Salem, MA – Several people were taken to the hospital Wednesday after being exposed to high levels of carbon monoxide in Salem.

First responders were called to the scene at 35 Congress St. at 8:15 a.m. for a report of an unconscious woman in a manufacturing facility on the fourth floor.

She was taken to the North Shore Medical Center, where they found elevated levels of carbon monoxide in her blood.

Four other people were also taken to the hospital with elevated carbon monoxide levels.

Two of the patients were taken to Massachusetts General Hospital for treatment in the hyperbaric chamber.

Fire officials said all the people are expected to be OK.

Officials said the problem was caused by crack in a gas-fired heater and exhaust was going into the building and not the chimney.