The heat stress compensability classification (HSCC) applied within the United States: model update and code...

The Heat Stress Compensability Classification (HSCC) is a physiology-based modeling system that categorizes uncompensable heat stress (UHS) in humans into four climate-based categories. These categories are based on the relative constraints of dry and evaporative heat exchanges in maintaining heat balance at a constant metabolic heat production (112Wm^- 2), applying basic principles of human heat exchange. The HSCC focuses on conditions in which sustained heat exposure can cause core temperatures to rise unless individuals engage in cool-seeking behaviors. Based on recent modeling advancements, this short communication updates the HSCC to incorporate physiological limits to sweating-specifically, the maximum whole-body sweat rate, SR_max-which can constrain the maximum evaporative heat loss, especially in dry conditions. Further, we provide background information to support HSCC application through a tutorial with published code on a public repository. Findings indicate that HSCC model adjustment results in minor changes, yet no shifts by category compared to the original application (i.e., all changes stayed within Category 4, or "Excessive dry heat gain") for a healthy young adult. Thus, the drivers for UHS type remain unchanged in the categorization, as the SR_max constraint addition only slightly alters the dry heat load. However, this model adjustment will become more significant if the HSCC is applied to older adults and/or those with sweating restrictions, as well as in hotter climates. Overall, the updated model enhances the physiological realism of the HSCC, while the code availability enhances accessibility as a tool for climate-health research and policy, supporting more impactful and collaborative research.