Abstract:

Objective Low-level heat flux densities (2-20 kW/m²) in conventional and hazardous thermal environments are commonly encountered in actual firefighting operations, especially in complex and variable forest fire conditions. Prolonged exposure in these environments can result in skin burns among firefighters, posing a threat to their occupational safety. In order to mitigate the risk of skin burns caused by firefighting environments, the influence of the air gap structure under firefighting clothing in low radiation heat environments on skin thermal protection was investigated. This research provides scientific insights for the rational design of firefighting gear and the prediction of safe operating durations for firefighters, thereby playing a crucial role in enhancing firefighters' occupational safety.

Method By constructing a three-dimensional heat transfer simulation device for the air gap, the heat exchange process between air gap close to clothing openings and external environment in actual dressing conditions is explored. Based on the stored energy test device, open and closed air gaps were set up, and thermal exposure experiments with various air gap thicknesses were conducted. The temperature variations on fabric surfaces under different air gap conditions, the thermal protection provided by the fabric system to the human body, and the contribution of the air gap therein were analyzed.

Results The results showed that an increase in air gap thickness and the openness of boundaries both positively impacted on the thermal protection capacity of the fabric system. The open air gaps exhibited stronger thermal protective performance, except for 3 mm-thick air gap. In comparison to situations without an air gap, closed air gaps ranging from 3 mm to 18 mm were found to reduce skin peak temperature by 9%-26.7% and prolong the second-degree burn time by 10.0%-100.8%. The conditions of open air gaps could reduce skin peak temperature by 4.7%-30.0%, and prolong the second-degree burn time by 7.2%-140.9%. The thermal flux density attenuation increased with the thickening of the air gap, yet its change rate exhibited inconsistency across different thickness intervals of the air gap. Under conditions of open and closed configurations, distinct heat transfer patterns existed within the space under the clothing. Results from linear regression fitting indicated a significant negative linear correlation between the peak temperature difference of the skin and the thickness of the air gap under closed conditions. Conversely, under open conditions, the relationship between the peak temperature difference of the skin and the thickness of the air gap was not statistically significant.

Conclusion In order to investigate the impact of air gap structural characteristics under firefighting clothing on thermal protection, the heat transfer within the clothing system and its influence on skin thermal protection were quantifies. The protective mechanisms associated with different air gap structural features was revealed. The findings reveal that increasing air gap thickness and openness positively influence the thermal protection capabilities of the fabric system. However, the thermal protection capacity of the fabric system does not exhibit a linear increase with thickness. These findings offer theoretical underpinnings for burn protection among firefighters and the prediction of safe operating durations.

Key words: firefighting clothing, occupational safety, air gap, thermal protection, second-degree burn time