College of Natural Resources, UC Berkeley

UC gives tips for coping with heat stress

August 1, 2005

by Pam Kan-Rice
The heat-related death of a man harvesting peppers in Kern County last month is a tragic reminder of the dangers of heat stress.

To help reduce dangers of becoming overheated, a University of California Cooperative Extension specialist has produced a heat-stress information card for farmworkers that explains in English and Spanish how heat-related illnesses develop and how to avoid them.

Download a fold-up heat stress information card in English and Spanish (PDF)

More references about heat stress are available here.

Although the advice is directed at farmworkers, it is useful to anyone who works in the heat.

UC Berkeley-based agricultural personnel management specialist Howard Rosenberg warns that excess heat can impair the body even before a person feels ill. Symptoms of heat stress may include general discomfort, loss of coordination and stamina, weakness, poor concentration, irritability, muscle pain and cramping, fatigue, blurry vision, headache, dizziness, nausea, confusion, and unconsciousness (see "Heat illness symptoms and first aid" sidebar).

Although some of the heat that people have to deal with at work comes from the sun and ambient air, most heat is generated by their own bodies, Rosenberg says. "At rest the body produces little heat, but at work it demands more energy and faster metabolism, which greatly increases internal heat production," he explains.

To cool itself, the body first increases blood flow toward the body surface. This reduces the flow available to carry oxygen and nutrients to the muscles, brain and other internal organs, which in turn impairs strength, diminishes alertness and accelerates fatigue.

"When this mechanism doesn't release heat fast enough, sweat glands kick in," says Rosenberg. "They draw water from the bloodstream to form sweat that carries heat across outer layers of the skin and then evaporates." The loss of water through sweating impairs the body's ability to cool itself later, and the loss of electrolytes in sweat can cause muscle cramps.

The longer sweating goes on, the less blood volume remains and the greater the health risk. Rosenberg gives this cautionary example: a 150-pound man working moderately in warm weather would lose about 3/4 quart of water -- or 1 percent of his body weight -- per hour. At that rate, without replacing the lost fluid, he would likely experience diminished energy and endurance after three hours, serious fatigue and nausea after six hours, and loss of consciousness after eight hours (see "How heat affects the body" sidebar).

He recommends drinking water even before being prompted by thirst because thirst is a late signal of a water deficit. "Chugging to quench an intense thirst is like pouring water on a wilted plant," Rosenberg says.

For farm operations, Rosenberg recommends that managers and foremen try to keep drinking water containers as close as possible to centers of activity. If the water is too far away, such as at the end of a long row, workers may not want to take time away from their tasks or exert the extra effort to get to it.

Rosenberg also recommends bringing "a little heat-stress physiology 101 to the field" -- helping workers understand the causes of heat stress, their own bodies' heat release mechanisms, and the critical importance of replenishing the fluid they lose as sweat. "We hope the new card enables more growers to effectively deliver information that their employees need to know."

If workers begin experiencing heat stress symptoms, Rosenberg advises having them rest, preferably in a cooler area, and drink plenty of water or electrolyte fluids. In case of heat stroke, immediate medical attention should be sought.

AB 805, a bill pending in the California Legislature, would add specific heat-illness prevention and response requirements to employers' existing obligations for workplace safety. This month, after more than three inactive years, a Cal/OSHA advisory committee resumed its consideration of a new industrial regulation that would help prevent heat illness and injury in the workplace.

The card is being produced in cooperation with California Farm Bureau Federation, California Grape and Tree Fruit League, and California Association of Winegrape Growers, with additional USDA support through its Western Center for Risk Management Education.

To order free copies of the bilingual heat-stress education cards for farmworkers, contact Elisa Noble at enoble@cfbf.com or (916) 561-5598.

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