MORGANTOWN, Pa. — A furnace explosion damaged the roof of a titanium plant in southeastern Pennsylvania on Thanksgiving Day, but no one was injured, authorities said.

Officer Kyle Tranovich of the Caernarvon Township police department said a skeleton crew of only six people was working in the TIMET Morgantown plant due to the holiday before the 2:30 p.m. Thursday blast. He said a smaller explosion had occurred earlier and the workers were “just walking out the door" when the main explosion occurred.

The cause of the blast is under investigation. TIMET, founded in 1950 as the Titanium Metals Corporation of America, bills itself on its website as “first in titanium worldwide,” saying it melts and refines ingot and slab and manufactures mill products.

A boiler explosion at the plant in March 2015 killed one worker and sent at least two others to a Reading hospital, the Reading Eagle reported.