Working in Cold Environments. Preventing Cold-related Injuries and Illnesses. January, 2011. How the body maintains thermal (heat) balance, constant internal temperature How the body reacts to cold conditions Injuries and illnesses caused by exposure to cold
Preventing Cold-related Injuries and Illnesses
How the body maintains thermal (heat) balance, constant internal temperature
See the module “Cold-related Injuries and Illnesses” for more detailed descriptions of hypothermia, frostbite, and other cold injuries.
Exposure to cold can occur when working outdoors or in artificial cold environments. Working for prolonged periods or in extreme cold conditions can lead to cold-related injuries and illnesses, permanent tissue damage, and death.
The body does this through balancing heat loss and heat production.
In cold conditions, the body reduces heat loss and increases heat production.
Most of the body’s energy is used to maintain an internal (core) body temperature of approximately 98.6°F (37°C).
Normal core body temperature:
Body’s core area:
(internal organs, especially ones vital for survival)
Over time, your body will decrease blood flow to your extremities and outer skin and shift it to the body core to keep the internal organs warm. However, this allows exposed skin and the extremities to cool rapidly and increases the risk of cold-related injuries, such as frostbite and hypothermia.
Cold conditions force your body to work harder to maintain its temperature. The challenges you face from a cold environment include:
Wetness: rain, snow, ice, humidity; sweat; wet clothes; water
Air movement: wind speed (5 miles per hour and higher); blown air from fan in cold rooms, etc.
Wind chill is the perceived temperature (what it “feels like”) resulting from the effect of wind (wind speed) in combination with cold air (air temperature). The combined effect increases the rate of heat loss from exposed skin. The stronger the wind at a given temperature, the cooler the wind chill will be.
(Refer to Wind Chill Chart on next slide)
Example: When the air temperature is 15°F and wind speed is 10 mph, your exposed skin receives conditions equivalent to the air temperature being 35°F. Frostbite will develop in 30 min.
If the wind speed doubles to 20 mph, it will feel like it’s -42°F and frostbite will occur in only 10 minutes.
Example: If the temperature is -15°F and wind speed is 10 mph, it will feel like it’s -35°F, and frostbite will develop in 30 minutes. If the wind speed doubles to 20 mph, the time for frostbite to occur drops to only 10 minutes.
Wind Chill Chart
Source: National Oceanic and Atmospheric Administration (NOAA), National Weather Service
EVAPORATION: Heat loss in the form of vapor when body uses heat to evaporate moisture from skin surface (perspiration or “sweat”)
RESPIRATION: Heat loss from lungs’ warming inhaled cold air, which is then exhaledHow the Body Loses Heat
Heat loss from exposed body areas to the environment due to the difference between the temperature of the body and that of the cooler air (when air is <98.6°F)
CONVECTION:Heat loss from wind (blown air from fan, etc.) removing the layer of warm air next to the skin; rate of heat loss depends on wind/air speed
Heat loss through contact with a cooler object and transfer of heat to the cooler object; increases when in contact with cold wet objects (generally, conduction accounts for 2-3% of total heat loss in dry conditions; with wet clothes the loss is increased 5x, and rate of heat loss is 25x faster when a person is immersed in cold water)
Each of these means of heat loss can play a large or small role in the development of a cold-related injury. In addition to air temperature, air movement (wind speed), and wetness, the skin surface area that is exposed to the cold is a factor in the amount of heat lost from the body.How the Body Loses Heat
Your body must produce an equal amount of heat to counter-balance the heat loss in order to survive and stay active in the cold. Heat is produced in the following ways:How the Body Produces Heat
Factors important in heat production:How the Body Produces Heat
If your body begins to lose heat faster than it is produced, your core body temperature drops below normal, and cold stress may result.Cold Stress
Cold stress doesn’t only happen when conditions are below freezing; it can also be brought about by temperatures in the 50's coupled with some rain and wind.
(combination of temperature, wetness, wind)How does cold affect work performance?
In general, people in good physical health are less susceptible to cold injury. In addition to weather conditions, the following factors may increase the risk of developing a cold injury:Factors Increasing Risk of Cold Injuries/Illnesses
Working in freezing conditions or under prolonged exposures to temperatures above freezing, along with other factors, can cause cold-related injuries and illnesses, tissue damage, possible amputation, or death.Injuries/Illnesses from Cold Exposure
The module “Cold-related Injuries and Illnesses” covers these topics at greater depth.
Planning: Plan for work in cold weather and implement controls to reduce and minimize exposure and the risk of cold stress.
Training: Provide training in the recognition and treatment of cold-related injuries and illnesses. Supervisors, workers, and co-workers should watch for signs of cold stress and allow workers to interrupt their work if they are extremely uncomfortable.
Awareness: Being aware of how your body is reacting to the cold is important in preventing cold stress.
Click to go to Wind Chill Chart on Slide #9
Body: Wear at least three layers of loose-fitting clothing to trap air and provide insulation, and allow better ventilation.
The following are recommendations to protect your body, hands, feet, and head when working in cold environments:
Outer layer for wind and water protection, made of “breathable” waterproof fabric that allows some ventilation (like Gortex® or nylon) and is windproof, and that may also need to be resistant to oil, fire, chemicals, or abrasion.
Any additional layer(s) of clothing should be large enough not to compress the inner layers and decrease the insulation properties.
Wear a wool knit cap or a liner under a hard hat to reduce excessive heat loss. A mask also helps protect the cheeks and nose. Up to 40% of body heat can be lost when the head is left exposed.
* The American Conference of Governmental Industrial Hygienists
Face and Eye Protection
Pace the work to avoid excessive sweating. Change into dry clothes if clothes become wet. New employees should be given enough time to get acclimatized to cold and protective clothing before assuming a full work load.
Work Practices are important preventive measures.
Recommended GuidelinesWork Practices
The following slide shows the ACGIH’s recommendations for working in cold conditions. The exposure times are based on the wind chill factor. The work/break schedule applies to any four-hour period with moderate or heavy activity.
The warm-up break periods are of 10 minute duration in a warm location. The schedule assumes that "normal breaks" are taken once every two hours.
At the end of a 4-hour period, an extended break (e.g. lunch break) in a warm location is recommended.
More information is available in the ACGIH publications "2000 TLVs and BEIs" and "Documentation of TLVs and BEIs."
Table applies only if workers are wearing dry clothing and doing moderate to heavy work activity. For light to moderate work activity, move down one line to decrease maximum work period and increase the number of breaks.
*2007 TLVs and BEIs - Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati : American Conference of Governmental Industrial Hygienists (ACGIH), 2007 p. 202
Training in recognition and treatment is important.