5. Textiles and clothing for protection from cold

Clothing plays the role of a passive insulation layer between the body and the environment. Both the textile layers and the layers of air between them in the clothing system perform this role. The adjustment of the passive insulation to the changing thermal conditions of the environment may be done through adding or removing textile layers. However, sometimes this is not possible to be done, or the textile layers, necessary to guarantee the body thermal comfort, are so thick that the movements will be limited.

The textiles, in the form of layers in clothing garments, headwear, handwear, or footwear, are of crucial importance for the survival and healthy work of people in the cold environment, as they are the only barrier between the human body and the cold. The ability of the textile layers to transfer the moisture from the body to the environment, while keeping the heat next to the skin and preventing the moisture transfer from the surroundings to the body, determines to a great extent the thermophysiological comfort of humans in the cold [19].

The main aim of the cold protective clothing is to entrap as much as possible air between the textile layers; at the same time, the clothing ensemble has to be as light as possible to assure proper activities and unimpeded movements. Therefore, different layers of clothing have to be worn—besides the better air encapsulation, the number of layers gives the advantage to remove one or more of them if the body's heat production increases (during activity) or the solar radiation heats the body in outdoor conditions.

At least three layers of loose-fitting clothing must be worn [19]. The inner, closer to the body layer, is usually made of polyester, polypropylene, or other synthetic fibers that draw moisture away from the skin and keep it dry. The middle layer is the most insulating one; it is made of down, wool, nonwoven webs of synthetic fibers, etc. and holds the body's heat. The outer layer aims to protect the body from wind and precipitation; it is made of "breathable" waterproof fabrics that allow some ventilation (like Gore-Tex® or polyamide). This layer may frequently need to be resistant to oil, fire, chemicals, or abrasion.

are classified in [18]: primary, secondary, and clinically induced (the last being out of the scope

Primary hypothermia is diagnosed when the thermoregulation responses to the cold exist, but they cannot beat the symptoms of hypothermia. Primary hypothermia can appear in any cold environment, when the low temperature overwhelms the body thermoregulatory system.

Secondary hypothermia differs from the primary as the thermoregulatory reactions of the body are impaired [17]. Symptoms of hypothermia appear again, but their severity is not proportional to the cold induced. Secondary hypothermia is due to additional peculiarities of human physical or physiological state: fatigue, illness, or injury. Insufficient clothing insulation, poor nutrition or dehydration, and short sleep are also reasons for secondary hypothermia. The onset of the secondary hypothermia can hardly be predicted, being dependent of several factors: clothing insulation, metabolic rate, body size, nutrition status, hydration, and

Cold allergy, expressed in red and itchy pimples on uncovered skin, exposed to cold air, is also frequently observed as cold injury. It usually disappears after warming. Severe cases of cold allergy are associated with fever, seizures, fever, increment of the heartbeat, and swelling of the

Clothing plays the role of a passive insulation layer between the body and the environment. Both the textile layers and the layers of air between them in the clothing system perform this role. The adjustment of the passive insulation to the changing thermal conditions of the environment may be done through adding or removing textile layers. However, sometimes this is not possible to be done, or the textile layers, necessary to guarantee the body thermal

The textiles, in the form of layers in clothing garments, headwear, handwear, or footwear, are of crucial importance for the survival and healthy work of people in the cold environment, as they are the only barrier between the human body and the cold. The ability of the textile layers to transfer the moisture from the body to the environment, while keeping the heat next to the skin and preventing the moisture transfer from the surroundings to the body, determines to a

The main aim of the cold protective clothing is to entrap as much as possible air between the textile layers; at the same time, the clothing ensemble has to be as light as possible to assure proper activities and unimpeded movements. Therefore, different layers of clothing have to be worn—besides the better air encapsulation, the number of layers gives the advantage to remove one or more of them if the body's heat production increases (during activity) or the

At least three layers of loose-fitting clothing must be worn [19]. The inner, closer to the body layer, is usually made of polyester, polypropylene, or other synthetic fibers that draw moisture

of cold-related injuries).

230 Occupational Health

torso or extremities.

physiological and even psychological status.

5. Textiles and clothing for protection from cold

comfort, are so thick that the movements will be limited.

solar radiation heats the body in outdoor conditions.

great extent the thermophysiological comfort of humans in the cold [19].

The fitting of each clothing item in the ensemble is extremely important. The tight clothes may press the body tissues and decrease the blood flow, thus increasing the risk of cold injuries. Any additional layer(s) of clothing should be large enough not to compress the inner layers and decrease the insulation properties due to omitting the insulating air layer between two consecutive textile layers.

Proper selection of footwear and handwear has to be done to prevent hands and feet from the cold. Mittens are better solution than gloves, as four of the fingers share one and the same "thermal environment," but gloves are needed if hands' finer movements are a key to the performed activity in the cold. The head has to be obligatory protected by a cap, as the heat may be seriously lost through the head to the environment when the other parts of the body are well insulated. The chicks and nose may be protected from the cold by a mask. In case of obligatory use of a helmet, a wool knit cap has to be worn beneath.

Insulated boots with removable felt liners are mostly used for protection in the cold. The liners and the socks are an important part of the footwear. They have to be kept dry so as to perform best in the cold environment as an insulating layer. Inner socks, made of polypropylene that helps keep feet dry and warm, are best to be combined with outer thicker socks. The boot liners have to be removed daily for complete drying. The socks have to be also changed if they get wet or damp.

The incorporation of phase change materials (PCMs) in textiles for cold protection adds an active thermal insulation effect to the passive insulation, performed by the clothing [20]. PCMs, applied in cold protective clothing, are mostly paraffins from different types, used in several combinations. PCMs can experience the process of change from one state to another, i.e., from liquid to solid and back; thus, they are able to absorb, store, or discharge heat, following the fluctuations of the surrounding temperature.

The paraffin is incorporated into microcapsules, which has to prevent its dissolution during the liquid phase. Outlast Technologies Inc., which is the leader in production of textiles with PCMs, have developed Thermocules microcapsules, which can be added in the structure of the synthetic fibers in the wet spinning process or can be incorporated in flat textiles (woven, knitted, and nonwoven) as part of surface coating.

Classical cold wear garments can hardly ensure the thermophysiological comfort of the body in extreme cold conditions for a long time. The application of PCMs can help the process of avoiding thermal stress and hypothermia during occupational activities, thus increasing the work performance under high thermal stress.

Heated clothing and accessories are an alternative of the classical cold protective clothing. They are wired and use different technologies to provide warmth to the body parts that need it with priority: core body, feet, and hands.

The Microwire™ technology of Gerbing uses thin conductive filaments, coated with Teflon® that form heating panels, incorporated in clothing items. In jackets the panels are placed on the back, chests, and collar. Incorporated in gloves, the Microwire™ heating panels help sustaining the finer finger movements as long as possible. PrimaLoft® microfibers are applied for insulation, while a breathable Aquatex™ membrane assures the waterproofness of the system. A heating panel can reach a temperature of 57–63°C, powered by a 7 V or 12 V batteries. Wireless heat control can be used, adjusted by a smart phone application.

Smart clothing for cold protection is also produced by Venture Heat: heated jackets, gloves, and basic line shirts and pants. The incorporated heating panels are made of micro-alloy fibers, powered by rechargeable Li-ion battery. Highly breathable layers from inside and breathable waterproof layers from outside the heating panels are used to assure the body's thermophysiological comfort. The heated gloves of Venture Heat can protect the hands from the cold up to 5 h, depending on the temperature, the applied heating power, and the body's activity. A heated scarf, which can be added to the clothing ensemble, may ensure cold protection from 2 to 6 h. The scarf is made of 100% polyester fibers, and a carbon fiber heating source is placed at the center of the scarf (in the neck zone).

The heated jacket of Flexwarm uses a technology that can add to the efforts of the body's thermoregulatory system to ensure the thermophysiological comfort. Two types of sensors are placed in the jacket: sensors that control the temperature of the body and sensors that detect the temperature of the surrounding air. The heating panels can be separately controlled. Their thickness is equal to the thickness of cotton fabrics, 0.5 mm. The wearer can control the temperature of the panels, which can be heated up to 65°C. Due to the flexible Flexwarm® heating layer, the cold protection garments can be rolled or twisted without a risk of damage.
