A FUZZY-SETS MODELING APPROACH FOR ERGONOMIC WORKLOAD STRESS-ANALYSIS

The Ergonomic Workload Stress Index (EWSI) model was developed to predict the existence and level of the ergonomic workload stress via the concept of the fuzzy sets theory. The linguistic values (e.g., ''heavy'', ''uncomfortable'', etc.) of the tasks and workplace variables (e.g., physical job demand, postural, environmental stressors, etc.) which have most influential factors on stress were defined. The computerized system was developed to investigate the inappropriate tasks and workplaces and to suggest alternative solutions to problems. The EWSI model was implemented in three industrial environments (i.e., grocery store distribution warehouse, drilling tools manufacturer, and linen and uniform rental service industry) from the epidemiological and physiological viewpoints to validate the model. The following results were obtained from the validation process: (1) a positive relationship between the EWSI value and the severity of injury and illness rate (coefficient of correlation = 0.716, 0.917, and 0.854 for the three different industries); (2) a close linear relationship between the EWSI value and heart rate (coefficient of correlation = 0.845); and (3) a close linear relationship between the EWSI value and blood pressure (coefficient of correlation = 0.804 and 0.775 for the systolic and diastolic blood pressure, respectively).