We sat down with Tony Clower, who oversees athletics for every school in Roane County, and Dr. David Martin of Perry Weather to walk through what TSSAA actually requires, and why the choice between WBGT and heat index matters more than it sounds. Here is what they covered, plus the live Q&A from the session.
The History of Heat Illness in High School Athletics
The timing of this conversation isn’t incidental. Most student athletes spend the bulk of their summer indoors, in air conditioning, then walk straight into full-intensity conditioning the moment practices resume — often while temperatures are still at their seasonal peak. Their bodies haven’t had time to acclimatize. That combination, more than any single hot afternoon in October, is where the data shows the risk concentrates: ramped-up activity, peak heat, and an athlete whose body hasn’t adjusted yet.
Between 1980 and 2009, there were 159 heat-related fatalities in youth, high school, and collegiate athletics. A sub-sample of 61 of those deaths was studied to look for common threads: 100 percent happened during conditioning drills, 97 percent of the victims were linemen, and 37 percent involved athletes being conditioned as punishment.
Heat stroke isn’t limited to hot days, either. Dr. Martin cited an account from an athletic trainer who worked the Boston Marathon on a 50-degree day that still produced nine exertional heat strokes, a reminder that awareness of symptoms matters as much as watching the thermometer.
The Georgia Study That Started It All
The research that got states moving toward activity-based heat policy came from the University of Georgia. Bud Cooper and Andrew Grundstein, both at the University of Georgia, looked at historical heat illness data and asked what would happen if schools modified activity, removed equipment, or added rest and hydration breaks once conditions crossed certain WBGT thresholds.
The result was a 30 to 100 percent decrease in exertional heat illness across every category tested. The same pattern showed up decades earlier in the military, where implementing a WBGT-based flag system at boot camps dramatically cut heat illness after two summers with roughly 600 cases at Parris Island alone.
What is Wet Bulb Globe Temperature, and Why Does Tennessee Also Allow Heat Index?
The three measurements schools encounter are not variations on each other. They count different things.
| Measurement | What it accounts for | Why it falls short for athletics |
|---|---|---|
|
Ambient temperature
|
Air temperature only. | Ignores humidity, sun, and wind. Two days at the same reading can carry very different risk. |
|
Heat index
|
Air temperature and humidity. | Built for a person walking in the shade in long clothing. Ignores solar load and wind, and athletes are not in the shade. |
|
Wet bulb globe temperature
Athletics standard
|
Air temperature, humidity, wind speed, and solar radiation. | It doesn’t. Measured on site, where the athletes actually are, which is why it’s the standard used by the military, OSHA guidance, and FHSAA. |
Heat index gets closer than a thermometer, but it was never built for athletes. WBGT adds wind and direct solar radiation, which is why it reflects whether an athlete can actually shed heat through sweat. It is also not new. It came out of the US military in the 1940s and 50s, after roughly 600 heat illness cases in the summer of 1952 and six recruit deaths there between 1951 and 1953. The flag system built on WBGT drove those numbers down and has been in use ever since
That’s why TSSAA policy names WBGT as the preferred reading but still allows heat index as a fallback when no WBGT instrument is available. The two numbers are not interchangeable, and mixing them up is the single most common mistake schools make.
The TSSAA WBGT and Heat Index Guidelines
Tennessee’s policy lets either measurement govern a decision, but the two thresholds are calibrated to roughly correspond to each other rather than being interchangeable minute to minute.
One rule trips schools up more than any other: if an on-site WBGT reading is available, it governs the decision even if the heat index reading would allow a different outcome. Schools cannot switch to whichever number is more convenient in the moment.
Choosing WBGT over heat index solves half the accuracy problem. The other half is where and how that WBGT reading is taken.
A regional weather station or a general weather app pulls conditions from the nearest reporting point, which may be miles away and doesn’t reflect what’s actually happening on a specific field. One Tennessee athletic director described a practice field sitting at the base of a mountain that picks up heavy shade in the late afternoon — shade that heat index couldn’t account for, since it only factors in air temperature and humidity. Going by heat index alone was canceling practices that, with an on-site WBGT reading, would have been safe to hold.
Phone-based WBGT apps introduce a second problem: volatility. During a side-by-side instrument test at White Sands Missile Range, a phone-based WBGT app spiked roughly 4°C above seven other devices — including the reference-standard instrument — measuring the same conditions at the same moment. That swing was large enough to cancel a practice the other seven instruments confirmed was safe to continue.
Emergency Action Plans, Cooling, and Hydration
Schools without an existing EAP template don’t need to start from scratch — the Korey Stringer Institute publishes one freely on its website. Having a written plan is only half the requirement, though. Research on emergency response cited in the session found that EAPs not rehearsed before the season starts are implemented less effectively when a real emergency happens. Tony’s district treats that rehearsal as non-negotiable: coaches run a walkthrough at the start of the year, record it, and send the video to him and the school nurse for review, so gaps get caught before they matter.
A cold water immersion tub, or another form of rapid on-site cooling, should be available for every warm-weather practice. If exertional heat stroke is suspected, cooling happens on site before transport, not the other way around. Dr. Martin pointed to a rule from another state as a reminder of how strict that sequencing can get:
“In the state of Connecticut, if you have an athlete in a cold tub and EMS comes to pick them up, they’re not allowed to take him out of the cold tub. It’s very important that we cool first, transport second. I also think it’s a great idea to talk to your local EMS professionals ahead of time, so everyone’s on the same page about who’s in charge and what happens in what order. I coached a 24-mile open water swim down Narragansett Bay once, passing through six different towns, so we ran a call with EMS, fire, and police from all six beforehand just to make sure everyone agreed on the plan before race day.”
– Dr. David Martin, Director of Science, Perry Weather
Water access has no on-off schedule, either; athletes need it available at all times during both practice and competition, not just during a designated break.
Do the Rules Change for Games?
Not as much as schools sometimes assume, and getting this wrong can mean delaying a kickoff. Practice activity limits apply in full, with modifications following the most recent 30-minute reading; a reading taken mid-practice can shorten a session already underway. TSSAA also requires at least 3 hours of continuous rest between two same-day practices.
Above 92.0°F WBGT or a heat index above 104°F, the rule for competitions is stricter than most people expect: a game can only proceed if both an appropriate health care professional and a cold water immersion tub are present and ready. Missing either one means the competition cannot start. Tony Clower described exactly this situation playing out in real time:
“We were at a middle school football game, and both readings were over the target we’re looking for: WBGT was over 92, and heat index was 106. We stopped kickoff because we did not have medical personnel on the sideline at that time. We did have the cold water immersion tub, but not the medical personnel. About ten minutes after seven, the WBGT went down because we had some cloud cover come over, and it dropped just under the threshold. If we’d had to wait on heat index instead, we would have waited almost twenty more minutes, because the cloud cover was still there but the heat index hadn’t caught up.”
– Tony Clower, Assistant Director of Schools & System Athletic Director, Roane County Schools
How Perry Weather Helps Tennessee Schools Stay Compliant
A physical weather station, mounted above a football field or on a press box, feeds live WBGT and heat index readings continuously, with a built-in black bulb sensor that measures WBGT directly rather than estimating it. Policies are configured to match TSSAA’s exact thresholds, so a notification includes not just the number but the required action — rest break counts, equipment rules, and everything else — tagged directly onto the alert a coach receives.
A forecast view shows where WBGT is headed for the days ahead, which is useful for more than reacting in the moment: scheduling a morning practice instead of a 4pm slot when the forecast shows the afternoon will run hot avoids the modification entirely rather than managing around it. Every reading is logged automatically, building a record schools can point to if a parent or the state office ever asks why a particular call was made.
If you want to see what automated WBGT and heat index monitoring looks like on your campus, get a quote today.
Live Q&A From the Webinar
Should you set an all-clear time after a heat threshold notification? Is there a minimum time before you can take another reading after entering a threshold?
The recommended approach, based on a NATA position statement, is to work from 30-minute aggregate readings rather than single instantaneous ones. Conditions can swing quickly, for instance if the sun goes behind a cloud and comes back out, so looking at a rolling 30-minute average smooths out that noise and gives a more reliable basis for deciding whether to modify activity going forward, rather than reacting to any single moment’s reading.
If wet bulb globe temperature is 89.6 and heat index is 105, what would you do with outdoor activity?
Go with the WBGT reading — it overrides heat index whenever both are available. At 89.6°F, WBGT falls in the 87.0–89.9°F tier, which caps practice at 2 hours with four rest breaks per hour (four minutes each) for all sports, plus the football-specific equipment rules at that level. The heat index reading of 105°F doesn’t change that outcome; if the two numbers point to different actions, TSSAA policy is explicit that the on-site WBGT reading governs.
