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Cold Weather Survival |
| Chapter
2 - Individual Clothing and Equipment
Section 1. GENERAL
2-1.
Basis of Issue
a. As used in this manual, individual clothing and equipment
are those items issued or sold to a soldier for his personal use, and include
certain organizational equipment utilized by the individual. The basis of issue
of cold weather clothing and equipment may be found in TA 50-901. Mandatory items
of personal clothing are listed in AR 700–8400–1.
b. The U.S. Army, through
continuous research and development, endeavors to maintain the best clothing and
equipment in the world. When properly fitted and properly utilized this clothing
will provide adequate protection from the elements and will enable trained, well
disciplined troops to carry out year-round field operations under cold weather
conditions, wherever they may be encountered.
c. To utilize fully the protection
afforded by the present standard cold weather clothing and equipment, it is necessary
to understand the principle involved and the correct function of each item. This
chapter covers basic principles and provides general guidance on the purpose and
use of cold weather clothing and equipment.
2-2. Commander's Responsibilities
a. Many factors will influence the commander’s decision as to what items of clothing
and equipment his troops should wear or carry. These include the weather, mission
at hand, actual duties to be performed, overall physical condition of individuals
and their degree of proficiency. If a movement is involved he must consider the
distance to be traveled, the method of travel, and how the troops will be fed
en route, if applicable. If the movement is on foot, he must bear in mind that
under normal winter conditions, 65 to 70 pounds is the maximum weight a man can
normally wear and carry and still be effective on reaching his destination.
b.
The weight of individual clothing and equipment is covered in appendix E. Commanders
should give particular attention to additional organizational equipment required
for a given operation. Some of the more common items are also listed in appendix
E. Since the individual soldier’s combat load in cold
weather operations exceeds
that of a temperate climate load by more than 20 pounds, these organizational
items (such as binoculars, compasses, radios and batteries, pioneer tools, crew
served weapons, etc. ) become major considerations and must be included at all
levels of planning.
c. In addition to the individual combat load, another 45
to 55 pounds of clothing and equipment is required for the protection and comfort
of each individual under conditions of extreme cold. Transportation must be provided
for this additional load whenever possible.
d. The commander must take positive
action to insure that a balance exists between what the individual is wearing
and what he is required to carry in the way of equipment. He must also insure
that troops dress as lightly as possible consistent with the weather in order
to reduce the danger of excessive perspiring and subsequent chilling. The complete
cold-wet or cold-dry uniform for the applicable environmental conditions must
be readily available. A large proportion of cold weather casualties results from
too few clothes being available to individuals when a severe change in the weather
occurs. Because of the differences in individual metabolism, commanders must not
be arbitrary in delineating strict uniform requirements, but must allow some
personal
choice of undergarments. 2-3.
Cold Weather Conditions
The use of cold weather clothing is affected by
two types of weather conditions: wet and dry. These conditions are amplified by
humidity coupled with temperature and wind velocity; high humidity (wet conditions),
low humidity (dry conditions).
a. Wet Conditions. Cold-wet conditions
occur when temperatures are near freezing and variations in day and night temperatures
cause alternate freezing and thawing. This freezing and thawing is often accompanied
by rain and wet snow, causing the ground to become muddy and slushy. During these
periods troops should wear clothing which consists of a water-repellent, wind-resistant
outer layer and inner layers with sufficient insulation to provide
ample protection
in moderately cold weather (above 14°F.).
b. Dry Conditions. Cold-dry
conditions occur when average temperatures are lower than 14°F. The ground
is usually frozen and snow is usually dry, in the form of fine crystals. Strong
winds cause low temperatures to seem colder and increase the need for protection
of the entire body (windchill) (fig. F-1). During these periods, troops should
have available additional insulating layers of clothing. This is particularly
true when entering static situations form a period of strenuous exercise. Section
II. CLOTHING
2-4. Purpose of Clothing
a. Protection of Body
Against Climatic Factors.
(1) If the body is to operate efficiently, it
must maintain a normal temperature. The body attempts to adjust itself to the
variable external conditions it encounters. These attempts are evidenced by the
need for more food to produce additional heat during colder weather, by perspiration
to increase removal of heat during hot weather, and by the gradual darkening of
the skin as protection against extended exposure to the rays of the sun.
(2)
Proper clothing, correctly worn, will assist the body in its adjustment to extreme
climatic conditions. The clothing does this by holding in the body heat, thereby
insulating the body against the cold outside air. The problem of protection becomes
acute when freezing temperatures are involved. To understand this problem requires
a knowledge of the methods by which the body resists the effects of climatic changes.
b.
Balancing Heat Production and Heat Loss. The body loses heat at variable rates.
This heat may flow from the body at a rate equal to or greater than the rate at
which it is produced. When heat loss exceeds heat production, the body uses up
the heat stored in its tissues, causing a rapid drop in body temperature. Excessive
heat loss can result in shivering. Shivering uses body energy to produce heat
which at least partially offsets the heat loss and slows the rate at which the
body temperature will drop. Shivering is an important warning to start action
to rewarm, either by adding more clothing, by exercising, by eating some food,
or by entering a warm shelter, or by any combination of these actions. In freezing
temperatures it is as important to remove and adjust clothing to prevent excessive
overheating as it is to add clothing to prevent heat loss. 2-5.
Principles of Clothing Design
Certain principles are involved in the design
of adequate cold weather clothing to control the loss of heat from the body, to
facilitate proper ventilation, and to protect the body.
a. Insulation.
Any material that resists the transmittance of heat is known as an insulating
material. Dry air is an excellent insulator. Woolen cloth contains thousands of
tiny pockets within its fibers. These air pockets trap the air warmed by the body
and hold it close to the skin. The principle of trapping air within the fibers
or layers of clothing provides the most efficient method of insulating the body
against heat loss. Fur provides warmth in the same way; warm, still air is trapped
in the hair and is kept close to the body.
b. Layer Principle.
(1)
Several layers of medium-weight clothing provide more warmth than one heavy garment,
even if the single heavy garment is as thick as the combined layers. The effect
results from the several thick layers of air which are trapped between the layers
of clothing, rather than one or two layers of large volume. These layers, as well
as the minute air pockets within the fibers, are warmed by the body heat.
(2)
The layers of clothing are of different design. The winter underwear is most porous
and has many air pockets. These air pockets trap and hold the air warmed by the
body. To keep the cold outside air from reaching the still inside air that has
been warmed by the body, the outer garments are made of windproof, water-repellent
fabric.
(3)The layer principle allows maximum freedom of action and permits
rapid adjustment of clothing through a wide range of temperatures and activities.
The addition or removal of layers of clothing allows the body to maintain proper
body heat balance.
c. Ventilation. Perspiration fills the airspaces
of the clothing with moisture laden air and reduces their insulating qualities.
As perspiration evaporates, it cools the body just as water evaporating from a
wet canteen cover cools the water in the canteen. To combat these effects, cold
weather clothing is designed so that the neck, waist, hip, sleeve, and ankle fastenings
can be opened or closed to provide ventilation. To control the amount of circulation,
the
body should be regarded as a house and the openings in the clothing as windows
of the house. Cool air enters next to the body through the openings in the clothing
just as cool air comes into a house when the windows are open. If the windows
are opened at opposite ends of a room, cross-draft ventilation results. In the
same way, if clothing is opened at the waist and neck, there is a circulation
of fresh air. If this gives too much ventilation, only the neck of the garment
should be opened to allow warm air to escape without permitting complete circulation. 2-6.
Winter Use of Clothing
a. Basic Principles of Keeping Warm.
(1) Keep
clothing Clean.
(2)Avoid Overheating.
(3)Wear Clothing Loose and in layers.
(4)
Keep clothing Dry
(5) Remember C-O-L-D to keep warm in winter.
b. Application
of Basic Principles.
(1) Keep clothing clean. This is always true
from a standpoint of sanitation and comfort: in winter, in addition to these considerations,
it is necessary for maximum warmth. If clothes are matted with dirt and grease,
much of their insulation property is destroyed; the air pockets in the clothes
are crushed or filled up and the heat can escape from the body more readily. Underwear
requires the closest attention because it will become soiled sooner. If available,
light cotton underwear may be worn beneath winter underwear to absorb body oils
and lengthen the time interval between necessary washings of these more difficult
to clean and dry garments. Winter underwear (Army issue is a 50/50 cotton/wool
blend) and cushion sole socks (Army issue socks are 50 percent wool, 30 percent
nylon, 20 percent cotton) should be washed in lukewarm water, if available. Hot
water should not be used because it is injurious to the wool fibers and causes
shrinkage. Synthetic detergents are more soluble than soap in cool water and also
prevent hard-water scum, and are therefore
recommended, if available. When
outer clothing gets dirty it should be washed with soap and water. All the soap
or detergent must be rinsed out of the clothes, since any left in the clothing
will lessen the water-shedding quality of the clothing. In addition to destroying
much of the normal insulation, grease will make the clothing more flammable. All
outer garments of the Cold Weather Clothing System are washable and have laundry
instruction labels attached. If washing is not possible for clothing that would
normally be washed with soap and water, dry rubbing and airing will rid them of
some dirt and
accumulated body oils.
(2) Avoid overheating. In cold
climates, overheating should be avoided whenever possible. Overheating causes
perspiration which in turn, causes clothing to become damp. This dampness will
lessen the insulating quality of the clothing. In addition, as the perspiration
evaporates it will cool the body even more. When indoors, a minimum of clothing
should be worn and the shelter should not be overheated. Outdoors, if the temperature
rises suddenly or if hard work is being performed, clothing should be adjusted
accordingly. This can be done by ventilating (by partially opening parka or jacket)
or by removing an inner layer of clothing, or by removing heavy mittens or by
throwing back parka hood or changing to lighter head cover. The head and hands,
being richly supplied with blood, act as efficient heat dissipators when overheated.
In cold temperature it is better to be slightly chilly than to be excessively
warm. This promotes maximum effectiveness of the body heat production processes.
(3)
Wear clothing loose and in layers. Clothing and footgear that are too tight
restrict blood circulation and invite cold injury. Wearing of more socks than
is correct for the type of footgear being worn might cause the boot to fit too
tightly. Similarly, a field jacket which fits snugly over a wool shirt would be
too tight when a liner is also worn under the jacket. If the outer garment fits
tightly, putting additional layers under it will restrict circulation. Additionally,
tight garments lessen the volume of trapped air layers and thereby reduce the
insulation and ventilation available.
(4) Keep clothing dry.
(a)
Under winter conditions, moisture will soak into clothing from two directions-inside
and outside. Dry snow and frost that collect on the uniform will be melted by
the heat radiated by the body.
(b) Outer clothing is water-repellent and will
shed most of the water collected from melting snow and frost. The surest way to
keep dry, however, is to prevent snow from collecting. Before entering heated
shelters, snow should be brushed or shaken from uniforms; it should not be rubbed
off, because this will work it into the fabric.
(c) In spite of all precautions,
there will be times when getting wet cannot be prevented and the drying of clothing
may become a major problem. On the march, damp mittens and socks may be hung on
the pack. Occasionally in freezing temperatures, wind and sun will help dry this
clothing. Damp socks or mittens may be placed, unfolded near the body, where the
body heat will dry them. In bivouac, damp clothing may be hung inside the tent
near the top, using drying lines or improvised drying racks. It may even by necessary
to dry each item, piece by piece, by holding before an open fire. Clothing and
footwear should not be dried to near a heat source. Leather articles, especially
boots, must be dried slowly. If boots cannot be dried by any other method,
it
is recommended that they be placed between the sleeping bag and liner. Heat from
the body will aid in drying the leather. 2-7.
Components of Cold Weather Uniforms
The items of clothing below are Standard
A as listed in SB 700-20. It should be borne in mind however that procurement
may or may not have been started on some of the items and upon requisitioning
some Standard B clothing may be issued. Although not shown as basic items of the
cold weather uniforms, light cotton underwear may be worn under the winter underwear
(para 2-6 b (l)).
a.
Cold-Wet Uniform. The basic components of the cold-wet uniform are illustrated
in figure 2-1 unless otherwise indicated.
(1) Undershirt Mans. 50 Cotton
50 Wool, Full Sleeve.
(2) Drawers Mens. 50 Cotton 50 Wool, Ankle Length.
(3)
Socks Mens. Wool Cushion Sole, OG 408, Stretch Type.
(4) Suspenders
Trousers. Scissors Back Type.
(5) Trousers Mens. Wool Serge, OG
108.
(6) Shirt Mans. Wool Nylon Flannel, OG 108.
(7) Trousers
Mens. Cotton Nylon, Wind Resistant Sateen, 8.5 oz, OG 107.
(8) Boot
Insulated Cold Weather. Mens Rubber Black (or Boot Combat: Mens Leather Black
8½" high with Overshoe: Rubber Man’s High Cleated 5 Buckle).
(9)
Coat Man. Cotton and Nylon Wind Resistant Sateen, 8.5 oz, OG 107, with integral
hood.
(10) Liner Coat Mens. Nylon Quilted 6.2 oz, OG 106.
(11)
Cap Insulating, Helmet Liner-Helmet. Cotton Nylon Oxford, OG 107.
(12)
Glove Shells. Leather Black with Glove Inserts; Wool and Nylon Knit, OG 208,
or Mitten Shells; Trigger Finger Leather Palm and Thumb with Mitten Inserts; Wool
and Nylon Knit, OG, Trigger Finger, or Mitten Set Arctic; Gauntlet Style Shell
with Leather Palm (fig. 2-5).
(13) Hood Winter. Cotton and Nylon Oxford,
OG 107, with drawcord and fur.
(14) Poncho. Coated Nylon Twill, OG
207 (not illustrated).
b. Cold-Dry Uniform. The basic components of
the cold-dry uniform are illustrated in figure 2-2 unless otherwise indicated.
(1)
Undershirt Mens. 50 Cotton 50 Wool, Full Sleeve.
(2) Drawers Mens.
50 Cotton 50 Wool, Ankle Length.
(3) Socks Mens. Wool Cushion Sole,
OG 408, Stretch Type.
(4) Suspenders Trousers. Scissors Back Type.
(5)
Shirt Mans. Wool Nylon Flannel, OG 108.
(6) Trousers Mens. Cotton
Nylon, Wind Resistant Sateen, 8.5 oz, OG 107.
(7) Liner Trousers. Nylon
Quilted, 6.2 oz, OG 106.
(8) Boot Insulated Cold Weather. Mens Rubber
White, w/release valve.
(9) Coat Man. Cotton and Nylon Wind Resistant
Sateen, 8.5 oz, OG 107.
(10) Liner Coat Mans. Nylon Quilted, 6.2 oz,
OG 106.
(11) Parka Mans. Cotton and Nylon Oxford OG 107, w/o hood (not
illustrated),
(12) Liner Parka Mans. Nylon Quilted, 6.2 oz, OG 106 (not
illustrated).
(13) Cap, Insulating, Helmet Liner. Cotton Nylon Oxford,
OG 107.
(14) Hood Winter. Cotton and Nylon Oxford, OG 107, w/drawcord
and fur.
(15) Glove Shells. Leather Black with Glove Inserts; Wool and
Nylon Knit, OG 108, or, Mitten Shells; Trigger Finger Leather Palm and Thumb with
Mitten Inserts; Wool and Nylon Knit, OG, Trigger Finger, or, Mitten Set Arctic;
Gauntlet Style Shell with Leather Palm (fig. 2-5).
(16) Poncho. Coated
Nylon Twill, OG 207 (not illustrated).
(17) Gloves Cloth. Work Type
(not illustrated).
 2-8.
Description and Wearing of the Uniform Components
a. Cold-Wet.
(1)
Inner layer.
(a) Underwear. The underwear is loose fitting and is made
of 50 percent cotton and 50 percent wool. It is constructed so that circulation
and ventilation are not restricted.
(b) Suspenders. The scissors-type
suspenders are worn over the undershirt. The drawers and all succeeding layers
of trousers are supported by the suspenders. The use of suspenders allows the
drawers and trousers to be worn loose at the waist so that neither circulation
nor ventilation is restricted.
(2) Intermediate layer. The intermediate
layer consists of the wool OG shirt and trousers which provide excellent insulation
against the cold. The shirt is worn outside the trousers for better control of
ventilation. The wool trousers and shirt are not designed to be worn as outer
garments under field conditions since they lose their insulating qualities if
they become wet or matted with dirt. When engaged in strenuous activity, care
must be taken so that the wool material will not come in contact with the skin,
thus causing possible irritation and discomfort.
(3) Outer layer.
(a)
Coat. The coat ensemble is made up of a shell and a detachable liner. The
coat has a combination slide, snap and touch-and-close fastener front closure.
The sleeves have adjustable cuffs with a hand shield extension. A lightweight
hood is an integral part of the coat. When not being used the hood is secured
under the collar and is concealed by a slide fastened enclosure. The detachable
liner is made of quilted nylon and is extremely light and warm. The liner has
a collar, open underarms, and buttonhole tabs for attachment to the coat.
(b)
Trousers. The trousers are made of smooth, light, wind resistant sateen. They
have extra closures and adjustments, to provide for ventilation and better fit.
(4)
Headgear.
(a) Cap. The insulating helmet liner cap (fig. 2-3) is close
fitting, visorless, and of helmet style. It has a combined one-piece earflap and
neck protector, and utilizes an overlap touch-and-close fastener. The cap is designed
to be worn under the steel helmet or under the winter hood. When worn as an outer
headpiece, the lower flap portion of the cap may be folded up around the top with
the touch-and-close fasteners crisscrossed in the front (fig. 2-3).
(b)
Hoods. The winter hood (fig. 2-4) is a one-piece covering for the head, face,
and neck. It utilizes touch-and-close fasteners and can be worn over the steel
helmet. A malleable wire inside the fur ruff may be shaped as desired for visibility
or greater protection of the head and face. Unit commanders must enforce “hood
discipline,” especially while men are on sentry duty or on patrols. The winter
hood and the cold weather cap with flaps down will greatly reduce a man’s hearing
capabilities. When the temperature or wind does not require the use of heavier
headgear, the cold weather cap and the lightweight hood should be worn. Hoods
should be removed before the head starts to perspire. Breathing into the winter
hood causes moisture and frost to accumulate and should be avoided as much as
possible. Accumulated frost should be removed frequently.
(5) Handwear.
See c below.
(6) Footwear. See d below.
b.
Cold-Dry.
(1) Inner Layer. Same as cold-wet.
(2) Intermediate Layer.
The wool OG shirt is worn as the basic upper body garment. The wind resistant
sateen trousers with the quilted nylon liner are worn as the basic lower body
garment. In extreme cold weather, the coat with detachable liner, used as an outer
layer in the cold-wet uniform, may be worn as an intermediate layer in cold-dry
conditions.
(3) Outer Layer. Depending on temperature the outer garment
may consist of the coat with detachable liner, the parka, with detachable liner,
or both, The parka is a three-quarter length, unlined coat with adjustable cuffs.
It has a combination slide and snap fastener front fly closure, waist and hem
drawcords and a split lower back. The parka has a detachable quilted nylon liner.
(4)
Headgear. Same as cold-wet.
(5) Handwear. See c below.
(6) Footwear.
See d below.
c. Handwear.
(1) Gloves.
(a) Standard
black leather gloves are worn in mild weather or when work must be done that requires
more freedom of finger movement than can be acquired with heavier handwear. In
colder weather the same gloves are worn with wool inserts (fig. 2-5). Gloves may
be worn with either the cold-wet or
cold-dry uniforms when the weather is not
cold enough to require the use of mittens.
(b) Personnel engaged in
delicate finger operations, such as instrument adjustment may be issued lightweight
cotton work gloves. These gloves allow for finger dexterity, have leather palms,
and prevent the skin from sticking to cold metal. They will provide protection
against cold for only a very short period.
(2) Mittens.
(a)
The trigger finger mitten shells (fig. 2-5), are worn with wool trigger finger
inserts during periods of moderate cold. The mittens may be worn with either the
cold-wet or cold-dry uniform. Figure 2-5 shows the Standard B mitten. The Standard
A item, although identical in outward appearance has had
the trigger finger
loop deleted and is lined on the inside upper surface with lightweight quilted
nylon.
(b) During periods of extreme cold the arctic mitten set is worn
(fig. 2-5). The mitten has a liner, a leather palm, a cheek warmer and a fastener
on the back. A neck strap is attached to both mittens to prevent loss. The neck
strap permits the mittens, when not required for warmth, to be conveniently carried
snapped together behind the back. The arctic mitten set is carried whenever there
is the possibility of the onset of severe cold weather, regardless of the mildness
of the weather when setting out.
(3) Utilization.
(a) The
general rules concerning the use of clothing apply also to handwear—keep it clean,
avoid overheating, wear loose in layers, and keep it dry.
(b) The outer
shells should always be worn with the minimum insulation necessary to provide
protection, thus avoiding perspiration. Inserts should never be worn by themselves
because they wear out quickly and provide little warmth alone. Trigger finger
inserts are designed to fit either hand. Changing them to opposite hands frequently
will insure even wear.
(c) Tight fitting sleeves should be avoided.
They may cut down circulation and cause hands to become cold.
(d) When
handling cold metals, the hands should be covered to prevent cold burns (immediate
freezing of the flesh in contact with cold soaked metals).
(e) To keep
hands warm when wearing mittens, the fingers should be curled (inside the mittens)
against the palm of the hand, thumb underneath the fingers, or flexed inside the
mitten whenever possible to increase the blood circulation. Hands may be exercised
by swinging the arms in a vertical circle. Frostbitten hands can be warmed by
placing them next to the skin under the armpits.
(f) An extra pair of
mitten inserts should be carried.
d. Footwear.
(1) General.
The feet are more vulnerable to cold than are other parts of the body. Cold attacks
feet most often because they get wet easily (both externally and from perspiration)
and because circulation is easily restricted. Footgear is therefore one of the
most important parts of cold weather clothing.
(2) Principles.
(a)
The rule of wearing clothing loose and in layers also applies to footgear. The
layers are made up by the boot itself and by the socks. Socks are worn in graduated
sizes. The instructions pertaining to fitting of footgear, as outlined in TM 10-228,
must be carefully adhered to. If blood circulation is restricted,
the feet
will be cold. Socks, worn too tightly, might easily mean freezing of the feet.
For the same reason: AVOID LACING FOOTGEAR TIGHTLY.
(b) Since the feet
perspire more readily than any other part of the body, the rules about avoiding
overheating and keeping dry are difficult to follow. Footgear is subjected to
becoming wet more often than are other items of equipment. The insulated boots
with release valve (white, cold-dry and black, cold-wet) are designed to contain
perspiration within the interior of the boots. A change of dry socks should be
carried at all times. Whenever the feet get wet, dry as soon as possible and put
on a pair of dry socks. Also, the inside of the boots should be wiped as dry as
possible.
(c) Footgear should be kept clean. Socks should be changed
when they become dirty. Socks and feet should be washed frequently. This washing
will help keep feet and socks in good condition.
(d) The feet should
be exercised. Stamping the feet, double-timings few steps back and forth, and
flexing and wiggling toes inside the boots all require muscular action, produces
heat, and will help keep the feet warm. The feet should be massaged when changing
the socks.
(e) Boots are designed to permit attachment to individual
oversnow equipment (skis and snowshoes). BINDINGS MUST BE ADJUSTED CAREFULLY.
If they
are too tight, the circulation of blood is restricted and feet will
get cold. Improperly adjusted bindings may soon chafe feet or badly wear and tear
the boot.
(3)
Types.
(a) Boot, insulated, cold weather: mens, rubber, black. These
boots (l, fig. 2-6) are particularly useful in snow, slush, mud, and water (cold-wet
conditions), but are not adequate for prolonged wear in temperatures below –20°
F. They are specifically designed for combat personnel who may not shave the opportunity
to frequently change to dry socks. Insulating material is hermetically sealed
into the sides and bottoms of the boots. The insulation takes the place of removable
innersoles and the secondary layer of socks worn in other types of cold weather
boots. Perspiration from the feet and water
spilling over the tops of the boots
cannot reach the insulating material because it is sealed-in and always remains
dry. Moisture from outside sources or from perspiration may make the socks damp;
this dampness is not harmful to the feet, provided they receive proper care such
as frequent drying and massaging. If socks are not changed and feet dried regularly
(at least twice daily) the skin becomes softened and is more readily chaffed or
blistered. These effects are occasionally mistaken for superficial frostbite.
Only one pair of cushion-sole socks are worn with the boots. Additional
socks should not
be worn as the feet may become cramped, resulting in restricted
blood circulation and cold feet.
(b) Boot, insulated, cold weather: mens,
rubber, white, w/release valve. The insulated white boot (2, fig. 2–6 ) is
designed for wear in cold-dry conditions and will protect the feet in temperatures
as low as –60° F. The boots have a seamless inner and outer carcass, sealed
insulation, and an outside air release valve used to compensate for air differentials.
The white boots are worn over one pair of cushion sole socks. The air release
valve provides airborne troops a means of equalizing external and internal air
pressures when undergoing extreme changes in altitude. This valve must remain
closed at all other times to prevent the possibility of introducing any amount
of moisture into the insulation of the boot and rendering it permanently unserviceable.
Continue to Nose and Cheek Protectors and Masks
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