Do I need an on-site sensor for WBGT?


Do I need an on-site sensor for WBGT?

Oct 18, 2023
Colin Perry

Without on-site measurements, Wet Bulb Globe Temperature (WBGT) readings use a patchwork of data, including data from the nearest government weather station.
These estimates can understate actual WBGT by as much as 3-6°F – a potentially dangerous difference. Keep reading to learn why it matters.

What goes into a WBGT reading?

Wet Bulb Globe Temperature (WBGT) is the most accurate way to measure heat stress on the human body (think: a much better heat index or “feels like”). The calculation for WBGT needs temperature, humidity, wind speed, and black globe temperature (sun angle and cloud cover).

This last one – black globe temperature – is critical because it’s measured with the only sensor not found on traditional or even professional weather stations, including government or airport stations.

What happens without an on-site sensor?

Without an on-site black globe sensor (i.e. black bulb) and weather station to measure real-time conditions, data is collected from the closest National Weather Service (NWS) station, typically an airport.

So what’s the problem with that? Three big issues:

⏳ NWS stations update hourly – think how much can change in an hour. For example, heavy cloud cover can dissipate quickly, and direct sunlight causes significantly more heat stress on the human body than with cloud cover.

☀️ NWS stations don’t have black globe sensors – so you’re stuck with outdated, often-inaccurate measurements on cloud cover and sun angle.

📍 NWS stations may be far from your actual location – and even if they’re only 1-2 miles away, readings may still differ wildly.

What’s my actual risk without an on-site sensor for WBGT?

In short: significant. Let us illustrate.

We compared estimated WBGT temperatures with actual WBGT (measured with on-site sensors) over the month of August 2021 in Dallas, Texas – an epicenter for Texas high school sports in one of the hottest months of that year. And as seen in 2023, Texas faced more extreme heat plus pressure to adopt WBGT into its high school sports heat policies.

When actual WBGT measured between 86-92° – i.e., when it matters most for safety – the estimated WBGT was consistently 3-6° too low. Even more alarming: the higher WBGT climbed, the more the gap grew between actual and estimated values.

⚠️ This means that when it matters most, organizations relying on estimated WBGT (instead of measured on-site) may not have taken the right measures to prevent heat stress.

This study included 7,000 individual measurements taken every 5 minutes from 5:00am to 11:55pm for the entire month of August in Dallas. Estimated WBGT values were calculated using airport weather station data from Dallas Love Field – only 3 miles away from the measured values – over the same period of time. Similar conclusions were drawn from three similar studies containing 13,000 individual measurements compared against data from BRO, CFD, and DFW airports. Estimated WBGT calculations used industry standard formulas and sources. More detail in the chart below:

Does this mean estimated WBGT is always wrong?

Not necessarily. Using estimated WBGT is still a step up from not relying on WBGT at all. But it certainly does not provide the safest, most accurate way to prevent heat stress injuries in outdoor activities. The best way to measure WBGT is with an on-site sensor.

Are WBGT sensors expensive? How do I get one?

Perry Weather provides on-site sensors as a simple, affordable subscription or purchase. Ensuring adherence to a WBGT policy is simple with our mobile/web apps and SMS notifications, which keep your team informed of real-time conditions. While we do provide in-app estimated WBGT for organizations lacking on-site sensors, we strongly recommend equipping your organization with the most accurate measurements.

Perry Weather is the leading weather safety platform for organizations keeping their teams safe in the midst of excessive heat and other environmental conditions. Learn more about how we can help your organization adequately monitor WBGT.

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