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Anyone working in a cold environment may be at risk of cold stress. Some workers may be required to work outdoors in cold environments and for extended periods of time. For example, snow cleanup crews, sanitation workers, police officers and emergency response and recovery personnel, firefighters and emergency medical technicians may spend long periods of time outdoors. Cold stress can be encountered in these types of work environments.

How cold is too cold?

What constitutes extreme cold and its effects can vary across different areas of the country. In regions that are not used to winter weather like California or Texas, near freezing temperatures are considered “extreme cold.” A cold environment forces the body to work harder to maintain its temperature. Whenever temperatures drop below normal and wind speed increases, heat can leave your body more rapidly.

Wind chill is the temperature your body feels when air temperature and wind speed are combined. For example, when the air temperature is 40°F, and the wind speed is 35 mph, the effect on the exposed skin is as if the air temperature 28°F.

Cold stress occurs by driving down the skin temperature and eventually the internal body temperature (core temperature). This may lead to serious health problems, and may cause tissue damage, and possibly death.

Risk factors

Some of the risk factors that contribute to cold stress are:

• Wetness/dampness, dressing improperly and exhaustion
• Predisposed health conditions such as hypertension, hypothyroidism and diabetes
• Poor physical conditioning
• How one’s body reacts to cold conditions

In a cold environment, most of the body’s energy is used to keep the internal core temperature warm. Over time, the body will begin to shift blood flow from the extremities (hands, feet, arms and legs) and outer skin to the core (chest and abdomen). This shift allows the exposed skin and the extremities to cool rapidly and increases the risk of frostbite and hypothermia. Combine this scenario with exposure to a wet environment, and trench foot may also be a problem.

What are the most common cold induced illnesses/injuries? According to OSHA, the following three conditions are the most common cold injuries/illnesses:

• Hypothermia
• Frostbite
• Trench Foot

Hypothermia occurs when body heat is lost faster than it can be replaced and the normal body temperature (98.6°F) drops to less than 95°F. Hypothermia is most likely at very cold temperatures, but can occur even at cool temperatures (above 40°F), if a person becomes chilled from rain, sweat or submersion in cold water.

Frostbite is an injury to the body that is caused by freezing of the skin and underlying tissues. The lower the temperature, the more quickly frostbite will occur. Frostbite typically affects the extremities, particularly the feet and hands. Amputation may be required in severe cases.

Trench Foot or immersion foot is caused by prolonged exposure to wet and cold temperatures. It can occur at temperatures as high as 60°F if the feet are constantly wet. Non-freezing injury occurs because wet feet lose heat 25 times faster than dry feet. To prevent heat loss, the body constricts the blood vessels to shut down circulation in the feet. The skin tissue begins to die because of a lack of oxygen and nutrients and due to the buildup of toxic products.

For additional questions or concerns, please contact the Division of Occupational Health and Safety at (301) 496-2960 or visit: http://www.ors.od.nih.gov/sr/dohs/aboutDOHS/Pages/about_dohs.aspx.