Effect of a 12-hour/day shift on performance

The operating crews at the Fast Flux Facility near Richland, Washington, changed their rotating shift schedule from an 8- to a 12-hour/day work schedule. The primary reason for the change was to reduce the attrition of operators by increasing their job satisfaction. A statistical analysis of 53 operator-related, off-normal events in 28 months concluded that there was no significant difference in either the number or the severity of off-normal events on the 12-hour shift. A statistical analysis of 200000 log entries concluded that the error rate in completing logs actually declined the 25% on the 12-hour shift. Alertness, which was measured using computerized tests of mathematics and logical reasoning, reach a nadir on the first night shift for the 8- and 12-hour schedules alike, which indicates that the primary cause of fatigue was sleep disruption, not cumulative hours of work. All supervisors and 52% of the operators believe their crews work more effectively on the 12-hour shift. Only 12% of the operators believe that their crews work less effectively.<>