You've been kicking this fire for six days and nights now, but it's stubborn. It's eaten up your hard-won line twice, made surprise runs behind your back, and flared up when it should have laid down. The tinder-dry brush crackles and snags at you, and the fire races through the light grasses. Prevailing winds, which you were told were from the south, have run in circles. The dry lightning at night -- and the blistering 100-degree-plus heat during the day -- have helped the fire along and nearly broken your crew.

You're packing hose and tools up near-vertical slopes and eating dust and smoke, going mostly without food and water in favor of kicking butt on the fire. Your squad boss was testy at the lunch break about drinking more water, but no one's really been willing to give this one a rest till you've gotten the upper hand. It's now a couple hours after lunch. It's the hottest day yet. You munch your way across the slope, saws whining and tools swinging.

Then the guy in front of you weirds out.

He turns around, stares off into the distance, and starts mumbling some crap about root beer. He's hunched red-faced over his pulaski, panting, and his eyes look like he's stoned. His hands are trembling and his legs quiver, then his knees buckle and he folds into the dirt.

Heat stroke. What do you do?

Three types of heat stress include heat cramps, heat exhaustion, and heat stroke. Though heat stroke -- which can be fatal or result in permanent damage -- is easily preventable, it's critical to bring it under control in order to avoid complications.

Those who are unaccustomed to the heat, or who become dehydrated from excessive perspiration or inadequate consumption of liquids (or a combination), are most likely to experience heat cramps. In the recently released second edition of Fitness and Work Capacity, Brian Sharkey explains that heat cramps are less likely when fluid intake is adequate and the diet includes bananas, oranges, fresh salads, and adequate table salt.

Prolonged exposure to heat in combination with dehydration can trigger heat exhaustion. Heat exhaustion is indicated by symptoms such as dizziness, sweating, dry mouth, headache, weakness, fatigue, clammy skin, and an unstable gait. Other indicators include muscle cramps and a weak and rapid pulse. Heat exhaustion can be treated with increased fluid and electrolyte intake, and by resting in a cool place.

According to the American Institute of Preventive Medicine, heat exhaustion takes time to develop. Heat stroke, though, strikes suddenly with little warning. Heat stroke is a medical emergency which can be fatal if untreated. Medical assistance should be obtained as soon as possible in order to prevent brain damage or death.

Signs of heat stroke include a very high temperature (104 degrees F. or higher) and skin that is hot, dry, and red. Sweating stops, and deep breathing with a fast pulse is followed by shallow breathing and a weak pulse. Pupils become dilated, speech may be incoherent, and confusion or delirium or even hallucinations and convulsions may occur.

Those most at risk for heat stroke are people with chronic medical conditions such as diabetes or heart disease. The use of alcohol can increase risk, and dehydration resulting from vomiting or diarrhea can also ratchet up the chances of heat stroke in hot weather.

Heat exhaustion and heat stroke can be prevented. At the first signs of heat exhaustion, get out of the sun or your body temperature will continue to rise. Drink extra liquids, especially if your urine is dark. Note that thirst is not a reliable sign that your body needs fluids. Drink water or water with salt added (1/2 teaspoon per quart) if you sweat a lot; beverages such as Gatorade are helpful. Alcohol and caffeine increase fluid loss, but salty foods can help retain fluids.

According to Dr. Gabe Mirkin of the Sportsmedicine Institute, the most effective treatment is to immerse the victim in ice water. He says 22 runners passed out at a road race in Falmouth, Massachusetts; half were immersed in ice water and half were wrapped in wet towels. The ice water bath cooled the runners twice as fast as the wet towels did. If you see someone pass out and suspect heat stroke, get medical help immediately and ice water if at all possible.

Buck Tilton of the Wilderness Medicine Institute in Pitkin, Colorado, says overheating can ruin your day -- and your life. "Human heat is lost in four ways: conduction, radiation, convection, and evaporation," he says. "Conduction, heat loss through direct contact with something cooler than you, does not help much on a hot day. On a desert-like afternoon, you may actually take in heat from a hot environment. Radiation is energy lost directly from your skin's surface and, as the air warms up around you, it may effectively stop on a sunny summer day. Convection is heat loss through the movement of air around your body. Without wind, convective heat loss practically stops when you're not moving, and it stops when the air temperature reaches approximately 92 degrees Fahrenheit."

Tilton explains that sweat evaporation is the primary method of heat loss. "Evaporation of the sweat cools your skin, heat is drawn from your blood near the surface of your body, and the cooler blood circulates to keep your insides maintained at an acceptable temperature," he says. "In other words, if you don't sweat, you ain't gonna make it."

It's not unusual to sweat out a liter of fluid in an hour, but that rate can reach three liters per hour under extreme conditions. "Prolonged sweating may move you along the spectrum to heat exhaustion, characterized by headache, dizziness, nausea, rapid breathing, and, of course, exhaustion," he says. "Sufferers are so sweaty they often feel cool, grow goose bumps and complain of chills. Treatment should include moving the exhausted person to a shady spot and oral rehydration with cool, very slightly salty water. Some experts prefer using an electrolyte-balanced drink such as Gatorade, but the drink should be watered down three or four times for more rapid absorption in a resting person. Maximum absorption ranges from 150 to 250 ml per 15 minutes, so it takes about an hour to get a liter back into circulation."

According to Tilton, heat stroke kills about 4000 people in the U.S. every year. "There are two varieties of heat stroke," he says. "In classic heat stroke, the patient is usually elderly or sick or both. Temperature and humidity have been high for several days, and the patient has dehydrated to the point where his or her heat loss mechanisms are overwhelmed. You might say they simply run out of sweat. Skin gets hot, red, and dry. They lapse into a coma and, if untreated, die.

"But more and more people are being killed of the second variety, exertional heat stroke," says Tilton. "The victim is usually young, fit, and unaccustomed to heat, sweating but producing heat faster than it can be shed. Signs include, primarily, a sudden and very noticeable alteration in normal mental function: disorientation, irritability, combativeness, bizarre delusions, incoherent speech. Skin is hot and red, but wet with sweat. Rapid breathing and rapid heart rates are almost universal. Collapse is imminent."

Tilton says quick cooling is necessary, and recommends removing clothing, covering with wet fabric, and fanning vigorously. Massaging arms and legs and applying ice packs at the neck, groin, and armpits can increase heat loss. "Throwing patients into cold water is less effective," he says, "and often dangerous since they are difficult to manage and may drown. Heat stroke victims should be seen by a physician as soon as possible, even if they seem to have recovered. Too much internal heat can cause breakdowns that show up later in some body systems."

PRE-SEASON PREVENTION

Pre-season preventive measures can help reduce chances of suffering heat stress. "Achieving and maintaining a high level of aerobic fitness is one of the best ways to protect yourself against heat stress," writes Brian Sharkey. "The fit worker has a well-developed circulatory capacity, as well as increased blood volume, which is essential to regulate body temperature in the heat. Fit people start to sweat at a lower body temperature, so they work with a lower body temperature and heart rate." Sharkey adds that those who are in peak form can adjust to heat twice as fast as those who are unfit.

"The effect of the wildland firefighter's uniform on firefighters working in heat was studied recently at the University of Montana Human Performance Laboratory," says Sharkey. "The fittest worker finished a two-hour work test in the heat chamber with a heart rate of 118 beats per minute, while the least fit labored at a rate of 164 beats per minute." He says differences in fitness far overshadowed variations in clothing worn.

The best defense against heat stress is to understand what causes it and recognize the conditions that will precipitate it. Temperature and humidity, according to Sharkey, are the best clues:

• Hot air because of sun or nearby flames
• Still air with no breeze
• Sweat dripping off your body
• Pounding heart and rapid pulse
• Feeling breathless, dizzy, chilled, or nauseated

REPLACE FLUIDS

Drinking lots of fluids before, during, and after exertion in the heat is vital. Replacement of water, salt, and potassium will help avoid heat disorders. "For every liter of water loss," says Sharkey, "the core temperature increases more than 0.5 degrees Fahrenheit, heart rate increases eight beats per minute, and the cardiac output declines, making work more difficult."

One or two cups of water or juice should be drunk before work, and about a liter per hour of water during work is recommended. Drink as much as possible at lunch and at the evening meal, and continue replacing fluids throughout the evening. Limit caffeine, and avoid alcohol.

SPORTS BEVERAGES

Carbohydrate/electrolyte drinks are popular with athletes; the beverages provide carbohydrates (glucose, sucrose, glucose polymers) to sustain energy and blood glucose levels, and electrolytes (sodium and potassium). Studies indicate that people drink more of lightly-flavored drinks than they do water, which is a benefit. Though adequate carbohydrates and electrolytes are normally consumed with regular meals and snacks, beverages such as Gatorade can help maintain energy during long periods without food or snacks -- especially for those not acclimatized to the heat. Carrying liters of beverage in packs is not always feasible, but some sport beverages are available in packets of dry mix. Beverages with glucose polymers provide more energy per liter.

ELECTROLYTE REPLACEMENT

Use the salt shaker liberally in the heat. Those who are not acclimatized sweat out more salt. Salt tablets are not recommended, because too much salt can impair temperature regulation and cause fatigue, high blood pressure, stomach distress, sore muscles, impaired heart function, potassium loss, and mental confusion. Drinking lemonade or tomato juice can help maintain potassium levels.

REHYDRATION

"Rehydration requires replacing body fluid," writes Sharkey. "Drinking plain water is not an effective way to rehydrate. Drinking large volumes of water suppresses the drive to drink, and stimulates urine production. Rehydration fluids should contain moderately high levels of sodium and some potassium, or food with these electrolytes should be consumed along with the fluids. Typical carbohydrate/electrolyte beverages do not contain enough sodium for rehydration."

DON'T LET THE HEAT GET TO YOU

When body temperature rises beyond tolerable limits, heat stress takes over. The combination of excessive air temperature, humidity, radiant heat, and limited air movement, added to the exertion of fighting fire in protective clothing, creates the perfect set-up for heat stress. It's easily preventable, and if you know what to watch for, you can prevent serious damage or even death from heat stroke.