The fire erupted after a furnace burst around 8:30 a.m. Monday at Victaulic Co. in Lower Macungie Township, just outside Allentown.
Officials said a third person was taken to the hospital for observation.
Victaulic spokesman Eric Luftig said the company did not have immediate details on the blaze. He said 59 people were in the building when it was evacuated.
Paul Ziegler, of the United Steelworkers of America Local 2599, said one worker was seriously burned. The conditions of the others weren't immediately known.
Victaulic makes mechanical pipe-joining systems. It employs about 140 people at its Lehigh Valley plant.
