Information Bulletin Number 0911314

Winter Weather Hazard Reminder
Wind Chill, Frost Bite, and Hypothermia are three hazards to firefighters during winter/cold weather operations.
Now is the time to prepare equipment, apparatus, and personnel for cold weather operations.
Wind chill is the apparent temperature felt on exposed skin due to wind. The degree of this phenomenon depends
on both air temperature and wind speed. The wind chill temperature (often popularly called the wind chill factor) is
always lower than the air temperature for values where the wind chill formula is valid.
The human body loses heat largely by evaporative cooling and convection. The rate of heat loss by a surface
depends on the wind speed above that surface: the faster the wind speed, the more readily the surface cools. For
inanimate objects, the effect of wind chill is to reduce any warmer objects to the ambient temperature more quickly.
For most biological organisms, the physiological response is to maintain surface temperature in an acceptable range
so as to avoid adverse effects. Thus, the attempt to maintain a given surface temperature in an environment of faster
heat loss results in both the perception of lower temperatures and an actual greater heat loss increasing the risk to
adverse effects such as frostbite and death.
Frostbite (congelatio in medical terminology) is the medical condition wherein localized damage is caused to skin
and other tissues due to extreme cold. Frostbite is most likely to happen in body parts farthest from the heart and
those with large exposed areas. The initial stages of frostbite are sometimes called “frostnip”.
At or below 0O C (32O F), blood vessels close to the skin start to constrict. The same response may also be a result
of exposure to high winds. This constriction helps to preserve core body temperature. In extreme cold, or when the
body is exposed to cold for long periods, this protective strategy can reduce blood flow in some areas of the body
to dangerously low levels. This lack of blood leads to the eventual freezing and death of skin tissue in the affected
areas. There are three stages of frostbite. Each of these stages have varying degrees of pain.
Stage 1
First degree frostbite causes skin to appear yellow or white. There may also be slight burning sensations. This stage
of frostbite is relatively mild and can be reversed by the gradual warming of the affected area.
Stage 2
Second degree frostbite develops after continued exposure. This stage is characterized by the disappearance of pain
and the reddening and swelling of the skin. Treatment in this stage may result in blisters and it may also peel the
Stage 3
Third degree frostbite results in waxy and hard skin. It is at this stage that the skin dies and edema may occur as a
result of the lack of blood.
If third degree frostbite is not treated immediately then the damage and the frostbite becomes permanent, nerve
damage will occur due to oxygen deprivation. Frostbitten areas will turn discolored, purplish at first, and soon turn
black. After a while nerve damage becomes so great that feeling is lost in the frostbitten areas. Blisters will also
occur. If feeling is lost in the damaged area, checking it for cuts and breaks in the skin is vital. Infected open skin
can lead to gangrene and amputation may be needed.Hypothermia is a condition in which an organism's temperature drops below that required for normal metabolism
and body functions. In warm-blooded animals, core body temperature is maintained near a constant level through
biologic homeostasis or thermoregulation. However, when the body is exposed to cold, its internal mechanisms
may be unable to replenish the heat that is being lost to the organism's surroundings.
Hypothermia may be divided into accidental hypothermia, which will be discussed here, and therapeutic
Normal body temperature in humans is 36.5O – 37.5O C, (97.7O F – 99.5O F). A number of skin conditions may
be associated with hypothermia or may occur with normal body temperature. Symptoms of hypothermia may be
divided into the three stages of severity.
Stage 1
Body temperature drops by 1O – 2O C (1.8O – 3.6O F) below normal temperature (down to 35O – 37O C or 95O – 98.6O
F). Mild to strong shivering occurs. The victim is unable to perform complex tasks with the hands; the hands
become numb. Blood vessels in the outer extremities constrict, lessening heat loss to the outside air. Breathing
becomes quick and shallow. Goose bumps form, raising body hair on end in an attempt to create an insulating layer
of air around the body (which is of limited use in humans due to lack of sufficient hair, but useful in other species).
Victim may feel sick to their stomach, and very tired. Often, a person will experience a warm sensation, as if they
have recovered, but they are in fact heading into Stage 2. Another test to see if the person is entering Stage 2 is
if they are unable to touch their thumb with their little finger, this is the first stage of muscles not working. They
might start to have trouble seeing.
Stage 2
Body temperature drops by 2O – 4O C (3.8O – 7.6O F) below normal temperature (33O – 35O C or 91O – 94.8O F).
Shivering becomes more violent. Muscle mis-coordination becomes apparent. Movements are slow and labored,
accompanied by a stumbling pace and mild confusion, although the victim may appear alert. Surface blood vessels
contract further as the body focuses its remaining resources on keeping the vital organs warm. The victim becomes
pale. Lips, ears, fingers and toes may become blue.
Stage 3
Body temperature drops below approximately 32O C (89.6O F). Shivering usually stops. Difficulty speaking,
sluggish thinking, and amnesia start to appear; inability to use hands and stumbling is also usually present.
Cellular metabolic processes shut down. Below 30O C (86.0O F), the exposed skin becomes blue and puffy, muscle
coordination becomes very poor, walking becomes almost impossible, and the victim exhibits incoherent/irrational
behavior including terminal burrowing or even a stupor. Pulse and respiration rates decrease significantly, but fast
heart rates (ventricular tachycardia, atrial fibrillation) can occur. Major organs fail. Clinical death occurs. Because
of decreased cellular activity in Stage 3 hypothermia, the body will actually take longer to undergo brain death.