Wet Bulb Globe Temperature (WBGT) – Why Should Your School Be Using It?

Wet Bulb Globe Temperature (WBGT) is the gold standard when it comes to measuring heat stress during hot weather. The WBGT device takes into account ambient temperature, humidity, wind speed, sun angle, direct sunlight and cloud cover. WBGT provides vital information for schools to use in helping school administration to determine if conditions are appropriate to hold activity programs during hot weather.

So why WBGT and not your local news forecast or weather app? The dangers associated with your local news weather forecast, weather apps on your phone or smart device is that those temperature readings are only for your area. These methods do not provide an accurate temperature for where you are conducting your outdoor activity. They also do not consider the other important variables that the WBGT readings take as previously mentioned.

So why WBGT and not heat index? First let’s discuss how heat index values are formulated:

• The individual is 5’7” tall and weighs 147 pounds.

• It is calculated in the shade.

• The individual is wearing long trousers and a short-sleeved shirt.

• The individual’s core temperature is 98.6 degrees (F).

• The individual is walking outside at 3.1 miles per hour.

We know that all of our students are not 5-7 and 147 pounds. We also know that our students do not participate in long trousers and a short-sleeved shirt. We know that at the moment that our student begins “warming up” for practice, the student’s core body temperature begins to rise above 98.6 degrees. We also know that by the sure nature of participation in high school sports that we often ask our students for more physical production than a 3.1 mph walk.

This is why professional athletic associations, the NCAA, U.S. military and OSHA no longer accept heat index as their means of measuring heat stress values. They all now require WBGT as the means of determining the appropriate temperature for hot weather activities.

Now that we know that WBGT is the gold standard for measuring heat stress, how do we apply WBGT in the secondary school setting? First, is to decide on a device that is right for your school. There are many options on the market, and it is recommended that before purchasing a WBGT device, you check to make sure that you are purchasing from a reputable manufacturer. The manufacturer should provide a warranty along with a secure return policy for the device.

The manufacturer should be able to provide a certificate of calibration for their device. The manufacturer should be able to answer any questions regarding function, quality, specifications, validation and regulation. Likewise, the manufacturer should be able to provide long-term calibration and maintenance for the device that you purchase to ensure that the device is compliant with any updates.

Remember, a true WBGT device will have a black globe on the device. Hence GLOBE in the title of Wet Bulb Globe Temperature. It is also recommended that your devices have a fan so that wind speed can accurately be registered. No longer is the old sling psychrometer recommended.

Now that you have chosen the right device for your school, it is now time to develop your school’s WBGT policies and procedures. Remember that the definition of a policy is a course or principle of action adopted or proposed by a government, party, business or individual. The definition of a procedure is an established or official way of doing something. So, your policy is only going to be as good as your follow-through to do the procedures. To make a policy but then not have the established way of doing the act has no merit.

• The WBGT device should be set up and allowed to acclimatize at the venue at least 15-20 minutes prior to starting the activity. (field, indoor, gym, weight room, etc., if non-air conditioned)

• The unit should be at least 3 feet off the ground and away from any obstructions.

• The WBGT should be set up in the sun, not under shade. If you are practicing on turf, it should be set on the turf. If in a non-climate-controlled building such as a gym, the WBGT should be switched to indoor mode.

• The WBGT should be monitored throughout the duration of the event.

• If the WBGT device moves into a different zone, the appropriate modifications should be made. ▪ If the WBGT increases, then you modify to follow the equivalent work:rest ratio.

• If the WBGT decreases, then you modify to follow the equivalent work:rest ratio.

• It is important to remember that the WBGT reading IS NOT the actual ambient temperature reading. This is often a topic of debate with athletic directors and coaches because they think that what this chart represents is, “you’re telling me if it is at 92 degrees or higher you cannot conduct extracurricular activities, then we will never get to practice.” However, you have to remember the formula of that goes into a WBGT reading; and if you have a WBGT >92.1, your staff does not want athletes practicing in those extreme conditions.

• You will notice on the Activities Guideline Chart (Fig. 4) that there are Cat 3, Cat 2, and Cat 1 listed.

• You can identify what category your state falls into by locating your state on this map. (Fig.5)

• The biggest takeaway with the category map is that Exertional Heat Illness (EHI) is not just something that happens in the southeast portion of our country. If it is a hot day where you are located, it is a hot day. It is important that your school have measures in place to protect your students and faculty from the dangers of exertional heat stress.

• Many schools have adopted WBGT for not only their athletic departments, but also have include WBGT with their marching bands, JRROTC, elementary recess, etc.

During the 2021-22 school year, the NFHS placed an emphasis on WBGT to all state associations. The emphasis was so great that the NFHS Board of Directors through the NFHS Foundation funded a grant opportunity that provided schools with a complimentary Kestrel 5400 Heat Stress Tracker with tripod. Kestrel Meters has long been recognized as the industry leader in WBGT devices.

The purpose of this grant process was to help school districts obtain a WBGT device, along with promoting risk minimization and providing leadership as it pertains to exertional heat stress, which is one of the leading causes of death while participating in school activity programs. Schools were able to apply for this grant process through their state’s activities association.

A six-minute video was produced and made available through the NFHS Learning Center to walk you through the step-by-step process of using the Kestrel 5400 Heat Stress Tracker.

https://nfhslearn.com/library/videos/wet-bulb-globe-thermometer-educational-video

References:

https://www.weather.govhttps://assets.nfhs.org/umbraco/media/ffc/ta_htindx.PDF
https://sperdirect.com/blogs/news/what-should-you-knowwhen- purchasing-a-wbgt-instrument
htthttps://ksi.uconn.edu/wp-content/uploads/sites/1222 /2018/08/RegionalWBGT_2015_AppliedGeography.pdfps://languages. oup.com/google-dictionary-en/
Grundstein A, Williams C, Phan M, Cooper E. Regional heat safety thresholds for athletics in the contiguous United States. Appl Geogr.2015;56:55-60
https://ksi.uconn.edu/prevention/wet-bulb-globe-temperature- monitoring/ https://nfhslearn.com/library/videos/wet-bulb-globe-thermometer- educational-video