The Possibility of Heat Stress Reduction by Contemporary Body Cooling Systems


By Col. Radovan Karkalic, Full Professor, Department of Military Chemical Engineering, Military Academy of the Republic of Serbia, Serbia


Personal protective equipment (PPE) is any physical material or equipment that is placed between the employee and workplace hazards to reduce the injury potential of the hazard. PPE are devices used to protect an employee from injury or illness resulting from contact with chemical, biological, radiological, nuclear, physical, electrical, mechanical or other workplace hazards.

Protection mechanisms are generally strongly associated with the physical state of the hazard. PPE must protect against CBRN agents in three physical states: gas or vapor, liquid, or aerosol (a solid particulate dust or liquid mist). Gases, vapors, and aerosols are airborne, whereas liquids are generally, short-range contact hazards only. Wearing PPE helps to reduce risk of exposure to different chemical warfare agents or other toxic chemicals. The level of protection depends of personal protective clothing types, wearing modality, environmental and other conditions. While working with pesticides that maximum attention should be paid the full chemical protection of the body and respiratory system. Body protection involves the use of different types of protective clothing, respiratory protection and adequate use of resources, from simple respirator to self-contained breathing apparatus.

One of the greatest tasks is the process of heat stress alleviation in the high toxic contamination environment. One of the methods is based on applying contemporary PCM (Phase Change Materials), cooling vests with different types of cartridges with salts or gels, cooling vests with tubes and specific compressors etc. All of these systems are more or less effective in the reduction of thermal stress. These technical and technological solutions greatly enhance safety and increase the user’s physiological suitability, especially during different activities connected with dangerous chemicals.


The needed thermal insulation of clothing systems mainly depends on the physical activity and on the surrounding conditions (temperature and relative humidity). The amount of heat produced by humans depends a lot on the physical activity and can differ from 100 W while resting to over 1.000 W during maximum physical performance. At extreme activity, which is often a case with winter sports, the body temperature rises with enhanced heat production. To make this increase within a certain limit, the body perspires in order to withdraw energy from the body by evaporative cooling. If the thermal insulation of the clothing is decreased during physical activity, a part of the generated heat can be removed by convection, thus the body is not needed expected to perspire so much.

The quality of insulation in a garment in terms of heat and cold will be widely managed by the thickness and density of its component fabrics. High thickness and low density make insulation better. It is observed in many cases that thermal insulation is offered by air gaps between the garment layers. However, the external temperature also influences the effectiveness of the insulation. The more extreme the temperature, be it very high or very low, the less effective the insulation becomes. Thus, a garment designed for its capability to protect against heat or cold is chosen by its wearer on the expectation of the climate in which the garment is to be worn. Though, a garment produced from a thick fabric will have more weight, and the freedom of movement of the wearer will be restricted. Clearly then a garment designed from an intelligent fabric, whose nature can change according the external temperature, can offer superior protection. However, such a garment must be comfortable for the wearer.


The specific accumulation of heat reflected by core and peripheral body temperature occurs during heavy physical exertion or exposure to warm and humid environment. Long-term accumulation of heat in a quantity of about 0.5 W/kg up to 2 hours results to an increase in body temperature that some people can’t tolerate. Because of that, heat stress may be compensated and uncompensated. Compensated heat stress (CHS) occurs when the heat loss is in balance with its production. It is possible to reach core temperature equilibrium (steady-state) at given physical activity. Compensated heat stress is usually present in most of the dedicated tasks. Uncompensated heat stress (UCHS) occurs when demands for disclosure of heat (sweat evaporation) overcome the evaporative capacity of the specific environment. During uncompensed heat stress, the body cannot achieve steady state core temperature, so it rises until it reaches physiological limits. Heat exhaustion in terms UCHS occurs at relatively low value of core temperature. In cases of inadequate cooling (caused by insufficient evaporation of sweat), skin temperature remains high. Bloodstream is relocated to expanded skin vascular compartment in order to remove the heat from inside the body, which reduces the minute volume and increases heart rate. Uncompensated heat stress extremely reduces physical performance, so these conditions demand special regimes of work and rest cycles, with the use of active cooling during breaks. Staying in the contaminated area request the best possible physiological comfort. Considering this, different systems for body cooling have been developed so far, with a main purpose to increase comfort as well as to reduce thermal stress.

Applications of cooling systems bring numerous additional benefits, such as increased mission duration, decrease in hydration needs, improved mental acuity and maintained physical performance. Generally, cooling systems can be classified in five basic groups: evaporative cooling products, products based on phase change materials (PCM), compressed air systems, liquid circulation systems, and thermoelectric systems. The application of particular cooling system type depends of many factors, such as cooling garment weight, readiness, cooling capacity, heat removal rate, compatibility, possibility for the monitoring and control by the wearer, environmental conditions, durability, and portability. Protective characteristics of body protection means depend on the type of protection materials and specificity of contamination applied. In the context of current development and production of cloth designed to protect the body from highly toxic substances, more types of protective materials are made. They can be classified into two main groups. In the first are insulating materials based on elastomer or thermoplastics, and in the second are thin carbon sorption materials which found application in the production of protective filtration suits. The basic advantage of the insulating materials is reflected in good protective properties against HTS, with a lack of permeability to air and sweat, what can cause the prerequisites for heat stress phenomenon. The use of these funds, in activities of medium and high intensity in hot conditions leads to rapid heat build-up in the body and heat load of users, so the time of their wearing is limited in depending on the external ambient temperature.

Body Cooling Systems

A Phase Change Material (PCM) is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage units. Phase change materials are waxes that have the distinctive capacity to soak and emit heat energy without altering the temperature. These waxes include eicosane, octadecane, nonadecane, heptadecane and hexadecane. They all possess different freezing and melting points and when mixed in a microcapsule it will accumulate heat energy and release heat energy and maintain their temperature range of 30-34 °C, which is very comfortable for the body. The micro encapsulated PCM can be combined with woven, non-woven or knitted fabrics. The capsules can be added to the fabric in various ways such as:

Microcapsules: Microcapsules of various shapes – round, square and triangular within fibers at the polymer stage. The PCM microcapsules are permanently fixed within the fiber structure during the wet spinning procedure of fiber manufacture. Micro encapsulation gives a softer hand, greater stretch, more breathability and air permeability to the fabrics.

Matrix coating during the finishing process: The PCM microcapsules are embedded in a coating compound like acrylic, polyurethane, etc., and are applied to the fabric. There are many coating methods available like knife-over-roll, knife-over-air, pad-dry-cure, gravure, dip coating and transfer coating.

Foam dispersion: Microcapsules are mixed into a water-blown polyurethane foam mix and these foams are applied to a fabric in a lamination procedure, where the water is removed from the system by the drying process.

The future intent is to use different nanoparticles. Nanoparticles are permanently attached to cotton or synthetic fibers. The change occurs at the molecular level, and the particles can be configured to imbue the fabric with various attributes. Nanotechnology combines the performance characteristics associated with synthetics with the hand and feel of cotton. Nanofibers 1/1000 the size of a typical cotton fiber are attached to the individual fibers. The changes to the fibers are undetectable and do not affect the natural hand and breathability of the fabric. The range and variety of high performance textiles that have been developed to meet present and future requirements are now considerable. Textile materials are now combined, modified and tailored in ways far beyond the performance limit of fibers drawn from the silkworm cocoon, grown in the fields, or spun Integrated with nanomaterials, textiles are imparted with very high energy absorption capacity and other functions such as stain proofing, abrasion resistance, light emission, etc.


Usage of personal body cooling systems significantly improves physiological suitability of people which conduct tasks and missions in complex field conditions, combined with high ambient temperature and highly toxic contamination. Generally, the evaluation of specific cooling system consists of two important conclusions: in case of wearing cooling vest, body core temperature (measured through tympanic temperature) grow slower, and mean body skin temperature is significantly lower. Moreover, heart rate values and subjective assessment of comfort levels point to the much expressed physiological stability, which is very important result from the aspect of confidence and efficiency in fulfilling the given specific missions. From the CBRN service point of view, the most important result is that cooling vest application, especially under the protective equipment can extend limited time of stay in hot and CBRN environment. Finally, the conducted laboratory tests and experiences based on a specific methodology, confirm that the use of a personal body cooling vest under the CBRN protective impermeable equipment significantly improves physiological suitability of the equipment in people who conduct tasks and missions in extreme situations including high ambient temperature and highly toxic contamination, and allow them to prolong mission duration.

Author: Bio

Colonel Radovan Karkalic, PhD, is a CBRN Professional with more than 20 years of lecturing and consulting experience working in military and academic settings in Serbia. He has a huge theoretical and practical experience in CBRN protective materials, contemporary CBRN devices, and first responders training in toxic/contaminated environment. He is a member of University of Defence, Military Academy, Belgrade, Republic of Serbia, responsible for teaching of military cadets and civilian students (Bachelor, Master and PhD courses) regarding following subjects: CBRN protection, Technology of CBRN decontamination, Prevention and dealing with accidental situations, Training in gas chambers in the proper use of respiratory protection devices in combination with irritant agents etc. During the 2019 he was elected as Visiting Professor at University “Tor Vergata” in Rome. He successfully cooperates and work on joint projects with the Czech Armed Forces NBC Defence Institute in Vyskov and many other relevant CBRN companies worldwide.

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