Medical disorders related to environmental heat exposure are exceptionally common in persons who perform hard work in hot climates. They are also common in competitive athletes as well as in persons who participate in casual exercise to maintain health. The important issue of salt and water disturbances consequent to heavy sweating in hot climates is discussed in detail as are mechanisms of potassium deficiency and its implications. The major forms of environmental heat illness including heat syncope, heat cramp, heat exhaustion, and heat stroke are presented in detail with relevant clinical examples. A discussion of the differential diagnosis of hyperthermia and rhabdomyolysis follows. Because of the difference in treatment and complications, heat stroke is subdivided into the classic variety that affects the elderly and very young and that form that follows heavy physical work and is always associated with rhabdomyolysis. Because severe heat exhaustion and heat stroke are life-threatening disorders, the chapter includes a detailed discussion of complications and plans for treatment.

Occupational health nurses must always be aware of changing job tasks that create new classes of employees at risk for developing heat stress disorders. Examples include chemical handlers or asbestos containment specialists who must wear non-permeable protective clothing. Heat induced occupational illnesses and injuries, and reduced productivity occur in situations in which the total heat load (environment plus metabolic heat) exceeds the capacities of the body to maintain normal body functions without strain. Health screening should include evaluation of an employee's age, sex, body size, level of fitness, chronic diseases, use of medications, drugs and alcohol, and ability to acclimate. Prevention of heat stress disorders is a team effort. The occupational health nurse, plant engineer, safety/industrial hygienist, and the employee all impact on the success of any heat stress disorder prevention program. Without cooperation, the possibility for harm exists.

Lettuce is a cool season crop susceptible to physiological disorders when exposed to supra optimal temperatures. Genotype (G) by environment (E) interaction (GE) of rib discolouration, tipburn, premature bolting and ribbiness in crisphead lettuce was characterized under high temperature and long day growing conditions. Replicated data of 10 crisphead lettuce varieties from two plantings in each of four growing seasons at two locations in Quebec were analysed using the GGE biplot method. Head‐weight‐over‐stem‐length ratio, ribbiness, rib discolouration incidence and tipburn incidence were affected (P = 0.00001) by E, G and GE. E explained more variation in head‐weight‐over‐stem‐length ratio (77.1%) and rib discolouration incidence (77.3%) than G and GE, whereas GE explained more variation (72.4%) in tipburn incidence and G explained more variation (38%) in ribbiness. Strong crossover GE was detected with rib discolouration and tipburn incidence, but not with head‐weight‐over‐stem‐length ratio and ribbiness. Under heat stress, varieties of the Vanguard group had lower ribbiness than those of the Great Lakes group. Cultivar ‘Estival’ showed consistent resistance to bolting, ribbiness, tipburn and rib discolouration across all E.

Morbidity rates associated with occupationally induced heat syndromes have been infrequently reported. In part this results from the inconsistency of diagnostic criteria for heat syncopy, exhaustion, and cramps. This problem is augmented by inconstant administration and completion of population survey instruments. With due regard for these shortcomings, we can provide only estimates of heat-induced morbidity, ranging between 0.12 and 1.4 cases per 1,000 man-years. To facilitate diagnosis of occupational heat stress disorders, a series of algorithms is presented for diagnosis of heat-induced syncopy, exhaustion, and cramps. A differentiation between heat-induced and heat-aggravated clinical states is proposed, and a heat disorder questionnaire with instructions for use is presented.