Quantification of Human Thermal Risks During Ambient Temperature Steps Based on Fuzzy Comprehensive Evaluation

Occupational workers in hot environments face heat strain during temperature up-steps and cardiovascular strain during temperature down-steps. However, existing thermal risk evaluation models primarily focus on heat strain, neglecting potential risk after large temperature down-steps. This study employs a comprehensive multi-indicator approach to assess both heat strain and cardiovascular strain. Method: Six physiological and psychological parameters were selected for evaluation indexes, and four levels of thermal risk were established. Then trigonometric membership functions were proposed to determine the membership degrees related to the evaluation grades. Combined with the entropy weight method, a fuzzy comprehensive evaluation model was developed to assess thermal health risk levels. Results: Results indicated that core temperature, heart rate, and mean skin temperature are important physiological factors for assessing heat strain, while thermal sensation and perceived exertion also contribute significantly. The variation in blood pressure is relevant to cardiovascular strain. The developed model can distinguish the effects of temperature step magnitude and clothing thermal resistance on heat strain. A temperature difference of 40°C (from 40°C to 0°C) leads to a moderate level of cardiovascular strain and a 24% probability of high cardiovascular strain risk. Conclusions: These findings underscore the significance of transitional spaces and appropriate clothing choices in mitigating thermal risks and promoting human health and comfort in environments with substantial temperature variations.