<![CDATA[Work fatigue in shift systems has the potential to reduce alertness, slow response time, and decrease operator performance, thereby affecting occupational safety and productivity. This study aims to analyze differences in fatigue levels and operator performance between the morning and afternoon shifts at PT. ABC, a manufacturing company located in Tegal Regency. A quantitative approach with a descriptive, comparative, and correlational design was employed. The study involved 14 production operators, all of whom were selected as respondents using total sampling (saturated sampling). Fatigue levels were measured using the Swedish Occupational Fatigue Inventory (SOFI), while operator performance was assessed through reaction time to visual, auditory, and motor stimuli. Data were analyzed using a paired-samples t-test to examine differences between shifts and Pearson correlation to determine the relationship between fatigue and reaction time. The results showed that fatigue levels were higher during the afternoon shift across all SOFI dimensions, with the largest increases in lack of motivation (128.99%) and physical discomfort (107.98%). Reaction time was also slower during the afternoon shift across all stimuli, with the largest increase in motor reaction time (18.90%). The paired-samples t-test showed significant differences between shifts in all SOFI dimensions and reaction time (p < 0.05). Pearson correlation analysis revealed a significant positive relationship between fatigue and reaction time, indicating that higher fatigue was associated with longer response times. Production output was also lower during the afternoon shift, decreasing by 14.36% for Operators 1–7 and 34.35% for Operators 8–14. The company is recommended to implement structured rest periods and periodic fatigue monitoring, particularly during the afternoon shift, to maintain operator performance and minimize safety risks.]]>
