Fourteen people, including nine construction workers who were renovating a Yale University-owned building, were hospitalized for carbon monoxide poisoning on Wednesday.

One of the workers was found lying unconscious outside of the building, which is a couple of blocks from Yale's New Haven campus, and was taken to a hospital's hyperbaric chamber in Brooklyn, New York, where he was in critical condition, said Rick Fontana, New Haven's emergency operations director. He said another worker was also in "pretty serious condition" but was uncertain where he was taken.

Of the 14 people who were hospitalized, nine were construction workers and five were Yale employees, said a spokesperson for Mayor Justin Elicker.

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Emergency crews initially thought they were responding to a "regular medical call" early Wednesday when they brought the unconscious man to the hospital, Fontana said. However, an hour-and-a-half later, the hospital informed them that the worker had extremely high levels of carbon monoxide in his bloodstream.

Crews then returned to the location and found 13 people at the building with elevated carbon monoxide levels and complaining of headaches. It was later determined that they had been using a propane-fueled saw to cut concrete. Even though they were venting it, Fontana said the fumes were not exiting the building.

Yale logo

Yale Bulldogs logo during the first half of the college basketball game between the Seton Hall Pirates and Yale Bulldogs on November 14, 2021 at the Prudential Center in Newark, New Jersey.  (Rich Graessle/Icon Sportswire via Getty Images)

"That carbon monoxide, it’s not like you could smell it or see it or feel it," he said. "Everybody thought that it was being vented properly until we were notified of this group of people."

Fontana said a typical home carbon monoxide detector sounds an alarm when it detects 35 parts per million. In this situation, there were 350 parts per million, or 10 times the permissible level.

"There was a disaster averted here," he said. "You could have had a lot more sick or a lot more death had this gone on for a longer period of time."

Inhaling carbon monoxide fumes hinders the body from properly using oxygen and can harm organs, including the heart and brain.

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The Occupational Safety and Health Administration is investigating the incident. A Yale spokesperson didn't immediately reply to a message seeking comment.