Four adults are in critical life-threatening condition after a basement suite fire.

Officials say a space heater located too close to combustible material started the blaze.

Sources tell CTV News there were security bars on some of the windows, they were screwed to the frames and in one of the bedrooms the bars were bent from the inside.

The fire was reported around 2 a.m. on Monday.

A tenant living upstairs in the home, in the 500 block of 33 Street N.W., called 911 after hearing screams and seeing smoke coming from the basement suite. "I could hear somebody screaming downstairs and I tried to yell to see if anybody would hear me to help them out," says Rob Hannigan.

Hannigan grabbed a fire extinguisher and tried to put out the flames but the smoke was too thick.

Firefighters arrived to find the basement suite fully engulfed.

They quickly knocked down the fire and rescued one man and three women. All were unconscious by the time they were pulled out of the basement.

The victims are all between the ages of 19 and 30 and are in Foothills Hospital in life threatening condition.

A friend of the victims told CTV News that 19-year-old Johnathon St. Pierre and 19-year-old Tiffany Cox lived in the suite. He says the couple had just broken up. One of the other victims was a new roommate in the process of moving in.

CTV News has also learned that two of the victims have been taken to an Edmonton hospital for hyperbaric treatment. The treatment helps reduce swelling, limits progression of the burn injury and may reduce lung damage from smoke inhalation.

A small dog died in the fire.

Investigators found only one smoke detector in the basement and say there is no evidence it contained a battery.