Heat stress
Health & Safety - Occupational Safety
Every year, a number of farmworkers die from heat-related illness while working in agricultural fields, and many times that number are injured by heat stress while on the job. With farmworkers, illnesses caused by heat can be easily overlooked because they are not specific to any crop, task, or equipment, and develop in commonly-occurring environmental conditions. But farmworkers are frequently at higher risk for these illnesses than workers in other industries: they work outdoors in direct sunlight and humidity of summer and the work activity generates large amounts body heat by, which is then retained in the body by heavy work clothing and equipment1. The resulting heat buildup - heat stress - can become more than the body can handle, creating a dangerous and potentially fatal situation. This type of occupational heat stress, and the resulting injuries and deaths, can be entirely avoided by means of a few straightforward precautions.
Heat stress occurs when body heat builds up from both external (e.g., the weather) and internal (e.g., muscle activity) sources. The resulting increase in core body temperature can lead to dehydration, electrolyte imbalance, and if permitted to continue, to neurological impairment, multi-organ failure, and death. Heat illness occurs along a continuum of severity, from mild to life-threatening, which are categorized clinically as follows:
• Heat edema, or swelling of the hands and/or feet, is the mildest form of heatrelated illness2.
• Heat cramps are spasms of the muscles of the arms, legs or abdomen, and are a warning sign of developing heat stress2.
• Heat syncope is dizziness that occurs when making abrupt posture changes2.
• Heat exhaustion occurs as a result of water or salt depletion when the body subjected to more heat than it can handle. Symptoms include intense thirst, weakness, anxiety, dizziness, fainting, headache, and excess sweating3.
• Heat stroke is life-threatening medical emergency that occurs when the heat buildup becomes more than the body can handle. Heat stroke occurs in two forms, classic and exertional3.
- Classic heat stroke occurs as a result of excessive environmental temperatures.
- Exertional heat stroke is caused by the production of excess heat in the body through strenuous activity4.
From a clinical perspective, the crucial distinction is between heat exhaustion and heat stroke, since the latter is a major medical emergency requiring immediate treatment. Heat stroke is clinically defined as a core body temperature over 105°F (40.6°C)5, while temperature may not be abnormal with heat exhaustion. Presence or absence of sweating is insufficient for diagnosing heat stroke because in classic heat stroke, the individual stops sweating due to deyhdration, but a victim of exertional heat stroke may continue sweating. The other major defining characteristic of heat stroke is the presence of significant central nervous system dysfunction. While heat exhaustion may cause anxiety, dizziness or fatigue, heat stroke victims will also exhibit confusion, irritability, altered mental status, irrational behavior, or lack of muscle coordination (i.e., ataxia)6. Heat stress may be difficult to distinguish from organophosphate poisoning7. Three ancillary symptoms of pesticide poisoning help in making a differential diagnosis: pinpoint pupils (as opposed to dilated pupils), slow pulse (rather than rapid), and wet membranes, i.e., mouth, eyes (rather than dry.) Of course, pesticide poisoning and heat stress can co-occur. If there is any possibility of pesticide poisoning in addition to heat-related illness, treatment for both conditions should be initiated immediately.
Prevention is the most important factor in avoiding the adverse effects of heat stress. Avoiding strenuous activity, especially outdoors, during the heat of the day, acclimatizing (gradually building up tolerance for working in heat), and drinking adequate quantities of water are important preventive measures. However, these factors are often beyond the control of farmworkers, who must work under the conditions required by their employers. Health care providers should be alert for signs of heat stress during the summer months and any time that crop work in their area involves long hours of unshaded strenuous activity.
Treatment for any form of heat illness is based on reducing core body temperature as quickly as is safe. In the early stages this includes removing the individual to a shaded area, ceasing all heat-producing activity, removing heat-retaining clothing and PPE, and drinking as much water as possible. If the individual exhibits signs of heat stroke (core body temperature over 104°F), s/he needs to be transported to an emergency medical treatment as soon as possible. Rehydration also becomes crucial; if the individual is conscious, s/he should be encouraged to drink as much unsalted water as possible.
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