Wet Bulb Globe Temperature (WBGT)
The Wet Bulb Globe Temperature is a measure of heat stress in direct sunlight which takes into account the temperature, humidity, wind speed, sun angle and cloud cover (solar radiation).
For the most up to date information, call the WBGT hotline at
571-231-HAZY (4299).
| Category |
WBGT (°F) |
Flag Color |
Easy Work Water Intake (Qt/H) |
Easy Work Work/Rest Times |
Moderate Work Water Intake (Qt/H) |
Moderate Work Work/Rest Times |
Hard Work Water Intake (Qt/H) |
Hard Work Work/Rest |
Intensity of Physical Exercise |
| 1 |
≤78-81.9 |
White |
1/2 |
No limit |
3/4 |
No limit |
3/4 |
40/20 minutes |
No flag condition |
| 2 |
82-84.9 |
Green |
1/2 |
No limit |
3/4 |
50/10 minutes |
1 |
30/30 minutes |
Discretion required in planning heavy exercise for unseasoned personnel. This is a marginal heat stress limit for all personnel. |
| 3 |
85-87.9 |
Yellow |
3/4 |
No limit |
3/4 |
40/20 minutes |
1 |
30/30 minutes |
Strenuous exercise and activity (e.g. close order drill) should be curtailed for new and unacclimated personnel during the first three weeks of exposure. |
| 4 |
88-89.9 |
Red |
3/4 |
No limit |
3/4 |
30/30 minutes |
1 |
20/40 minutes |
Strenuous exercise curtailed for all personnel with less than 12 weeks training in hot weather. |
| 5 |
≥90 |
Black |
1 |
50/1 minutes |
1 |
20/40 minutes |
1 |
10/50 minutes |
Physical training and strenuous exercise suspended for all personnel (excluding operational commitment not for training purposes). |
CAUTION: Hourly fluid intake should not exceed 1.5 quarts. Daily fluid intake should not exceed 12 quarts.
- The work-rest times and fluid replacement volumes will sustain performance and hydration for at least 4 hours of work in the specified heat category. Fluid needs can vary based on individual differences. (plus or minus .25 quart per hour) and exposure to full sun or full shade (plus or minus .25 quart per hour).
- NL = No limit to work time per hour.
- Rest means minimal physical activity (sitting or standing), accomplished in shade if possible.
- CAUTION: Hourly fluid intake should not exceed 1.5 quarts.
- If wearing body armor add 5°F to WBGT in humid climates.
- If wearing NBC clothing (MOPP 4) add 10°F to WBGT.
NOTE: Wearing of body armor or NBC uniform adds approximately 10 points to the measured WBGT index. Exposure limits should be adjusted accordingly.