A man and three women were unconscious when firefighters pulled them out of the smoky basement. ((CBC))

The smoke detector was likely not working during a basement blaze that sent four people to hospital in critical condition early Monday morning, Calgary fire investigators say.

Firefighters pulled a man and three women, all unconscious, from the smoke-filled basement of a house in the 500 block of 33 Street N.W. about 2 a.m., spokesman Jeff Budai said.

Robin Hannigan, who lives upstairs in the rental home, told CBC News that yelling and the dog barking woke him up at about 2 a.m.

"As soon as I stood up off my bed, I couldn't see anything. I could hardly breathe," he said. "There was just smoke billowing up from downstairs."

Hannigan said he grabbed his fire extinguisher but could not get downstairs, so he called 911.


A space heater may have started the fire, said the Calgary fire department. ((CBC))

When firefighters arrived, they broke down the door and found the four people, all in their 20s. They also found a small dog that had died of smoke inhalation.

Although the fire was contained to one corner of the basement, heavy smoke made the search for those inside a real challenge, Budai said.

Hannigan said his smoke detector did not go off until "a little while" after he woke up, adding he wasn't sure whether the detector in the basement was working.

Investigators found one smoke detector in the suite but it had melted from the heat of the blaze, said Budai.

"The detector is not believed to have been wired directly, nor did investigators find any evidence that it contained a battery," he said.

A space heater that was positioned "too close to combustibles" is believed to have started the fire, he added.

The man taken to hospital was in the process of moving out, his friend Leo Pinto said. He believed the three women taken to hospital were his friend's ex-girlfriend, a new roommate and another friend.

"From what I hear, they're in intensive care," Pinto said.

The fire caused about $100,000 worth of damage to the building.

Fire investigators said they're checking to see whether the security bars on some of the windows had been installed properly.