b. Environmental Factors.
(1) Weather. Weather is a major influence in causing cold injury. The rate
of body heat loss is affected by temperature, humidity, precipitation, and wind. Low
temperatures and low relative humidity favor frostbite, whereas higher temperatures
together with moisture are usually associated with trench foot. Wind velocity
accelerates body heat loss under both wet and cold conditions. This windchill effect is
shown in Table 5-1; this effect should be thoroughly understood by all personnel in areas
where cold injury is possible. The equivalent temperature shown on the windchill chart
relates to the cooling effect on exposed skin, primarily face or ears. When considering
host factors in general, personnel should recognize that increasing wind is a significant
factor in body heat loss.
(2) Type of combat action. The incidence of cold injury varies according to
type of combat action. Units in reserve or in rest areas have few cases; on holding
missions or on static defense, exposure is greater and a moderate increase in incidence
is expected; on active defense or offense, marked increases usually occur. Immobility
under fire, prolonged exposure, lack of opportunity to rewarm and change clothing or
carry out personal hygienic measures, fatigue, and state of nutrition may all be involved.
(3) Clothing. In warfare, where exposure to cold may be prolonged,
adequate clothing properly worn is essential to welfare and survival. Clothing for cold
weather combat has been designed to be worn as an assembly for protection of the
head, torso, and extremities. Failure to wear the total assembly and inadequate
supplies of proper sizes of clothing are important factors in cold injury.
(a) Cold weather clothing depends on the layering principle to
conserve body heat. Loose layers of clothing with air space between them, under an
outer wind-resistant and water-resistant garment provide maximum protection. Layers
of clothing may be removed for comfort and efficiency to permit perspiration to escape
when the temperature is higher or during strenuous physical exertion.
(b) Clothing which is wet from perspiration loses much of its insulating
value, and care must be taken to prevent perspiration from accumulating in the clothing.
(c) In all forms of cold injury, prevention of loss of body heat is
important. All articles of clothing must be loose to avoid constriction and tightness.
Clothing must be kept free of grease and dirt.
c. Host Factors.
Age. Within the usual age range of combat personnel, age is not