Chapter 1
What is WBGT?
WBGT stands for "Wet Bulb Globe Temperature," which in Japanese is called "shitsukyu kurokyu onten" (湿球黒球温). It is commonly referred to as the "heat index."
WBGT is an index used to evaluate hot environments in order to prevent heatstroke. It takes into account not only the temperature but also humidity and radiant heat, which are related to heat exchange in the human body.
In high-temperature environments, even if the temperature is the same, high humidity or strong solar radiation and radiant heat from the surroundings can make it difficult for the human body to release heat. Therefore, temperature alone may not be sufficient to adequately assess the severity of a hot environment.
WBGT is calculated using dry-bulb temperature, wet-bulb temperature, and black-globe temperature. The Ministry of the Environment provides information on how to measure and calculate WBGT using these parameters.
Chapter 2
WBGT (configuration Bulb Globe Scale)
The WBGT (Wet Bulb Globe Temperature) is calculated using dry-bulb temperature, wet-bulb temperature, and black-globe temperature, each reflecting different elements of the hot environment.
dry bulb temperature
This is the temperature measured using a standard thermometer. It corresponds to the general ambient temperature.
wet bulb temperature
This temperature is measured using a thermometer moistened with water and reflects the cooling effect due to moisture evaporation. The drier the air, the greater the difference between this temperature and the dry-bulb temperature.
black bulb temperature
The temperature of a black-painted sphere is measured to reflect the effects of solar radiation and radiant heat from the surroundings.
Especially in outdoor environments with sunlight, it is important to incorporate the effects of radiant heat, which are difficult to evaluate using air temperature alone, by using black globe temperature.
For detailed information on measurement methods, please also refer the Ministry of the Environment's "Detailed Information on Measurement Methods for the Heat Stress Index (WBGT)."
Chapter 3
How is WBGT calculated?
The formula for calculating WBGT differs depending on whether you are outdoors with sunlight or indoors where there is no sunlight.
| environment | Calculation formula | Way of thinking |
|---|---|---|
| Outdoors, with sunlight. | WBGT =0.7×wet bulb temperature +0.2×black bulb temperature +0.1×dry bulb temperature |
We combine the wet-bulb temperature, which reflects the effect of humidity, the black-globe temperature, which reflects radiant heat, and the dry-bulb temperature. |
| Indoors, no sunlight | WBGT =0.7×wet bulb temperature +0.3×black bulb temperature |
This formula is used in environments without the influence of sunlight. |
The terms "outdoor" and "indoor" here are not simply determined by whether the location is inside or outside a building. Appropriate calculation methods are used depending on the actual measurement environment, including factors such as the presence or absence of sunlight.
For electronic WBGT (Wet Bulb Globe Temperature) meters, JIS B 7922 is the established standard. When selecting a measuring instrument, please check its compliance with the target measurement environment and the standard.
Chapter 4
How to interpret WBGT values? A guide to risk levels.
There are various pointer for WBGT depending on its intended use. Here, we will show the "pointer for Daily Life" introduced by the Ministry of the Environment as an example.
| WBGT | classification | Guidelines for daily life |
|---|---|---|
| Under 25 | Note | While generally not very dangerous, there is a risk of heatstroke during strenuous exercise or heavy labor. |
| 25 or older but under 28 | Caution | When exercising or doing strenuous work, be sure to take regular and sufficient rest breaks. |
| 28 years old or older but less than 31 | High security | When going outside, avoid direct sunlight, and when indoors, be mindful of the temperature rising. |
| 31 or older | danger | Elderly people are at high risk of developing this condition even at rest, so they should avoid going outside as much as possible and move to a cool indoor location. |
pointer provided here pertain to daily life. For exercise and work, please refer to the respective pointer and management standards. Work suspensions and other similar decisions should not be made solely based on WBGT values.
The Ministry of the Environment also publishes real-time and predicted WBGT values for the entire country.
Chapter 5
What is the difference between WBGT and heatstroke warning alerts?
While both WBGT and heatstroke warning alerts are used for heatstroke prevention, they are not the same thing.
| Item | WBGT | Heatstroke warning alert |
|---|---|---|
| something? | Indicators for evaluating the heat environment | Information urging widespread vigilance against heatstroke. |
| Applications | Evaluating the heat environment at sites and facilities. | Warnings about the risk of heatstroke in the region |
| How to use | Can be measured and monitored on-site. | Check the information released by the Ministry of the Environment and other relevant organizations. |
Therefore, to understand the situation across the entire region, it is advisable to check information such as heatstroke warning alerts, while to understand "what the situation is like at this factory, this gymnasium, or this workplace right now," it is advisable to measure and monitor the local WBGT.
The Ministry of the Environment's "Heatstroke Prevention Information Site" provides real-time and forecast WBGT data, as well as information on heatstroke warning alerts.
Chapter 6
What is required of a WBGT monitoring system?
When using WBGT for heatstroke prevention, it's crucial to have a system that allows for continuous monitoring of on-site conditions, rather than just a one-time measurement.
Real-time monitoring
We will measure temperature/humidity, and black globe temperature to allow us to check the current WBGT.
Alarm/Notification
Based on pre-configured management conditions, the system will notify the responsible person via screen display, email, or other means.
List/Graphic display
The system will be configuration to allow users to view multiple gymnasiums, school grounds, factory areas, and other locations from a single screen.
History Record
We record WBGT and related measurement data so that we can later review the changes in the environment.
The WBGT monitoring system is not a device that automatically stops work if it becomes dangerous. Its primary purpose is to use the measured values as a basis for making decisions regarding safety management, such as taking breaks, replenishing moisture and electrolytes, improving the environment, and reviewing activity plans.
Chapter 7
Case Study | Fujioka City Ono Elementary School
At Fujioka Municipal Ono Elementary School in Fujioka City, Gunma Prefecture, WBGT measurement unit have been installed in the gymnasium and schoolyard to measure WBGT, temperature, and humidity.
The heat index is display in different ways depending on the level, and by combining it with illustrations and comments, display is designed to make it easy for on-site users to understand the situation.
When high-order level alarm is issued, the system is designed to notify the person in charge via email, which is then used to make decisions about whether or not to conduct classes using the gymnasium or school grounds.
This is an example of how the system can be implemented. Actual activity decisions must be based on the school's or facility's management policies and relevant pointer.
Chapter 8
System specifications Example | Centralized Monitoring of WBGT
configuration conforming to JIS B 7922 Class 1.5 Electronic Wet Bulb Globe Temperature (WBGT) Index Meter.
Chino offers configuration example that combines a WBGT measurement unit with data logging and monitoring system to centrally monitor the heat environment at multiple locations, such as factories.
configuration monitors temperature/humidity, black globe temperature, and WBGT (Wet Bulb Globe Temperature) inside the factory in real time.
When an alarm is triggered, you can check the situation via email notification, a graphical display, or the alarm history.
In outdoor environments with solar radiation, it is important to use appropriate measurement methods, including black globe temperature, to evaluate the effects of radiant heat.
System configuration example
| Monitoring and recording | Monitoring application software CISAS/V4 100 points Graphics 1 Real-time trends Data List Alarm list / Alarm history |
|---|---|
| data logging | Wireless logger transmitter MD8000 series Total 15 points Temperature sensors and WBGT measurement unit tailored to the measurement environment |
The system configuration and number of points configuration are examples. In an actual system, configuration will be considered based on the measurement location, required number of points, communication environment, alarm method, etc.
Chapter 9
Heatstroke monitoring unit can be used simply by placing it down.
In addition to large-scale monitoring systems, Chino also offers a "Simply Place Heatstroke Monitoring unit" for sites that want to check WBGT more simply.
It is important to consider the appropriate configuration based on the system's scale, monitoring locations, and required recording and notification functions.
FAQ
Frequently Asked Questions about WBGT
What is WBGT?
WBGT stands for "Wet Bulb Globe Temperature," which in Japanese is called "shitsukyu kurokyu onten." It is commonly referred to as the "heat index" and is used as an indicator to evaluate the heat environment in order to prevent heatstroke.
Is WBGT a measure of temperature?
No. It's an index that takes into account not only temperature but also the effects of humidity and radiant heat. Even at the same temperature, the WBGT will vary depending on environmental conditions.
Is a higher WBGT level necessarily more dangerous?
Generally, the higher the WBGT value, the more attention should be paid to the risks associated with the hot environment. However, it is important not to make a decision based solely on the WBGT value, as factors such as the type of activity, load, individual differences, and facility environment also play a role.
Should work be stopped if the WBGT is 28°C?
It's not possible to make such a blanket judgment. The Ministry of the Environment's pointer for daily life designate temperatures between 28°C and 31°C as requiring "extreme caution," but for work and exercise, judgments must be made based on the respective pointer and standards.
Is it necessary to measure WBGT indoors as well?
Even indoors, in high-temperature and high-humidity environments, or when there is radiant heat from high-temperature equipment, it may be necessary to evaluate the heat environment. Since the WBGT calculation formula differs between indoors and outdoors, it is important to select equipment that is appropriate for the measurement environment.
Is it necessary to measure the black globe temperature outdoors?
In outdoor environments with solar radiation, the black globe temperature is used to evaluate the effects of radiant heat. The Ministry of the Environment specifies a method for measuring WBGT using dry bulb temperature, wet bulb temperature, and black globe temperature.
Can heatstroke be prevented simply by monitoring the WBGT (Wet Bulb Globe Temperature)?
Simply monitoring the WBGT (Wet Bulb Globe Temperature) does not completely prevent heatstroke. It is important to use WBGT as a safety management tool and combine it with measures such as moisture and salt replenishment, rest, improvement of the work environment, and adjustment of working hours.
What are the benefits of recording WBGT values?
This allows you to review past trends in heat environments and compare the work environment before and after improvements. It can be used as a record necessary for safety management in facilities and workplaces.
Summary
WBGT is not just a tool for "measuring heat," but also an indicator to be used for safety management.
The WBGT (Wet Bulb Globe Temperature) is an index used to evaluate the heat environment by taking into account not only temperature but also thermal conditions such as humidity and radiant heat.
Especially in outdoor work areas during the summer, sports facilities, schools, and factories, WBGT can be used to evaluate the heat environment, which is difficult to grasp by temperature alone.
However, it is important not to mechanically judge safety or danger based solely on the WBGT value, but to consider the nature of the activity, load, individual differences, and facility environment, and to implement it in combination with measures such as moisture, salt replenishment, rest, and improvement of the work environment.
The latest heat index and heatstroke warning alerts can be found on the Ministry of the Environment's "Heatstroke Prevention Information Website."
Reference
For those who want to learn more about WBGT
For information on the definition and calculation method of WBGT, as well as current heat index and heatstroke warning alerts, please also refer to information from public institutions.
- Ministry of the Environment "Heatstroke Prevention Information Website"
- Ministry of the Environment: "What is the heat index?"
- Ministry of the Environment: "Detailed information on how to measure the Wet Bulb Globe Temperature (WBGT) index"
*You will be redirected to an external website. Please check the latest information regarding standards and pointer.
Consult about measuring and monitoring WBGT.
configuration can be tailored to the installation location, number of monitoring points, alarm method, and data recording requirements, such as factories, schools, gymnasiums, and outdoor work areas.
Consult about WBGT monitoring.
