The heat coming from the surrounding environment is not the only source of heat for the body. If a person is carrying out heavy work in a hot place additional heat can be generated by the persons (Parsons, 2003). As little as 20% of muscle energy contributes to external “work” (Parsons, 2003), and the rest becomes “waste heat” inside the body that needs to be released to the external environment. At high air temperatures (above 34-37 °C), the only method of heat loss to counteract bodily heat gain caused by work, is by evaporation of sweat. When there is high humidity, sweat evaporation is insufficient and other physiological changes cannot prevent the core body temperature from rising to dangerous levels (Bridger, 2003).
WORKING HEAT STRESS
There are a number of different tools for measuring occupational heat exposure. Published evidence concerning the impact on health and work capacity has used WBGT (Wet Bulb Globe Temperature) as the main heat exposure variable (Parsons, 2003), which makes it possible to use exposure-response relationships from such analysis in our impact assessments. However, it must be emphasized that any method produces approximate estimates (Epstein and Moran, 2006), and that individual variation is great. As long as the four climate variables and the two additional variables are considered and available for calculations, any heat stress index can be calculated (McLaurin et al., 1962; Budd, 2001, 2008; Brotherhoood, 2008).
what's my work level?
Sitting, standing, light manual work, writing, typing, casual walking
e.g. Office worker, services
Sustained hand/arm work, operation of construction equipment, gardening, pushing light carts
e.g. Industrial worker, gardener
Intense work, carrying heavy loads, shoveling, digging, pushing heavy carts, concrete block laying
e.g. Agricultural worker, farmer