Athlete
Practice modification, break schedules and equipment limits for outdoor training.
Heat stress monitoring splits into two questions that get run together. Environmental monitoring asks how hot the environment is. Physiological monitoring asks what it is doing to a specific person.
Most people searching for a heat stress monitor want the first, and want it without buying, calibrating and maintaining an instrument. That is what this app does: a live WBGT reading for wherever you are, computed from live weather data with the peer-reviewed Liljegren model, with a forecast attached.
What it monitors
Live WBGT
For your current location or any city you search, recomputed as conditions change.
Flag level and guidance
The current category with the activity guidance for your selected mode, not a raw number to interpret yourself.
Forecast
Hourly through the day and out to 14 days, which is what planning actually requires.
The underlying conditions
Humidity, wind, solar radiation, cloud cover and pressure, so you can see why the number is where it is.
Five modes, because the thresholds differ
An athletic threshold applied to industrial work is wrong, and vice versa. The app carries separate guidance sets rather than one generic scale.
Military
Heat categories 1 to 5 with work-rest cycles and water intake guidance.
Outdoors and OSHA
Occupational thresholds for crews, with the longer exposures and lower limits that implies.
Aviation
Ramp and flight line operations, where crews work long stretches on open pavement in full sun.
App compared with a dedicated instrument
Both have a place. Being clear about which does what prevents the mistake of using one for the other's job.
| App | Instrument | |
|---|---|---|
| Measures your exact microclimate | No, computes ambient conditions | Yes, that is its whole advantage |
| Forecasts ahead | Yes, hourly and 14 days | No |
| Works at a site you are not at | Yes, any location | No |
| Needs calibration and a wetted wick | No | Yes |
| Available to every supervisor | Yes | Only where the device is |
| Satisfies a measure-on-site requirement | No | Yes |
The practical split: the app for planning, scheduling, awareness and cross-checking; the instrument for the compliance reading and for known hot spots like roofs and trenches.
Physiological monitoring, and when you need it
Environmental monitoring stops being sufficient in two situations. The first is impermeable or encapsulating clothing, where evaporation is blocked almost completely and WBGT screening no longer describes the problem. The second is when screening limits are exceeded but the work genuinely has to continue under controls.
In both cases the monitoring has to move to the individual: heart rate and recovery, core temperature where ingestible sensors or rectal thermometry are feasible, body mass change across a shift, and systematic observation for symptoms. Body mass change is the one most organisations can actually do, and it is worth more than it looks: losing more than about two percent of body mass across a shift or a session indicates dehydration that needs correcting before the next one.
Warning signs of heat illness
Heat stress shows up before it becomes an emergency. Anyone on site should speak up immediately on any of these:
Dizziness or lightheadedness
Nausea or vomiting
Chills or goosebumps in the heat
Severe or throbbing headache
Confusion or out-of-character behavior
Stumbling, cramping or collapse
When in doubt, cool first and call for help. Collapse or confusion in the heat should be treated as possible exertional heat stroke: begin cold-water immersion immediately and call 911. Cooling comes before transport.
Free on the App Store
Real-time WBGT, flag levels, five guidance modes and a 14-day forecast. Free to download, with an optional Pro upgrade.
- Live WBGT for your location or any city
- Hourly and 14-day WBGT forecasts
- Flag levels with mode-specific guidance
- Fahrenheit or Celsius
WBGT is estimated from weather data with the peer-reviewed Liljegren model. Where a policy requires on-site measurement, use the app for planning and as a cross-check alongside your instrument.
Common questions
What is a heat stress monitor?
Usually an instrument that measures WBGT on site using dry bulb, natural wet bulb and black globe sensors. The term also covers apps that compute WBGT from weather data, and physiological monitors that track an individual's heart rate or core temperature.
Is there a free heat stress app?
Yes. The WBGT app is free to download on iPhone and gives real-time WBGT, flag levels and forecasts, with an optional Pro upgrade. It carries separate guidance modes for athletics, military, outdoor work, aviation and OSHA.
Can an app replace a heat stress monitor?
For planning, scheduling and awareness, it covers the same ground more conveniently and in more places. For a compliance reading, or in a microclimate like a trench or a dark roof, an on-site instrument is still required.
How does the app calculate WBGT?
It applies the Liljegren et al. (2008) model, a peer-reviewed method from Argonne National Laboratory that solves the physical heat balance of the black globe and wet bulb, to live weather data from Open-Meteo.
What is the difference between environmental and physiological monitoring?
Environmental monitoring measures the heat load in the surroundings, usually as WBGT. Physiological monitoring measures what that load is doing to a specific person: core temperature, heart rate, sweat rate or body mass change. Extreme conditions and impermeable clothing require the second.
Related WBGT guides
Know the real heat number
Real-time WBGT, flag levels and forecasts. Free on iPhone.
