Written by: V. K. Kothari and Soumyajit Sarkar
With the rapid technological development and progress, human beings have accepted the challenge of working in the increasingly hostile and adverse environment. Despite the growth of technology, work places still exist where we have to work in hot or/and humid conditions. Examples of such work areas include aerospace, firefighting, chemical warfare conditions, working in foundry and mines, working in arid/desert regions, etc.
Two stress generators act simultaneously in such cases, work load and the hot environmental condition. People working in such conditions experience gradual increase in body temperature and find it difficult to achieve thermal equilibrium. Continuing work in such uncomfortable conditions may lead to heat strain or even heat stroke, if necessary preventive measures are not taken.
Heat strain is the outcome of the heat stress, which occurs as heat input to the body surpasses the heat dissipation from the body. The resulting heat stress not only reduces the apparent thermal comfort and the work capacity but also encompasses the chances of heat collapse. Studies have found the highest tolerable heat storage to be 150 kcal, corresponding to a core body temperature of 40C.
Exposure to high temperature during working is a potentially fatal occupational hazard. Heat stress management is a critical and sensitive area for protection of people who are working in hot and/or humid environments. Regulation of core body temperature (Tc) is a very important aspect of heat stress management. From clinical point of view, Tc should be regulated in a very narrow range of 36.7 0.3C. Thermal balance will be lost if Tc differs by more than 2C on either side of 37C. While working in extreme hot environments, mostly a two way approach is adapted to control the core body temperature.
Firstly, a heat protective suit is worn by the worker which can act as a shield against the incoming radiative heat from the hot environment outside. Unfortunately, such types of protective clothing impede dissipation of metabolic heat generated due to work. The second approach is to use cooling garments to remove this metabolic heat. Cooling garments play an important role in alleviating the thermal discomfort experienced by individuals working in hot environmental conditions. It has found a wide range of applications in daily life to serve personnel working in thermally uncomfortable areas, to assist evaporation of sweating (astronauts and military), or to enhance athlete performance. Cooling garments also serves the patients with multiple sclerosis (MS).
The operating principle of such cooling garments is to create a cooler microclimate to facilitate the removal of metabolic heat and block heat exchange between the user and the environment. The cooling garments can be broadly classified in two groups based on their working principle, namely active and passive cooling garments. The operating principle of active cooling garments is to circulate cold air or liquids through tubing networked inside the garment. The mode of heat transfer is mainly conduction and convection. Passive cooling garment uses either phase change materials like ice-pack, polymer gels, paraffin waxes or chemically frozen gels or evaporation of cooling liquids.