Beat the heat through Wet Bulb Globe Temperature Index Published May 13, 2015 By George Baskin 412 Test Wing Ground Safety EDWARDS AIR FORCE BASE, Calif. -- As a safety professional and working here at Edwards AFB in the summer, you are at the mercy of the heat. Because of the heat, I will discuss the Wet Bulb Globe Temperature (WBGT). The WBGT combines four thermal components: ambient air temperatures, relative humidity, air velocity and radiant heat. At Edwards, heat related incidents can happen. It is determined that high ambient temperatures, high air velocity and high radiant heat could lead to these incidents. An effective means in reducing heat related incidents is the use of the WBGT heat index flags. When engineering controls cannot control heat stress, another option is to limit the time personnel remain in a hot environment. Heat index flags are a quick way to see how dangerous the conditions are and what precautions must be taken when working and playing outside. The flags are based on the Wet Bulb Globe Temperature Index, a calculated measurement based on the outside air temperature, radiant heat, humidity and air movement. The scale has five categories. The white flag is the lowest, it has no restrictions attached and allows strenuous activities without rest. Next is the green flag and it's in effect between 80 and 84.9 degrees. This flag allows supervised heavy exercise outdoors with a 30-minute rest every half hour. When the temperature reaches 85 to 87.9 degrees a yellow flag is raised. While under a yellow flag, the same 30/30 rest-work rule as the green flag applies. However, personnel who are not acclimated to the area should refrain from these activities. A red flag is raised when the temperature reaches 88 degrees. While in this condition, extreme caution should be used when working outdoors. After 20 minutes of work, a 40-minute rest should be taken. When the WBGTI reaches 90 degrees, a black flag is in effect. While under black flag conditions, all non-essential outdoor physical exercise should be postponed until the temperatures cool. In this category, only 10 minutes of the hour should be spent engaging in strenuous activities. For more information on WBGTI conditions, base personnel should go to the Heat Stress Flag Condition Update link under "Thermal Stress" on the left-hand column via the My Base Air Force Portal site.