The Razor's Edge:

Balancing Chemical Protection and Thermal Strain in CBRN Operations

By Adam Potter, Madeline Poley-Bogan, Karleigh Bradbury, Karl Friedl, and William Tharion

Article published on: January 1, 2026 in the Army Chemical Review 2026 issue of the Army Chemical Review

Read Time: < 11 mins

Figure 1: Trade-offs in CBRN Protection and heat dissipation. There is an inverse relationship between protection from CBRN threats and the human body’s ability to dissipate heat.

The contents of this article do not represent the official views of, nor are they endorsed by, the U.S. Army, the Department of War (DoW), or the U.S. Government.

This article was edited with the assistance of AI tools, and subsequently reviewed and edited by relevant Department of War (DoW) personnel to ensure accuracy, clarity, and compliance with DoW policies and guidance.

Introduction

Balancing robust Chemical, Biological, Radiological, Nuclear (CBRN) protection with minimal thermal strain is critical for warfighter readiness and operational effectiveness. The inherent impermeability of chemical protective clothing (CPC), while blocking hazardous agents, imposes a significant thermal and physiological burden, as seen in Figure 1. By restricting natural cooling mechanisms, CPC leads to heat stress, performance degradation, and potentially life-threatening hyperthermia (heat stroke). The ultimate goal is to safeguard operators from CBRN threats while mitigating the severe risks of heat illness, injury, and fatality.

The U.S. Army Research Institute of Environmental Medicine (USARIEM) addresses this challenge through a vertically integrated scientific approach. As the premier human performance laboratory for the Department of War (DoW), USARIEM provides guidance on material solutions and develops standard operating procedures (SOPs) for CBRN personnel. The work at USARIEM spans the entire developmental lifecycle: from foundational research on heat transfer and basic CPC testing to post-acquisition assessments of fielded solutions. All this is to rigorously evaluate effectiveness, usability, and operator acceptance based on controlled studies and real-world utilization.

The Challenge: Chemical Protection vs. Thermal Strain

CPC is designed with impermeable or selectively permeable materials that block hazardous agents. This barrier, however, also impedes the evaporation of sweat—the body's primary means of dissipating heat. The trapped moisture increases humidity within the suit, further hindering evaporative cooling and leading to a rapid rise in skin and core body temperatures. The physiological consequences of this thermal burden are significant:

• Impaired cognitive function: Heat stress can degrade decision making, reaction time, and overall cognitive performance.
• Decreased physical performance: Muscle fatigue, dehydration, and cardiovascular strain limit physical endurance and strength.
• Increased risk of heat illness: Prolonged exposure to high heat and humidity, especially during exercise or while wearing CPC, significantly increases the risk of heat exhaustion, heat stroke, and death.

Optimizing CPC design and operational strategies is therefore a critical need for the military to minimize thermal strain without compromising protective capabilities.

USARIEM's Role: Assessing and Predicting Thermal Burden

Figure 3: Human Subjects Research in Climate Chamber. Soldiers in a climate-controlled chamber, instrumented with body-worn sensors, simulating marching activities while in different chemical protective clothing.(Photo by David Kamm)

USARIEM employs a multifaceted approach to understand and mitigate the physiological burden of CPC, combining controlled laboratory studies, predictive modeling, and real-world field deployments.

Biophysical Clothing Assessments Using Specialized Thermal Manikins

USARIEM uses advanced thermal manikins to build a foundational understanding of how clothing impacts human physiology, as seen in Figure 2. These manikins mimic human thermoregulation, including sweating rates and skin temperature regulation. In controlled climate chambers, researchers precisely measure the thermal and evaporative resistance of different CPC configurations, quantifying the inherent burden a suit will impose.1 This work provides critical data on heat exchange characteristics, including:

• Thermal resistance: The measure of dry heat exchange or insulation provided by clothing.
• Evaporative resistance: The measure of resistance to moisture vapor transfer through clothing, indicating how much sweat can evaporate.
• Water vapor permeability: The ease with which water vapor passes through the material.
• Wind effects on biophysics: The influence of wind on biophysical properties, revealing environmental impacts on protection or burden.

Controlled Human Laboratory Trials

Figure 2: USARIEM’s Specialized Thermal Manikins. USARIEM’s sweating thermal manikins being used to evaluate the biophysical properties of chemical protective clothing in a controlled climate chamber (left), undressed manikin with articulated walking system (right). (Photo by Madeline Poley-Bogan)

USARIEM conducts rigorous, direct human studies in state-of-the-art climate chambers.2 Human volunteers perform simulated military tasks or exercise protocols while wearing various CPC configurations under precisely controlled temperature, humidity, and wind conditions, as shown in Figures 3 and 4. A comprehensive suite of physiological parameters (core and skin temperatures, heart rate, metabolic rate, sweat rate, and hydration status) and performance metrics (physical and cognitive) are continuously monitored. These laboratory studies may be conducted if the system or conditions of use are substantially different than previously tested and modeled systems. Otherwise, model predictions can provide immediate assessment as the physiological models should have already been used in the development of a new CPC. The lab studies provide empirical data used for further validating models. As noted, these models are used by materiel developers early in the development of new ensembles, and by combat developers for evidence-based guidelines for safe operations.

Advanced Predictive Modeling

USARIEM has developed mathematical models that predict the physiological responses of warfighters wearing CPC under various environmental conditions and activity levels. This began with the massive 1985 P2NBC (Physiological and Psychological Effects of the NBC Environment and Protective Equipment) program, when USARIEM was asked to develop early predictive thermal models.3 The models have continued to develop, incorporating more conditions, and evolving from average group predictions to detailed personalized forecasts including algorithms linked to wearable physiological monitoring. These models incorporate a wide array of human-centric and environmental factors, including individual characteristics (age, fitness, acclimatization, metabolic rate), clothing properties (thermal and evaporative resistance, permeability), environmental conditions (temperature, humidity, wind, solar radiation), and terrain.

One key tool is the Heat Strain Decision Aid (HSDA), an empirically based thermoregulatory model that predicts core body temperature by integrating inputs related to the individual, clothing values, environmental conditions, and activity.4 The HSDA relies on the heat balance equation, accounting for heat production, environmental heat gain, and heat dissipation. It has been instrumental in quantifying critical details for major guidance documents, such as the U.S. Army Technical Bulletin Medical (TB Med) 507,5 and has since been transitioned to multiple DoW organizations and international partners.

Real-Time Physiological Status Monitoring and Field Studies

Bridging the gap between laboratory predictions and dynamic, real-world variability, USARIEM leads the development and deployment of Real-Time Physiological Status Monitoring (RT-PSM) systems. As seen in Figure 5, these wearable sensors continuously collect individualized physiological data (core and skin temperatures, heart rate, respiration rate, activity levels) from users in operational or simulated field environments. RT-PSM provides real-time assessments of a Soldier's status, allowing for timely intervention to prevent heat illness and providing empirical data to refine protective strategies and future CPC designs. USARIEM has led development and technical oversight for both commercial and government RT-PSM solutions and pursues its own algorithm development for health status predictions.

Figure 4: Human Subject Research in Climate Chamber (Marching Simulation). A USARIEM scientist (Dr. Karleigh Bradbury) monitoring Soldiers in a climate-controlled chamber, instrumented with body-worn sensors, simulating marching activities while in chemical protective clothing.(Photo by David Kamm)

Real-World Impact and Continuous Improvement: The Civil Support Team Initiative

The National Guard Bureau Weapons of Mass Destruction – Civil Support Teams (CSTs) are specialized units responsible for responding to CBRN incidents domestically. Given the inherent thermal and respiratory risks associated with full encapsulation, CSTs are prime candidates for early implementation of RT-PSM technologies and leveraging USARIEM's modeling capabilities, including the HSDA. The National Guard Bureau, co-led by USARIEM through an integrated product team (IPT), has led a nationwide effort to integrate RT-PSM into all 57 CST units.6 This comprehensive initiative encompasses the deployment of multiple technologies—including a wearable physiological device, a communication element, and an end-user display—and necessitates diverse expertise for successful system integration.

This initiative involves:

• Technology evaluation: Rigorous testing of commercially available RT-PSM systems for reliability, accuracy, and user-friendliness in CST applications.
• Training and education: Comprehensive programs for CST personnel on RT-PSM use, sensor placement, data interpretation, and intervention strategies.
• Integration into operational protocols: Development of SOPs for integrating RT-PSM data into CBRN response decision making.
• Data analytics and reporting: Establishment of platforms to track physiological trends, identify risk factors, and improve heat mitigation strategies.

This comprehensive rollout also includes rigorous post-acquisition and deployment assessments, critical for continuous improvement.7 Surveys and structured focus groups with experienced CST users (6+ months of use) revealed valuable insights. While 97% of respondents believed a system meeting their expectations would be useful, only 60% found the fielded RT-PSM system acceptable. Primary drawbacks included communications issues, lengthy setup times, and system unreliability. Though not a deciding factor for acceptability, the chest harness design was also reviewed negatively.8 This feedback is crucial for refining RT-PSM technologies and expanding their application to other military and civilian CBRN response units.

Figure 5: Real-Time Physiological Status Monitoring (RT-PSM) in Field Training. 95th Civil Support Team Soldiers conducting training while instrumented with RT-PSM systems, including a prototype external buddy display showing individualized health metrics. The arm-mounted display on the right shows a low (green) risk metric of 2 on a 1-10 scale (10 being significant risk of heat injury). (Photo by William Tharion)

Conclusion

Balancing chemical protection and thermal strain remains a critical challenge in CBRN operations. USARIEM's comprehensive research efforts, including controlled human trials, advanced clothing assessments with thermal manikins, sophisticated predictive modeling such as HSDA, and the development and deployment of RT-PSM technologies, are essential for mitigating the physiological burden imposed by CPC. The ongoing rollout of RT-PSM to National Guard Bureau CSTs exemplifies the commitment to leveraging innovation to protect our nation's first responders and enhance their ability to respond to CBRN threats. Continued research and development are crucial for forming the next generation of CPC and optimizing operational strategies to minimize thermal strain and maximize warfighter performance in the face of evolving CBRN challenges. The "razor's edge" between robust protection and optimal performance demands constant vigilance and innovation to ensure warfighters can operate safely and effectively in the most demanding CBRN environments.

Endnotes