A preliminary investigation into the cause of a carbon monoxide leak that sent dozens of people to hospital Tuesday is pointing to inadequate ventilation of exhaust from a hotel’s boiler.

It happened at the Super 8 Hotel on Portage Avenue in west Winnipeg. Of 52 guests and staff at the hotel, 46 were rushed to hospital - 15 of them who were initially assessed to be in critical condition.

On Wednesday, officials from a number of organizations that worked to respond to the emergency told media they are investigating together to nail down a cause.

“It appears carbon monoxide built up in the building because of inadequate ventilation related to gas-fired appliances,” said Chuck Steele, director of engineering and construction, Manitoba Hydro.

“Instead of being safely vented, exhaust was being drawn back into the building,” he said, adding “significant further testing” is needed to pinpoint why the exhaust wasn’t venting correctly.

A spokesperson for the Office of the Fire Commissioner described the phenomena as a vacuum.

“There appears to be a cause in relation to a vacuum of exhaust within the building which allowed chimney exhaust from the boiler to be pulled back into the building,” said Candace Russell Summers, deputy fire commissioner.

Russell Summers said it’s too early to answer questions over carbon monoxide detectors in the building.

“We’re aware that there were CO detectors in the building, but at this time it’s premature to comment with certainty about the type or the number of detectors that were found, and whether or not they met regulatory requirements,” she said.

The city previously said a problem in boiler room set off an alarm in the room at 10:19 a.m. Tuesday.

However at least two guests of the hotel, who were treated in hospital for carbon monoxide poisoning, told CTV News said they did not hear an alarm at the time of the leak. Already feeling the effects, they were told about the leak from a firefighter who knocked on their door.

Officials have said the hotel was last fire-inspected in 2017 and was found to be compliant. Winnipeg Fire Paramedic Chief John Lane explained on Wednesday that hotels are inspected on a three-year cycle and the Super 8 was due to be inspected again in 2020.

Standards for CO detectors

Russell Summers said fire and building codes in Manitoba have requirements above national standards for carbon monoxide detection, and Manitoba is the only province to require CO detectors for buildings that aren’t regular residential occupancies.

But the union representing Manitoba firefighters suggested there may be room for improvement.

Alex Forrest, president of the United Fire Fighters of Winnipeg, said Wednesday that carbon monoxide detectors do not have the same regulations as smoke detectors.

“Especially in the hotel, motel industry we need to have standards at the highest level. So we need to examine what happened here, how did it get to this level, and hopefully this never happens again, because we are going to put bylaws in place for detection, to ensure that there is better systems for carbon monoxide detection as there is for smoke detection.”

Forrest was asked if a building should have several carbon monoxide detectors.

“Generally speaking yes, carbon monoxide detectors can be inserted alongside smoke detectors, that’s what we do with homes, you would think that would also occur in the hotel industry,” said Forrest.

“This was a nightmare scenario.”

Forrest said because crews were able to quickly identify the hazard and get the carbon monoxide victims to the hospital, a disastrous situation may have avoided.

He also said the highest number of carbon monoxide cases happen during very hot weather and very cold weather.

“Because windows are shut, and a lot of machines, the air-conditioner, your furnace, everything is working, and if those elements are not working it can cause carbon monoxide to be displaced … or if there is a malfunction,” said Forrest.

‘You worry and pray’: hotel manager

Karina Bueckert is the hotel’s director of business and development.

In an interview with CTV News Wednesday, she said staff started helping get people out of the building when the alarm went off, before emergency responders arrived.

She said seven staff members were among the patients sent to hospital.

“Obviously panic. You worry about your guest, our guests safety is our first top priority. We were very concerned about our guests and our staff. That’s not a good text to get, it’s not a good a call to get, so you worry and pray,” she said.

Winnipeg Fire Paramedic Chief John Lane said none of the patients required “invasive resuscitation, intubation, ventilation or anything of that nature,” but said, “they were potentially in some significant danger.”

Lane said the decision to classify a patient as being in stable, unstable or critical decision is made after assessing for symptoms of carbon monoxide poisoning and the level measured in the blood.

He said first responders play it safe when making that call outside of a hospital setting.

“We are very, very grateful for all the first responders and medical team,” said Bueckert.

The chemistry of carbon monoxide

The city said Tuesday it will evacuate buildings at carbon monoxide levels between 12 and 20 parts per million.

Francois Gauvin, a chemistry professor at St. Boniface University, said he considers a carbon monoxide level of 70 parts per million very serious.

The city said places in the hotel showed readings as high as 385 parts per million.

"I was really surprised to hear that. I fell on my chair literally, that big an amount is really serious," said Gauvin.

Gauvin said carbon monoxide can move through the ventilation system.

"From the place where the leak started, it would be normal to have a higher concentration there, the farther you are away from there, the lower the concentration would be," he said.

Gauvin expects the investigation -- which is being conducted jointly by the Office of the Fire Commissioner, Manitoba Hydro, Manitoba Workplace Health and Safety and the Winnipeg Fire Paramedic Service -- will look at what type of work was done on the heating, ventilation, and air conditioning.

"Any combustible that is burned for a furnace, there is always the risk of forming carbon monoxide. Nowadays the motor and furnaces, will have the entrance of air and the exhaust of the furnace directly to the outside, which minimizes the risk of having leaks inside house,” he said.

"But in the old furnaces, the air from combustion was taken from the air in the house and if the system was faulty, then the leaks could also leak in the house, so we recommend people have a CO detector."