Impact of exposure intensity on thermal performance of protective clothing of firefighters of various age groups under diverse thermal environments

Safeguarding the thermal safety and physical well-being of emergency responders, industrial workers, military personnel, and race car drivers is a critical concern. Consequently, extensive research has been carried out in recent years on thermal protective apparel. The present study examines the effects of thermal exposure conditions, firefighter age, and variations in the heat transfer coefficient on thermal injury. This study further examines the combined effects of age- and temperature-dependent blood perfusion, metabolic heat, shivering, and work-induced heat on basal layer temperature distribution and thermal damage across different age groups and body sites. Increased exposure density negates the protective benefits of the first air gap, resulting in adverse effects, while the other air gaps (AG2, AG3, and AG4) maintain their protective function. Older firefighters exhibit elevated basal layer temperatures across all conditions, with peak temperature increases of 41.59 % and 18.30 % observed in radiative exposure relative to flame and 50/50 convective-radiative exposures, respectively. Adjusting the heat transfer coefficient (HTC) from 0 to 50 W/m²K during the post-exposure phase markedly lowers maximum temperatures across all age groups and exposure scenarios. During the cooling phase, such variations effectively prevent third-degree burns in older firefighters, extending the time to thermal damage by 11.57 % and 3.19 % for 50/50 convective-radiative and radiative exposures, respectively. The arms are identified as the most susceptible body region, followed by the legs, back, chest, and abdomen during high-intensity exposures, although variations in the heat transfer coefficient significantly reduce peak temperatures. While the transition time to second-degree burns increases marginally, the progression to third-degree burns is substantially delayed across all body regions under all exposure conditions. Age- and temperature-dependent blood perfusion lowered the peak temperature by ∼2.5 % under radiative exposure, while metabolic, shivering, and work-induced heat had negligible effects at high intensity. These findings underscore the critical need for advancements in thermal protective clothing and cooling interventions to minimize thermal injuries.