It happened just before 10:00 Thursday night at the Arcelor-Mittal Plant on the 1000 block of South 1st Avenue.
Investigators say a bucket, containing molten steel, apparently exploded.
The accident sent one person to Crozier Chester Medical Center with burns. Two others were taken to Brandywine Hospital.
No word on their conditions.
Officials are still working to determine the cause of the accident.