Here's a little "Did You Know?" that you might have missed in high school science class: The human body's core temperature is normally within the narrow range of 98 to 99 degrees F. When the core body temperature exceeds that by just a few degrees you go into heat exhaustion. And when it reaches 104 to 106 degrees you are in the danger zone of heat stroke.

So within a range of 8 degrees For less, you can go from perfectly healthy to risking death or permanent injury. This is not meant to be alarmist, but it just goes to show the importance of protecting yourself-not just from a wreck, but also from heat-when you are inside your racecar.

Granted, the human body can take quite a bit of punishment before it allows core body temps to reach the danger zone. Driving a feature race in a racecar in July doesn't guarantee heat stroke, but we all know that the environment inside a racecar can often be a lot like spending a half hour or more in an oven.

Rick Shafer of Cool Shirt is one of the most knowledgeable people in the racing industry on the subject of just how heat affects racecar drivers, both mentally and physically. He not only has done extensive research himself, but he's also gathered the research results of such organizations as NASA and applied their findings to our sport.

Before you can understand exactly how important some sort of cooling method is to the racer, you must first understand the science of how the body cools itself naturally. Shafer points out that there are four ways the body gets rid of excess heat. Just as a matter of living and breathing-not necessarily exercising or racing-the human body generates up to 50 degrees of extra heat over a 24 hour period. Approximately 65 percent of that is released through radiation, which occurs when the air temperature is lower than the body's temperature. Ten to 15 percent of body heat is lost through convection, which is, according to Shafer, heat loss to air and water vapor around your body which must be lower than your skin temperature. Conduction, which is the transfer of heat from warmer to cooler objects by direct contact, accounts for only two percent. And finally, evaporation, which is the release of perspiration through the sweat glands which cools the body when the liquid evaporates, is responsible for the final 25 percent.

The important part to understand here is that when the air temperature around you is over 95 degrees, three of the four methods the body uses to cool itself no longer work. Only evaporation is still a reliable method.

Now consider the fact that in order to protect himself or herself from the threat of fire, a racecar driver must wear a protective driver's suit that is not only flame-retardant, but also able to insulate the driver's body from extreme heat. "The insulating qualities of a good driver's suit are important," says Bob Mantell, executive sales director of safety equipment manufacturer RaceQuip. "The thing you have to understand is that the suit is about thermal protection. It's not the flame that burns you inside the suit, it's the heat. Unfortunately, the suit also works in reverse. The heat you generate as you drive the racecar is trapped inside the suit."

So in an environment where the air temperature is over 95 degrees (and how often does that happen inside your racecar?) you have already lost three of the four ways your body cools itself, and now you've put on a driver's suit that not only traps the heat your body generates against you but also isn't breathable so the sweat your body produces isn't evaporating. Can you see how overheating can be a concern?

Just like overheating your engine can result in stuck exhaust valves, cracked cylinder heads, and detonation, there are very tangible-and very negative-effects when your body overheats. Again, we'll refer to research Cool Shirt's Shafer has compiled and shared with us.

The first thing we need to understand is how the body physiologically handles heat removal. The typical person has approximately 5.6 liters of blood coursing through his veins. For normal heat loss, Shafer says one-fourth of a liter is sent to your skin per minute to aid cooling. This heat is transferred through the blood to the skin to be lost through one of the four methods mentioned earlier. But when heavy perspiration occurs the body ups the ante considerably. Now, up to half of your blood is sent to the skin's surface (that's why you get flushed) to get as much heat out as possible. This means your body's organs, muscles and your brain are only working on half of the oxygen-providing blood supply they normally have at their disposal (see the illustration at the top of this page.)