PLYMOUTH, Mich. (AP) _ An explosion today ripped through a plant where industrial equipment is cleaned, injuring at least 18 people who inhaled chemical fumes, authorities said.

The blast at a Cygnet Automated plant ''blew the walls off the place, literally destroyed the building,'' said Plymouth Township Supervisor Gerald Law. ''Fortunately because of equipment in there and the main frame of the building, the roof did not fully collapse on the employees.'

Eighteen people went to St. Joseph's Hospital in Ann Arbor, where they were being treated for inhaling fumes, said a spokeswoman who refused to give her name.

The injuries were not believed to be life-threatening, she said. Some of the workers were even able to drive themselves to the hospital, she said.

WDIV-TV in Detroit said 30 people were being treated, most for breathing difficulties, but the hospital spokeswoman would confirm only that it had 18 in its emergency room.

The plant uses chemical solvents to clean the equipment, Law said. The blast happened about 9:30 a.m.

''All's I know is I heard a bang, turned around and saw a giant flame coming toward me,'' said employee Mike Giacomo. ''The walls started caving in.''

A Plymouth Township police dispatcher who refused to give her name confirmed the blast but would give no details.