Since the early 20th century, numerous methods, instruments, and models have been developed to assess hot environments in absolute and relative terms.  Many people are most familiar with the “feels like” temperature cited in local weather reports, though its method of determination can also vary.  Index calculations vary in complexity and the number of included variables.
     Despite the ever-improving accuracy and precision of instrumentation, heat indices remain models, or approximations, of the effects of hot environments on comfort and performance.  The models may also be applicable only in a narrow range of conditions.  When indices are routinely cited by confident “experts,” without qualifying information, those in the audience may attribute greater value to them than is warranted.
     Incorporating the range of possible environmental conditions and human variability requires an extremely complex model, rendering its use in highly-dynamic workplaces infeasible.  Though imperfect, there are models and methods that can be practically implemented for the protection of workers in hot environments.

     When the human body’s thermoregulatory functions are unable to maintain heat balance in a hot environment, any of several maladies may result.  Collectively known as “heat illness,” these maladies vary widely in severity.  Therefore, a generic diagnosis of heat illness may provide insufficient information to assess future risks to individuals and populations or to develop effective management plans.
     This installment of the “Thermal Work Environments” series describes the range of heat illnesses that workers may experience.  This information can be used to identify risk factors and develop preventive measures.  It also facilitates effective monitoring of conditions, recognition of symptoms, and proper treatment of heat-effected employees.