A 9-1-1 call Friday evening sent Saskatoon firefighters to a Greystone Heights apartment building.
In the call at 6:17 p.m., a resident described hearing a loud bang before the carbon monoxide alarms began to ring in the hallway.
When crews arrived at 20 Bateman Cres. they discovered 1,600 parts per million (ppm) of carbon monoxide, safe levels are typically lower than 100 ppm.
More fire crews were called in to help evacuate residents at the property.
SaskEnergy and the City of Saskatoon assisted as well.
The investigation determined kids playing in the area used exterior exhaust pipes to hang from which caused a break.
SaskEnergy and the property owner repaired the ventilation issues and got the boiler running safely again.
People were allowed to return to their suites a few hours after the evacuation.