Heat stress is the sum of the heat generated in the body (metabolic heat) plus the heat
gained from the environment (environmental heat) minus the heat lost from the body to the
environment [NIOSH 2013]. Many bodily responses to heat stress are desirable and beneficial;
however, at some stage of heat stress, the body’s compensatory measures cannot maintain
internal body temperature at the level required for normal functioning. As a result, the risk of
HRI and accidents occurring as a result of HRI-related impaired mental status increase.
The body’s response to heat stress is called heat strain. Heat strain is dependent upon
a number of factors and cannot be predicted on the basis of environmental heat stress
measurements alone. As a result of working in a hot environment, HRI may develop. HRI
includes disorders such as: