The Shale Oil Company contains several operating units that comprise its Aston, Ohio, manufacturing complex. These units process the crude oil that is pumped through and transform it into a multitude of hydrocarbon products. The units run 24 hours a day, seven days a week, and must be shut down for maintenance on a pre-determined schedule. One such unit is Distillation Unit No. 5, or DU5. Studies have shown that DU5 can operate only 3 1/2 years without major equipment breakdowns and excessive loss of efficiency. Therefore, DU5 is shut down every 3 1/2 years for cleaning, inspection, and repairs.