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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Heat Safety

This article was published originally on 6/20/1997
As temperatures rise, so can problems related to heat. As gardeners and horticultural workers, we need to be aware of how serious heat related illnesses can be and how to avoid them. If the body does not rid itself of excess heat fast enough, it cooks the brain and other vital organs. Heat stroke is often fatal, and those who survive may have permanent damage to their vital organs.

The human body loses heat through the skin by radiation and evaporation (vaporization of sweat). When the temperature is 70 or less, the body releases its heat by radiation. As the air temperature approaches body temperature, less heat is lost through radiation. In fact,people working on hot summer days actually gain heat through radiation from the sun. This leaves evaporation as the only way to effectively control body temperature. Since the body is made up of about 50% water, a working adult can produce 2 quarts of sweat per hour for short periods and up to 15 quarts per day. The body can only absorb water at the rate of 1.5 quarts per hour. This is less than what can be lost through sweat and, as a result, dehydration occurs. If liquids are consumed only when you are thirsty, you are dehydrated already. Thirst is not a good indicator for when to drink water. While working in hot weather, drink 8 ounces of water every 20 minutes. Generally, 16 ounces is the most a person can comfortably drink at once. Unfortunately, the human body cannot "catch up" by drinking extra water later in the day because only about 1 quart of water per hour can pass out of the stomach. Therefore, people should begin drinking water before working outdoors.

Cool water (50 F) is easier for the stomach to absorb than warm water, and a little flavoring may make the water taste better. The best fluids are those that leave the stomach fast, contain little sodium, and less than 8% sugar (water). Avoid coffee and tea because they contain caffeine which increases water loss through urination. Alcoholic beverages also dehydrate by increasing urination. Pop and fruit juices contain more sugar than needed so they aren't absorbed as easily or quickly as water or commercial sports drinks. Commercial sports drinks contain about 5 to 8 percent sugar. These can be useful if you are participating in vigorous physical activity for longer than 1 to 4 hours.

Can a person drink too much water? Yes, drinking more that 1 quart of water an hour can cause water intoxication which can be signaled by frequent urination and behavior changes such as irrationality, combativeness, coma, seizures, etc.

Sweat only cools the body if it evaporates. In dry air, we won't notice sweat evaporating. At about 70% humidity, sweating is ineffective in cooling the body because it just drips off the skin. Because humidity can significantly reduce evaporative cooling, a highly humid but mildly warm day can be more stressful than a hot, dry one. The higher the humidity, the lower the temperature at which heat risk begins, especially for those who are working vigorously. Thus there is truth to the saying that it's not the heat but the humidity that will kill you.

Everyone is susceptible to heat illness if environmental conditions are favorable. People who are obese, chronically ill, elderly, outdoor laborers, infants and small children can be of higher risk for heat illness. Certain medications can also predispose individuals to heatstroke or interfere with thermoregulation. Several heat illnesses exist with varying degrees of severity. Heat cramps, heat exhaustion, and heatstroke are on the more serous side, while heat syncope, heat edema, and prickly heat are less serious.

Heat cramps are painful muscular spasms that occur suddenly usually involving muscles in the back of the leg or the abdomen. They tend to occur immediately after exertion. To remedy the situation, sit or lie in a shaded, cool location. Drink cool, lightly salted water (0.25 tsp inwater) or a diluted sports drink. Also, stretch affected muscles.

Heat exhaustion or severe dehydration is characterized by heavy perspiration with normal or slightly above-normal body temperatures. Symptoms include severe thirst, fatigue, headache, nausea, vomiting and diarrhea. Affected individuals often mistakenly believe they have the flu.Uncontrolled this can evolve into heat stroke. To relieve the symptoms, follow the same recommendations given for heat cramps. If symptoms persist longer than 20 minutes, apply wet towels and call for an ambulance. Do not give salt tablets. Raise the victim's legs 8 to 12 inches keeping legs straight. Remove excess clothing and sponge with cool water and fan.

Heat stroke is classified in two ways: classic and exertional. Classic heat stroke may take days to develop and is prevalent during summer heat waves. It typically affects the elderly, chronically ill, alcoholic or obese persons. Exertional heat stroke is more common in athletes, laborers and military personnel who sweat profusely. Because uncontrolled heat exhaustion can evolve into heat stroke, you should know how to tell the difference between them. If the victim feels extremely hot when touched, suspect heat stroke. Another symptom characteristic of heat stroke is that the victim's mental status (behavior) changes drastically ranging from being slightly confused and disoriented to falling into a coma. In between these conditions, victims usually become irrational, agitated or even aggressive and may have seizures. A third way to tell is through rectal temperature, which may not be the most practical method when time is of utmost importance. If you suspect heat stroke, seek emergency help immediately.

Heat syncope occurs when a person becomes dizzy or faints after exposure to high temperatures. Victims should lie down in a cool place when it occurs. Victims who are not nauseated can drink water.

Heat edema causes ankles and feet to swell from heat exposure. It is more common in women unacclimated to a hot climate. Wearing support stockings and elevating the legs often helps reduce swelling.

Prickly heat, also known as heat rash, is an itchy rash that develops on the skin that is wet from sweating. Dry and cool the skin to relieve the condition.

Prevention and protective measures are the best way to avoid problems. Acclimating to the heat is an important preventive measure. Year-round exercise can help outdoor workers prepare for hot weather. Exercising for 60 to 90 minutes in the heat each day for 1 to 2 weeks will help the body decrease salt content in the sweat and increase the sweating rate. When new workers are exposed to hot weather, team them with veterans who know how much water to drink to avoid dehydration. A good rule of thumb for fluid replacement is to drink 1 cup of water every 20 minutes while working. Dress in light colors to reflect the heat. Wear porous and loose fitting clothing that allows evaporative heat loss and air to circulate to your body. Rest frequently, preferably in the shade. Wipe cool water on exposed areas in the skin. Dip clothing periodically in water to help cool the skin.

Sometimes the only way to stop possible heat illness and prevent irreparable damage is to cool the victim as quickly as possible. Ice baths cool a victim quickly but require large amount of ice to be effective. Cool water baths can be successful if you stir the water to prevent a warm layer from forming around the body. This is the most effective method in highly humid conditions. Spraying the victim with water combined with fanning is another effective method, though not as effective in high humidity. Ice bags wrapped in wet towels and placed against the large veins in the groin, armpits and sides of the neck also cool the body, though not nearly as quickly as immersion. Some cautions need to be remembered when employing any cooling method. Do not delay the onset of cooling while waiting for an ambulance. Doing so increases the risk of tissue damage and prolonged hospitalization. Stop cooling when the victim's mental status improves to avoid hypothermia. Do not use rubbing alcohol to cool the skin. It can be absorbed into the blood, causing alcohol poisoning. Do not use aspirin or acetaminophen. They are not effective in reducing body temperature because the brain's control-center temperature is not elevated as it is with fever caused by diseases.

Summer is upon us, take the necessary precautions to make sure it as safe as possible.



This article originally appeared in the June 20, 1997 issue, pp. 95-97.

Year of Publication: 
1997
Issue: 
IC-477(16) -- June 20, 1997