HEAT STRESS MONITORING
Heat stress is not just a temperature reading
The conditions affecting people at work are more complicated than air temperature alone. The MaxiMet GMX552 measures the environmental factors that drive heat stress and calculates both Wet Bulb Globe Temperature (WBGT) and Thermal Work Limit (TWL) onboard.
One compact weather station. Two recognised heat-stress indices. No additional hardware required for the TWL capability.
WBGT onboard
Calculated in accordance with ISO 7243:2017
Thermal Work Limit
Calculated onboard, in W/m²
150 mm black globe
Radiant heat input to the WBGT calculation
No extra hardware
TWL by firmware update
- WBGT and Thermal Work LimitBoth heat-stress indices calculated onboard
- One compact stationBlack globe, wind, air temperature, humidity and pressure
- No extra hardware for TWLBuilt into the MaxiMet GMX552
- Measured where people workLocal, real-time heat-stress information, not a distant station
The measurement
Measure the conditions. Calculate the risk.
Heat stress depends on the combined effect of environmental conditions, not temperature in isolation.
The GMX552 measures black globe temperature, wind speed and direction, air temperature, humidity and pressure. It can then calculate both WBGT and Thermal Work Limit from the same environmental dataset.
That means the heat-stress index is calculated at the point of measurement rather than relying on a separate system to collect the inputs and perform the calculation later.
WBGT in accordance with ISO 7243:2017
How stressful the environmental conditions are, calculated onboard.
Thermal Work Limit
The maximum sustainable metabolic work rate, in W/m², from the same data.
Black globe temperature
Radiant heat, measured alongside wind, air temperature, humidity and pressure.
Calculated where people work
Local, real-time heat-stress information, not a distant station.
The instrument
One station. Two recognised heat-stress indices.
The GMX552 combines environmental measurement and onboard heat-stress calculation in one compact weather station.
MaxiMet GMX552
One compact weather station that measures the conditions and calculates WBGT and Thermal Work Limit (TWL) onboard.
No single Heat stress does all of that. Our team can suggest a pairing.
Measured: black globe temperature, wind speed and direction, air temperature, humidity, atmospheric pressure and optional GPS. Calculated: WBGT in accordance with ISO 7243:2017, Thermal Work Limit in W/m², and true wind when GPS is fitted. An optional wet bulb sensor is available where direct wet bulb measurement is required for increased WBGT accuracy.
Two indices
Two questions. One set of measurements.
WBGT and Thermal Work Limit assess heat stress from different perspectives. The two indices are complementary rather than competing measurements: WBGT describes environmental heat stress, TWL adds an indication of sustainable work capacity.
| Specification | Environmental heat stressWBGT | Sustainable work rateThermal Work Limit |
|---|---|---|
| The question it answers | How stressful are the environmental conditions? | How much work can be sustained safely? |
| What it gives you | An assessment of environmental heat stress | The maximum sustainable metabolic work rate |
| Calculated | Onboard, in accordance with ISO 7243:2017 | Onboard, in W/m² |
| Background | The widely adopted international method | Originally developed for Australia's mining industry |
| Most established in | Construction, defence, manufacturing, utilities and sport | Mining and heavy industry, including Australia and the Middle East |
| On the GMX552 | Every GMX552 | Latest firmware, compatible units updated without new hardware |
| Datasheet | Datasheet | Datasheet |
Why both
Different standards. Different decisions. Same station.
Heat-stress requirements vary between industries, regions and occupational programmes. WBGT remains the most widely recognised approach to occupational heat-stress assessment and is used across sectors including construction, defence, manufacturing, utilities and sport.
TWL provides a different operational perspective, helping organisations understand the sustainable work rate under prevailing conditions. It is particularly established in mining and heavy industry. For organisations operating across different regions or industries, measuring both provides greater flexibility without requiring two separate environmental measurement systems.
More capability. No new hardware.
Thermal Work Limit has been added to the GMX552 through the latest firmware. Compatible units already in the field can be updated without adding new measurement hardware.
Make an enquiry →The calculation belongs where the measurement happens
Battery or solar power, with communication options for integration into wider monitoring systems.
View the specification →Optional wet bulb sensor
Available where direct wet bulb measurement is required for increased WBGT accuracy.
View MaxiMet GMX552 →Applications
Where people work in the heat, the environment becomes part of the safety system
The GMX552 can be used wherever local environmental conditions need to be monitored for heat-stress management, from mines and worksites to farms, training grounds, sports venues and cities.
MiningMonitor heat stress in demanding environments where TWL can help inform safe work rates and operational planning.Mining, quarrying and cement →
Construction and manufacturingProvide local environmental data to support heat-stress procedures across exposed worksites, plants and hot-work environments.Industrial process →
AgricultureMonitor local conditions during periods of high heat to help protect workers while maintaining productive working patterns.Agriculture →
Military trainingMeasure environmental heat stress during training and demanding outdoor activities where conditions can change rapidly.Defence and security →
Smart citiesMeasure local heat conditions to support public-health monitoring and responses during extreme heat events.Cities and buildings →Technical information
Everything that affects heat stress, measured in one place
| Measurement or output | GMX552 |
|---|---|
| Black globe temperature | Integrated |
| Wind speed and direction | Integrated |
| Air temperature | Integrated |
| Humidity | Integrated |
| Atmospheric pressure | Integrated |
| WBGT | Onboard calculation |
| Thermal Work Limit | Onboard calculation |
| Wet bulb temperature | Optional sensor |
| GPS | Optional |
| True wind | Calculated with GPS |
The WBGT calculation is in accordance with ISO 7243:2017. TWL is calculated in W/m². Take electrical, accuracy, power and communication specifications from the GMX552 datasheet.
See it work
Heat stress, measured rather than estimated
Six short films on WBGT measurement and the places it decides whether play continues, or work does.
One match. One trophy. One place in history.
Two globally recognised heat stress indices
Centre Court has Hawk-Eye
Heat advantage in court
Heat stress monitoring
Preserving history demands more than admiration
Prefer to watch them together? Watch them all on the Gill Group channel
Technical resources
Everything you need to specify, install and configure the GMX552
Questions
Frequently asked questions
What is heat stress monitoring?
Heat stress monitoring measures the environmental conditions that affect how the human body responds to heat. These can include air temperature, humidity, wind speed, radiant heat and atmospheric pressure. Heat-stress indices such as WBGT and Thermal Work Limit use these measurements to provide information for managing occupational heat exposure.
What is WBGT?
Wet Bulb Globe Temperature (WBGT) is a widely used index for assessing environmental heat stress. It accounts for factors including air temperature, humidity, wind and radiant heat, using black globe temperature as part of the measurement. The GMX552 calculates WBGT onboard, in accordance with ISO 7243:2017.
What is Thermal Work Limit?
Thermal Work Limit (TWL) estimates the maximum sustainable metabolic work rate under prevailing environmental conditions. It is expressed in watts per square metre (W/m²) and provides an indication of how much work an acclimatised person can safely sustain under those conditions.
What is the difference between WBGT and Thermal Work Limit?
WBGT indicates how stressful the environmental conditions are, while TWL estimates the sustainable work capacity under those conditions. They provide different perspectives on heat stress and can be used together.
Should I use WBGT or TWL?
The appropriate index depends on the industry, region, applicable standards and heat-stress management programme. WBGT is the most widely recognised occupational heat-stress index, while TWL is particularly established in mining and heavy industry. Organisations operating across different requirements may benefit from monitoring both.
Does adding TWL require new hardware?
No. Compatible GMX552 units already in the field can be updated with the latest firmware because the station already measures the environmental parameters required to calculate TWL.
Does the GMX552 need a wet bulb sensor?
An optional wet bulb sensor is available where direct wet bulb measurement is required for increased WBGT accuracy. The GMX552 can provide WBGT without the optional wet bulb sensor using its available measurement configuration.
Where can the GMX552 be used?
The GMX552 can be used wherever local environmental conditions need to be monitored for heat-stress management, including mining, construction, manufacturing, agriculture, military training, sports and events, and smart-city applications.
Can GMX552 data be integrated into an existing system?
Yes. The GMX552 provides communication and output options for integration with wider monitoring systems. The appropriate interface depends on the receiving system and configuration.
Have an application to discuss?
Speak to our team
Tell us what you need to measure, where and under what conditions. We’ll help you work out the appropriate approach.
Enquiring about MaxiMet GMX552
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