Human health and the environment are closely associated. The western part of India (Gujarat) is highly prone to heat waves at regular frequency. In Gujarat the average summer month temperature ranges from 27°C to 42°C and have been known to reach as high as 48°C. During the winter month average temperature ranges from 15°Cto28°C.

The increase in surface temperature and industrial activity are leading to higher temperatures res which resulted in the potential risk of high heat exposure to workers. The summer of 2010 records the hottest summer in many areas of Gujarat, with temperatures approximately 48°C. The effects include hospitalization because of heat stroke, suffering of livestock, and severe drought in some regions that affected health as well as agriculture.

Besides naturally occurring hot climate in these geographical regions, artificial exposure situations such as working in workplaces near the boilers, furnaces, heat treatment tanks, steam pipes, foundries, glass manufacturing, ceramic tile work, molten metal operations etc. often exceed the climatic stresses as a consequence of the cumulative effect on the health of the workers. For example, working in the ceramic tile or metal foundry industry around furnaces or kilns is extremely hot. Significant heat stress problems can occur during routine work in firing or melting processes.

Severe thermal burns or heat disorders can result from direct skin contact with hot surfaces or molten materials. Such heat stress causes health risks and manifest in decrease in work productivity, with a consequent negative impact on family income and the community economy [1]. Thus protecting workers against heat illness is important from both moral and economic perspectives. Epidemiological and experimental researches elucidate the challenges of thermoregulation among people in an extreme hot environment [2]. Dash and Kjellstrom [3] reported that in western India during summer season there is relatively more increase in the daily maximum temperature followed by Bihar, Uttar Pradesh and Orissa.

Management of heat exposure is important to safeguard human health in the industry and community environment. Heat stress is a potential health hazard for workers who are exposed to high environmental heat for prolonged periods.

The workers more than 18 years of age participated in the study and the informed consent was taken as per the Indian Council of Medical Research (2000) ethical guidelines [10]. The environmental measurements includes ambient dry bulb (T_a), dew point, wetbulb (Twb), globe temperature (Tg), wind velocity, Relative humidity and WBGT index measured by WBGT Monitor, Delta OHM (HD 32.1

Thermal Microclimate, Italy) and Lascar data logger (Lascar EL-USB-2-LCD, Sweden) for several hours ofobservation period and continued for a number of days at each workplace. The environmental warmth was expressed in terms of WBGT index [11,12]. Thephysiological heat strain parameters include sweating response, heart rate and blood pressure measurements. Sweating response is the net change in body weight after a given period of exposure [13].

The digital BP instrument was used to record the blood pressure during the work [14,15]. Heart rate was measured by polar heart rate meter (S810TM Polar Electro Oy, Finland) [16]. Due to safety and convenience in measurement of large number of workers in field situations, the oral temperature was taken as the Tcr.

The infrared thermographic camera (ThermoCAM, FLIR system, Sweden) was used for body temperature profiling of the local skin areas (Tsk) forentiresample population. The weighted average Tsk was obtained from the segmental surface area and sensitivity weighting of local skin areas [17], as below:

Weighted TSk = 0.095Head Tsk + 0.255 Trunk Tsk + 0.245 Ba + 0.205 Thigh Tsk + 0.04 Foot Tsk

All data were analyzed using SPSS16.0 software. The statistical analysis used in the present work includesdescriptivestatistics, analysis of variance (ANOVA) and Tukey’s HSD post-hoc test.

The physical characteristics of the workers are given inTable1. On average, the workers had similar anthropometric dimensions. The Ceramic workers were relatively younger (25.5±7.4 year)thaniron foundry worker (31.9±11.0 year).

Table 1: Physical characters of workers

Data indicated that the combined stress of work and heat imposed significant physical load on the workers, with potential health consequences. About32% of iron foundry and ceramic workers, had working heart rate greater than 100 beats/min. Whereas, 3% of iron foundry and ceramic workers had heart rates beyond 130 beats/min during the working day.

The systolic blood pressures of iron foundry and ceramic workers varied closely in different seasons, while the observations during the month of winter were marginally higher, as compared to the summer months (i.e., 2 mm Hg in case of iron foundry work and 11 mm Hg in ceramic work). Also there was no difference in diastolic blood pressure among the occupational groups during three seasons [18].

The sweat loss of the workers in iron foundry and ceramic during summer were 12.6±1.3 and 14.8±2.0 gm/min respectively (i.e., 3 to 3.7 litre ofsweating for 4 hours of exposure). During summer, the heat stress index (HSI) of iron foundry workers was comparatively higher (114±46), than ceramic work (100±36). Exceeding of HSI values above100 indicating considerable body heating and physiological strain.

Table-3: Physiological responses of the workers

The environmental conditions among indoor occupational groups with respect to different working seasons determine its influence on physiological responses, with reference to limit of heat tolerance. It was noted that even the habitual workers were at potential risks of developing heat-related illness in the summer and post monsoon month exposures.

The most effective way of heat dissipation is sweat production and its evaporation from skin surface that results in loss of water and electrolyte [23,24]. Increase in sweat output often exceeds water intake which results in body water deficit (dehydration) or fatigue of sweat gland. Consequent, performance may be impaired and workers may pose a threat to health. The conditions of water requirement of informal workers are very much excruciating. It is critically important for the public system to develop a consistent approach to make able essential requirements for the workers where they live and work.

The study provided an understanding of the peripheral thermoregulatory adjustability that limits the ability of a worker to withstand heat exposure in indoor work environment. It was evident from the present study that towards body's thermoregulatory efforts, the local T_sk responses showed an increasing trend with the increasing thermal stress. In order to bring in proactive response in the event of extreme heat, therefore, the limit of peripheral thermoregulatory adjustability may be considered beneficial to devise actionable public health interventions, in order that the vulnerable groups can be taken away from the fury of high heat.

The above study bears considerable practical importance to assess the magnitude of worker’s thermal stress and physiological reaction to ensure optimal conditions for health and productivity. The comprehensive analysis of the physiological and thermoregulatory responses of workers to heat stress and strain would eventually ascertain the relative vulnerability of the occupational groups for their exposure to extreme hot environment.

The climatic load and the metabolic heat load due to the severity of work to which a person is engaged together exert stress on the thermoregulatory system. The study provided an understanding that the limit of peripheral thermoregulatory adjustability which may be considered beneficial to devise actionable public health interventions, in order that the vulnerable groups canbe taken away from the fury of high heat. Often the discomforts attributed to environmental heat remains neglectedand unrecognized, and therefore, the perception of heat stress and associated illnesses carry substantial value.