The Wet Bulb Globe Temperature is a calculation that takes into account temperature, humidity, wind speed and radian heat. It factors all the conditions into one value, a heat category.
The heat categories 1 through 5 are indicated with flag conditions. The flag conditions or heat category determine recommended work-rest cycles.
Flag Conditions
White flag (78 to 81.9) - Normal activity for people accustomed to climate; extremely intense physical exertion may cause heat stroke for people who aren't. No limits on light and moderate work; heavy work 40 minutes, rest 20 minutes.
Green flag (82 to 84.9) - Normal activity for those accustomed to the climate; people who aren't should use discretion in planning intense physical activity. No limit on light work; moderate work 50 minutes, rest 10; heavy work 30 minutes, rest 30.
Yellow flag (85 to 87.9) - People accustomed to the climate should use caution in planning intense physical activity; those who aren't should curtail strenuous activities. No limit on light work; moderate work 40 minutes, rest 20; heavy work 30 minutes, rest 30.
Red flag (88 to 89.9) - Those accustomed to the climate should curtail strenuous exercise and limit conditioning for periods not exceeding six hours; people who aren't should terminate all physical conditioning. No limit on light work; moderate work 30 minutes, rest 30; heavy work 20 minutes, rest 50.
Black flag (90 and above) - Light work 50 minutes, rest 10; moderate work 20 minutes, rest 40; heavy work 10 minutes, rest 50.