ELKHART, Ind. — More than 40 factory workers were treated at a hospital after they suffered carbon monoxide poisoning, officials said.

Managers at Specialty Window Coverings began sending workers to the hospital about 11 a.m. Wednesday after several employees in a new addition that makes blinds for recreational vehicles began complaining of headaches.

Randy Ferris, the plant manager, said supervisors realized there was a problem because of the number of complaints.

Seven workers were taken to Elkhart General Hospital by ambulance and 41 others were transported in company vans, South Bend television station WNDU reported. It was not immediately clear how many were admitted, but emergency room director David Van Ryn said most of the workers suffered low-level carbon monoxide exposure.

“They all received high dose oxygen treatment and their levels were monitored to make sure they are going down,” he told WNDU.

Fire Department spokesman Wes Johnson said the carbon monoxide apparently came from exhaust from a tow motor that was being used inside the building.

The company closed the building for the day after the workers became ill.