Your mother was right. Remember when our parents insisted
that we wear warm clothes and a hat when we play outside? The colder
weather is here, and those of us that must work outside must be aware
of the effects of cold stress, including hypothermia, trench foot and
How cold is too cold? (top)
When most people think of hypothermia, they think of
frigid temperatures or blizzard-like conditions. Actually, hypothermia
occurs most often in the spring and fall, rather than winter.
Four factors contribute to cold stress: cold temperatures, high
or cold wind, dampness and cold water. A cold environment forces
the body to work harder to maintain it's temperature. Cold air, water,
and snow all draw heat from the body. Wind chill is the combination
of air temperature and wind speed. For example, when the air temperature
is 40°F, and the wind speed is 35 mph, your exposed skin receives
conditions equivalent to the air temperature being 11° F.
So, while it is obvious that below freezing conditions combined
with inadequate clothing could bring about cold stress, it is important
to understand that it can also be brought about by temperatures in
the 50's coupled with some rain and wind.
How your body reacts to cold conditions (top)
When in a cold environment, most of your body's energy
is used to keep your internal temperature warm. Over time, your body
will begin to shift blood flow from your extremities (hands, feet,
arms, and legs) and outer skin to the core (chest and abdomen). This
allows exposed skin and the extremities to cool rapidly and increases
the risk of frostbite and hypothermia. Combine this with cold water,
and trench foot may also be a problem.
Hypothermia means "low heat" and is a potentially
serious health condition. This occurs when body heat is lost from
being in a cold environment faster than it can be replaced. When
the body temperature drops below the normal 98.6° F to around
95° F, the onset of symptoms normally begins. The person begins
to shiver and stomp feet in order to generate heat. As the body temperature
continues to fall, slurred speech, lack of coordination and memory
loss develop and the person will stop shivering. Once the body temperature
falls to around 85° F, the person may become unconscious, and
at 78°, the person could die.
Who is at risk:
Anyone working in a cold environment may be at risk for cold stress.
However, older people may be at more risk than younger adults,
since older people are not able to generate heat as quickly.
Certain medications may prevent the body from generating heat
normally. These include anti-depressants, sedatives, tranquilizers and some
Mild hypothermia (98 - 90° F)
Moderate hypothermia (90 - 86° F)
Unable to walk or stand
Confused and irrational
Severe hypothermia (86 - 78° F)
Very sleepy or unconscious
What to do:
(Proper treatment depends on the severity of the hypothermia.)
Frostbite occurs when the skin actually freezes and loses water.
In severe cases, amputation of the frostbitten area may be required.
While frostbite usually occurs when the temperatures are 30° F
or lower, wind chill factors can allow frostbite to occur in above
freezing temperatures. Frostbite typically affects the extremities,
particularly the feet and hands.
Cold, tingling, stinging or aching
feeling in the frostbitten area, followed by numbness
Skin color turns red, then purple,
then white or very pale skin, cold to the touch
Blisters in severe cases
Trench foot or immersion foot is caused by having feet immersed
in cold water for long periods of time. It is similar to frostbite,
but considered less severe.
What to do:
Preventing Cold Stress (top)
Planning for work in cold weather is the most important
defense. Wearing appropriate clothing and being aware of how your body
is reacting to the cold are important to preventing cold stress. Avoiding
alcohol, certain medications and smoking can also help to minimize
Wearing the right clothing is the most important way to avoid cold
stress. The type of fabric also makes a difference. Cotton loses
its insulation value when it becomes wet. Wool, on the other hand,
retains its insulation even when wet. The following are recommendations
for working in cold environments:
- Wear at least three layers of clothing:
- An outer layer to break the wind and allow some ventilation
(like Gortex® or
- A middle layer of down or wool to absorb sweat and provide
insulation even when wet
- An inner layer of cotton or synthetic weave to allow ventilation
- Wear a hat. Up to 40% of body heat can be lost when the head is
- Wear insulated boots or other footwear.
- Keep a change of dry clothing available in case work clothes become
- Do not wear tight clothing. Loose clothing allows better ventilation.
- Drinking: Drink plenty of liquids, avoiding
caffeine and alcohol. It is easy to become dehydrated in cold weather.
- Work Schedule: If possible, heavy work
should be scheduled during the warmer parts of the day. Take breaks
out of the cold.
- Buddy System: Try to work in pairs
to keep an eye on each other and watch for signs of cold stress
Some engineering controls are available to reduce the risk of cold
Radiant heaters may
be used to warm workers
Shield work areas from
drafts or wind
Use insulating material on
equipment handles when temperatures drop below 30° F.
Employees and supervisors need to be trained to be able to detect
early signs of cold stress.
Supervisors should watch for signs of cold stress and allow workers
to interrupt their work if they are extremely uncomfortable. Supervisors
should also ensure that work schedules allow appropriate rest periods
and ensure liquids are available. They should use appropriate engineering
controls, personal protective equipment and work practices to reduce
the risk of cold stress.
For more information (top)