UC gives tips for coping with heat stress
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July 21, 2005
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CONTACT: Pam Kan-Rice
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(530) 754-3912
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pskanrice@ucdavis.edu
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Howard Rosenberg, UC Berkeley agricultural personnel management specialist, (510) 642-7103, rosenberg@berkeley.edu
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The heat-related death of a man harvesting peppers in Kern County last week 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.
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.
Heat illness symptoms and first aid
Heat rash
Acute skin inflammation and clogging of sweat ducts. Regarded as the least severe of heat illnesses. Though it usually causes only temporary discomfort, it can lead to a bacterial infection that shuts down the function of sweat glands.
Advice: Cleanse the affected area thoroughly and dry completely. Calamine or other soothing lotion may relieve discomfort.
Heat syncope
Loss of consciousness, generally sudden, due to lack of sufficient blood and oxygen to the brain. Greatest danger is secondary injury from a fall. Most likely to affect people not yet acclimatized to work in hot environments. Heat stress can cause it by diverting blood to extremities or lower body at the expense of the brain.
Advice: Rest, ventilate, and drink plenty of water or electrolyte fluids.
Heat cramps
Heavy sweating, thirst, and painful, involuntary muscle contractions -- most commonly in calves, thighs, arms and abdomen. Often extremely uncomfortable and can be completely disabling. Typically occur during or after hard work and are induced by electrolyte deficiencies that result from extended periods of intense sweating.
Advice: Rest and drink plenty of water or electrolyte fluids.
Heat exhaustion
Symptoms include fatigue, headache, dizziness, muscle weakness, nausea and chills, tingling of hands or feet, confusion, loss of coordination, fainting and collapse. Occurs during work and results from dehydration, lack of acclimatization, reduction of blood in circulation, strain on circulatory system and reduced flow of blood to the brain.
Advice: Rest in the shade or a cool place. Drink plenty of water (preferred) or electrolyte fluids.
Heat stroke
The most extreme consequence of heat stress, a medical emergency that can occur suddenly if heat exhaustion is not treated. Skin is hot and dry, body is typically hotter than 104 degrees and no longer able to cool itself, and mind is confused, delirious or convulsive. Brain damage and death may result.
Advice: Immediately move to coolest place available, loosen clothing, fan and douse or spray the body continuously with a cool liquid, begin to replenish body fluids by drinking, and summon or rush to aid. Get medical attention or/and transport to a medical facility as soon as possible.
How heat affects the body- Your bodily functions depend on blood circulation and many chemical reactions that occur best at about 98.6 degrees. The body has natural ways of gaining or losing heat to maintain that "normal" temperature.
- Your own body is the main source of heat that may stress you. Three-fourths of the energy you convert for physical work turns into heat, only one-fourth into motion. When your body is active, it usually generates more heat than it needs and therefore has to release some.
- The harder you work, the faster you generate heat, and the more your body has to get rid of heat. Hot weather and high humidity increase your risks by slowing the transfer of heat to the air around you.
- When you produce heat that raises internal temperature, your heart rate increases and vessels expand to bring more blood to the outer layers of skin, where the heat is released.
- If excess heat is not released fast enough this way or the surrounding air is warmer than your body, your sweat glands go to work. They draw water from the bloodstream to make sweat that carries heat through pores and onto the skin surface, where it evaporates and releases the heat.
- When more blood goes toward your body surface for cooling, less is available to serve your muscles, brain and other internal organs. And prolonged sweating draws a lot of water from the bloodstream, further reducing its capacity to deliver nutrients, clear out wastes, lubricate joints and cool you later. You can easily sweat out one quart of water during an hour of heavy work in hot weather, 3/4 quart in less strenuous work.
- If your body continues to lose fluid, you are likely to experience increasingly severe symptoms of heat illness -- general discomfort, loss of coordination and stamina, weakness, poor concentration, irritability, muscle pain and cramping, fatigue, blurry vision, headache, dizziness, nausea, confusion and unconsciousness. These symptoms and even mild effects of heat stress also increase your chance of suffering an accidental injury.
- The single best way to reduce your heat stress risks while working is to steadily replenish the water you lose as sweat. Drinking small amounts frequently, such as 6 to 8 ounces every 15 minutes, is more effective than large amounts less often.
- Relying on thirst as a signal to drink is dangerous. Most people do not feel thirsty until their fluid loss reaches 2 percent of body weight and is already affecting them.
- If you notice heat illness symptoms in yourself (or a co-worker), rest to stop generating heat, get fluids, and tell your supervisor as soon as possible. If fluid loss approaches 8 percent of body weight, there is serious risk of heat stroke -- a life-threatening emergency in which the brain is deprived of oxygen and the body can no longer cool itself. Don't let it get this far! But if it does, seek medical help right away.
