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Everything you need to know about WBGT

Wet bulb globe Temperature (WBGT) is a measure of heat stress that considers several environmental and personal factors. It is a key factor used to determine heat risks associated with persons working in adverse conditions. Temperature alone does not provide a full picture when assessing heat stress.

This article reveals everything you need to know about WBGT, including; what it is, what it measures, the difference between heat index and WBGT, and the unique insights WBGT offers into heat stress. We also provide some WBGT meter examples.

About WBGT

Wet bulb globe Temperature (WBGT) is a specialised heat stress index used across several professions and industries, including athletes, the military, and industrial hygienists. Essentially, the WBGT value represents the thermal environment an individual is exposed to and can be used to determine the climactic effects on humans exposed by establishing the presence or absence of heat stress.

Why use WBGT to measure Heat Stress?

The exposure to heat stress experienced by a person depends on:

  1. The production of heat inside the body as a result of physical activity.
  2. The characteristics of the environment determining heat transfer between the body and the ambient environment. To understand the ambient environment, you need to consider temperature, humidity, wind speed, sun angle, and cloud cover (solar radiation).
  3. The clothing that is worn by individuals, this will modify the exchange of heat.

WBGT heat stress measurement should take all the contributing factors listed above into consideration. The resulting WBGT calculation can aid in mitigating the risk of heat-related illness. Heat-related illness can vary from mild to severe. For example;

  • Mild heat-illness can be a person experiencing dizziness or weakness.
  • Heat exhaustion is mid-spectrum where a person may collapse, experience headaches, low blood pressure, and lethargy.
  • Heat-stroke is a dangerous form of heat illness; this is a severe condition and can result in permanent injury or death.

Measuring WBGT and enacting a suitable work/rest schedule tailored to your industry, activity, and environment is a crucial way of reducing the risk of heat-related illness within your working environment.

The table below created by Sports Medicine Australia is an example of WBGT levels, the risk of thermal injury associated with each level, and the possible actions or modifications to activity required to manage the risk.

 

What is the difference between heat index and wet bulb globe temperature?

WBGT uses a combination of factors and environmental elements to obtain a heat stress estimate. Essentially this calculation is a measure of heat stress in direct sunlight, considering temperature, humidity, sun angle, wind speed, and solar radiation. Heat Index is calculated for shady areas and only measures the combination of temperature and humidity. The comparison in the table below illustrates why WBGT is the more appropriate index to use where people must (or choose to) perform under stress in direct sunlight.

Examples of WBGT meters

The Instrument Choice scientists have put together three examples of Heat Stress Meters capable of accurately measuring WBGT.

Kestrel 5400 Heat Stress WBGT Meter

Product Code: IC-0854ORA

The IC-0854ORA is a professional-grade and intuitive-to-operate heat stress WBGT meter. This device is versatile featuring a user-selectable indoor feature where the setting turns off the function of taking into account direct solar radiation. Instrument Choice scientists recommend it for both outdoor and indoor environments, such as warehouses.

WBGT Alarm: Yes, User-adjustable audio and LED alarm.

WBGT Threshold: Adjustable

WBGT Accuracy: ±0.7°C

Other Features: Approximately 10,000 data point storage, included impeller cover and a durable, scratch, and break-resistant screen.

WBGT Meter SD Card with Data Logger

Product Code: IC800037


Able to quickly and accurately determine WBGT, the IC800037 also captures sample time and date and records data onto standard SD cards. All data recorded onto the SD is preformatted for excel without the need for any additional software or cables.

WBGT Alarm: Yes, User-adjustable audible alarm.

WBGT Threshold: Adjustable

WBGT Accuracy: ±2°C

Other Features: Records relative humidity, air temperature, dew point and black globe temperature, large easy to lead backlit display, included carrying case and included SD card.

WBGT Heat Stress Meter

Product Code: IC800036


With a typical response time of 15 seconds, the IC800036 can give you the information you need quickly while being compact enough to carry anywhere.

WBGT Alarm: Yes, User-adjustable audible alarm.

WBGT Threshold: Adjustable

WBGT Accuracy: ±2ºC indoor, 3ºC outdoor (-15~40ºC) otherwise ±2.5 indoor, 3.5ºC outdoor

Other Features: Measures air temperature, globe temperature, relative humidity, and has RS232 computer connectivity.

Conclusion

Using WBGT as a heat stress measurement establishes a clear picture of heat stress contributing factors, both environmental and personal. Measuring WBGT using a capable meter and enacting a suitable work/rest schedule is a crucial way to reduce the risk of heat-related illness within your working environment.

Have more questions about WBGT or WBGT meters? Want more information on any of the above products? Contact one of the Instrument Choice Scientists. We’re here to help!

Call 1300 737 871 or email customer-service@instrumentchoice.com.au