Heat and WBGT Policies: What Published Guidance and State Tables Say

What WBGT measures, and why heat index is not enough

The NWS describes WBGT as a measure of heat stress in direct sunlight that takes into account temperature, humidity, wind speed, sun angle and cloud cover. It adds that the military, OSHA and many nations use WBGT as a guide to managing workload in the sun. The standard calculation weights three readings: WBGT = 0.7 (wet bulb temperature) + 0.2 (black globe temperature) + 0.1 (dry bulb temperature), as printed in the Inter-Association Task Force consensus statement on exertional heat illness. A WBGT meter takes those readings and does the arithmetic.

The heat index uses temperature and humidity only, and the NWS says it is calculated for shady areas. A field in full sun can be harder on the body than the heat index suggests, because the heat index leaves out sun and wind. The Korey Stringer Institute at the University of Connecticut adds that as humidity rises the body loses less heat through evaporation, and WBGT builds that in. OSHA calls a WBGT meter the most accurate way to measure heat stress, and notes that its own heat app reports heat index rather than WBGT.

Published thresholds, and why they differ by state

There is no single national WBGT table. State high school associations publish their own, and the cutoffs vary. Two examples show the spread. Both add rest breaks and cut practice time as WBGT rises, and Kansas also calls for a cold water tub or other rapid cooling method to be ready from 80°F WBGT.

Same weather, different answer: at 91°F WBGT, Georgia's table allows one hour of practice with 20 minutes of breaks, and the Kansas policy says no outdoor activity. Texas takes a third approach. The University Interscholastic League requires WBGT monitoring for all UIL outdoor athletic and marching band activities starting with the 2026-2027 school year, and uses different thresholds for its Class 2 and Class 3 regions.

Researchers who studied this (Grundstein and colleagues, 2015) found large regional differences in extreme WBGT across the contiguous United States and proposed regional heat safety categories. The Korey Stringer Institute makes the same point: WBGT guidelines must be region specific, because athletes in different regions are acclimatized to different heat. Policies generally follow the table of the association that governs the activity. Which table applies when teams from several states meet is a question for the host, the associations involved and their medical staff.

Heat at work: what OSHA says

OSHA has no federal heat standard. It relies on the General Duty Clause, which requires employers to provide a workplace free from recognized hazards that are causing or likely to cause death or serious physical harm. OSHA's heat page lists five states with their own heat rules: Washington, Minnesota, California, Oregon and Colorado. Some other states have adopted rules too, and each state's workplace safety agency publishes its current requirements.

OSHA recommends a heat illness prevention program built into the broader safety and health program, time for workers new to the heat to build tolerance (acclimatization), and a WBGT meter as the most accurate way to measure heat stress. OSHA's heat page carries the current status of federal rulemaking.

Questions a heat policy usually answers

This is an outline, not a fill-in template. The answers, including every WBGT band and time limit, come from the governing body's published table and the policy's medical or safety lead. The examples quote the sources listed below.

1. Who measures, and with what? Which role takes readings, who backs them up, which instrument is used and how it is calibrated. Georgia's policy: a scientifically approved WBGT instrument at each practice held before October 1.
2. When are readings taken? How long before the activity and how often during it. Georgia's policy: at least every 30 minutes, starting 30 minutes before practice. Kansas policy: at the activity site 30 to 60 minutes before the activity whenever air temperature is 80°F or higher.
3. Which table sets the limits? The governing body's WBGT table and its version year, and the region category if the table uses one.
4. How are water, rest and shade handled? The Kansas policy describes unrestricted access to water and a cooling area, with rest breaks set by the table.
5. Who can change or stop activity? The Inter-Association Task Force describes onsite medical staff with the authority to alter work and rest ratios.
6. What is the emergency plan? The written emergency action plan for each venue and where rapid cooling equipment is kept. Kansas policy: a cold water tub or other rapid cooling method ready from 80°F WBGT.
7. How does acclimatization work? The governing body's schedule for new and returning athletes, or the employer's plan for workers new to the heat, which OSHA describes.
8. How is the forecast used? Who reviews it and when, and how schedule changes are decided. The Kansas policy says to watch the forecast and make schedule changes days in advance to avoid last-minute postponements.
9. How are decisions recorded and reviewed? What is logged for each reading (time, WBGT value, table band, action taken and who decided) and when staff review the policy each season.

These questions follow the elements in the sources below: measurement at the site (Georgia and Kansas), unrestricted water and a cooling area (Kansas), medical staff authority to modify or cancel (Inter-Association Task Force), and an emergency action plan with rapid cooling ready (Kansas and the NATA position statement).

How forecasts fit into heat planning

A WBGT meter reads conditions now. A forecast shows which hours are expected to reach the higher bands of a table, often days ahead, which is why the Kansas policy ties schedule changes to the forecast. The forecast details that bear on WBGT are hourly temperature, humidity, cloud cover and wind for the site itself. Those can change overnight, since clearing skies add sun and a shift in wind changes how the afternoon feels.

With 4070 for business, WDS provides site forecasts for the locations you save, with hourly detail and heat alerts, and a meteorologist to talk with ahead of a high-stakes event. These can support the people who make the call. They do not replace the policy, the on-site WBGT reading or medical staff judgment. See how this works for sports teams and construction crews.

Frequently asked questions

Sources

Sources checked October 6, 2026. Association tables change, and each governing body publishes its current version.

1. National Weather Service Albany, Wet Bulb Globe Temperature information guide (PDF)What WBGT includes, and how it differs from the heat index calculated for shady areas.
2. Korey Stringer Institute, Wet Bulb Globe Temperature monitoringHumidity and heat loss, and the need for region-specific WBGT guidelines.
3. Georgia High School Association, Section 2.67 Practice Policy for Heat and Humidity (PDF)WBGT bands, rest breaks, measurement frequency and the instrument requirement.
4. Kansas State High School Activities Association, Exertional Heat Illness: Information, Guidelines and Best Practices (PDF)Recommended WBGT modification policy, measurement timing, cooling area and emergency plan.
5. University Interscholastic League (Texas), Heat Stress and Athletic ParticipationWBGT required for UIL outdoor athletic and marching band activities from 2026-2027; Class 2 and Class 3 thresholds.
6. NATA position statement, Exertional Heat Illnesses (Casa et al., Journal of Athletic Training 2015;50(9):986-1000)Best-practice recommendations for prevention, recognition and treatment; onsite emergency action plans.
7. Inter-Association Task Force on Exertional Heat Illnesses, Consensus Statement (PDF hosted by NATA)The WBGT formula, and onsite medical staff authority to alter work and rest ratios.
8. Grundstein et al., Regional heat safety thresholds for athletics in the contiguous United States, Applied Geography 2015;56:55-60Regional variation in extreme WBGT and proposed regional categories.
9. OSHA, Heat ExposureNo federal heat standard, General Duty Clause, state heat rules, program elements, WBGT meter and acclimatization.

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