Page 133 - 2020 JSOM Winter

electrolyte content of the intracellular and extracellular fluids. to provide versatility in different environmental conditions.
Experimental studies indicate this freezing temperature var- The layers in the ECWCS are shown in Figure 5. Layer 1 is the
ies somewhat among individuals but is generally near –4°C lightweight base layer (Undershirt and Drawers) worn next
to –5°C (23°F). 92,95,96 Wet skin cools faster than dry skin and to the skin and constructed of polyester designed to remove
reaches a lower temperature, 96,97 so wetness should be avoided excess moisture from the skin. Layer 2 is the Midweight Shirt
as much as possible. A small change in skin temperature (from and Drawers worn with the base layer or alone (to serve as
–5°C to –8°C [23°F–18°F]) is estimated to increase frostbite a base layer) and is composed of polyester fleece. Layer 3 is
risk from 5% to 95%. Risk of frostbite appears to be minor the Fleece Cold Weather Jacket worn underneath shell layers
92
if the air temperature is >–10°C (>14°F) but increases substan- (described below) or as an outer layer on moderately cool
tially at –25°C (–13°F). 92,95,98 days. Layer 4 is the Wind Cold Weather Jacket, which is a
minimal outer layer made of lightweight, wind-resistant, and
At a given temperature, an individual subjectively feels colder water- repellent materials designed to assist in the removal of
when exposed to wind. This is because the wind more quickly moisture from the skin. Layer 5 is the Soft Shell Cold Weather
removes heat from exposed skin, resulting in more rapid skin Jacket and Trousers, an outer layer designed for use in mod-
cooling. The Wind Chill Chart (Figure 4) describes the effect erate to cold weather and composed of stretchable and water
of wind on the loss of body heat. It also estimates the risk of resistant materials. Layer 6 is the Extreme Cold/Wet Weather
frostbite as a function of temperature and wind. The tempera- Jacket and Trousers, which provide a waterproof barrier, com-
tures shown in the Wind Chill Chart are those resulting from posed of Gore-Tex for use in prolonged hard rain and cold/
heat loss from the skin in a wide range of decreasing tempera- wet conditions. Level 7 is the Extreme Cold Weather Parka/
tures and increasing wind speeds. The chart was developed Trousers designed for use in static operations in extreme cold
from a model of the head, examining heat transfer under vari- conditions and is highly water and wind resistant, with high
ous temperature and wind conditions. Parts of the model were loft insulation. 10
refined from data on individuals walking on a treadmill in var-
ious environmental conditions. 99,100 The model assumes a per- For foot protection in cold weather, the current military boots
son is walking in an open field with a bare face. Wind speeds are the Intermediate Cold/Wet Boot (Figure 6A) and the Ex-
obtained from weather reports do not account for additional treme Cold Vapor Barrier Boot (Figure 6B). The Intermediate
wind from activities such as running or skiing. The wind chill Cold/Wet Boot is waterproof and consists of leather with a
apparent temperature (i.e., a number on the chart) is always removable Gore-Tex liner. It is designed for military person-
lower than the air temperature if there is wind. The decrease nel operating in cold and wet environments with temperatures
in apparent temperature becomes less over high wind speeds, between 20°C and –10°C (between 68°F and 14°F). 105,106 The
whereas air temperature effects are relatively linear. The Wind Extreme Cold Vapor Boot was originally developed during
Chill Chart generally corresponds with experimental data 91,92 the Korean War and has since been modified several times.
and is an improvement on previous wind chill models, but The outer and inner layers are composed of wool insulation
101
could be further improved. 102 sandwiched between two layers of seamless rubber. The boot
Clothing
Because clothing protects skin exposed to subfreezing tem- FIGURE 5 The seven layers of the Extended Cold Weather Clothing
peratures by sequestering body heat, 103,104 clothing is consid- System, Generation III.
ered the primary deterrent to cold injury. For the military,
the Generation III Extended Cold Weather Clothing System
(ECWCS) is a flexible clothing ensemble designed to provide
insulation to reduce heat loss and provide ventilation for mois-
ture to escape. The Generation III ECWCS has 12 pieces and
10
7 layers designed for temperatures ranging from 4°C to –51°C
(40°F to –60°F). It is compatible with other military systems
(e.g., body armor, load-bearing equipment). Each part of the
system can be used alone or with other parts of the ensemble
Source: https://ciehub.info/clothing/CW/ECWCS/GEN3.html
FIGURE 4 Wind Chill Apparent Temperature chart.
FIGURE 6 Boot and Hand Protection Systems for Cold Weather.
Intermediate Cold/Wet Boot (A), Extreme Cold Vapor Barrier Boot
(B), Generation 3 Modular Glove System (C).
(A) (B) (C)

Sources: (A) https://ciehub.info/clothing/footwear/BootsICW.html. (B)
https://upload.wikimedia.org/wikipedia/commons/8/8d/White_Bata
_Bunny_Boots.jpg (photo credit Randall McNair). (C) https://soldier
systems.net/2016/01/29/post-shot-show-wrapup-outdoor-research
Source: https://www.weather.gov/safety/cold-wind-chill-chart -glove-system/. The one glove system is shown twice.

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