Forty-six people have been hospitalized and 15 are in critical condition after they were exposed to carbon monoxide at a motel in Winnipeg, Manitoba, city officials said Tuesday.

Fifty-two staff and guests, along with one dog, were evacuated from the Super 8 Motel, the City of Winnipeg said in a series of Tweets after the fire department responded to an alarm shortly after 10 a.m. indicating carbon monoxide gas was present in the building. Winnipeg Fire and Paramedic Chief John Lane told reporters that the alarm in question was in the hotel's boiler room.

Lane added that carbon monoxide levels in some areas of the building were as high as 385 parts per million. By comparison, Lane said, a safe level of carbon monoxide is between 20 and 30 parts per million.

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Steve Brglez, acting platoon chief, said the 15 patients were listed as critical because of high carbon monoxide readings in their blood, as well as "other symptoms, such as nausea, vomiting, shortness of breath, a decrease in level consciousness."

"We don't expect any fatalities from this," Brglez added, saying some of the patients were expected to be released from hospitals within a few hours while other could be held overnight.

Carbon monoxide, often referred to as the "silent killer," is a colorless and odorless gas. Exposure victims begin showing symptoms when the gas is present at 70 ppm, according to Winnipeg Fire and Paramedic Service.

Local utility Manitoba Hydro cut off the gas supply to the motel to further investigate the source of the carbon monoxide and begin ventilating the building.

Justin Schinkel, the hotel's owner, said it had recently passed a fire inspection and had never experienced a carbon monoxide leak before.

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"We're just super happy that the first responders are so helpful, and they've been able to get here so quick and help us out here," he said.

Manitoba Premier Brian Pallister, who was attending a meeting with other premiers and Indigenous leaders in Saskatchewan, said he was shocked to hear about the incident.

"To see this many people impacted by carbon monoxide poisoning — it's unprecedented in my experience," he said.

The Associated Press contributed to this report.

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