VDU

They halted work on the pump and began preparing to address the leak but then retreated from the VDU, fearing for their own safety.

The conflagration burned for three hours at the base of the VDU, causing heat distress to the supports.

"It about burned that VDU up," one of the sources said.

The blaze caused no injuries, but it damaged piping interconnecting the VDU with the refinery's crude distillation unit.

The process of operating the CDU while bypassing the VDU, as Citgo plans to do at the Lemont refinery, is often compared to major surgery, and called "cutting out" the unit.