Heat stress evaluation and worker fatigue in a steel plant.

This study assessed fatigue in electric arc melting workers (ER) and continuous casting workers (CC) in a steel plant and evaluated their physiological response to different levels of heat stress. Fifty-five men participated in the study. The ER group (mean, standard deviation [SD]=41.6, 7.4 years) was significantly older than the CC group (34.9, 6.4 years). The wet bulb globe temperature (WBGT) index of the workplace was measured. Workers' subjective fatigue symptoms were investigated by a 30-item constructive questionnaire, and physiological conditions and response time were measured before and after work for 2 consecutive days. WBGT ranged from 25.4 approximately 28.7 degrees C and 30.0 approximately 33.2 degrees C for the CC and ER areas, respectively. After age adjustment the ER group had significantly higher prevalence rates in subjective symptoms and slower response time than the CC group. The response "thirsty" was the highest after work (75 and 60% for the 2 ER interview days, respectively). A high prevalence (over 40%) of "eyes feel strained," "perception of shoulders stiff," or "feel waist pain" also was observed. Average pre- and postwork ER group systolic pressures were 129.1+/-11.4 mmHg (mean+/-SD) and 126.1+/-12.1 mmHg, 132.5+/-11.4 and 130.6+/-11.2 mmHg for the CC group. Continuous heat-strain monitoring data from one ER and one CC worker indicated that average working heart rate and body temperature were well below 150 beats/min and 38 degrees C. Faster response in critical flicker fusion was found after work than before work, but the differences were not statistically significant (p>.05). Response time for the falling bar grasp was faster at the beginning of work, declined with working time, and rebounded at the end of work. Workers exposed to a hot environment are inclined to subjective fatigue, and their fatigue symptoms increase with the heat exposure levels. However, low resting heart rate and systolic pressure are two characteristics for high heat exposure workers.