Table 1.

Classification, medical aspects and prevention of heat illness (from (6))

Category and clinical features	Predisposing factors	Underlying physiological disturbance	Treatment	Prevention
1. Temperature regulation heatstroke
Heatstroke: (1) hot dry skin usually red, mottled or cyanotic; (2) tre, 40.5°C (104°F) and over; (3) confusion, loss of consciousness, convulsions, tre continues to rise; fatal if treatment delayed	(1) Sustained exertion in heat by unacclimatised workers; (2) lack of physical fitness and obesity; (3) recent alcohol intake; (4) dehydration; (5) individual susceptibility; and (6) chronic cardiovascular disease	Failure of the central drive for sweating (cause unknown) leading to loss of evaporative cooling and an uncontrolled accelerating rise in tre, there may be partial rather than complete failure of sweating	Immediate and rapid cooling by immersion in chilled water with massage or by wrapping in wet sheet with vigorous fanning with cool dry air, avoid overcooling, treat shock if present	Medical screening of workers, selection based on health and physical fitness, acclimatisation for 5–7 days by graded work and heat exposure, monitoring workers during sustained work in severe heat
2. Circulatory hypostasis heat syncope
Fainting while standing erect and immobile in heat	Lack of acclimatisation	Pooling of blood in dilated vessels of skin and lower parts of body	Remove to cooler area, rest recumbent position, recovery prompt and complete	Acclimatisation, intermittent activity to assist venous return to the heart
3. Water and/or salt depletion
(a) Heat exhaustion
(1) Fatigue, nausea, headache and giddiness; (2) skin clammy and moist; complexion pale, muddy or hectic flush; (3) may faint on standing with rapid thready pulse and low blood pressure; (4) oral temperature normal or low but rectal temperature usually elevated (37.5–38.5°C) (99.5–101.3°F); water restriction type; urine volume small, highly concentrated; salt restriction type; urine less concentrated, chlorides less than 3 g/L	(1) Sustained exertion in heat; (2) lack of acclimatisation; and (3) failure to replace water lost in sweat	(1) Dehydration from deficiency of water; (2) depletion of circulating blood volume; (3) circulatory strain from competing demands for blood flow to skin and to active muscles	Remove to cooler environment, rest recumbent position, administer fluids by mouth, keep at rest until urine volume indicates that water balances have been restored	Acclimatise workers using a breaking-in schedule for 5–7 days, supplement dietary salt only during acclimatisation, ample drinking water to be available at all times and to be taken frequently during work day
(b) Heat cramps
Painful spasms of muscles used during work (arms, legs or abdominal); onset during or after work hours	(1) Heavy sweating during hot work; (2) drinking large volumes of water without replacing salt loss	Loss of body salt in sweat, water intake dilutes electrolytes, water enters muscles, causing spasm	Salted liquids by mouth or more prompt relief by I-V infusion	Adequate salt intake with meals; in unacclimatised workers supplement salt intake at meals
4. Skin eruptions
(a) Heat rash (miliaria rubra; ‘prickly heat’)
Profuse tiny raised red vesicles (blister-like) on affected areas, pricking sensations during heat exposure	Unrelieved exposure to humid heat with skin continuously wet with unevaporated sweat	Plugging of sweat gland ducts with retention of sweat and inflammatory reaction	Mild drying lotions, skin cleanliness to prevent infection	Cool sleeping quarters to allow skin to dry between heat exposures
(b) Anhydrotic heat exhaustion (miliaria profunda)
Extensive areas of skin which do not sweat on heat exposure, but present gooseflesh appearance, which subsides with cool environments; associated with incapacitation in heat	Weeks or months of constant exposure to climatic heat with previous history of extensive heat rash and sunburn	Skin trauma (heat rash; sunburn) causes sweat retention deep in skin, reduced evaporative cooling causes heat intolerance	No effective treatment available for anhydrotic areas of skin, recovery of sweating occurs gradually in return to cooler climate	Treat heat rash and avoid further skin trauma by sunburn, periodic relief from sustained heat
5. Behavioural disorders
(a) Heat fatigue – transient
Impaired performance of skilled sensorimotor, mental or vigilance tasks, in heat	Performance decrement greater in unacclimatised and unskilled worker	Discomfort and physiologic strain	Not indicated unless accompanied by other heat illness	Acclimatisation and training for work in the heat
(b) Heat fatigue – chronic
Reduced performance capacity, lowering of self-imposed standards of social behaviour (e.g. alcoholic over-indulgence), inability to concentrate, etc.	Workers at risk come from temperate climates, for long residence in tropical latitudes	Psychosocial stresses probably as important as heat stress, may involve hormonal imbalance but no positive evidence	Medical treatment for serious cases, speedy relief of symptoms on returning home	Orientation on life in hot regions (customs, climate, living conditions, etc.)