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What is WBGT?
WBGT stands for Wet Bulb Globe Temperature. It is a composite temperature used to estimate the effect of temperature, humidity, wind speed, and solar radiation on human thermal comfort, especially during outdoor physical activities. Unlike regular temperature readings, WBGT provides a more accurate reflection of heat stress on the body.
The outdoor WBGT is calculated as:
WBGToutdoor = 0.7 × Tnw + 0.2 × Tg + 0.1 × Ta
- Tnw: natural wet bulb temperature, which reflects humidity and evaporative cooling
- Tg: black globe temperature, which measures radiant heat from the sun and surroundings
- Ta: standard air temperature in the shade
Senseca WBGT monitoring instruments
Key features:
- Made in Italy by a reputable manufacturer: Senseca
- Highly reliable and accurate
- With wet and dry versions
- With 4G connectivity
- Basic cloud function included (free of charge)
Shown below is the dry version system configuration.
In the dry version, the natural wet bulb temperature (Tnw) is calculated from the measured air temperature and relative humidity results, but not measured directly. It can meet the requirements described in this guideline.
Listed below are the key specifications:
| Quantity | Resolution | Typical accuracy |
|---|---|---|
| Globe temperature (Tg) | 0.1 °C | ±0.15 °C |
| Air temperature (Ta) | 0.1 °C | ±0.15 °C |
| Relative humidity (RH) | 0.1%RH | ±2%RH |
| Natural wet bulb temperature (Tnw, calculated) | 0.1 °C | ±0.5 °C |
| Outdoor WBGT (WBGToutdoor, calculated) | 0.1 °C | ±0.6 °C |
Shown below is the wet version system configuration.
In the wet version, the natural wet bulb temperature (Tnw) is measured directly. It can meet the requirements described in this guideline and ISO 7243.
Listed below are the key specifications:
| Quantity | Resolution | Typical accuracy |
|---|---|---|
| Globe temperature (Tg) | 0.1 °C | ±0.15 °C |
| Air temperature (Ta) | 0.1 °C | ±0.15 °C |
| Natural wet bulb temperature (Tnw) | 0.1 °C | ±0.25 °C |
| Outdoor WBGT (WBGToutdoor, calculated) | 0.1 °C | ±0.3 °C |
A cloud portal is provided by Senseca. The service is currently free of charge.
Shown below is a screenshot of the result page:
Features of the Delta OHM cloud:
- Free of charge at the moment, with unlimited data storage for data from Senseca loggers
- Historical data can be downloaded in CSV format
- No cloud-based notification or alert functions
- It is possible to send alarms for 1 threshhold to maximum 4 phone numbers (as SMS) or 4 email addresses (as email)
- The alarms are sent directly by the 4G base unit, not through the cloud server
- The message formats are fixed and not customizable.
The Delta OHM cloud is designed primarily for quiet data logging — ideal for long-term storage and basic access to historical records.
For more advanced features aligned with industry safety practices in WBGT management, such as averaged WBGT results, timely alerts and notifications, Daily/weekly/monthly reporting, and Integration with external displays, please consider the OTM WBGT Monitoring App — a powerful, purpose-built solution for WBGT management in Singapore.
The measurement part is powered by an internal battery, requiring no external power supply, and is suitable for outdoor installation. A mounting bracket is included for installation on poles with a diameter of less than 60 mm.
As a general guideline, the measurement part should be exposed to natural sunlight and wind. The recommended installation height is around 2 m, which corresponds to typical human height while ensuring it does not obstruct traffic.
Below are some example installations for reference. Please click the thumbnails to enlarge the image.
The data transmission part requires 230 VAC power via a standard 3-pin UK power socket. This part must be installed in a sheltered area and cannot be exposed to rain. It can be wall-mounted, and a wall-mounting accessory is included.
The data communication between the data transmission part and the measurement part is wireless.
As a general guideline, the wireless signal coverage is similar to a home Wi-Fi router. It is recommended to maintain a direct line of sight between the data transmission unit and the measurement unit, and to avoid excessive signal attenuation caused by metal walls or wire mesh.
Below are some example installations for reference. Please click the thumbnails to enlarge the image.
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OTM WBGT Monitoring App
Key features:
- 15-minute average WBGT results
- Provides smoother and more meaningful values for practical decision-making, instead of fluctuating instantaneous readings
- Seamless integration with WhatsApp/Telegram — the most popular messaging apps in Singapore
- Real-time WBGT on request
- Hourly notifications and alerts when WBGT levels are high
- Alerts on instrument issues
- User account configuration via WhatsApp
- Supports up to 5 WhatsApp numbers by default
- Supports up to 1 Telegram group by default
- Automated WBGT reports via email
- Daily, weekly, monthly, or on-demand reports
- Monthly and on-demand reports available in both PDF and CSV formats
- Supports up to 20 email recipients by default
WBGT values fluctuate naturally due to changes in sunlight, wind, and humidity. Shown below is a sample of instantaneous WBGT readings recorded over the course of one hour:
The outdoor WBGT value crosses the 31 °C and 32 °C thresholds multiple times within a single hour, making it difficult to decide when to implement safety measures based on those brief fluctuations.
To address this challenge, industry guidelines and international standards, such as ISO 7243, recommend using averaged WBGT values instead of instantaneous readings. The recommended averaging time typically ranges from 15 minutes to 1 hour.
We adopt a 15-minute averaging interval for WBGT readings to strike a balance between responsiveness and stability. Shown below is the average WBGT calculated in the four 15-min blocks in one hour:
Four risk levels are defined:
- < 31 °C: Low risk (green)
- 31 °C – 32 °C: Moderate risk (amber)
- 32 °C – 33 °C: High risk (red)
- > 33 °C: Very high risk (purple)
The WBGT is averaged into four blocks of 15 minutes, resulting in clearer, more actionable values. With this approach, frontline workers and supervisors can
- Quickly understand the current heat stress level
- Take appropriate safety actions with confidence
- Avoid reacting to short-lived spikes that don’t reflect sustained conditions
Display module for TV, LED and/or beacon
Features:
- Displays real-time WBGT results from the past hour on any TV or monitor with HDMI input
- Automatically refreshes every 15 minutes with up-to-date WBGT results
- One-time hardware cost only — no recurring subscription fee for the display module itself
- Optional LED display to show WBGT results in large, colour-coded digits
- Optional beacon for clear visual indication of WBGT risk levels
Shown below is the display module configuration:
The display module retrieves data from the OTM WBGT Monitoring App server and presents it on any TV or monitor with HDMI support. Functioning like a compact TV box, the module offers high reliability and low power consumption, making it ideal for continuous WBGT monitoring displays.
A customized LED display can also be connected to the module. The numeric display changes colour according to the associated risk level:
- Low risk (WBGT < 31 °C): green
- Moderate risk (31 °C WBGT < 32 °C): yellow
- High risk (32 °C < WBGT < 33 °C): red
- Very high risk (WBGT > 33 °C): purple
In additional, a beacon can be added to the display module to provide clear visual alerts. The beacon indicates risk levels with the following signals:
- Low risk (WBGT < 31 °C): green
- Moderate risk (31 °C WBGT < 32 °C): amber
- High risk (32 °C < WBGT < 33 °C): red
- Very high risk (WBGT > 33 °C): flashing red
Both the LED display and the beacon come with a 10 m cable (extendable upon request) and are suitable for outdoor installation.
More photos:
