Indian Journal of Fibre & Textile Research Vol. 22, December 1997, pp. 297-296

Protective clothing for extreme cold region

G N Mathur , Hans Raj & Nishkam Kasturiya

Defence Materials Stores Research & Development Establishment , Kanpur 208 013, India

The advancement in the warfare technology has taken wars and battles to the places till now deemed unfit for normal human life and habitation due to the extreme weather conditions. Cold mountains and Siachin region are examples of such areas . In these areas, temperature goes down to as low as -40°C. In different countries, the range of sub-zero region varies but the period of exposure of the forces to the extreme cold is lesser than that faced by Indian troops. For the people exposed to sub-zero region for a long time at a stretch the requirement of the protective clothing is very critical. This paper discusses, in brief, the human endurance in cold climate, various factors that influence the protection of an individual in a cold environment, the component materials for protective clothing for extreme cold regions, and the development of clothing systems at DMSRDE, Kanpur.

Keywords: Composite multilayered garment, Protective clothing, Thermal insulation

1 Human Endurance in Cold Climate

The individual liking and disliking for cold and warm conditions and climate is very personalized, and so the endurance limit for cold and warm environment may also vary to some extent, but there are certain limits beyond which all normal human beings cannot bear extreme cold. A number of studies have been conducted to quantify these endurance limits so that clothing, equipments, shelters, etc . may be designed accordingly. It has been brought out that the mean skin temperature of human beings who are at rest and are thermally comfortable is approximately 33°C, and metabolic heat generation at this level is 150 watts I . Under cold conditions, body generates more heat by muscular exertion and shivering to balance the temperature difference. The blood supply to skin is reduced to create thermal insulating layer. Further, at the same temperature, the feeling of cold would be more in damp . .-conditions. This is because air being bad conduc'tor of heat, the heat losses would be less in dry air but when some water vapour to the air is added, the convection heat losses are increased. Generally, heat losses are 25 times greater in water than in dry air at the same temperature. To maintain thermal balance and comfort in the water, the water temperature should be around 34°C. The problems and effects of high altitude were raised by India in 1965 in the Commonwealth Conference on Defence Clothings.

Subsequently, a number of studies were taken up to understand and appreciate these effects. The altitude IS associated with lower ambient temperature but USARIEM (U.S. Army Research Institute of Environmental Medicine) studies have shown2 that when subjects were exposed to high altitude in a chamber at the same temperature level as at sea, they felt cold and a fall in skin temperature was noted. This may be attributed to an increased diffusion loss of perspiration at altitude. USARIEM studies3 brought out effects of temperature and wind chill on a neutral human body and indicated that sensation of warmth and cold at wind velocities between 2 mls to 32 mls may be summarized as follows:

32°C 28°C 22°C 16°C lOoC SoC

O°C -SoC

Hot Pleasant Cool Very cool Cold Very cold Bitterly cold Exposed flesh freezes (travel and life in temporary shelters become disagreeable) Exposed area of face freezes within one minute (travel and life in temporary shelters become dangerous) Exposed area of face freezes within y, minute

MATHUR e/ at. : PROTECTIVE CLOTHING FOR EXTREME COLD REGION 293

The effect of cooling power of wind on exposed flesh , expressed as an equivalent temperature (under calm conditions), is shown in Table 1.

The protection of an individual in a cold environment would depend on following main factors4

.6

: (i) Metabolic heat, (ii) Wind chill, (iii) Thermal insulation, (iv) Air permeability, and (v) Moisture vapour transmission.

The survival depends on the balance of heat losses due to (ii)- (v) and heat output due to (i).

1.1 Metabolic Heat

The heat output due to metabolism depends on the body parameters as well as the activity involved. This heat output would be lowest at rest and maximum during hard work. For a normal youth of 18-30 years weighing 70 kg, the heat out­put would be of the order of 60 kcallh during rest or sleeping,100 kcallh during guard duty, 250 kcallh during patrolling and 425 kcallh during hard work. However, the garment system should r be capable of providing protection at the lowest level of activity i.e. sleeping or rest. This should be kept in view while designing protective clothing.

1.2 Wind Chill

Wind chill6.7 depends on the temperature as well

as velocity of the wind. In the cold climate, consideration of wind chill effect IS very

important, because 80% of heat losses are due to wind chilI effect.

Wind chill factor can be derived from Siple Passel formula 7

Ko = (.Jv x 100 + 10.45- v) (33- TA )

where, Ko = Cooling power of the atmosphere In

kcallm 21h, v = Wind velocity in mis, and TA = Air temperature in dc. 33°C is taken as the skin temperature under calm conditions. The significance of wind chill factor may be understood by reviewing its effect on the freezing time of exposed flesh. At a wind chill factor of 1000, an individual would feel very cold and at 1200, bitterly cold. When the wind . chill factor is 1400, the exposed flesh would freeze in 20 min, at wind chill factor of 1800, the exposed flesh would freeze in 10 min and when the wind

chill factor is 2400, exposed flesh freezes in I min only.

1.3 Thermal InsulationS

The protection against cold is dependent on thermal resistance or thermal insulation of the garment or clothing.

The measurement of thermal insulation of a fabric surface is made by measuring heat flow in

Table I--Cooling power of wind on exposed flesh expressed as an equivalent temperature) (under calm conditions)

Estimated Actual thennometer reading

wind speed 50 40 30 20 10 0 -10 -20 -30 -40 -SO - 60 mph

Equivalent temperature (OF)

Calm 50 40 30 20 0 -30 - 50 -60 5 48 37. 27 16 -36 -S7 -68 10 40 28 16 4 -83 -95 15 36 22 9 -5 -45 -99 -122 20 32 18 4 -10 -25 -S3 -67 -96 -110 -124 25 30 16 0 -15 -29 -44 -59 -74 -104 -118 -133 30 28 13 -2 -18 -33 -48 -63 -79 -94 -\09 -125 -140 35 27 II -4 -21 - 35 - 51 -67 -82 - 98 -113 - 129 -145 40 26 10 -6 -21 -37 -S3 -69 -85 -100 -116 -132 - 148

(Wind speeds LITTLE DANGER INCREASING GREAT DANGER greater than 40 (for properly clothed DANGER mph have little person) Danger from

additional Maximum danger of freezing of effect) false sense of security exposed flesh

Trenchfoot and immersion foot may occur at any point on this chart.

294 INDI AN 1. FIBRE TEXT. RES., DECEMBER 1997

unit time from unit area of the surface. The thermal 18

insulation is the ratio of the temperature difference between the two faces of the fabric to the rate of heat flow .

R=(T,-T)/H where T, and Tz are the temperatures of the fabric surfaces; and H, the heat flux through the fabric (flow of heat in unit time from unit area of the surface) .

Air is a good thermal insulator and the insulation of air is defined b-y the equation:

l 4=(Tc-T;JIH where, Tc = Clothing surface temperature, TA = Air temperature, l A = Air insulation , and H = Heat flux through the clothing.

Generally, we see decrease in insulation for wider spaces which may be attributed to development of more convection currents when void becomes wider. The thermal insulation effects between two surfaces (polished or blackened) have been studied and the results have been summarized in Fig. 1. The insul ation achieved with the polished surfaces is 40% higher to that achieved with blackened surfaces. Thus, narrow voids separated by reflecting partitions are an excellent form of thermal insulation . To make an insulating material effective , it should have low compression setlhigh resiliency to maintain the still air entrapped into the material.

1.4 Air Permeabili ty9. 11

The interlacement of yams in a fabric structure is such that a large volume of fabric consists of air space. These air spaces influence a number of important fabric properties such as warmth, protection against wind and rain. In general , a wearer would be more comfortable with a fabric of high air permeability than with a fabric of less air permeability. However, the open structure would enhance the effect of wind chill. The thermal resistance obtained in still air with a fabric of a particular structure would be ineffective even In

cold breeze if the air permeability is high.

1.5 Moisture Vapour Transmission The tTansmission of water through a fabric is a

very critical parameter l2 from comfort point of

l-l.

1·2

~ 10

Z ::l 0 ·8 (:l

00 '6 ,...

0 -2

REFLECTING

BLACKENED

OL-__ ~L-__ ~~ __ ~~ __ ~~ __ ~~ 2-7 52 10 ·2 15·2 20 ·2 25-4

THICKN ESS (m m)

Fig. I- Effect of in sulation with increasing thickness in refl ecting and blackened surfaces

view. In winter, it is possible that water vapour produced by perspiration at the skin can be condensed to the liquid , which may subsequently freeze to ice as the water molecules move towards the cold air at the external surface. If a fabric can not permit sufficiently rapid disposal of water to occur, perspiration related discomfort would be felt. A serious drain of body heat may also be realized because of the diminished thermal resistance of the wet cloth and the tendency of reevaporation of the water to take place . The movement of water can be increased by either increasing water vapour permeability or enhancing the ability of the fabric to transport liquid water to the surface. The ability of water vapour transmission can be increased by increasing pore size whereas liquid transport can be increased by reducing pore size to increase capillary action .

2 Component Materials for Protective Clothing The protective clothing are generally composite

multilayered garments developed in view of various factors mentioned above . Each of the component materials for these composite garments has a specific role to play and so their roles, requirements and expected performance are necessary to be discussed.

2.1 Outer Fabrics The outermost cover for most of the protective

clothing and equipments should create a barrier for wind and provide moisture vapour transmission so that the wearer is comfortable and protected from

MATHUR e/ al. : PROTECTIVE CLOTH I G FOR EXTREME COLD REG ION 295

Table 2---Characteri stics of acrylic woven and knitted pil e fabrics and polyester batting

Type of fabri c Composition Weight per Thickness under Therillal Warillth to unita rea 7 g / C1ll

1 in sul ation we ight factor g/ml pressure, Illill Tog cl ax 1000

Woven acry li c (9 mm) Knitted acrylic (9 mm) Polyester batting

Acryl ic/cotton (67:33) Acrylic/cotton (65:35) 3-6 denier crimped fibre ; 40 mm staple length

wind chill and allied factors. The choice falls on light weight coated fabrics. The coatings act as a wind barrier. After experimentation with different weight, types and classes of coatings, the polyurethane coated nylon fabric has been found to provide the 'wind barrier ' effect with flexibility and lightness of the basic fabric. The Goretex which has a breathable microporous polyurethane coat~ng is also used for special breathable protective clothing.

2.2 Reflective Inner Liner

The studies were made to assess the effect of heat losse~ with different liners. It was observed 13

that a reflective liner like aluminium foil placed at a distance of 8 mm from woollen gabardine showed decrease in heat losses to the extent of 27% . This has laid way for the use of reflective material to improve thermal insulation properties. At present, aluminium foil is becoming popular for such applications . The knitted light weight nylon fabric laminated with aluminium film is used for thermal insulation in the protective clothing.

2.3 Thermal Insulating Materials

The woollen piles and fabrics which are generally useful for other regions are not sufficient to meet the requirements of the extreme cold region . For this purpose, in other countries the down feathers of good quality are successfully used, but the down feathers of Indian birds do not provide the requisite warmth, most probably due to the climatic conditions prevailing in the area. A critical observation 14 of insulatiorilweight ratio shown in Table 2 reveals that this value is much higher for polyester batting and it is very useful for the purpose of insulation in the extreme cold region. Acrylic pile fabric is also very useful due to its good dimensional stability, low rate of creep .

(a) (b) (c)

470 5.8 2.9 6 469 5.3 3 6.4 120 4.5 1.65 13.75

and lower moi sture absorption than that of wool. New advancement of fibre technology has introduced a number of synthetic insulating materials IS. Some of them are Thinsulate, Thintech, Primaloft, Thermoloft,Hydrofil and Goretex .

2.4 Multilayered Clothing

The thermal resi stance of a single layered clothing would depend on the individual and cumulative resistance effect of the layer of textile material , air adjacent to textile material , and the air entrapped between skin and textile layers. When the clothing is made of a multilayered textile material, these effects would get further increased due to the cumulative resistance of textile layers, air entrapped between different textile layers and air entrapped between skin and textile assembly. Thus, the thermal protection provided by a protective clothing having multi layers would be better than that of a single layered clothing.

3 Development of Clothing Systems A number of clothing items for the extreme cold

region have been developed by DMSRDE, Kanpur, based on the parameters discussed above . These clothing items were extensively evaluated by a number of army units deployed in the extreme cold regions . These stores have been accepted for introduction in the army, on the basis of the reports of the trial units . Some of these clothings have been used by the Antarctica expedition teams and the performance of these protective clothings brought laurels to DMSRDE, Kanpur. A brief description of the thermal protective systems of some of these successfully accepted stores, viz. jackets, trousers, caps and gloves, is summarized here to give an overview of practical applications of the facts and theories discussed. All these

296 I DIAN J. FII3RE TEXT RES, DECEMBER 1997

clothing systems for extreme cold weather are based on the multiple layer principle for better thermal protection.

3, I Jackets

These jackets are basically three-layered system. The innermost layer is like a waist coat and is made of acrylic pile fabric. The second layer is an insulating liner consisting of polyester batting and aluminised fabric. The aluminised surface is kept towards the body to prevent heat loss. The outermost layer is a wind cheater made up of polyurethane coated nylon fabric.

3,2 Trousers

These trousers are two-layered clothing. The inner insulating layer itself is multicomponent and multilayered . It consists of one layer of polyester batting and one layer of aluminised fabric sandwiched between two layers of siliconised nylon fabric of different weights. The outer layer

of the trousers is wind cheater made up of polyurethane coated nylon fabric.

3,3 Caps

The outer part of the cap is made up of siliconised and fluorochemical-treated nylon fabric having flame , water and oil repellency. The inner portions coming in contact with the body are lined with acrylic pile fabric.

3.4 Gloves Heat losses involved in the five fingured gloves

are higher due to a number of terminal extremities of fingers coming into play . So, for extreme cold region, three-compartment gloves on the principle of the mitten are more favourable . The three compartments are for (i) thumb, (ii) fore finger and (iii) remaining three fingers . The outer layer of dorsal side of glove is made up of polyurethane­coated nylon . The inner side is made up of soft variety of Napa leather. An inner layer of acrylic pile is used for insulation in these gloves. For further added insulation, polyester batting is used

on the dorsal side.

4 Conclusion Development of protective clothing for extreme

cold regions is a complicated and difficult task and

depends on a number of theories of heat losses and thermal insulation . The choice of materials, design parameters, fibre and fabric properties all play critical roles in the designing o f a protective clothing, However, for an efficient protective system a multilayered garment having different layers of different textile materials should be used .

References I Walters J D, The capability alld vullierability ol lllall ,

Keynote address of plenary session, 12'h Co mmonwealth

Defence Conference on Operation~1 C lothing and Combat Equipment, Ghana, 1978 .

2 Godman R F, Maximal performallce at high altitude, paper presented at the 13 ' h Commonwealth Defence

Conference on Opcrational C lothing and Combat

Equipment , Malaysia, 1981 3 Godman R F, Tolerance limits lor military operations in

hot andlor cold environments, paper presented at the 12'h

Commonwealth Defence Conference on Operational C lothing and Combat Equipment, Ghana, 1978.

4 Hollies N R S, Th e comlort characteristics 01 next to skin garments, including shirts, paper presented at the Shirley International Seminar on Textiles for Comfort , Manchester, England , 1971 .

5 US Army Natwick Labs. Th e comfo rt alld lunction 01 clothing , Technical Report 69-74-CE (1969)

6 Morris J V, Development in cold weatlrer c/o thing, paper presented at the British Occupational Hygiene Society Conference on Occupational Hygiene and the Armed

Forces, 1974. 7 Siple P A & Passel C F, Proc, American PhYSiological

Society (1945). 8 Peirce F T & Rees W H, The transmission of heat through

textile fabrics, J Textlnst, 37 (1946) T181. 9 Booth J E, Principles 01 textile testing, (Heywood Books,

London), 1964.

10 Skinkle J H, Textile testing, (Chemical Publishing Co., New York , USA ), 1954.

II Clayton F H, The measurement of air permeability of fabric, J Text Inst, 26 (1935) T 171.

12 Hollies Norman R S & Goldman Ralph F, Clothing comlort (Ann Arbor Science Publishers Inc., Ann Arbor, Mich . ,USA), 1977.

13 Morris J V, Developments in cold weather clothing, paper presented at the Commonwealth Defence Conference on Operational Clothing and Combat Equipment, India, 1975.

14 Singh R, Bahrani M L & Chatterji G N, Extreme weather clothing, paper presented at the Commonwealth Defence Conference on Operational Clothing and Equipments, Canada, 1989.

15 Adanur . S & Wellington Sears, Handbook of industrial textiles (Technomic Publishing Company Inc., Lancaster, USA), 1995.