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All about Wet Bulb Globe Temperature

You have to do more than just stay out of the heat to prevent heat illness.

What is Wet Bulb Globe Temperature?

Wet Bulb Globe Temperature (WBGT) is an environmental index representing
temperature, humidity and radiation*1
as major factors affecting human heat balance*2.
It has been specified as a heat illness risk on the Japanese Ministry of the Environment’s heat illness prevention website since 2006.
WBGT is calculated from dry bulb temperature, wet bulb temperature and globe temperature.

Details about WBGT observations (in Japanese).

*1    Radiation heat comes from the ground, buildings, people and other sources. Hotter bodies emit larger amounts.

*2    Wind also affects human heat balance.

WBGT is calculated from dry bulb temperature, wet bulb temperature and globe temperature. The unit for WBGT is °C, but this is different form regular temperature measurements, right? That's right. Humidity is an important factor in WBGT. Why does humidity contribute to 70 percent of the WBGT value? Well, sweat doesn't evaporate well when it's humid, which makes it harder for people to cool down. This increases the risk of heat illness. Heat conditions on 6th and 9th of July, 2011 in Tokyo. This table shows that heat illness happens more when it's humid, even if the temperature is the same. So which WBGT criteria are more important? Daily occurrence per million people vs. daily maximum WBGT. Well, this figure shows that heat illness is much more common on hot days when the WBGT value is over 29 °C. Right. Days like this are a real risk. You have to be careful!

Find out more about WBGT.

How much do you know about WBGT?
Check out your local WBGT.

Click to find out your local WBGT. Heat Stress Index: WBGT

Preventing heat illness

What shoud I do if the WBGT is high? You've got to plan to avoid heat illness. Wear a hat, drink frequently and take frequent breaks in the shade or a cool place. To avoid heat illness

Heat illness symptoms:

Heat illness symptoms

First Aid in heat illness (in Japanese).

Get the person into the shade or an air-conditioned place and provide something to drink. You have to cool them down quickly. If the person is unconscious, call 119 for an ambulance urgently. What you can do: This hou-to resource (in Japanese) will help to prevent heat illness at amusement parks, summer festivals and summer sporting events. Sample pages of How-to resource (in Japanese) How-to resource (in Japanese)
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