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Heat Stress

From mid-May through September, NAF El Centro operates at Black Flag approximately 16 hours a day.

Heat related illness includes: heat rash, cramps, exhaustion and stroke. These illnesses are a real danger to people not accustomed to the stress of hot weather exercise. The Wet-Bulb Globe Temperature Index (WBGT) takes into account four variables: air temperature, humidity, radiant heat and air movement. Please advise personnel on the location of the flag poles are located in front of the Station Gym and Ops Security Gate

Heat Index and Physical Exercise Chart

WBGT Index (F) Flag Color Intensity of Physical Exercise
Less than 80 White Extremely intense physical exertion may precipitate heat exhaustion or heat stroke, therefore, caution should be taken.
80-84 Green Discretion required in planning heavy exercise for unseasoned personnel. This is a marginal heat stress limit for all personnel.
85-87 Yellow Strenuous exercise and activity (e.g., close order drill) should be curtailed for new and unseasoned personnel during the first 3 weeks of heat exposure.
88-89 Red Strenuous exercise curtailed for all personnel with less than 12 weeks training in hot weather.
90 and Above Black Physical training and strenuous exercise suspended for all personnel (excludes operational commitment not for training purposes).

Work/rest regimes of permissible Heat Exposure Threshold Limit Values, as recommended by the American Conference of Governmental Industrial Hygienist handbook, "Threshold Limit Values and Biological Exposure Indices", are illustrated below for a normal 8-hour workday. Percentages are for each work hour.  Temperatures are listed as WBGT values in Fahrenheit, not to be confused with actual air temperatures in Fahrenheit.

Work Rest Regime Light Moderate Heavy Flag
Continuous Work 86F 80.1 F 77 F  
75% Work/25% Rest 87.1F 82.4 F 78.6 F Yellow
50% Work/50% Rest 88.5F 84.9 F 82.2 F Red
25% Work/75% Rest 90 F 88 F 86 F Black


For additional information call (760) 339-2488

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