirement."

Alberta does not have laws governing carbon monoxide detectors but Ontario just voted last month to make them mandatory.

The carbon monoxide leak is the third major incident in the past 24 hours.

Fire and ATCO crews worked until midnight Thursday after a major gas line break affected about 400 homes in the Kensington area. 19 homes in the neighbourhood were evacuated.

Not long after that, another gas line rupture affected dozens of businesses in Crowfoot.

The breaks were quickly repaired and no one was reported injured.