What is W B G T?

When a coach steps out onto the field in mid-August and says, “It’s a hot one today,” they are usually referring to the number on a standard thermometer. While the ambient air temperature is a vital piece of the puzzle, it only tells a fraction of the story. For the safety of student-athletes, relying solely on a traditional thermometer is not just inaccurate—it can be a fatal mistake.

To truly understand the risk of exertional heatstroke, we must look at the Wet Bulb Globe Temperature (WBGT). At IceAthletes.com, we believe that understanding the science of the air around us is the most effective way to prevent heat-related tragedies.

The Problem with the “Heat Index”

Most people are familiar with the “Heat Index,” which you might see on a weather app. The Heat Index is a calculation of air temperature and relative humidity. While it is better than looking at temperature alone, it is designed for people standing in the shade wearing light clothing.

Athletes are not standing in the shade. They are sprinting in direct sunlight, often wearing heavy pads and helmets, on surfaces like synthetic turf that can be 20 to 50 degrees hotter than the air. This is where the WBGT comes in. It provides a much more comprehensive assessment of heat stress by measuring four variables:

  1. Air Temperature
  2. Humidity
  3. Wind Speed
  4. Sun Angle (Solar Radiation)

The Science of Sweating: Why Humidity Kills

To understand why WBGT is the gold standard, we have to look at how the human body cools itself. During exercise, the body’s primary cooling mechanism is evaporation. We produce sweat, and as that sweat turns from a liquid to a gas on our skin, it carries heat away from the body.

In low humidity, this process works efficiently. However, when the humidity is high, the air is already saturated with moisture. The sweat stays on the athlete’s skin; it cannot evaporate. This means the body’s primary “exhaust system” is blocked. Even if the air temperature is a relatively modest 85°F, if the humidity is 90%, an athlete can reach a critical core temperature faster than on a 100°F day in a desert climate.

Breaking Down the WBGT Reading

A WBGT device looks different than a regular thermometer. It typically features three sensors:

  • The Dry Bulb: Measures the standard air temperature.
  • The Natural Wet Bulb: Measures the ability of the air to evaporate moisture (simulating how sweat works).
  • The Black Globe: Measures solar radiation (the intensity of the sun hitting the athlete).

When these three readings are combined, they give a single number that represents the true level of heat stress. For example, a WBGT reading of 82°F might seem “cool,” but it actually represents a high-risk category where practices must be modified—heavy equipment should be removed, and rest breaks must be tripled.

The “Danger Zones”: Using the WBGT Scale

State high school associations across the country are increasingly mandating the use of WBGT to dictate practice schedules. Here is a general breakdown of how those levels typically impact a practice:

  • Under 82.0°F (Green): Normal activities. Provide at least three separate rest breaks per hour.
  • 82.2°F – 86.9°F (Yellow): Increase rest breaks. Use caution. Limit intense exercise for unacclimatized athletes.
  • 87.0°F – 89.9°F (Orange/Red): Maximum practice time is 2 hours. Football players must be in “shells” (helmets and shoulder pads only). No conditioning drills.
  • Over 90.0°F (Black): No outdoor workouts. All practices must be moved indoors or canceled.

For an athletic director, having a WBGT device on the sideline removes the “guesswork.” It provides a data-driven defense if a practice is canceled, and more importantly, it provides a data-driven safeguard for every child on that field.

Implementing WBGT at Your School

Transitioning to a WBGT-based safety protocol requires more than just buying a device. It requires a cultural shift within the coaching staff.

  1. Designate a “Heat Monitor”: This should ideally be a Certified Athletic Trainer. They should take readings at the site of the practice (the actual turf or grass) every 30 minutes during the “Danger Zone” months.
  2. Document Everything: Keep a log of WBGT readings. This is vital for legal protection and for identifying patterns in local micro-climates.
  3. Communication: Ensure that coaches have a direct line of communication with the monitor. When the WBGT hits a specific threshold, the practice must change immediately—no exceptions.

Conclusion: Respecting the Environment

We cannot control the weather, but we can control our response to it. By moving away from the standard thermometer and embracing the Wet Bulb Globe Temperature, we acknowledge the complex way the environment interacts with the human body.

At IceAthletes.com, we are committed to providing the training necessary to help schools implement these protocols. Safety isn’t just about being “tough”; it’s about being smart enough to respect the science of the air.