Thermal Work Environments – Part 7: Cold Injury and Other Cold-Related Effects

     Loss of heat balance in a cold environment leads to cold injury, an umbrella term for several afflictions, of varying severity, resulting from overexposure to low temperatures.  Recognizing symptoms of cold injuries is critical to timely treatment and successful recovery.
     This installment is a companion to Part 3 (“Heat Illness”) of the “Thermal Work Environments” series, in which a range of cold-related effects and injuries are presented.  The objective of this discussion is to raise awareness of the risks of working in cold environments and the severity of potential outcomes.  These are serious conditions, all but the mildest of which require medical attention from trained healthcare professionals.

Cold Injury
     The following descriptions of cold injuries include information to aid in their identification and understanding of proper treatment.  Minor issues can often be resolved by the affected individual or nearby coworkers.  Though information is shared regarding identification and treatment of cold injuries and related effects, it should not be construed as “medical advice.”  As the severity of injury increases, the more critical professional medical care becomes to survival and recovery.
     The ensuing presentation begins with the least-severe issue and progresses to the most-severe at its conclusion.  The intervening sequence, however, is not a reliable reflection of the relative severity of all occurrences of injury; individuals’ circumstances, sensitivities, and, therefore, experience of injuries differ.  Also, the absence of recognizable symptoms of “low-level” injury does not preclude the onset of a serious condition.  All signs of cold stress must be acknowledged and treated accordingly.
Cold Discomfort
     Discomfort is not an injury, but is, nonetheless, worth noting at the outset.  It is often the first warning or reminder that cold stress is an important element of the workplace that requires attention and proper management.  Discomfort is a common precursor to more-serious injury.
Chilblains
     A chilblain is a swelling of a foot or hand; ears and cheeks may exhibit a similar condition.  It is characterized by redness, itching, and pain.  Bare skin can develop chilblains with repeated exposure to temperatures below 60° F (16° C).  Permanent damage increases susceptibility to recurrence of redness and itching upon subsequent exposure.  Keeping affected areas warm and dry is the default treatment.
Frozen Cornea
     The combination of low temperature, strong wind, and the absence of eye protection (i.e. goggles) can result in frozen cornea.  Treatment usually consists of warming the closed eye with one’s hand or a warm compress, followed by 24 – 48 hours of complete coverage with an eye patch.
Trench Foot
     Trench foot is caused by exposure to cold, wet conditions.  Wet feet suffer from accelerated heat loss, with increased risk of trench foot in temperatures as high as 59° F (15° C).  The hypothalamus responds to the increased heat loss by restricting circulation to the feet, causing them to become cold and numb.  As the condition progresses, hot, shooting pain may be experienced, with swelling, redness, and blisters appearing.
     Tissue damage caused by reduced circulation becomes permanent after approximately 6 hours of exposure with vasoconstriction.  Tissue is damaged further by walking, as it is soft and weak.  After 24 hours of exposure with vasoconstriction, amputation may be necessary.
     Treatment of trench foot is limited to gentle warming and drying and slight elevation of the feet.  Use of over-the-counter pain medication and bed rest (i.e. no walking) are common during the recovery period.
     To prevent trench foot, waterproof insulated boots that are not constricting (tight fitting) should be worn.  Socks should be changed when they become damp and the inside of the boots should be dried regularly (e.g. overnight).
     This condition is also called “immersion foot.”  A similar condition can develop in the hands; the same cause, treatment, and prevention principles are applicable.  Generalizing, this type of injury can be called cold-immersion injury.
Frostnip
     Freezing of the top layers of skin tissue is called frostnip; it is most common in the cheeks, earlobes, fingers, and toes.  It is characterized by numbness, white, waxy appearance, and a hard, rubbery feeling of the skin while the tissue underneath remains soft.  Frostnip is usually reversible with gentle warming; rubbing effected areas should be avoided as this can damage the frozen tissue.
Frostbite
     Freezing that extends through all layers of skin is called superficial frostbite; deep frostbite includes freezing underlying tissue, such as muscle, and can extend into bone.  The extremities – fingers, toes, nose, ears, etc. – are most susceptible to frostbite.  Skin in frostbitten areas is white, with a “wooden” feel, and may develop a bluish hue.  Numbness and stinging are also common symptoms.
     Superficial frostbite is treated similarly to frostnip.  Ice crystals that form in the skin make the tissue susceptible to damage; rubbing or other stress on effected tissue must be avoided.  Treatment of deep frostbite introduces additional risks and is best left to medical professionals whenever possible.  Areas of deep frostbite should not be warmed until the victim is safe from potential refreezing.  Refreezing of frostbitten areas can result in damage and loss of tissue in excess of that caused by the initial frostbite.
     Warming is accomplished in a water bath maintained at 105 – 110 ° F (41 – 43° C).  Dry heat can cause burns and should not be used.  When thawing is complete, the water bath is discontinued and effected areas are wrapped in gauze, separated (i.e. fingers, toes), and immobilized.  Attempting to use rewarmed body parts can cause further damage.
Hypothermia
     A core temperature below one’s normal (diurnal) range is termed hypothermia.  Hypothermia advances from mild to moderate to severe as core temperature drops.  The temperature ranges that characterize each level of severity differ among sources; there is greater agreement on the progression of symptoms.  A summary of this progression and one possible temperature range breakdown are shown in Exhibit 1.

     One possible element of a “field diagnosis” of hypothermia is “the –umbles.”  If observations of a person’s behavior include “stumbles, mumbles, fumbles, and grumbles,” a closer look for other signs of hypothermia is warranted.  This assumes, of course, that these observations represent a deviation from the person’s normal behavior.  Severity of the –umbles typically correlates with that of the hypothermia of which it is symptomatic.
     Significant physiological changes can occur during the earliest stages of hypothermia.  Mild hypothermia can cause vasoconstriction, limiting circulation to the extremities, loss of fine motor skills (“fumbles”) and shivering.  Onset can occur in ambient temperatures as high as 50° F (10° C).
     Fine motor skills continue to degrade in moderate hypothermia; tasks such as zipping a coat can become very difficult or impossible.  Shivering intensifies and can become uncontrollable.  Slurred speech (“mumbles”) and irrational behavior (“grumbles”) also manifest at this stage.
     When hypothermia becomes severe, shivering becomes intermittent, then ceases.  The person loses his/her ability to walk (“stumbles”) and becomes stiff.  Pulse and respiration rates decline and the person loses consciousness; cardiac arrest may be induced.  Severe hypothermia brings a person to the brink of death; emergency medical care is critical to survival.

     Recovery from mild hypothermia is fairly straightforward.  Increasing physical activity increases the metabolic rate of heat generation, offsetting heat loss.  Moving to a warm shelter, removing wet clothing and replacing with additional dry layers, if necessary, may be sufficient to rebound from a mild case of hypothermia.
     The techniques for treating mild hypothermia are also applicable to moderate cases.  However, as a case of hypothermia worsens, the response must be scaled accordingly.  The human body requires fuel to generate heat; carbohydrate-rich foods provide the fastest conversion to energy.  Proteins are converted more slowly, over a longer period.  Fats are also converted slowly over a long period, but more water and energy are consumed in the conversion.  In short, carbohydrates facilitate recovery, while proteins and fats (to a lesser degree, with sufficient hydration) are better for long-term sustenance.
     Warm to hot (but not too hot) drinks are very beneficial.  They can provide immediate heat, an energy source (calories), and hydration simultaneously.  Alcohol and caffeine should be avoided because their consumption causes counterproductive physiological responses.
     If increased physical activity and warm shelter are insufficient, or unavailable, an external heat source may be needed.  A nearby fire or heater can warm the person and dry his/her clothing before redressing.  Hot water bottles, chemical heat packs, or similar heat source applied to the neck, armpits, and groin effectively warm the core.  Another person can also serve as an external heat source, provided that person is not also experiencing a heat deficit (i.e. s/he is normothermic).
     If the victim is able to drink, s/he should be given warm sugar water.  In severe conditions, the digestive system is incapable of processing solid food; a sugar mixture provides fuel the body needs to generate heat in a form it can process.  A gelatin dessert mix can also be used; the combination of sugar and protein provides fast- and slow-release energy.  Any drink must be dilute for the body to convert it to energy.
     A severe case may require a hypothermia wrap and transport to a medical facility.  Multiple blankets and sleeping bags can be used to create the wrap.  It is imperative that the victim and the wrap remain dry; this may require a wicking layer next to the skin and a waterproof outer layer.
     The heart is the organ most vulnerable to functional disruption in cold conditions.  The combined stress of hypothermia and physical shocks, such as those caused by being moved or carried, can induce cardiac fibrillation.  Performing CPR can also hasten the death it is intended to prevent because of the heart’s hypersensitivity in these conditions.
     “Rescue breathing” is the practice of a normothermic person gently blowing warm air into the victim’s mouth.  The pre-warmed air reduces respirational heat loss; it may also add oxygen needed to metabolize sugar and generate heat.
     To reiterate, severe hypothermia is a life-threatening condition; any missteps during treatment can hasten death.  Seek emergency medical care.
Afterdrop
     Afterdrop is a dangerous drop in core temperature that occurs while rewarming a victim of hypothermia.  It is caused by vasodilation in the extremities allowing very cold blood to return to the core.  Blood stagnated in the arms and legs also becomes acetic; upon recirculation, it may cause the sensitive heart to become arrhythmic.
     Prevention of afterdrop requires a carefully-controlled warming process; only the core should be warmed.  Exposure to extreme heat, such as moving into a hot room, can cause superficial warming of the extremities that initiates vasodilation and recirculation before the core is warm enough to tolerate it.
Death
     Recovery from a core temperature below 77° F (25° C) would be miraculous; death is a near-certainty.  A victim may lose consciousness and exhibit pulse and respiratory rates so low that they are difficult to detect, causing a premature declaration of death.  Entering such a state is the body’s final attempt at survival, reducing energy expenditure to its absolute minimum.

Other Cold-Related Effects
     Commonly-experienced effects of exposure to cold, such as numbness, redness, and stinging upon rewarming occur with such regularity that little attention is paid to them.  Many do not consider these to be cold injuries; it is only upon increased severity that they take note.  This is unfortunate, as proper attention to all occurrences of potential injury is key to the prevention of severe injury.
     Manual dexterity and flexibility are reduced with exposure to temperatures as high as 59° F (15° C).  A one-hour exposure at 45° F (7° C) can cause as much as a 20% loss of dexterity.  Continued exposure can reduce blood flow to the fingers to as little as 2% of normal.  Mild shivering exacerbates the loss of fine motor skill.  When shivering becomes severe, or violent, even coarse motor control becomes extremely difficult. The impact on task performance is intuitive; however, the potential for increased accident rates may be less so.
     Cognitive ability and psychomotor function, such as the ability to skillfully operate tools, also decline in cold environments.  The connection to safety may be more obvious here, though the extent of the decline may be surprising.  When core body temperature drops by as little as 7° F (4° C), a person loses the ability to make life-saving (“fight or flight”) decisions.  Core temperature may drop another 10° F (6° C) or more before the person loses consciousness; in the interim, a person can put him/herself in much greater peril with poor decision-making.
     Maximum vasoconstriction (i.e. minimum blood flow) in the extremities occurs at approximately 59° F (15° C).  If further cooled, to approximately 50° F (10° C), alternating periods of vasodilation and vasoconstriction begin.  This cold-induced vasodilation (CIVD) occurs in 5 – 10-minute cycles, providing some protection against cold injury via periodic rewarming of the extremities.  This phenomenon has been observed, but not fully explained; it remains unclear when this vascular behavior ceases and precisely why it occurs.
     Cold exposure can also modify the body’s response to heat upon rewarming.  During cold exposure, the sweating mechanism is disabled; upon rewarming, an increased threshold temperature and latent period delay the onset of sweating during subsequent heat exposure.  This shifting response reinforces the need for an acclimatization period, particularly for those exposed to both high- and low-temperature environments.

     Preparation for exposure and recovery between exposures is equally important in hot and cold environments.  The following cold-recovery guidelines are similar to those presented in Part 3 for heat exposure:

• Spend the “downtime” in a warm, dry environment.
• Tailor diet to the energy needs of the cold environment – proteins and fats for extended energy release and carbohydrates for quicker conversion to energy.
• Replenish fluids.  Converting food to life-saving heat requires water.  Fluid loss is easily overlooked in a cold environment, but hydration must be given proper attention.  Alcoholic and caffeinated beverages should be avoided.
• Use the time to verify that plenty of warm, dry layers are available for the next work shift, including hats, boots, and gloves.  Other gear, such as goggles, should also be checked to ensure proper protection will be provided.
• Get plenty of rest.  Working in cold conditions is energy-intensive; the body needs time to recover and “rebuild.”

 
Risk Factors
     Several factors affect the risk one assumes when exposing him/herself to cold conditions.  A person’s overall condition, or general health, provides the baseline assessment.  In general, the better one’s physical fitness, the greater his/her resistance to cold injury.
     Specific health issues of concern include heart conditions and previous cardiac events (i.e. heart attacks).  As the heart is most susceptible to disruption by cold, any “imperfection” can become a significant liability as conditions degrade.
     Previous exposures, particularly overexposures, can reduce a person’s tolerance for cold conditions.  Previously-damaged tissue is susceptible to re-injury; each occurrence tends to be worse than the previous.
     Perhaps the greatest risk in cold conditions is overconfidence.  Overconfidence increases exposure unnecessarily when one convinces him/herself that additional precautions are excessive.  There are several workplace factors in which one might be overconfident, including:

• One’s personal fortitude (i.e. ability to maintain efficacy in cold conditions; ego).
• Performance capability of selected clothing and gear.
• Stability of conditions during the planned work period (e.g. temperature, wind).
• Stability of schedule (i.e. ability to complete tasks in allotted time).

 
     As a person’s condition deteriorates – hypothermia deepens – s/he becomes less aware of his/her condition and endangerment.  This makes coworkers that are aware of signs of cold injury in others critical to a team’s safety.  Individuals’ susceptibility to conditions varies widely; these are not always known in advance.  The ability to recognize changes in a person’s behavior or physical condition and respond accordingly is paramount.


     For additional guidance or assistance with Safety, Health, and Environmental (SHE) issues, or other Operations challenges, feel free to leave a comment, contact JayWink Solutions, or schedule an appointment.

     For a directory of “Thermal Work Environments” entries on “The Third Degree,” see Part 1:  An Introduction to Biometeorology and Job Design (17May2023).

References
[Link] Human Factors in Technology.  Edward Bennett, James Degan, Joseph Spiegel (eds).  McGraw-Hill Book Company, Inc., 1963.
[Link] Kodak's Ergonomic Design for People at Work.  The Eastman Kodak Company (ed).  John Wiley & Sons, Inc., 2004.
[Link] “Hypothermia and Cold Weather Injuries.”  Rick Curtis.  Princeton University Outdoor Action Program, 1995.
[Link] “Fire and Ice: Protecting Workers in Extreme Temperatures.”  Donald J. Garvey.  Professional Safety; September 2017.
[Link] “Cold Weather Exposure.”  Agricultural Safety and Health Program, Ohio State University Extension; May 17, 2019.
[Link] “Cold Stress – Cold Related Illnesses.”  National Institute for Occupational Safety and Health; June 6, 2018.
[Link] “Effect of body temperature on cold induced vasodilation.”  Andreas D. Flouris, David A. Westwood, Igor B. Mekjavic, and Stephen S. Cheung.  European Journal of Applied Physiology; June 21, 2008.
[Link] “Influence of thermal balance on cold-induced vasodilation.”  Andreas D. Flouris and Stephen S. Cheung.  Journal of Applied Physiology; April 2009.

Jody W. Phelps, MSc, PMP®, MBA
Principal Consultant
JayWink Solutions, LLC
jody@jaywink.com