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
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.