Body temperature is one of the four vital signs that are standard in medical settings along with heart rate, blood pressure, and respiratory rate. Vital signs are measurements of the physiological condition of the human body and reveal the body’s ability to regulate body temperature, maintain blood flow, and oxygenate body tissues.
Thermal stress generally occurs due to a failure of the thermoregulatory system to keep body core temperature within its boundaries. Thermal stress is not caused by any diseases but results from a combination of various factors such as extra metabolic heat generation within the body during exercise, prolonged exposure to an extremely hot thermal environment (high air and radiant temperature and high humidity), low air velocity, and reduced evaporation of sweat [3]. When the body becomes unable to cool itself, heatinduced illness such as heat stress and heat exhaustion may result.
The level of the heat and vapour transfer rate from the human body to the outer environment determines heat stress.In addition to this, heat capacity and moisture absorption also have effect on heat stress. The parameters affecting this rate are thermal resistance (Rct) and moisture vapour resistance(Re) [4]. At this stage, if the situation is not treated quickly,it may lead to a deadly form of heat illness called heat stroke which might occur when the core body temperature exceeds 40?C.
The aforementioned scenario is a big concern for people who are exposed to heat for prolonged periods of time and this applies generally to firefighters due to their working conditions. Normally, the human body makes adjustments in the vasomotor tone in order to retain its core body temperature [7, 8]. If these adjustments are not enough to maintain the temperature within its set limits, additional mechanisms, such as sweating, are initiated [9]. It is also found that when the human body is exposed to radiant heat at the level of 4 kW/m2,second-degree burn occurs in 30 seconds [10]. Thus, when clothing is designed for firefighters,it should not only offer flame resistance but also allow a high level of wearing comfort in terms of allowing vapor transfer from the body to reduce the excessive heat on human body.
Not only the protective performance of the clothing is greatly dependent on the presence of moisture, but also the thermal protection of the clothing is also affected by the amount of moisture and its distribution, types of materials used for the clothing system and the design of clothing, and the level of thermal intensity [11–13]. Accumulated moisture on the human skin and in the fabric ensembles can alter the level of protection. In one study, it was proven that moisture has both positive and negative effects on the thermal protection performance of the protective clothing [14]. The presence of moisture in the clothing system can actually improve the thermal protection under low radiant.
