Development of job performance aids to increase human performance reliability: a case study in the evaluation of human factors principles

A study of criticality safety, commissioned by the U.S. Department of Energy, was conducted by Scientech Inc. at the Rocky Flats nuclear weapons facility. The study concluded that human performance is the driving factor in the risk of an inadvertent criticality incident at the Rocky Flats Plant (RFP). A study of the infractions which have occurred at this facility bears this point out. A human factors team was established to identify a means of reducing human error in every day operations. The team determined that the posted instructions near each work area are key to operators having a clear understanding of operating requirements. An evaluation of the posted instructions revealed that they were very complex, required operators to monitor multiple parameters, and resulted in the operators' attention being divided between operational tasks and the task of monitoring nuclear safety parameters. Alternative graphics, textual, and graphics and textual formats combined with color coding were developed to improve comprehensibility, understandability, controllability and usability in the Job Performance Aids (JPAs). Results of field tests of the different formats provide clear indication that operators prefer short, concise textual statements summarizing important information over both other formats. Although operators indicated interest in the graphics formats, the magnitude of change in presentation techniques and the generalizability of the icons argued against their immediate use. Issues in the development of candidate JPAs and other usability requirements are discussed.