**2. What is occupational heat stress?**

Heat stress includes many physical reactions that result from a body's capacity to regulate its temperature in response to the environment [6, 7]. Failure in the body regulatory mechanism will lead to heat stress which may cause increase in core body temperature and heat rate. This may further cause accumulation of excess heat in the body which cause the worker to lose concentration in working environment and may become irritable or sick [8]. High air temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, and strenuous physical activities may cause increase risk of developing heat related illness.

Occupational heat stress is that the net load to which a worker is exposed from the combined contributions of metabolic heat, environmental factors, and clothing worn which leads to rise in heat storage within the body [1]. Workers who are working in hot environment are at increased risk of developing heat related illness. Heat stress results in heat related illness and also it may account for an increase in workplace accidents, and a decrease in worker productivity [7, 9]. Heat stress related health impacts ranges from less severe heat rash to more severe heat stroke. Sweaty palms, fogged-up safety glasses and dizziness are the main causes for workplace injury. Burns may also occur as a result of accidental contact with hot surfaces or steam [6, 10]. In India occupational heat stress is becoming more significant as the average temperatures increase but remains overlooked [3, 11, 12]. Both indoor and outdoor workers are at risk of developing heat related illness. Outdoor work sector includes agriculture, construction, brick industry where as indoor work includes firefighters, bakery workers, farmers, miners, boiler room workers, factory workers [12, 13].

## **3. Physiology of thermoregulation**

The internal temperature (Core) of healthy human body should be maintained around 37°C for the various metabolic processes to function at optimum range inside the human body [14]. Variations, usually of less than 1°C occur with the time of the day, level of physical activity or emotional state [15]. As the environment warms-up, the body tends to warm-up as well. In this way, the body increases the rate of heat loss to balance the heat burden created by the environment. In a very hot environment, the rate of heat gain exceeds the rate of heat loss and the body temperature begins to rise. There are number of physiological heat control mechanisms playing a vital role in maintaining the core body temperature even when the external air temperature is greater than 37° C [16]. The pre-optic area in the anterior hypothalamus of the brain along with posterior hypothalamus, medulla, pons and spinal cord maintain core body temperature within normal range. The thermal sensors maintain a constant core body temperature by increasing blood flow to the skin (Vasodilatation) and by increasing sweat production [15]. To balance the heat burden created by the environment, the body increases the rate of heat loss. A rise in the body temperature results in heat related illnesses [17].

The main source of heat gain in a human body is production of its own internal heat called metabolic heat. It is generated within the body by the biochemical processes that keep us alive and by the energy we use during physical activity. The body exchanges heat with its surroundings mainly through radiation, convection, and evaporation of sweat [6]. Radiation is the process by which the body gains heat from surrounding hot objects, such as hot metal, furnaces or steam pipes and lose heat to objects such as chilled metallic surfaces without contact with them [14]. Convection is the process by which the body exchanges heat with the surrounding air. The body gains heat from hot air and loses heat to cold air which comes in

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**Figure 1.** *WBGT.*

*Occupational Heat Stress: A Technical Scan DOI: http://dx.doi.org/10.5772/intechopen.93900*

of sweat produced by the body [6].

**4. Heat stress and heat strain indicators**

ducted in different occupational sectors [19] (**Figure 1**).

contact with the skin. Convective heat exchange increases with increasing air speed and increased differences between air and skin temperature [14]. The body cools as the evaporation of sweat from the skin occurs. Evaporation sets in very quickly and effect is more enhanced with high wind speeds and low relative humidity. In hot and dry workplaces, the cooling due to sweat evaporation is limited by the amount

The body also exchanges small amounts of heat by conduction and breathing. By conduction the body gain or lose heat when it comes into direct contact with hot or cold objects. Breathing exchanges heat because the respiratory system warms the inhaled air. The body's excess heat is pushed away as the exhalation sets in. However, the amount of heat exchanged through conduction and breathing is normally small enough to be ignored in assessing the heat load on the body [18].

There are many indices that are used to assess heat stress such asWet bulb Globe Thermometer (WBGT), Universal Thermal Climate Index, Humidex, etc. WBGT is the gold standard internationally accepted indices for measuring heat stress and it was used to measure the heat stress in most of the previous research work con-

#### *Occupational Heat Stress: A Technical Scan DOI: http://dx.doi.org/10.5772/intechopen.93900*

*Occupational Wellbeing*

**2. What is occupational heat stress?**

**3. Physiology of thermoregulation**

may cause increase risk of developing heat related illness.

workers, farmers, miners, boiler room workers, factory workers [12, 13].

in the body temperature results in heat related illnesses [17].

The internal temperature (Core) of healthy human body should be maintained around 37°C for the various metabolic processes to function at optimum range inside the human body [14]. Variations, usually of less than 1°C occur with the time of the day, level of physical activity or emotional state [15]. As the environment warms-up, the body tends to warm-up as well. In this way, the body increases the rate of heat loss to balance the heat burden created by the environment. In a very hot environment, the rate of heat gain exceeds the rate of heat loss and the body temperature begins to rise. There are number of physiological heat control mechanisms playing a vital role in maintaining the core body temperature even when the external air temperature is greater than 37° C [16]. The pre-optic area in the anterior hypothalamus of the brain along with posterior hypothalamus, medulla, pons and spinal cord maintain core body temperature within normal range. The thermal sensors maintain a constant core body temperature by increasing blood flow to the skin (Vasodilatation) and by increasing sweat production [15]. To balance the heat burden created by the environment, the body increases the rate of heat loss. A rise

The main source of heat gain in a human body is production of its own internal

heat called metabolic heat. It is generated within the body by the biochemical processes that keep us alive and by the energy we use during physical activity. The body exchanges heat with its surroundings mainly through radiation, convection, and evaporation of sweat [6]. Radiation is the process by which the body gains heat from surrounding hot objects, such as hot metal, furnaces or steam pipes and lose heat to objects such as chilled metallic surfaces without contact with them [14]. Convection is the process by which the body exchanges heat with the surrounding air. The body gains heat from hot air and loses heat to cold air which comes in

Heat stress includes many physical reactions that result from a body's capacity to regulate its temperature in response to the environment [6, 7]. Failure in the body regulatory mechanism will lead to heat stress which may cause increase in core body temperature and heat rate. This may further cause accumulation of excess heat in the body which cause the worker to lose concentration in working environment and may become irritable or sick [8]. High air temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, and strenuous physical activities

Occupational heat stress is that the net load to which a worker is exposed from the combined contributions of metabolic heat, environmental factors, and clothing worn which leads to rise in heat storage within the body [1]. Workers who are working in hot environment are at increased risk of developing heat related illness. Heat stress results in heat related illness and also it may account for an increase in workplace accidents, and a decrease in worker productivity [7, 9]. Heat stress related health impacts ranges from less severe heat rash to more severe heat stroke. Sweaty palms, fogged-up safety glasses and dizziness are the main causes for workplace injury. Burns may also occur as a result of accidental contact with hot surfaces or steam [6, 10]. In India occupational heat stress is becoming more significant as the average temperatures increase but remains overlooked [3, 11, 12]. Both indoor and outdoor workers are at risk of developing heat related illness. Outdoor work sector includes agriculture, construction, brick industry where as indoor work includes firefighters, bakery

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contact with the skin. Convective heat exchange increases with increasing air speed and increased differences between air and skin temperature [14]. The body cools as the evaporation of sweat from the skin occurs. Evaporation sets in very quickly and effect is more enhanced with high wind speeds and low relative humidity. In hot and dry workplaces, the cooling due to sweat evaporation is limited by the amount of sweat produced by the body [6].

The body also exchanges small amounts of heat by conduction and breathing. By conduction the body gain or lose heat when it comes into direct contact with hot or cold objects. Breathing exchanges heat because the respiratory system warms the inhaled air. The body's excess heat is pushed away as the exhalation sets in. However, the amount of heat exchanged through conduction and breathing is normally small enough to be ignored in assessing the heat load on the body [18].
