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At least four people have been sickened, including one who is in “critical condition,” after a carbon dioxide leak at Los Angeles International Airport Monday morning.

The incident was reported around 7 a.m. in the Terminal 8 baggage area, according to a Los Angeles Fire Department news alert.

The leak apparently occurred after a popping sound was heard inside a small utility room at the airport. The four patients were all workers who were in or near the room.

The utility room is equipped with a carbon dioxide fire suppression system that is designed to extinguish a fire without damaging the electrical equipment inside, LAFD Capt. Erik Scott said during a morning news conference.

Three patients, described as two men and a woman, were treated at the scene for minor complaints.

The fourth patient, said to be a man in his 50s, was found pulseless and not breathing inside the utility room, according to the fire department.

“The carbon dioxide displaces the oxygen in the individual’s blood stream and they went into cardiac arrest,” Scott said. He described the carbon dioxide as colorless, odorless and tasteless.

The worker was given CPR right away by airport police. “The good news is that individual had a return of spontaneous circulation. What that means, they’re breathing. Their blood is pumping on their own now,” Scott said.

The man was taken to an area hospital where his condition was updated to critical.

Although as many as 100 people had to leave Terminal 8, no passengers or travelers were medically affected by the release, according to the Fire Department.

The utility room is apparently located more than 200 feet from the Terminal 8 baggage area.

A fire department hazardous materials team was sent to the airport to investigate the leak and only trace residue of carbon dioxide remained in the room, according to an update.

Scott said the situation was under control but the system needed to be reset before operations could return to normal. “We don’t want to rush a hazardous material’s incident,” he said.

United flights inbound to LAX were held at their airport of origin during the hazmat investigation, according to a tweet from LAX.

Travelers were urged to check with their airline for updates on flights.