WorkSafe Scenarios: Case and Questions

Scenario
As an Industrial Safety Manager,you are asked to review the weekend contract work of an industrial oven maintenance contractor, performing welding operations on a 250 ft. long industrial oven, which is serviced by a conveyor belt.(Items move through the furnace for curing on the belt.) The Plant has identified the oven as a permit required confined space, but when you arrive, the contractor has not implemented typical precautions for this type entry. His men are in the 18" space on their backs welding, approximately 150 ft. inside the conveyor/oven. When you question the contractor, he identifies that this is not a PRCS, as he has tested the air (although no documentation is on site), and found acceptable levels of O2 and combustible vapors. He has moved his welding gas cylinders into the oven, and states he has notified the local volunteer FD and the telephone operator of his work.
Questions for this Scenario: Is this a PRCS? What immediate precautions would you implement?	Type your answers here for comparison.