Heat Stress Lesson

Heat Stress Program
Navy Region Singapore 2007
A. Physiology of Heat Stress
Physiology of Heat Stress
• The effect of factors on the body as it
tries to regulate body temperature
– The body generates heat; is sensitive to
external heat factors
– The body tries to regulate internal
temperatures naturally
– Failure of natural cooling ability causes heat
Types of Heat Affecting the
Air temperature
Thermal radiation
Air flow (ventilation)
Symptoms of Heat Stress
Severe headaches
Decreased performance
– Physical
– Mental
Causes of Heat Stress
High humidity + Heavy exercise + Heat
Radiation + Low convective heat loss
• High humidity decreases heat loss through evaporation
of sweat
• Heavy exercise increases metabolic heat production
• Heat radiation from the sun or hot objects (asphalt,
• Heat layer next to skin can be caused by lack of air
currents over skin (low convective heat loss)
• Poor physical condition
Heat Stress Prevention
• Avoid caffeine
• Avoid salt tablets
– Salt is generally well-replenished in food
• Allow time for acclimatization
– Increased tolerance to heat and more efficient
cooling by body (more sweat, less salt loss, etc.)
– Can be achieved in as little as 3 weeks
• Two 50 minute periods of work per day (in heat)
• Does not necessarily indicate that no health effects will be
experienced under higher heat conditions
B. Navy Heat Stress Control
– Set Policy in OPNAVINST 5100.23 (shore
– Assist and consult with heat stress program
implementation, follow through, and
• Commanding Officer (or designee)
– Establishes and enforces Heat Stress
– Ensures Heat Stress Deficiencies corrected
– Requests assistance to identify problems
– Reports injuries & conducts investigations
C. Heat Stress Program
Heat Stress Program
• Monitor heat stress potential
– Take outdoor WBGT readings daily
• Should be taken at:
– 0900, 1100, 1300, and 1500 on any day when the dry
bulb > 80 degrees F.
– Log readings!
– Exhibit proper colored flag as needed
– Consult NEPMU6 Industrial Hygiene for
Flag Codes
• White Flag
– WBGT is <80 degrees F
• Green Flag
– WBGT between 80 and 84.9 degrees F
• Yellow Flag
– WBGT between 85 and 87.9 degrees F
• Red Flag
– WBGT between 88 and 89.9 degrees F
• Black Flag
– WBGT > 90 degrees F
Flag Meanings
• White Flag
– Heat Condition V- Extremely intense physical
exertion may precipitate heat exhaustion or
heat stroke in un-acclimatized personnel.
Therefore, caution should be taken.
• Green Flag
– Heat Condition IV- Discretion is required in
planning heavy exercise for acclimatized
Flag Meanings Continued
• Yellow Flag
– Heat Condition III- Strenuous exercise and
activity (i.e. close order drill) should be
curtailed for new and un-acclimatized
personnel during the first three weeks of
heat exposure.
• Red Flag
– Heat Condition II- Strenuous exercise should
be curtailed for all personnel with less
than 12 weeks training in hot weather.
Flag Meanings Continued
• Black Flag
– Heat Condition I- Physical training
and exercise should be suspended for
all personnel (excludes operational
commitment not for training
– Heat stroke likelihood high under
conditions of high exertion.
Signs and Symptoms
Heat Exhaustion
• Symptoms
Profuse sweating
Pale and clammy skin
Pulse fast and weak
Breathing fast and shallow
Heat Cramps
• Caused primarily through excessive salt
loss through sweating
– Painful and severe cramping of voluntary
– Need to stop exercising, replenish
fluids/electrolytes, and stretch
Heat Syncope
• Caused by pooling of blood in extremities
– Caused by dilation of blood vessels to cool
body by heat transfer to air
– Can cause loss of consciousness
– Cool victim quickly and begin
fluid/electrolyte replacement
– Transport to medical treatment facility
Heat Exhaustion
• Caused by peripheral vascular collapse
– Symptoms include
Profuse sweating
Blurred vision
Muscle cramps
Possible loss of consciousness
If unconscious, Call a Medical Emergency
Loosen clothing
Move victim to cooler space
If faint, lower head to knees
Fluid/electrolyte replenishment
Transport to medical treatment facility
Heat Stroke
• SEVERE Medical Emergency!!
• Caused by shutdown of the body’s cooling system
– Body “gives up” on trying to cool down
• Symptoms
– Skin--Hot, Flushed, Dry
• Sweating ceases
– Pulse fast and strong
– Breathing deep
– Vomiting, Cramps, Twitching
– Will go into shock
• Can and WILL be FATAL if body is not cooled
IMMEDIATELY by any means possible!
– Ice, alcohol, remove clothing, fans, etc.
• Transport to Medical Treatment right away!

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