As an athletic trainer or director, ensuring the safety of your athletes during practices and games is a top priority. One major aspect is monitoring the Wet Bulb Globe Temperature (WBGT), which helps determine the risk of heat-related illnesses.
While Kestrel devices are widely used for WBGT monitoring, recent studies have raised concerns about their accuracy and the potential impact on athletic activities.
The Accuracy Issue
Multiple independent studies have shown that the Kestrel 5400, a popular device for WBGT monitoring, tends to provide readings that are higher than the actual WBGT.
This discrepancy becomes more pronounced as the WBGT values increase.
For example, at a WBGT of 86°F, about 75% of Kestrel 5400 readings are higher than the actual WBGT, and this disparity reaches nearly 100% at a WBGT of 92°F.
Multiple independent studies have found that nearly 40% of the Kestrel readings would have resulted in restricting athletic activity when the ISO standard device showed activities could safely continue.
Reasons Behind the Inaccuracy
Several factors contribute to the Kestrel 5400’s inaccurate readings.
One issue is that the device heats up in the sun, resulting in elevated temperature readings. Kestrel’s own information calls out this issue.
Lack of Solar Radiation Shield
Kestrels’ temperature and humidity sensors are not properly shielded from solar radiation. This causes the temperature sensor to read higher than the true ambient air temperature when exposed to direct sunlight, resulting in erroneously high WBGT readings.
Why the Size of the Black Bulb Matters
The size of the black globe plays a major role in how Wet Bulb Globe Temperature (WBGT) is measured because globe temperature is one of the most sensitive components of the calculation. Globe size directly affects how radiant heat is absorbed, how quickly the sensor responds, and how stable the readings remain in real-world conditions.
- Heat Absorption: Larger globes absorb radiant heat more evenly and over a broader surface area, creating a more representative measure of heat stress. Smaller globes heat and cool more rapidly, which can exaggerate quick changes in solar exposure.
- Response Stability: A larger globe has greater thermal mass, which naturally smooths out short-term fluctuations from intermittent clouds, wind gusts, or brief shading. Smaller globes are more reactive, leading to readings that can spike or drop faster than the true environmental trend.
- Convective Cooling: Wind has a stronger cooling effect on smaller globes. This can pull readings down more quickly, especially in breezy conditions. Larger globes resist this cooling effect, maintaining a steadier and more physiologically relevant temperature.
Learn more about black bulb sensors and how they work here.
Click here to read a well-known evaluation of portable WBGT monitors confirms these effects, demonstrating how globe size drives both accuracy and reading stability.
Impact on Athletic Activities
The inaccuracies in WBGT readings can have a significant impact on athletic practices and games.
While it’s better to err on the side of caution, excessive overestimation of WBGT can lead to unnecessary practice cancellations, disrupting training schedules and acclimatization plans.
The chart shows Kestrels have a bias towards higher readings, resulting in fewer normal activities compared to other devices.
A study at the University of Georgia found that nearly 40% of the Kestrel readings would have resulted in restricting athletic activity when the ISO standard device showed that activities could safely continue.
Impracticality For Use in The Field
Handheld WBGT devices can be inconvenient for athletic trainers who are required to take and document readings every hour, as mandated by many states like Georgia and California. Some drawbacks include:
- Setup time: Handheld devices often need 10-20 minutes for sensors to equilibrate with the environment before providing accurate readings.
- Frequent adjustments: Accurate measurements require positioning a device in advance of practices or games at the correct height and orientation, resulting in time away from treating athletes or laborers.
- Limited data logging: Many handheld devices lack customizable reports or automated report sends, with data only accessible to whoever has the mobile app—limiting visibility and collaboration across teams.
These factors make handheld WBGT devices less practical for consistent, long-term monitoring and documentation of environmental conditions.
Lack of Warning Functionality
When WBGT monitors like Kestrel are used for student athletics, they often require immediate responses or alterations to practices or games when WBGT temperatures reach certain heat stress policy thresholds.
This results in Athletic Trainers or those responsible for ensuring compliance with heat stress policies needing to communicate with many people simultaneously.
Kestrel cannot alert coaches and athletes of what practice alterations are required. Products like Perry Weather integrate school heat stress policies into the platform and automatically send text messages and mobile push notifications to everyone on campus with concise instructions on what alterations are required.
Alternative Options to Handhelds
While the Kestrel 5400 has its limitations, there are alternative WBGT monitoring systems available.
Perry Weather stations take a different approach to WBGT monitoring. Here’s how Perry Weather offers a better WBGT monitoring solution:
In conclusion, accurate WBGT monitoring is crucial for ensuring the safety of athletes during practices and games. As an athletic trainer or director, it is essential to be aware of the potential inaccuracies in Kestrel devices and to consider alternative options that provide more reliable and precise WBGT readings.
By investing in the right professional-grade equipment and utilizing it properly, you can optimize safety while maximizing practice productivity.
Ensuring Accurate WBGT Monitoring
To ensure the safety of your athletes, it is essential to use reliable and accurate WBGT monitoring devices. On-site devices that utilize meteorological-grade sensors are the best option for obtaining actionable data.
When choosing a WBGT monitoring system, look for reputable commercial-grade devices that adhere to ISO safety standards and provide maximum accuracy under sunny and humid conditions. Proper installation, calibration, and maintenance of these devices are also crucial to maintain precision throughout the season.
Learn more about Perry Weather
Perry Weather offers accurate and done-for-you WBGT measuring and monitoring, providing solutions and features like an outdoor weather station, customizable alerts, policy consultations, and 24/7 on-call meteorologist support. We ensure you can provide comprehensive heat safety to those you’re responsible for.
If you’d like to better understand how Perry Weather can elevate your WBGT monitoring and ensure safety, contact us to learn more.
