About WBGT

Wet Bulb Globe Temperature
 

In the early 1950's the US Marine Corps suffered significant casualties due to heat stroke during training activities at Parris Island, South Carolina. Prompted by this experience, the Department of the Navy commissioned studies on the effects of heat on exercise performance. These studies resulted in a heat index called the Wet Bulb Globe Temperature. In 1989, WBGT was suggested as an international standard (ISO 7243).

 The Wet Bulb Globe Temperature is measured using three different thermometers:

(1) A standard dry bulb thermometer (Dry Bulb Temperature; DB)

(2) A standard dry bulb thermometer whose bulb is wrapped  in a cotton sleeve, the bottom of the sleeve lying in a pool of distilled water, so that the cotton sleeve will always be wet, allowing continuous evaporative cooling of the thermometer's bulb, simulating the evaporation of sweat (Wet Bulb Temperature; WB)

 (3) A standard dry bulb thermometer whose bulb is inserted into a large (6 inch) black ball, to allow measurement of the effects of sunshine and other radiant heat (Black Globe Temperature; GT). These three temperatures are integrated as follows:

 WBGT = 0.7 WB + 0.2 GT + 0.1 DB

 The studies performed by the author that have served as the basis for formulas used in Heat Stress Adviser have been carried out using WBGT devices from Quest Technologies (Oconomowoc, WI, USA). A total of 4 instruments have been used, including the QuesTemp 15 and the QuesTemp 34.