How cold is too cold?

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 its core temperature of 98.6^oF.  Cold air, water, and snow all draw heat from the body. 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 rain and/or wind.

Wind chill is the combination of air temperature and air movement.  The higher the wind speed and the lower the temperature in the work environment, the greater the danger.  If weather information is not available, the following signs may help to estimate wind speeds in the field:

• 5 mph: light flag just moves
• 10 mph: light flag is fully extended by wind
• 15 mph: raises a newspaper sheet off the ground
• 20 mph: wind capable of blowing snow

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How your body reacts to cold conditions

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.  When the body can no longer maintain core temperature by constricting blood vessels, it shivers to increase heat production.  Maximum severe shivering develops when the body temperature has fallen to 95^oF.  Hypothermia becomes an issue at this point.

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Cold-Related Illnesses

Hypothermia

Hypothermia means “low heat” and is a potentially serious health condition.  It occurs when body heat is lost from being in a cold environment faster than it can be replaced.  Symptoms begin with shivering.  As the body temperature continues to fall, slurred speech, lack of coordination and memory loss develop and shivering ceases.  Once the body temperature falls to around 85° F, the person may become unconscious, and at 78°, the person could die.

Risk Factors

Anyone working in a cold environment may be at risk for hypothermia.  However, older people may be at more risk than younger adults, since older people are not able to generate heat or regulate body temperature as quickly.

Certain medications may prevent the body from generating heat normally.  These include anti-depressants, sedatives, tranquilizers and some heart medications.

Signs and symptoms

Mild hypothermia (98 – 90° F)

• shivering
• lack of coordination, stumbling, fumbling hands
• slurred speech
• pale, cold skin

Moderate hypothermia (90 – 86° F)

• shivering stops
• mental confusion or impairment
• reduced breathing and/or heart rate
• unable to walk or stand
• confused and irrational

Severe hypothermia (86 – 78° F)

• severe muscle stiffness
• very sleepy or unconscious
• extremely cold skin
• irregular or difficult to find pulse

First Aid

Proper treatment depends on the severity of the hypothermia.

Mild hypothermia

• move to warm area
• stay active
• remove wet clothes and replace with dry clothes or blankets, cover the head
• drink warm (not hot) sugary drinks such as sports drinks.  Avoid caffeinated beverages and alcohol.

Moderate hypothermia

All of the above, plus

• Call 911
• Cover all extremities completely
• Place warm objects, such as hot packs or water bottles on the victim’s head, neck, chest and groin

Severe hypothermia

• Call 911
• Handle the victim carefully.  Sudden movement or rough handling can upset heart rhythms.
• Do not attempt to re-warm — the victim should receive treatment in a hospital

Frostbite 

Frostbite occurs when layers of skin tissue freeze.  In severe cases, amputation of the frostbitten area may be required. Frostbite can be caused by exposure to severe cold or by contact with extremely cold objects.  In fact, frostbite occurs more readily from touching cold metal objects because heat is rapidly transferred from skin to metal.

Frostbite typically affects the extremities, particularly the face, ears, fingers and toes.  Initial symptoms vary, but typically include skin that looks waxy and feels numb.  Once damaged, tissues will always be more susceptible to frostbite in the future.

Signs and symptoms

• 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
• Hard or blistering skin in severe cases

First Aid

• DO NOT rub the area
• Wrap in soft cloth
• If help is delayed, immerse in warm, not hot, water.  Don’t pour water directly on the affected area because it will warm the tissue too fast.  Warming should take about 25-40 minutes.
• Do not warm the skin if there is a chance of refreezing.  Severe tissue damage can occur.

Trench foot 

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.

Signs and symptoms:

• Tingling, itching or burning sensation
• Blisters

What to do

• Soak feet in warm water, then wrap with dry cloth bandages
• Drink a warm, sugary drink

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Preventing Cold Stress

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 the risk.

Protective Clothing

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 insulative qualities 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 nylon)
  • A middle layer of down or wool to absorb sweat and provide insulation even when wet
  • An inner layer of synthetic weave to allow ventilation
• Wear a hat.  Up to 40% of body heat can be lost when the head is left exposed.
• Wear insulated boots or other footwear sized appropriately.  Tight-fitting footwear restricts blood flow, as can wearing too many socks.
• Wear insulated gloves sized appropriately, especially when contacting metallic surfaces and tool handles.
• If you get hot while working, open your jacket, but keep hats and gloves on.
• Keep a change of dry clothing available in case work clothes become wet.

Do not wear tight clothing which can restrict blood flow.  Loose clothing allows better ventilation

Work Practices

• 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.  Victims of hypothermia may not recognize symptoms.

Engineering Controls

Some engineering controls are available to reduce the risk of cold stress:

• 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.

Training

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.

Be safe, think safe, act safe!