SASKATOON -- Residents of an apartment building in the city's Greystone Heights neighbourhood were evacuated Thursday evening after an emergency room doctor's hunch led to the discovery of potentially lethal levels of carbon monoxide (CO).

Around 6 p.m., an emergency room physician reported the potential issue, asking for a check on the building located on Bateman Crescent after observing symptoms in a patient.

After firefighters arrived and took readings, high levels of CO were detected, especially in the building's boiler room.

"When you have a reading such as we had in this building when it's over 400 parts per million (in the boiler room), people can die within two to three hours of exposure," said Saskatoon Fire Department Chief Morgan Hackl during a virtual news conference Friday morning.

Close to 50 people including some children, were evacuated from the building, Hackl said.

Twenty-nine people were taken to hospital by paramedics, according to Medavie Health Services, which activated its Special Operations Unit used for large numbers of patients. All were in stable condition.

Medavie spokesperson Troy Davies said the doctor's quick thinking "probably saved lives."

In its media release concerning the incident, Medavie thanked Dr. [Mark] Wahba for his role in potentially preventing a tragedy.

Amit Kotwani, along with his wife and six-year-old daughter, was among the dozens of people sent to hospital.

“I was told that if I stayed one more night over here, I would have died,” Kotwani said.

Kotwani said his apartment unit is located right next to the boiler room, where the highest CO levels were detected.

During Monday's news conference Hackl said more people have since sought medical attention, bringing the total to 47.

Due to the high CO readings, firefighters geared up in self-contained breathing equipment while they cleared the building.

Saskatoon Transit assisted paramedics in transporting patients to hospital and the Salvation Army helped the building's residents to find a place to stay for the night as SaskEnergy workers began searching for the cause of the elevated CO levels.

In response to the incident, a "Code Orange" was declared at City Hospital and Royal University Hospital (RUH), an operational status reserved for mass casualty events.

City Hospital's emergency department provided care for 33 patients, 16 of whom were pediatric patients, according to the Saskatchewan Health Authority (SHA).

Another four adults and six children received care at RUH and Jim Pattison Children's Hospital, the SHA said in a statement.

Additional staff and physicians were called in to help handle the high number of patients. All of the patients were treated and discharged from the emergency department, the SHA said

During the news conference, Assistant Chief Yvonne Raymer said it was unlikely residents would be able to return to the building Friday.

Raymer said the SaskEnergy inspector found a "venting issue" with the building's boiler and the property's owner, Mainstreet Equity Corporation, had a plumber on-site working to fix the problem.

After checking three other buildings in the complex as part of what Raymer described as a "proactive approach," the fire and gas inspectors on scene determined another boiler also needed to be shut down due to "carbon monoxide issues" — forcing the evacuation of roughly another 50 people.

"Currently, we are placing a notice of closure on the two buildings," Raymer said.

The fire inspector on scene determined the building where the dangerous levels of CO were found was not equipped with carbon monoxide sensors.

While they are recommended, the sensors aren't mandatory for all buildings, Chief Hackl said.

"It was enacted in October of 2009 that any building that was renovated or built after that time required carbon monoxide alarms," Hackl said.

According to Raymer, Mainstreet is in discussion with SaskEnergy about potentially installing the alarms.

The company declined an interview with CTV News but in an emailed statement said it is in the process of undertaking an investigation and has moved all affected tenants into nearby hotels.

"The health and wellbeing of Mainstreet tenants are our utmost priority," the statement said.

"Mainstreet Equity takes this matter extremely seriously."

Raymer said there will be no fines issued because CO alarms aren't legally required due to the age of the building.

"But we're definitely going to make sure that this is a safe and habitable environment before we're done," Raymer said.

Carbon monoxide has no smell, taste or colour and is produced whenever fuel, such as natural gas, is burned.

Low levels of CO poisoning can result in flu-like symptoms such as tiredness, headaches and muscle weakness.

At higher levels of exposure, CO can cause poor vision, dizziness and difficulty thinking.

At very high levels, CO can result in convulsions, coma or death.

  --With files from Pat McKay.