UPDATE — Dec. 6, 2018: Vancouver Coastal Health says 12 of the 13 people poisoned were released from hospital by Wednesday evening. As of 5 p.m. PT that day, the condition of the final person in hospital is listed as stable.

Thirteen people at a Vancouver office were taken to hospital Wednesday morning due to a poisoning incident involving carbon monoxide, according to B.C. Emergency Health Services.

B.C. EHS, which administers the province's ambulance service, said in a tweet two people were critical when taken to hospital.

A spokesperson for the health service said a 911 call came in just before 10 a.m. PT reporting a collapsed person at an office on West Fifth Avenue, between Fir and Pine streets.

In the 1600 block of west 5th Avenue in Vancouver following reports that 13 people were sent to hospital due to a carbon monoxide exposure <a href="https://twitter.com/cbcnewsbc?ref_src=twsrc%5Etfw">@cbcnewsbc</a> <a href="https://t.co/UwpqKSobcw">pic.twitter.com/UwpqKSobcw</a> —@CoryCorreia

EHS says ambulances responded two minutes later and carbon monoxide detectors worn by the paramedics detected the gas. In all, EHS says, five ambulances and two paramedic supervisor vehicles attended the scene.

An employee at the office said three units were evacuated due to the incident.

Fans were put in place to clear the air and, with the doors left open, employees were allowed back in around noon, he said.

BCEHS Paramedic Specialist Jodi Butterman on today’s response to a medical emergency at a building in Vancouver, and the importance of carbon monoxide monitors worn by paramedics. <a href="https://t.co/RYYAdAu0xf">pic.twitter.com/RYYAdAu0xf</a> —@BC_EHS

'It would have been a disaster'

Dr. Bruce Campana is one of the physicians who treated the 13 people poisoned Wednesday.

Campana works with the hyperbaric chamber unit at Vancouver General Hospital where patients suffering severe carbon monoxide poisoning are cared for.

He said one patient from the incident was placed in the massive steel device while the rest were "unwell" and would likely remain in hospital.

Dr. Bruce Campana stands in front of the hyperbaric chamber at Vancouver General Hospital. (CBC)

"If they had stayed there they would have gotten very sick. They would have started having seizures and would have died," Campana said.

"Fortunately they did have detectors — which for some reason went off later than I would have thought — and they were able to remove the people before too much damage was done.

"Had they stayed there, it would have been a disaster."

Campana explained that he has not heard what the exact cause of the poisoning was but said it may have had something to do with a faulty furnace exhaust system.

'Silent killer'

Carbon monoxide is a gas that cannot be seen, smelled or tasted.

HealthLink B.C. says it is called the "silent killer" and breathing in too much of it can cause poisoning death in minutes as it replaces oxygen in the blood.

Carbon monoxide can be given off by furnaces and other heating devices in the home if they are improperly installed or used or malfunction, it said.

Patients with severe carbon monoxide poisoning are treated inside this hyperbaric chamber at Vancouver General Hospital. (Meera Bains/CBC)

The provincial health information website recommends getting carbon monoxide detectors for the home and provides other safety tips online.

Campana said this mass poisoning incident was not isolated during what he called an "insane" week.

He's aware of 17 cases of carbon monoxide poisoning in the last few weeks.

"There are many more that I'm not aware of," Campana said. "We've had three that we've had to treat, one of whom, unfortunately, is probably going to die."

He said as temperatures have been dropping more people are cranking up the heat. He was emphatic on the importance of carbon monoxide detectors, not having unventilated burning in the home — including gasoline, propane or anything else.

Learn more about carbon monoxide detectors

Jonathan Gormick of the Vancouver Fire Department answers the top five questions about carbon monoxide safety. 1:32

With files from Joshua McLean, Meera Bains and Cory Correia