In a matter of hours Calgary Fire rushed to the scene of not one but two carbon monoxide calls in the city which impacted hundreds of people.

It began Monday night in the northwest community of Royal Oak.

Crews were called out to the 8000 block of Royal Birch Boulevard NW around 10pm after a carbon monoxide detector went off at a 142 unit condo complex.

Approximately 200 people were forced out of their homes and into the cold, until Calgary Transit buses arrived.

Calgary Fire determined that carbon monoxide levels were twice the acceptable amount inside the condo complex.

The source of the problem, iced over vents that blocked fresh air from getting into the building, instead producing dangerous levels of the odourless and colourless gas.

The second incident happened around 3am Tuesday morning on Bannister Road in the SE. The source of the CO build up there was a faulty heating unit on the roof of the building.

When carbon monoxide scares make headlines, it’s a somber reminder for Oksana Irwin. She lost a loved one earlier this year to CO poisoning and their passing acted as the catalyst to get a CO detector for her home.

“It was disturbing, that’s kind of put me on other level of concern and say it happened to my friend It can happen to anyone.” says Irwin.

Here’s a checklist for homeowners to help prevent carbon monoxide build up:

Have experts annually inspect fuel burning appliances

Check furnace filters monthly

Clear debris or snow from vents and chimneys

Make sure flames from all natural gas appliances are blue

Install and maintain CO detectors

Don’t leave vehicles idling in garages

Ontario is the only province in Canada that has made carbon monoxide detectors mandatory.

The Hawkins Gignac Act was named after members of a Woodstock, Ontario family died from carbon monoxide poisoning in 2008.