Heat Stress
Our muscles release about 70% of their energy as heat. Since our bodies work well at a constant inner
temperature of 98.6 degrees Fahrenheit, thermoregulation is important. When the environmental
temperature is higher than our body temperature, we actually absorb heat. The amount of heat that stays
stored in our bodies as well as the length of time we remain hot can result in several conditions:
Major Heat Stress
Conditions
• Heat cramps
• Heat exhaustion
• Heat stroke
Minor Heat Stress
Conditions
• Heat rash
• Sunburn
• Perspiration and
mineral loss
Four Ways to Regulate Extra Heat
Toolbox Talk
Your body is affected by heat stress on the
job more than you might think. A hot
environment with high humidity may overload
your body with heat. The result of this extra
body heat can range from simple sunburn to
very serious disorders like heat stroke. The
process of regulating this extra heat is called
thermoregulation.
1. Conduction: Use conduction to transfer body heat to objects
cooler or warmer than your body.
2. Convection: Use convection to transfer body heat to or from air
moving over your skin.
3. Radiation: Use radiation to transfer heat to or from objects not
in direct contact with your body.
4. Evaporation: Use evaporation to remove body heat by air or
moisture exiting lungs or skin.
In radiation, convection and conduction, your blood vessels expand
carrying internal body heat to your skin surface for release to
the air. In evaporation, perspiration cools on your skin releasing
heat to the air.
© Copyright 2009, Jacobs Engineering Group Inc. All rights reserved. xxxx 05/09
Heat Cramps
Heat Exhaustion
Heat Stroke
Heat cramps are severe muscle cramps.
They occur when your body’s cellular fluid
is depleted through perspiration, cooling or
decreased mineral content. Your arms, legs
or abdominal muscles can cramp while
working or later when relaxing.
Heat exhaustion occurs when the body’s
thermoregulation is over-whelmed, but not
completely broken down. Since perspiration
glands have secreted salts and water onto
your skin, fluid loss increases and blood
volume drops. You may feel pain from heat
cramps, suffer from nausea, headache and
eventually collapse.
Heat stroke is the most severe of the heat
disorders. Heat stroke is a life-threatening
emergency that requires immediate
medical attention. Early signs of heat
stroke are:
• High body temperature, typically above
103 degrees Fahrenheit
• Hot, red or flushed skin
• Little or no perspiration on skin
• Rapid pulse
• Difficulty breathing
• Weakness
• Nausea or vomiting
If you or a co-worker is suffering from
heat cramps:
• Move into a shaded area
• Drink lightly
Heat exhaustion victims must be given
immediate medical attention.
If you suspect heat exhaustion:
• Move victim into shade
• Loosen clothing and boots
• Circulate air by fanning to cool
• Elevate the victim’s legs
• If victim is conscious, give lightl
salted water
• Pour water and ice on victim
• Stay with victim until medical help
arrives
With heat stroke, the victim’s body
temperature must be lowered as quickly as
possible. Complete immersion in water or
applying ice packs to armpits, wrists or
backs of knees may help. Heat stroke is the
deadliest of the heat disorders. Call for
medical help immediately. Never give fluids
to an unconscious person.
Controlling Heat Stress
In addition to recognizing the signs of heat stress and knowing first aid measures, you can prevent
heat stress disorders:
Acclimatization
Acclimatization is developing the ability to work in a
hot environment by gradually getting yourself used to
the conditions. Physical work is necessary for full
acclimatization, but should be done with appropriate
rest and fluid intake, and at a reasonable pace.
Work/Rest Cycles
The proper work cycles for reducing the ill
effects of heat stress avoid “overdoing it.”
It may be that rest means minimal activity
instead of stopping work completely.
• Try to alternate light and heavy work
• When possible, cycle between indoor
and outdoor work
• Consider rotation of work teams
if possible
Fluid Replacement
Fluid replacement is the most important way to protect
your body’s thermoregulation. You must take in as much
fluid as you lose during the day and replace salts your
body uses up in cooling. If water and vital electrolytes
(salts) are not replaced, dehydration occurs which
means there is no perspiration for cooling and
results in retained body heat leading to heat
stress. Most sports drinks provide
electrolyte replacement our bodies need. If
you are going to work in the heat, and have
no medical reason to avoid salt, add a little
to your meals or snacks to help avoid heat
stress disorders.
© Copyright 2009, Jacobs Engineering Group Inc. All rights reserved. xxxx 05/09