A bizarre carbon monoxide leak in Point Grey forced a family to evacuate their home on Wednesday after poisonous gas started leaking from the furnace of a neighbouring house into theirs.

The public information officer for Vancouver Fire and Rescue Services said he's never seen anything like it in his career.

"That is exceedingly unusual," Jonathan Gormick said. "The carbon monoxide was actually coming from a neighbouring house and being pulled into the air intake of the house in which the alarm was going off."

He says it must have been the perfect combination of exhaust vent placement, air intake placement and air currents that night.

When fire crews arrived around 8 p.m., they found high and irregular carbon monoxide levels and called in a hazmat team.

After discovering the problem, crews shut down the furnace.

Gormick says this scare goes to show how important it is to have working carbon monoxide detectors—even if your home doesn't use any gas-powered appliances.

"No one would ever know [carbon monoxide is] present without the alarm," he said. "That's a deadly circumstance."

Carbon monoxide attaches to the same hemoglobin receptors in red blood cells that are meant to carry oxygen. With all the red blood cells full of the wrong gas, the body becomes starved of oxygen and can die.

Poisoning starts with decreased level-of-consciousness and fatigue.

"People tend to go to sleep and the carbon monoxide accumulates and you have tragic results," Gormick said.

Thankfully, the residents in this scenario did everything right—they exited the building when their detector went off and phoned the fire department.

With a report from CTV Vancouver's Shannon Paterson.