Human susceptibility to outdoor hot environment.

A cross-sectional study examined the human susceptibility of a sample farmworker (N = 1144) in eastern India, who were exposed to the tropical hot outdoor environment during paddy and potato cropping activities (November to April). The study explored the efficacy of human thermal indices in human susceptibility categorization, based on analysis of indices, such as WBGT, HI, Humidex, UTCI, PET, SET*, PMV, and objective and subjective responses to heat-related symptoms and disorders. Analysis indicated dissimilarities in the estimated temperature levels of indices, attributed to different numerical weights of the meteorological and behavioural parameters. Therefore, the study explored the thermal stress level identified by different indices. December and January were recognized the comfortable months by most of the thermal indices. March and April were strong to very strong heat stress, with exception noted for SET*. In comparison to rational indices, the E, a thermoregulatory parameter, signified the relative change in the evaporative exchange with the increasing environmental warmth. The defined level of E at ~200 W/sq·m corresponded to the comfortable temperature range within 19.5 to 22.5 °C for WBGT, PET, and T. Beyond this specific range of warmth, a proportionate increase in E would result in cumulative heat-related symptoms of stress and strain. The study noted a sizeable number of farmworkers manifested moderate to high intensity of heat-related symptoms, with a relatively higher percentage in case of females. The principal component analysis yielded three principal components of heat-related responses, labeled as (a) physical fatigue and responses, (b) neural stressors, and (c) behavioural effects. Normalized component scores transformed into a generalized quantitative climatic susceptibility indicator may be applied to the moderate intensity of physical activity in the tropical hot and humid environment.