Keeping Cool 
Eight Steps for Preventing Heat Stress 

by Dr. Richard Jennings

Sport Aviation - April 2000

Summer is approaching, and the first bright warm days of spring always make me start thinking about heading north to EAA AirVenture Oshkosh. There is nothing in aviation like AirVenture with its activities and exhibits to attract anyone with even the slightest interest in aviation. Airplanes and activities stretch from the aircraft parking and camping areas adjacent to Runway 9/27 all the way to the south end of Runway 18/36, about two miles away, where the ultralights fly. 

While the weather often varies considerably during the week, and at least one thunderstorm visits, I have been impressed by the number of hot days we’ve had during the past few years. Because AirVenture is predominately an outdoor activity that attracts almost a million participants, people need to prepare for the weather and all of its changes. If it’s chilly, as it sometimes is, keeping comfortable is a matter of dressing appropriately. But when it’s hot, there’s only so much people can do. One important thing they can do is learn about what causes heat-related stress and how to prevent heat-related illness. Heat stress in humans depends on the thermal environment, clothing, workload, and individual tolerance. Individual risk factors include age, increased body weight, low degree of physical fitness, low levels of acclimatization and hydration, and certain preexisting medical conditions. 

Some medications can also increase individual risk. Workload varies on the intensity of the exercise and its duration. Environmental factors include the ambient temperature, humidity, wind velocity, and radiant heat load (sun exposure). Clothing can vary heat loading based on its thermal resistance, wind permeability, evaporative resistance, and effect on blocking radiant heat load. In other words, a person who is physically fit, is visiting from a warm climate, and drinks a lot of water during the day is less susceptible to heat stress than an older or younger person from a colder climate who doesn’t exercise regularly and doesn’t drink a lot of water. 

In general, humans have the ability to remain in thermal balance because we can reject heat through increased respiratory cooling, increased heart rate, increased evaporative cooling through sweating, and increased radiation and convection cooling through vasodilatation near the skin.

However, with enough workload and environmental heat load, our homoiothermic compensation mechanisms can be overwhelmed and our core temperature begins to climb. When we are no longer able to compensate for heat loading, we are at risk from heat-related illnesses such as heat exhaustion, heat cramps, heat syncope, and heat stroke. 

For AirVenture performers, heat stress may cause narrowed attention, delayed reaction time, decreased mental performance, decreased G-tolerance, increased error rate, and decreased safety margins. Many times these deleterious effects are insidious and may go unnoticed. Fortunately, most full-time performers are conditioned to summer heat and the stress of their performance routine. Pilots flying to AirVenture and participants on the ground may not be so aware or acclimated. 

In addition, many pilots tend to avoid fluids before flying to avoid unscheduled pit stops. Dehydration compounds the problems of heat loading and interferes with our ability to maintain core temperature. In the air or on the ground, when it’s hot—drink water. EAA provides excellent medical facilities and emergency medical services on the AirVenture grounds, but availing themselves of these services isn’t how most people would prefer to spend their time in Oshkosh. The best way to avoid heat-related illnesses at AirVenture is prevention. Here are eight steps that will help you prevent heat stress and be healthy and comfortable during AirVenture. 

1. Be realistic about your general condition prior to arriving at AirVenture. If you are sedentary, start walking every day. Start with short distances and slowly extend them. Not only will this help prepare you for AirVenture, it will help you shed a few pounds. I know that no pilot has ever attended AirVenture with his/her plane over gross weight, but a little exercise and dieting can help with our own mobility and help the aircraft’s weight and balance as well. Your daily walks will also help acclimate you to warm temperatures. To best acclimate yourself, spend several hours outdoors starting one or two weeks before arriving at AirVenture. 
2. Consider the effect of any preexisting medical condition or medication. Medications that might reduce heat tolerance include the diuretics, anticholinergics, phenothiazines, MAO inhibitors, and tricyclic antidepressants. Given appropriate precautions, most individuals with preexisting medical conditions can enjoy the show; however, it may be prudent to exercise more caution. If you are on medications that may cause problems, consult with your physician before leaving for Oshkosh. 
3. Pack comfortable clothing that is light colored, lightweight, single layer, loose fitting, and breathes. Cotton is a nice choice. A ventilated, broad-brimmed hat for UV protection and shade is a must. 
4. Wear comfortable shoes that give your feet good support. Jogging shoes that have previously been worn are an excellent choice. Shoes should have broad heels and provide impact absorption to reduce discomfort for your feet. Don’t forget sunscreen, but if you do, it is available outside the medical facility.
5. Pace yourself. You can’t see all that AirVenture has to offer in one day. When the environmental stress is the greatest, that is a good time to reduce workload. High-heat times of the day are a good time to visit the air-conditioned museum, relax in the shade at the Theater in the Woods, or sit down for a light meal. Develop an appropriate schedule. If you need to cover some distance, plan to do it early in the morning, when it’s cooler. Plan your more sedentary activities during the afternoon. Consider riding on the trams or renting motorized scooters and wheelchairs, which are available, as are handicapped transportation services. 
6. Keep well hydrated. Adequate hydration is needed for continued evaporative cooling. During high-heat activities, our need for water is initially greater than our thirst. EAA has made great strides in providing water fountains, and carrying several liters of water in your backpack is always a good idea. Plain water is a great choice when you are exposed to a hot environment for a prolonged period. It may also help to pre-hydrate prior to heat exposure. EAA has provided plenty of bathroom facilities around the site, so don’t worry if you have to stop periodically. 
7. Avoid alcohol and caffeine drinks. Remember, alcohol and caffeine are diuretics and can make dehydration worse. 
8. If for some reason you feel that you have become too hot, let someone help you to an area that has shade, air conditioning, or cooling fans. Limit physical activity, drink cold water, and consider cooling the skin with a spray of water or wet towels. Remember that EMS personnel are on-site and can help if these efforts don’t work. 

AirVenture is a wonderful event and the highlight of the year for many pilots and aviation fans. Truly, there is something here for everyone. Hopefully AirVenture 2000 will enjoy clear, cool, and dry weather. However, if heat is a factor again this year, plan to preflight yourself and develop a prevention plan for avoiding heat-related illness.