The Wet-Bulb Globe Temperature (WGBT) is the standard used by the US military to obtain an index to measure heat stress. Medical or Disaster Preparedness personnel usually determine and disseminate the WBGT. The WGBT Effects Table shows the water requirements, rest intervals and activity restrictions based on the WBGT.

Heat condition may be reported as: Wet-Bulb Globe Temperature (WBGT). Use heat condition information to determine required water intake and work/rest cycles.

WBGT Effects Table
OUTDOOR
(IN SUN) WBGT INDEX
(° F)
Easy Work/Rest
(Minutes)
Water Intake/Hr
(Qts)
Moderate Work/Rest
(Minutes)
Water Intake/Hr
(Qts)
Hard Work/Rest
(Minutes)
Water Intake/Hr
(Qts)
< 82 NL N/A NL N/A NL N/A
82-84.9 NL 1/2 50/10 3/4 30/30 1
85-87.9 NL 3/4 40/20 3/4 30/30 1
88-89.9 NL 3/4 30/30 1 20/40 2
> 90 50/10 1 20/40 2 10/50 3
N/A - Not Applicable
NL - No Limit

Easy Work Moderate Work Hard Work

Weapon Maintenance
Walking Hard Surface at 2.5 mph, with ≤ 30 lb Load
Manual of Arms
Drill and ceremony
Marksmanship Training

Walking in loose sand at 2.5 mph, no load
Walking Hard Surface at 3.5 mph, < 40 lb Load
Calisthenics
Patroling
Individual Movement Techniques. i.e. low crawl, high crawl
Defensive Position Construction
Field Assaults

Walking in loose sand at 2.5 mph with load
Walking Hard Surface at 3.5 mph, with ≥ 40 lb Load

The work/rest time and fluid replacement volumes will sustain performance and hydration for at least 4 hours of work in the specified heat category. Individual water needs will vary ± ¼ qt/hr.
NL= no limit to work time per hour.
Rest means minimal physical activity (sitting or standing) and should be accomplish in shade if possible.
Daily fluid intake should not exceed 12 quarts.

This information is from the Industrial Hygiene & Environmental Health Office, Fort Detrick, Maryland