Extreme heat can be very dangerous. In extreme heat and high humidity, evaporation is slowed and the
human body must work extra hard to maintain a normal temperature. This can push the body beyond its
limits. In the United States each year, hundreds of people die from heat-related complications.
Aboard Navy installations, Flag Conditions are used to communicate hazardous heat conditions. It is
important for Navy personnel and families to understand these flag conditions and what each color
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.
White Flag (WGBT Index less than 80° Fahrenheit) — Extremely intense physical exertion may
precipitate heat exhaustion or heat stroke, therefore, caution should be taken.
Green Flag (WGBT Index 80-84.9° Fahrenheit) — Discretion required in planning heavy exercise
for unseasoned personnel. This is a marginal heat stress limit for all personnel.
Yellow Flag (WGBT Index 85-87.9° Fahrenheit) — Strenuous exercise and activity (e.g. close
order drill) should be curtailed for new and personnel not acclimated to the heat during the first
three weeks of heat exposure.
Red Flag (WGBT Index 88-89.9° Fahrenheit) — Strenuous exercise curtailed for all personnel with
less than 12 weeks training in hot weather.
Black Flag (WGBT Index 90° Fahrenheit and above) — Physical training and strenuous exercise
suspended for all personnel (excluding operational commitment not for training purposes).
How to Prepare For Extreme Heat
Be informed and know heat terminology:
Heat Wave — An extended period of extreme heat, usually combined with excessive humidity.
Heat Index — A number of degrees in Fahrenheit (F) added to the air temperature that tells how
hot it feels with the relative humidity.
Excessive Heat Watch — Conditions are favorable for an excessive heat event to meet or exceed
local Excessive Heat Warning criteria in the next 24 to 72 hours.
Excessive Heat Warning — Heat Index values are forecast to meet or exceed locally defined
warning criteria for at least two days (daytime highs = 105-110° Fahrenheit).
Heat Advisory — Heat Index values are forecast to meet locally defined advisory criteria for one
to two days (daytime highs = 100-105° Fahrenheit).
Listen to local weather forecasts and stay aware of upcoming temperature changes.
Be aware that people living in urban areas may be at greater risk from the effects of a prolonged
heat wave than are people living in rural areas, due to stagnant and poor air quality, as well as
stored heat in asphalt and concrete.
Make a plan to keep you and your family safe from the effects of extreme heat.
Make sure you have a fan, snugly fit window air conditioner, or something to circulate air in
extreme heat as many heat-related deaths can be attributed to stagnant atmospheric conditions
or poor air quality.
Insulate air ducts and weather-strip doors and sills to keep cool air in.
Cover windows that receive morning or afternoon sun with drapes, shades, awnings, etc.
Keep storm windows up year round.
Understand that elderly, young, sick and overweight individuals are at greater risk and learn first
aid to help treat heat related emergencies.
Build an emergency kit.
What to Do If There Is Extreme Heat
Slow down and don’t do anything too strenuous.
Stay inside as much as possible.
Never leave children or pets alone in closed vehicles.
If air conditioning is not available in your home, stay on the lowest level or go to a public
building with air conditioning.
If you stay in your home without air conditioning, make sure there is a way, such as a fan, to
circulate the air around you.
Drink lots of water, even if you don’t feel thirsty.
Eat well-balanced, light and regular meals.
Avoid alcohol, caffeine and salt.
Wear loose-fitting, lightweight and light-colored clothing.
Be aware that a power outage or drought can result from a heat wave.
Keep a lookout for possible heat emergencies:
Heat cramps — Muscle spasms and aches from heavy exertion in extreme heat. They are usually
the first sign of heat-related complications.
Heat exhaustion — A form of mild shock that results from insufficient body fluids due to
extreme heat and excessive exercising. The blood flow to the skin increases, decreasing blood
flow to vital organs and raising the body temperature, increasing the risk of a heat stroke.
Heat stroke/sun stroke — The body’s temperature control system stops working, causing body
temperature to rise so high (103° F or more) that there may be brain damage or death.
If you experience or observe any of the above conditions, seek medical attention immediately … and Be
Editor’s Note: The content of this article is provided for educational purposes only. The content provided
is not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek
the advice of your physician or other qualified health professional with any questions you may have
regarding a medical condition.