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Tuesday, 22 March 2011 20:22

Prevention of Cold Stress in Extreme Outdoor Conditions

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The prevention of the physiopathological effects of exposure to cold must be considered from two points of view: the first concerns the physiopathological effects observed during general exposure to cold (that is, the entire body), and the second concerns those observed during local exposure to cold, mainly affecting the extremities (hands and feet). Preventive measures in this connection aim to reduce the incidence of the two main types of cold stress—accidental hypothermia and frostbite of the extremities. A twofold approach is required: physiological methods (e.g., adequate feeding and hydration, development of adaptational mechanisms) and pharmacological and technological measures (e.g., shelter, clothing). Ultimately all these methods aim to increase tolerance to cold at both the general and local levels. Moreover, it is essential that workers exposed to cold have the information and the understanding of such injury needed to ensure effective prevention.

Physiological Methods for Preventing Cold Injury

Exposure to cold in the human being at rest is accompanied by peripheral vasoconstriction, which limits cutaneous heat loss, and by metabolic heat production (essentially by means of the activity of shivering), which implies the necessity of food intake. The expenditure of energy required by all physical activity in the cold is increased on account of the difficulty of walking in snow or on ice and the frequent need to deal with heavy equipment. Moreover, water loss may be considerable on account of the sweating associated with this physical activity. If this water loss is not compensated for, dehydration may occur, increasing susceptibility to frostbite. The dehydration is often aggravated not only by voluntary restriction of water intake because of the difficulty of taking in adequate fluid (available water may be frozen, or one may have to melt snow) but also by the tendency to avoid adequately frequent micturition (urination), which requires leaving the shelter. The need for water in the cold is difficult to estimate because it depends on the individual’s workload and on the insulation of the clothing. But in any case, fluid intake must be abundant and in the form of hot drinks (5 to 6 l per day in the case of physical activity). Observation of the colour of the urine, which must remain clear, gives a good indication of the course of fluid intake.

As regards caloric intake, it may be assumed that an increase of 25 to 50% in a cold climate, as compared with temperate or hot climates, is necessary. A formula allows the calculation of the caloric intake (in kcal) essential for energy equilibrium in the cold per person and per day: kcal/person per day = 4,151–28.62Ta, where Ta is the ambient temperature in °C (1 kcal = 4.18 joule). Thus, for a Ta of –20ºC, a need for about 4,723 kcal (2.0 x 104 J) must be anticipated. Food intake does not seem to have to be modified qualitatively in order to avoid digestive troubles of the diarrhoea type. For example, the cold weather ration (RCW) of the United States Army consists of 4,568 kcal (1.9 x 104 J), in dehydrated form, per day and per person, and is divided qualitatively as follows: 58% carbohydrate, 11% protein and 31% fat (Edwards, Roberts and Mutter 1992). Dehydrated foods have the advantage of being light and easy to prepare, but they have to be rehydrated before consumption.

As far as possible, meals must be taken hot and divided into breakfast and lunch in normal amounts. A supplement is provided by hot soups, dry biscuits and cereal bars nibbled throughout the day, and by increasing the caloric intake at dinner. This lattermost expedient augments diet-induced thermogenesis and helps the subject to fall asleep. The consumption of alcohol is extremely inadvisable in a cold climate because alcohol induces cutaneous vasodilatation (a source of heat loss) and increases diuresis (a source of water loss), while modifying the sensitivity of the skin and impairing the judgement (which are basic factors involved in recognizing the first signs of cold injury). Excessive consumption of drinks containing caffeine is also harmful because this substance has a peripheral vasoconstrictor effect (increased risk of frostbite) and a diuretic effect.

In addition to adequate food, the development of both general and local adaptational mechanisms can reduce the incidence of cold injury and improve psychological and physical performance by reducing the stress caused by a cold environment. However, it is necessary to define the concepts of adaptation, acclimatization and habituation to cold, the three terms varying in their implications according to the usage of different theorists.

In Eagan’s view (1963), the term adaptation to cold is a generic term. He groups under the concept of adaptation the concepts of genetic adaptation, acclimatization and habituation. Genetic adaptation refers to physiological changes transmitted genetically that favour survival in a hostile environment. Bligh and Johnson (1973) differentiate between genetic adaptation and phenotypic adaptation, defining the concept of adaptation as “changes which reduce the physiological strain produced by a stressful component of the total environment”.

Acclimatization may be defined as functional compensation that is established over a period of several days to several weeks in response either to complex factors of the surroundings such as climatic variations in a natural environment, or to a unique factor in the surroundings, such as in the laboratory (the “artificial acclimatization” or “acclimation” of those writers) (Eagan 1963).

Habituation is the result of a change in physiological responses resulting from a diminution in the responses of the central nervous system to certain stimuli (Eagan 1963). This habituation can be specific or general. Specific habituation is the process involved when a certain part of the body becomes accustomed to a repeated stimulus, while general habituation is that by which the whole body becomes accustomed to a repeated stimulus. Local or general adaptation to cold is generally acquired through habituation.

Both in the laboratory and in natural surroundings, different types of general adaptation to cold have been observed. Hammel (1963) established a classification of these different adaptational types. The metabolic type of adaptation is shown by maintenance of the internal temperature combined with a greater production of metabolic heat, as in the Alacalufs of Tierra del Fuego or the Indians of the Arctic. Adaptation of the insulational type is also shown by maintenance of the internal temperature but with a diminution in the mean cutaneous temperature (aborigines of the tropical coast of Australia). Adaptation of the hypothermal type is shown by a more or less considerable fall in the internal temperature (tribe of the Kalahari Desert, Quechua Indians of Peru). Finally, there is adaptation of mixed isolational and hypothermal type (aborigines of central Australia, Lapps, Amas Korean divers).

In reality, this classification is merely qualitative in character and does not take into account all the components of thermal balance. We have therefore recently proposed a classification that is not only qualitative but also quantitative (see Table 1). Modification in body temperature alone does not necessarily indicate the existence of general adaptation to cold. Indeed, a change in the delay in starting to shiver is a good indication of the sensitivity of the thermoregulatory system. Bittel (1987) has also proposed reduction in the thermal debt as an indicator of adaptation to cold. In addition, this author demonstrated the importance of the caloric intake in the development of adaptational mechanisms. We have confirmed this observation in our laboratory: subjects acclimatized to cold in the laboratory at 1 °C for 1 month in a discontinuous manner developed an adaptation of the hypothermal type (Savourey et al. 1994, 1996). The hypothermia is directly related to the reduction in the percentage of the body’s fat mass. The level of aerobic physical aptitude (VO2max) does not seem to be involved in the development of this type of adaptation to cold (Bittel et al. 1988; Savourey, Vallerand and Bittel 1992). Adaptation of the hypothermal type appears to be the most advantageous because it maintains the energy reserves by delaying the onset of shivering but without the hypothermia’s being dangerous (Bittel et al. 1989). Recent work in the laboratory has shown that it is possible to induce this type of adaptation by subjecting people to intermittent localized immersion of the lower limbs in iced water. Moreover, this type of acclimatization has developed a “polar tri-iodothyronine syndrome” described by Reed and co-workers in 1990 in subjects who had spent long periods in the polar region. This complex syndrome remains imperfectly understood and is evidenced mainly by a diminution in the pool of total tri-iodothyronine both when the environment is thermally neutral and during acute exposure to cold. The relationship between this syndrome and adaptation of the hypo-thermal type has yet to be defined, however (Savourey et al. 1996).

Table 1. General adaptational mechanisms to cold studied during a standard cold test carried out before and after a period of acclimatization.

Measure

Use of measure as indicator
of adaptation

Change in
indicator

Type of adaptation

Rectal
temperature tre(°C)

Difference between tre at the end of the cold test and tre at thermal neutrality after acclimatization

+ or =

normothermal
hypothermal


Mean skin temperature tsk(°C)


‾tsk°C after/‾tsk°C before,
where `tsk is the level of
at the end of the cold test


<1
=1
>1


insulational
iso-insulational
hypoinsulational


Mean
metabolism ‾M (W/m2)


Ratio of ‾M after acclimatization
to ‾M before acclimatization


<1
=
>1


metabolic
isometabolic
hypometabolic

 

Local adaptation of the extremities is well documented (LeBlanc 1975). It has been studied both in native tribes or professional groups naturally exposed to cold in the extremities (Eskimos, Lapps, fishermen on the island of Gaspé, English fish carvers, letter carriers in Quebec) and in subjects artificially adapted in the laboratory. All these studies have shown that this adaptation is evidenced by higher skin temperatures, less pain and earlier paradoxical vasodilatation that occurs at higher skin temperatures, thus permitting the prevention of frostbite. These changes are basically connected with an increase in peripheral skin blood flow and not with local production of heat at the muscular level, as we have recently shown (Savourey, Vallerand and Bittel 1992). Immersion of the extremities several times a day in cold water (5ºC) over several weeks is sufficient to induce the establishment of these local adaptational mechanisms. On the other hand, there are few scientific data on the persistence of these different types of adaptation.

Pharmacological Methods for Preventing Cold Injury

The use of drugs to enhance tolerance to cold has been the subject of a number of studies. General tolerance to cold can be enhanced by favouring thermogenesis with drugs. Indeed, it has been shown in human subjects that the activity of shivering is accompanied notably by an increase in the oxidation of carbohydrates, combined with an increased consumption of muscular glycogen (Martineau and Jacob 1988). Methylxanthinic compounds exert their effects by stimulating the sympathetic system, exactly like cold, thereby increasing the oxidation of carbohydrates. However, Wang, Man and Bel Castro (1987) have shown that theophylline was ineffective in preventing the fall in body temperature in resting human subjects in the cold. On the other hand, the combination of caffeine with ephedrine permits a better maintenance of body temperature under the same conditions (Vallerand, Jacob and Kavanagh 1989), while the ingestion of caffeine alone modifies neither the body temperature nor the metabolic response (Kenneth et al. 1990). The pharmacological prevention of the effects of cold at the general level is still a matter for research. At the local level, few studies have been carried out on the pharmacological prevention of frostbite. Using an animal model for frostbite, a certain number of drugs were tested. Platelet anti-aggregants, corticoids and also various other substances had a protective effect provided that they were administered before the rewarming period. To our knowledge, no study has been carried out in humans on this subject.

Technical Methods for PreventingCold Injury

These methods are a basic element in the prevention of cold injury, and without their use human beings would be incapable of living in cold climatic zones. The construction of shelters, the use of a source of heat and also the use of clothing permit people to live in very cold regions by creating a favourable ambient microclimate. However, the advantages provided by civilization are sometimes not available (in the case of civil and military expeditions, shipwrecked persons, injured persons, vagrants, victims of avalanches, etc.). These groups are therefore particularly liable to cold injury.

Precautions for Work in the Cold

The problem of conditioning for work in the cold relates mainly to people who are not accustomed to work in the cold and/or who come from temperate climatic zones. Information on injury that can be caused by cold is of basic importance, but it is also necessary to acquire information about a certain number of types of behaviour too. Every worker in a cold zone must be familiar with the first signs of injury, especially local injury (skin colour, pain). Behaviour as regards clothing is vital: several layers of clothing permit the wearer to adjust the insulation given by clothing to current levels of energy expenditure and external stress. Wet garments (rain, sweat) must be dried. Every attention must be given to the protection of the hands and feet (no tight bandages, attention to adequate covering, timely changing of socks—say twice or three times a day—because of sweating). Direct contact with all cold metallic objects must be avoided (risk of immediate frostbite). The clothing must be guaranteed against cold and tested before any exposure to cold. Feeding rules should be remembered (with attention to caloric intake and hydration needs). Abuse of alcohol, caffeine and nicotine must be forbidden. Accessory equipment (shelter, tents, sleeping bags) must be checked. Condensation in tents and sleeping bags must be removed in order to avoid ice formation. Workers must not blow into their gloves to warm them or this will also cause the formation of ice. Finally, recommendations should be made for improving physical fitness. Indeed, a good level of aerobic physical fitness allows greater thermogenesis in severe cold (Bittel et al. 1988) but also ensures better physical endurance, a favourable factor because of the extra energy loss from physical activity in the cold.

Middle-aged persons must be kept under careful surveillance because they are more susceptible to cold injury than younger people on account of their more limited vascular response. Excessive fatigue and a sedentary occupation increase the risk of injury. Persons with certain medical conditions (cold urticaria, Raynaud’s syndrome, angina pectoris, prior frostbite) must avoid exposure to intense cold. Certain additional advice may be useful: protect exposed skin against solar radiation, protect the lips with special creams and protect the eyes with sunglasses against ultraviolet radiation.

When a problem does occur, workers in a cold zone must keep calm, must not separate themselves from the group, and must maintain their body heat by digging holes and huddling together. Careful attention must be paid to the provision of food and means of calling for help (radio, distress rockets, signal mirrors, etc.). Where there is a risk of immersion in cold water, lifeboats must be provided as well as equipment that is watertight and gives good thermal insulation. In case of shipwreck without a lifeboat, the individual must try to limit heat loss to the maximum by hanging on to floating materials, curling up and swimming in moderation with the chest out of the water if possible, because the convection created by swimming considerably increases heat loss. Drinking sea-water is harmful because of its high salt level.

Modification of Tasks in the Cold

In a cold zone, work tasks are considerably modified. The weight of the clothing, the carrying of loads (tents, food, etc.) and the need to traverse difficult terrain increase the energy expended by physical activity. Moreover, movement, coordination and manual dexterity are hindered by clothing. The field of vision is often reduced by the wearing of sunglasses. Further, perception of the background is altered and reduced to 6 m when the temperature of dry air is below –18ºC or when there is a wind. Visibility may be nil in a snowfall or in fog. The presence of gloves makes difficult certain tasks requiring fine work. Because of condensation, tools are often coated with ice, and grasping them with bare hands carries a certain risk of frostbite. The physical structure of clothing is altered in extreme cold, and the ice that may form as a result of freezing combined with condensation often blocks zip-fasteners. Finally, fuels must be protected against freezing by the use of antifreeze.

Thus, for the optimal performance of tasks in a cold climate there must be several layers of clothing; adequate protection of the extremities; measures against condensation in clothing, on tools and in tents; and regular warming in a heated shelter. Work tasks must be undertaken as a sequence of simple tasks, if possible carried out by two work teams, one working while the other is warming itself. Inactivity in the cold must be avoided, as must solitary work, away from used paths. A competent person may be designated to be responsible for protection and accident prevention.

In conclusion, it appears that a good knowledge of cold injury, a knowledge of the surroundings, good preparation (physical fitness, feeding, induction of adaptational mechanisms), appropriate clothing and suitable distribution of tasks can prevent cold injury. Where injury does occur, the worst can be avoided by means of rapid assistance and immediate treatment.

Protective Clothing: Waterproof Garments

Wearing waterproof garments has the object of protecting against the consequences of accidental immersion and therefore concerns not only all workers likely to suffer such accidents (sailors, air pilots) but also those working in cold water (professional divers). Table 2, extracted from the Oceanographic Atlas of the North American Ocean, shows that even in the western Mediterranean the water temperature rarely exceeds 15ºC. Under conditions of immersion, the survival time for a clothed individual with a lifebelt but without anti-immersion equipment has been estimated at 1.5 hours in the Baltic and 6 hours in the Mediterranean in January, whereas in August it is 12 hours in the Baltic and is limited only by exhaustion in the Mediterranean. Wearing protective equipment is therefore a necessity for workers at sea, particularly those liable to be immersed without immediate assistance.

Table 2. Monthly and annual mean of the number of days when water temperature is below 15 °C.

Month

Western Baltic

German Gulf

Atlantic Ocean
(off Brest)

Western Mediterranean

January

31

31

31

31

February

28

28

28

28

March

31

31

31

31

April

30

30

30

26 to 30

May

31

31

31

8

June

25

25

25

sometimes

July

4

6

sometimes

sometimes

August

4

sometimes

sometimes

0

September

19

3

sometimes

sometimes

October

31

22

20

2

November

30

30

30

30

December

31

31

31

31

Total

295

268

257

187

 

The difficulties of producing such equipment are complex, because account has to be taken of multiple, often conflicting, requirements. These constraints include: (1) the fact that the thermal protection must be effective in both air and water without impeding evaporation of sweat (2) the need to keep the subject at the surface of the water and (3) the tasks to be carried out. The equipment must furthermore be designed in accordance with the risk involved. This requires exact definition of the anticipated needs: thermal environment (temperature of water, air, wind), time before help arrives, and presence or absence of a lifeboat, for example. The insulation characteristics of the clothing depend on the materials used, the contours of the body, the compressibility of the protective fabric (which determines the thickness of the layer of air imprisoned in the clothing on account of the pressure exerted by the water), and the humidity that may be present in the clothing. The presence of humidity in this type of clothing depends mainly on how watertight it is. Evaluation of such equipment must take into account the effectiveness of the thermal protection provided not only in the water but also in cold air, and involve estimates of both probable survival time in terms of the water and air temperatures, and the anticipated thermal stress and the possible mechanical hindrance of the clothing (Boutelier 1979). Finally, tests of watertightness carried out on a moving subject will allow possible deficiencies in this respect to be detected. Ultimately, anti-immersion equipment must meet three requirements:

  • It must provide effective thermal protection in both water and air.
  • It must be comfortable.
  • It must be neither too restrictive nor too heavy.

 

To meet these requirements, two principles have been adopted: either to use a material that is not watertight but maintains its insulating properties in the water (as is the case of so-called “wet” suiting) or to ensure total watertightness with materials that are in addition insulating (“dry” suiting). At present, the principle of the wet garment is being applied less and less, especially in aviation. During the last decade, the International Maritime Organization has recommended the use of an anti-immersion or survival suit meeting the criteria of the International Convention for the safety of human life at sea (SOLAS) adopted in 1974. These criteria concern in particular insulation, minimum infiltration of water into the suit, the size of the suit, ergonomics, compatibility with aids for floating, and testing procedures. However, the application of these criteria poses a certain number of problems (notably, those to do with the definition of the tests to be applied).

Although they have been known for a very long time, since the Eskimos used sealskin or seal intestines sewn together, anti- immersion suits are difficult to perfect and the criteria for standardization will probably be reviewed in future years.

 

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Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides