CHICAGO (CBS) — A construction worker was critically injured inside Chicago’s Museum of Science and Industry Monday night.

The 51-year-old man’s left arm was seriously injured when he was trapped under heavy machinery, according to the Chicago Fire Department.

Fire Department officials said the worker was found pinned underneath a 2,000-pound forklift on the museum’s lower level.

“The forks were through the gentleman’s arm,” Chief of Special Operations Tim Walsh said

Walsh said the independent contractor was doing electrical work around 10:30 p.m. Monday, when an access panel gave way under the forklift.

“The subfloor had given way. They were trying to lift that electrical vault out with the forklift, and it tipped and pinned the man below it,” Walsh said.

Rescue teams used heavy equipment to free the man, who was taken to the University of Chicago Medical Center in critical but stable condition.

Walsh said the worker is expected to survive, and isn’t expected to lose his arm.

“As far as we know, right now everything’s fine, and U of C’s doing a good job. They have excellent trauma surgeons there,” he said.

The museum said the accident happened while crews were working on a renovation project.

“We take the safety and well-being of everyone onsite at MSI very seriously and are working with the contractor to thoroughly review the situation. Our thoughts are with him and his loved ones,” spokeswoman Amy Patti stated in an email.

The U.S. Occupational Safety and Health Administration said it has opened an investigation into the accident. OSHA said the work was being performed by Huen Electric, Inc., but declined further comment on the incident.

Eric Cox