The Wet Bulb, Globe Temperature (WBGT) Index is the most effective means of assessing the effect of heat stress on the human body. The WBGT Index is used to determine Flag Conditions as a safety standard for how long individuals can safely work out of doors in hot humid conditions. Knowing and understanding these Flag Conditions will help keep you safe from heat-related emergencies like heat cramps, heat exhaustion, and heat/sun stroke. Color coded flags are flown in strategic locations on Naval Installations to communicate hazardous conditions to personnel so that work and outdoor activity can be adjusted accordingly.
Flag Color |
WGBT Index (F) |
Intensity of Physical Exercise |
White |
Less than 80 |
Extremely intense physical exertion may precipitate heat exhaustion or heat stroke, therefore, caution should be taken. |
Green |
80 – 84.9 |
Discretion required in planning heavy exercise for unseasoned personnel. This is a marginal heat stress limit for all personnel. |
Yellow |
85 – 87.9 |
Strenuous exercise and activity (e.g. close order drill) should be curtailed for new and unacclimated personnel during the first three weeks of heat exposure. |
Red |
88 – 89.9 |
Strenuous exercise curtailed for all personnel with less than 12 weeks training in hot weather. |
Black |
90 and Above |
Physical training and strenuous exercise suspended for all personnel (excluding operational commitment not for training purposes). |
(NAVMED P-5010-3)
Note: Wearing of body armour or NBC uniform adds approximately 10 points to the measured WBGT index. Exposure limits should be adjusted accordingly.
