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Heat Production, Heat Illnesses,
and First Aid
chart below
A body at work generates
heat faster than at rest, often more than needed. Roughly three-fourths
of the stored energy the body draws on during activity converts to heat
rather than motion, and more strenuous activity naturally generates more
heat. Elevation of core body temperature disturbs functioning,
so the body protects itself by dissipating excess heat. The mechanisms
of vasodilation and sweating are critical to moving heat from a human body
to the environment.
When the body's core
temperature exceeds its norm (generally 98.6 degrees), veins and
capillaries expand, the heart beats faster, and blood flow increases to
outer layers of skin, from which heat is radiated to the cooler exterior
environment. If, however, the body cannot cool fast enough through
this means, or when surrounding air is warmer than the skin, the brain
signals sweat glands to release sweat to the skin surface. Evaporation
of the sweat carries additional heat from the body. Because high
humidity decreases the sweat evaporation rate, it slows cooling.
After becoming "acclimatized" to a hot environment over time, people sweat
more readily and thus cool more efficiently.
These cooling mechanisms,
however, can impair strength and comfort. Increasing blood flow to
the body surface reduces the volume carrying oxygen to muscles, brain,
and other internal organs, which in turn accelerates fatigue and diminishes
mental alertness. The loss of water volume through sweating also
contributes to fatigue by increasing blood viscosity, making it more difficult
for the heart to pump and reducing the body's capacity for subsequent cooling.
Finally, because prolonged sweating depletes not only heat but also electrolytes
that are needed for muscle functioning, it can cause cramping.
To maintain comfort
and health when working in a hot environment, it is critical for people
to replace both the water and electrolytes they lose through sweating.
If body fluid is not replenished at the same rate as it is lost, or if
replacement lacks electrolytes, the cooling mechanisms lose effectiveness
and exposure to heat stress rises.
Heat Illnesses and First
Aid
Heat stress is a condition
in which the body has elevated core temperature, which may be manifest
by or lead to illnesses of varying severity. Consequences of inadequate
heat dissipation range from general discomfort to heat stroke, as briefly
described in the chart below. Beyond the more subtle impairments
to personal capacity that result from fatigue, heat illnesses may also
cause extreme discomfort and even complete temporary disability.
Heat stroke is potentially fatal and may occur suddenly if heat exhaustion
is ignored.
| Heat Illness |
First Aid |
Heat rash
Regarded as least severe
of heat illnesses, occurs when sweat clogs pores. Though heat rash
usually causes only temporary discomfort, it can develop into an infection. |
Cleanse the affected area
thoroughly and dry completely. Calamine or other soothing lotion may help
relieve the discomfort. |
Heat syncope
Most likely to affect people
who are not acclimatized to working in hot environments. Syncope
generally is the sudden loss of consciousness due to lack of sufficient
blood and oxygen to the brain. Heat stress can cause it by "diverting"
blood to the lower body or extremities at the expense of the brain. |
Rest in shade, drink plenty
of water (recommended) or electrolyte fluids. |
Heat cramps
Heat cramps are often extremely
uncomfortable and can be completely disabling. They typically occur
during or after hard work and are caused by electrolyte deficiencies that
result from extended periods of intense sweating. Symptoms include
painful spasms of leg, arm or abdominal muscles, heavy sweating, and thirst. |
Rest, drink plenty of water
or electrolyte fluids. |
Heat exhaustion
Heat exhaustion also occurs
during work but results from dehydration, lack of acclimatization, reduction
of blood in circulation, strain on circulatory system, and reduced flow
of blood to the brain. Symptoms of heat exhaustion include fatigue,
headache, dizziness, muscle weakness, nausea, chills, tingling of hands
or feet, confusion, loss of coordination, fainting and collapse. |
Rest in the shade or cool
place. Drink plenty of water (preferred) or electrolyte fluids. |
Heat stroke
Heat Stroke can occur suddenly
if heat exhaustion is not treated, and it can be fatal. At this extreme
state of heat stress, the body typically has a core temperature exceeding
104 degrees F and can no longer cool itself. A person suffering heat
stroke needs immediate attention and should be taken to a medical facility
as soon as possible. |
A
medical emergency! Brain damage and death
are possible. Douse the body continuously with a cool liquid and summon
medical aid immediately. |
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