Ideas for Keeping Workers Safe in the Cold
Managing Shiftworkers in Cold Weather: Challenges and Proper Prevention Strategies
In the winter months, many shiftworkers routinely work in cold conditions to keep our 24-hour society running. To do this job properly, shiftworkers, and their managers, should be aware of cold’s effect on the body and proper prevention strategies for dealing with cold conditions.
Failure to educate shiftworkers who work in cold conditions, can lead to adverse effects on human performance and health. Additionally, cold can interfere with other factors in the workplace, modifying or aggravating the risk of common hazards and increasing the risk of injuries. Prolonged exposure to freezing temperatures can result in serious health problems, such as frostbite and hypothermia.
Why is working in the cold challenging?
The human body is designed to work best at a constant core temperature of 98.6ºF (37ºC). The body maintains this temperature constant by producing heat (from food and muscular work) and by losing heat through:
Radiation – the loss of heat to the environment due to the difference between the temperature of the air and the temperature of the body;
Conduction – the loss of heat through direct contact with a cooler object;
Convection – the loss of heat from the body to the surrounding air as the air moves across the surface of the body;
Evaporation – the loss of heat due to the conversion of water from a liquid to a gas, by perspiration/sweating and respiration.
It is important to recognize the strong connection between fluid levels, fluid loss, and heat loss. As body moisture is lost through the various processes, the overall circulating volume is reduced which can lead to dehydration. This decrease in fluid level makes the body more susceptible to hypothermia and other cold injuries.
How the body responds to the cold
In a cold environment, the body uses most of its energy to maintain its core temperature. Under cold conditions, blood vessels in skin, arms and legs constrict, to reduce blood flow to extremities, in order to conserve heat (minimizing cooling of the blood) and keep critical internal organs warm. At very low temperatures, when blood flow to exposed skin and extremities is reduced, they can cool rapidly, which increases the risk of frostbite and hypothermia. When the body can not maintain temperature by vasoconstriction, it starts shivering to increase metabolic rate and generate heat.
Cold related stress
1. Air Temperature
2. Wind Speed: if accurate information is not available, the following can help estimate wind speed:
• 8 km/h (5 mph): light flag moves,
• 16 km/h (10 mph): light flag fully extended,
• 24 km/h (15 mph): raises newspaper sheet,
• 32 km/h (20 mph): causes blowing and drifting snow.
3. Humidity: Water conducts heat away from the body 25 times faster then dry air.
4. Wind chill (combination of temperature and air velocity) is a key factor to evaluate. It is essentially the air temperature that would feel the same on exposed human skin as the given combination of air temperature and wind speed. It can be used as a general guideline for deciding clothing requirements and the possible health effects of cold. For example, a situation with wind temperature of 40ºF, and a velocity of 35 mph, is equivalent to still air temperature of 11ºF.
In general, people in good physical health are less susceptible to cold injury. The following factors increase the risk of cold injuries:
Age: older adults are more susceptible
Gender: women are generally at greater risk of cold injuries
Certain diseases such as diabetes and cardiovascular disease
Consumption of alcohol, nicotine and caffeine
Handling evaporative liquids (such as gasoline) presents an additional risk, due to evaporative cooling. Workers should take precautions to avoid soaking of clothing or contact with skin. Liquid oxygen and nitrogen present particularly acute splash hazards in cold weather.
Vibration from tools and equipment also presents increased risk. As air temperature drops, risk arising from tools that cause significant hand-transmitted or whole body vibration may be increased.
Work/rest schedule: The “work warm-up schedule,” as developed by the Saskatchewan Department of Labour, has been adopted by the American Conference of Governmental Industrial Hygienists (ACGIH) as Threshold Limit Values (TLVs) for cold stress. These guidelines describe exposure conditions and techniques for working in cold conditions under which it is believed that nearly all workers can be repeatedly exposed without any adverse health effects. The TLV objective is to maintain core body temperature from falling below 96.8F
Cold stress related injuries
Prolonged exposure to cold can lead to fatigue, lowered concentration, slowed reflexes and loss of physical coordination. Manual tasks are impaired because the sensitivity and dexterity of fingers are reduced in the cold. At even lower temperatures, the cold affects the deeper muscles resulting in reduced muscular strength, stiffened joints and musculoskeletal injuries. Mental alertness is reduced due to cold-related discomfort. Exposure to cold could impair decision-making and affect the ability to follow safe working procedures. All of these can increase the risk of injuries.
Early-warning signs of cold-related illness
– Hands become numb
– Involuntary shivering
– Loss of fine motor coordination (particularly in hands, i.e., having trouble with buttons, zips, laces)
– Slurred speech
– Difficulty in thinking clearly
Once two or more signs have been experienced or observed, the worker should stop working and take steps to safeguard health.
Musculoskeletal strains, sprains and tears
Employees working in the cold are more susceptible to these problems. The risk increase is due to:
– Vasoconstriction, which can reduce maximal strength and power output
– Reduced blood flow leads to more rapid muscle fatigue
– Decreased manual dexterity may reduce ability to sustain a firm or controlled grip
– Thermal discomfort, as well as bulky clothing may prevent smooth movements or full range of movements.
Warm up stretches before handling heavy equipment and material are recommended to avoid musculoskeletal injuries.
Frostbite occurs when the skin freezes and loses water. It usually occurs at temperatures below 30ºF, but wind chill effect can cause frostbite at above-freezing temperatures. Frostbite can also be caused by contact with extremely cold objects. Initial symptoms of frostbite are uncomfortable cold sensation, tingling, stinging, followed by numbness. Outer extremities, such as ears, fingers, toes, cheeks and nose are primarily affected. Frostbitten areas appear white and cold to touch.
Hypothermia occurs when body heat is lost faster than it can be replaced. Symptoms usually begin when core body temperature drops to around 95ºF. Mild hypothermia signs are shivering, blue lips and fingers, and poor coordination. Moderate hypothermia signs are mental impairment and confusion, poor decision-making, disorientation, inability to take precautions from the cold, heart slowdown and slow breathing. Severe hypothermia signs are unconsciousness, significant heart slowdown, no shivering and no detectable breathing.
What can be done to help prevent the adverse effects of cold?
The risk of injury due to prolonged exposure to cold can be minimized by proper equipment design, safe work practices and appropriate clothing. The following is a summary of actions including some from recommendations from the ACGIH (American Conference of Governmental Industrial Hygienists).
For work below the freezing point, metal handles and bars should be covered by thermal insulating material. Also, machines and tools should be designed so that they can be operated without having to remove mittens or gloves.
Procedures for providing first aid and obtaining medical care should be clearly outlined. For each shift, at least one trained person should be assigned the responsibility of attending to emergencies.
Workers and supervisors involved with work in cold environments should be informed about symptoms of adverse effect exposure to cold, proper clothing habits, safe work practices, physical fitness requirements for work in cold, and emergency procedures in case of cold injury.
Limit exposure to cold environment
– Increase task variation and rotation
– Activities that minimize blood circulation (static, cramped positions) should be reduced/eliminated to the best degree possible
Individuals may not recognize their own symptoms. A buddy system approach would allow for earlier recognition of signs of frostbite and hypothermia.
Balanced meals and adequate liquid intake are essential to maintain body heat and prevent dehydration. Working in the cold requires more energy than in warm weather because the body is working to keep itself warm. It also requires more effort to work when wearing bulky clothing and winter boots, especially when walking through snow.
Workers should drink fluids often especially when doing strenuous work (e.g., 3-5 liters/day, including liquids from food). For warming purposes, hot non-alcoholic beverages or soup are best. Caffeinated drinks are not recommended because they increase urine production and contribute to dehydration. Caffeine also increases the blood flow at the skin surface which can increase the loss of body heat.
Alcohol should not be consumed as it causes expansion of blood vessels in the skin and impairs the body’s ability to regulate temperature (it affects shivering). These effects cause the body to lose heat and thus increase the risk of hypothermia.
Personal protective equipment
Protective clothing is needed for work at or below 39°F (4°C). Clothing should be selected to suit the temperature, weather conditions, the level and duration of activity, and job design. Clothing should be worn in multiple layers, since the air between layers of clothing provides better insulation than the clothing itself. Having several layers also gives the option to remove or to add a layer depending on the circumstances.
The inner layer should provide insulation and be able to “wick” moisture away from the skin to help keep it dry. Thermal underwear made from polyesters or polypropylene is suitable for this purpose. Cotton is not recommended because it tends to get damp or wet quickly, and loses its insulating properties. The additional layers of clothing should provide adequate insulation for the weather conditions under which the work being done. They should also be easy to open or remove before getting too warm to prevent excessive sweating during strenuous activity. Outer jackets should have the means for closing off and opening the waist, neck and wrists to help control how much heat is retained or given off. For work in wet conditions, the outer layer of clothing should be waterproof. If the work area cannot be shielded against wind, an easily removable windbreaker garment should be used. Almost 50 percent of body heat is lost through the head. A wool knit cap, balaclava or a liner under a hard hat can reduce excessive heat loss.
Clothing must be dry and should be kept clean since dirt fills air cells in fibers of clothing and diminishes its insulating ability.
If fine manual dexterity is not required, gloves should be used below 39°F (4°C) for light work and below 19°F (-7°C) for moderate work. For work below 1°F (-17°C), mittens should be used, instead of “fingered” gloves.
Felt-lined, rubber bottomed, leather-topped boots with removable felt insoles are best suited for heavy work in cold since leather is porous, allowing the boots to “breathe” and let perspiration evaporate. Leather boots can be “waterproofed” with some products that do not block the pores in the leather. Boots made from Gore-Tex TM materials also provide for breathable waterproofing.
Workers could wear one pair of thick, bulky socks or two pairs – one inner sock of silk, nylon, or thin wool and a slightly larger, thick outer sock. Liner socks made from polypropylene will help keep feet dry and warmer by wicking sweat away from the skin. However, as the outer sock becomes damper, its insulation properties decrease. If work conditions permit, it is advisable to have extra socks available to change socks during the day.
Face and Eye Protection
In extremely cold conditions, where face protection is used, eye protection must be separated from the nose and mouth to prevent exhaled moisture from fogging and frosting eye shields or glasses.
Extreme Hot or Cold Temperature Conditions. Canada’s National Occupational Health & Safety Resource. http://www.ccohs.ca
Cold Environments-General. Canada’s National Occupational Health & Safety Resource. http://www.ccohs.ca
Cold Environments-Working in the Cold. Canada’s National Occupational Health & Safety Resource. http://www.ccohs.ca
Work in Hot or Cold Environments. Code of Practice 2001. WorkCover NSW Health and Safety Code of Practice. http://www.workcover.nsw.gov.au
Cold Stress. Electronic Library of Construction. Occupational Safety and Health. http://www.cdc.gov
Cold Stress Policy. City of Toronto-Human Resources-Guidelines. http://wi.toronto.ca
Cold Stress. Occupational Safety and Health Administration. http://www.osha.gov
Protecting Workers in Cold Environments. U.S. Department of Labor. Occupational Safety and Health Administration. http://www.osha.gov
Working in a Cold Environment. Cambridge Integrated Services Australia Pty.Ltd.
Threshold Limit Values (TLVTM) and Biological Exposure Indices (BEITM) booklet. ACGIH, Cincinnati, OH. 2008.
Free White Papers – Check out CIRCADIAN’s white papers, such as “The Advantages & Disadvantages of 12-Hour Shifts”
Take the Shiftwork Practices 2008 Survey