Abstract
BACKGROUND:
Exposure to severe cold thermal environment (SCE) is a significant risk factor in the frozen food industry, influencing health and safety of the employees.
OBJECTIVE:
The aim of this work is to present the level of knowledge on the influence of SCE on core and skin temperatures.
METHODS:
The review has been conducted using appropriated keywords and expressions, by searching 21 electronic databases and references of the included articles. Only research articles with healthy subjects and considering exposure to SCE conditions (– 5°C or lower) were considered.
RESULTS:
Thirteen articles were included in the systematic review which met the research objective and were in accordance with the inclusion and exclusion criteria. All the included studies measured core or skin temperatures.
CONCLUSIONS:
The main findings of this review indicate that working in SCE is and will remain an added risk factor. Further studies should be conducted in laboratory and industrial severe cold thermal environments on acclimatized and non-acclimatized subjects, in order to evaluate core and skin temperature variations and its recovery periods.
Background
Despite an overall trend toward increasing global temperatures, climate models forecast more variable weather, which can result in important cold-related health consequences for humans. Increases in winter weather variability have been associated with excess morbidity and mortality across various populations and geographic locations [1]. Exposure to cold environment is also a significant risk factor in industrial activities, present in outdoor during the winter season and indoor present in all seasons [2].
Cold exposure in outdoor activities is present in occupations such as marine, army, agriculture, forestry, mining, factory work, construction work [3], among winter sport athletic disciplines [4] and related occupations. Outdoor exposure to cold is of particular interest for regions in high latitude environments where winter seasons last for several months (for example Finland with winter lasting for 3–7 months [5]. Indoor exposure is mostly related to working activities in the fresh food industry with temperatures from 0°C to 10°C and frozen goods at temperatures below – 20°C. Indoor exposure to cold is of concern for all regions all year.
For outdoor work, climatic conditions vary and include changes in temperature, wind and precipitation which complicate appropriate cold protection [6]. For indoor work, on the other hand, the climatic conditions are constant and predictable, which facilitates effective cold risk management.
The structure of the labor market is constantly undergoing change, away from fresh and home-grown towards chilled and frozen food, and its future trend is shown clearly through the development in recent years [7].
Cold work involves several adverse health effects that are observed both in outdoor and indoor work. Many of these adverse outcomes may be further aggravated in persons having a chronic disease [6].
Severe cold thermal environment reduces skin body temperature (Tsk) and therefore physical working performance, with decreased muscle performance, maximal grip frequency and grip strength, hand and finger dexterity, maximal voluntary contraction, and increased muscle fatigue [8]. In cold, musculoskeletal symptoms are common [9–14], which might in the future lead to work-related pathology [6]. For example a study by Taylor, Penzkofer, Kluth and Strasser [15], found that order-picking work in the cold leads to frequent complaints, especially in the upper part of the body. Repeated, prolonged hyperpnoea with cold dry air represents a significant environmental stress to the proximal and distal airways, leading to the development of respiratory symptoms, airway hyper-responsiveness and injury, and inflammation and remodeling of the airway [4].
The different types of cold adaptations are related to the intensity of the cold stress and to individual factors such as body fat, level of physical fitness and diet. The hypothermic general cold adaptation seems the most beneficial for surviving in the cold [16, 17] but an interest in the development of general cold adaptation of workers in the cold is questionable since occupational activities can be organized to avoid cold disturbances (shelter, clothes, heat sources, time sharing). On the other hand cold adaptations of the extremities are beneficial for cold jobs workers since this adaptation is easy to develop and it improves manual dexterity and limits pain by developing the cold induced vasodilatation [18].
Workers with less years of activity seem to be more satisfied with the cold thermal ambient than veterans with more than 10 years of activity [19]. In addition, the results highlight that the average feeling of cold and the occurrence of metabolic and other health problems are slightly higher among women. The subjective survey shows that the food distribution sector is characterized by a young population, mainly women with a short-length professional career. An analysis by gender has shown statistically significant results in terms of both higher feeling of cold and less tolerance to cold among women [19].
When the human body is exposed to cold, the initial response is to preserve heat by reducing heat loss. The skin blood flow, especially in extremities is reduced by vasoconstriction [20], which leads to increased systolic and diastolic blood pressure, lowered heart rate and body temperature in extremities [21]. It is well documented that there is an increase mortality related to acute myocardial infarction (AMI) during the cold season [22–28]. Nevertheless, cardiovascular diseases can be reduced by good management program of risk factors at work [29, 30]. The effects of occupational exposure to cold on human health is also well documented and summarized [6] into three main categories:
Cold-related symptoms and complaints: Respiratory related (increased excretion of mucus, shortness of breath, wheezing and cough); Cardiovascular diseases related (chest pain, arrhythmias, shortness of breath); Circulatory related (colour changes in digits, pain in cold, numbness and tickling); Musculoskeletal related (pain, stiffness, swelling, restriction of movements, paresthesia, muscle weakness); Dermatological related (itching, eruption of skin, pale skin, erythema, edema); Cold-related illnesses and diseases: Respiratory related diseases (asthma, Chronic obstructive pulmonary disease (COPD) and Rhinorrhea); Cardiovascular diseases related (coronary and other heart diseases, myocardial infarction and cerebral vascular incidents); Circulatory related (Raynaud’s phenomenon and hand-arm vibration syndrome); Muscular related (carpal tunnel syndrome, tension neck syndrome, tenosynovitis, peritendonitis); Dermatological related (cold urticaria, pernio, psoriasis and atopic dermatitis); Cold injuries and cold associated injuries: Freezing injuries (frostbite); Non-freezing injuries (trench foot and hypothermia); Cold associated injuries (slips, trips and falls, other injuries).
Cold related symptoms and complains, illnesses and diseases as cold injuries and cold associated injuries could be managed more effectively.
Objective
The aim of this work is to present the level of knowledge on the influence of severe cold thermal environment on core and skin temperatures.
Methods
Searching strategy
The academic and clinic PRISMA Statement for Reporting Systematic Reviews and Meta-Analyses was used in creating and modeling this article [31], which is originally part of a doctoral dissertation [32]. References were managed using the Mendeley 1.15.3.
For searching purposes, the following keywords were defined: “cold human performance”, “cold human effect”, “cold human influence” and “cold human fatigue”. After keywords were defined, the electronic databases were searched by title, without using quotation marks on keywords, in order to allow a different order of words in the title. Thorough databases search was conducted in engineering (“Compendex”, “Inspec”, “IEEE Xplore” and “ScienceDirect (eJournals)”), health (“MEDLINE (EBSCO)”, “PsycArticles”, “PubMed”, “BioMed Central Journals”, “nature.com” and “Science Magazine”) and multidisciplinary area (“Current Contents”, “Web of Science”, “SCOPUS”, “Informaworld (Taylor and Francis)”, “SpringerLink”, “Directory of Open Acces Journals (DOAJ)”, “Emerald Fulltext”, “Oxford Journals”, “SAGE Journals Online”, “Wiley Online Library” and “Cambridge Journals Online”). In total, 21 databases were searched thoroughly by title, using same keywords.
All articles that were connected with the topic were screened by abstract according to the exclusion and inclusion criteria, and if connected with the systematic review objective, they were downloaded.
Keywords of chosen articles were also screened, and afterwards some of them selected for a new search thorough all the 21 previously mentioned databases, by using new keywords-expressions: “cold temperature” and “cold exposure” crossing with keywords: “injury”, “illnesses”, “vasoconstriction”, “skin temperature”, “core temperature”, “heart rate”, “psychomotor performance”, “musculoskeletal”, “cardiovascular”, “respiratory”, “dexterity”, “metabolic pressure”, “blood flow”, “handgrip”, “body temperature”, “thermography”, “blood pressure” and “accidents”.
References of the included articles were also screened and if relevant included in this systematic review, even if published before the year 2000.
Exclusion criteria
During the Meta search, the articles were excluded if published before the year 2000. The same exclusion criterion was repeated through the search of databases in engineering, health and multidisciplinary areas. Articles were considered only if published in English. The articles were excluded if not conducting experiments on humans, if conducting experiment in cold water, ice or any other type of environment except for cold air exposure.
Inclusion criteria
The articles were included if they were research articles considering exposure to severe cold environment (air temperatures of – 5°C or lower) with constant air temperature throughout the trial time, measured skin and/or core temperature (with the exclusion of articles which only give the temperature of a part of the body like fingers and/or face), considering normal cold protective clothing (not heating vests); and if all body was exposed to cold (not just hands and/or face).
Selection of studies: summary of studies in order of level of evidence, with extracted data.
The identification process resulted with 398 articles published after the year 2000 in English language. By screening references of included articles, additional 3197 articles were found to be related to exposure to cold. Therefore, the total number of found articles was 3595. After excluding 1865 repeated articles, only 1730 articles were left to screen. By screening article titles, abstracts or being unreachable, additional 1225 articles were excluded. In total, 505 articles were screened in full text versions. Of these, 187 were excluded for not being a research article, but a review, questionnaire, report, cross-sectional study, abstract or other. Exclusion was made if articles considered exposing volunteers to cold water, ice or any other type except for cold air temperatures, which resulted with an exclusion of 151 articles. By excluding 119 articles which considered exposure to air temperatures of – 5°C or higher, 48 articles were included for the final thorough screen.
After a thorough screen, 10 articles were excluded due to conducting research on patients with a history of cold intolerance, being hypertensive, with heart or respiratory diseases and 1 article due to researching the influence of touching cold materials instead of cold air exposure. Three more articles were excluded due to conducting a cold therapy. Finally, 13 articles were included in this systematic review, which is illustrated in the Fig. 1. From those 13 articles, 2 were the same study but discussing different parameters. Therefore, in further tables, only 12 studies were shown (one integrating those 2 articles). Included articles were published between 1998 and 2013. Main results of this systematic review are shown in the (Tables 1, 2 and appendix Tables 3, 4 and 5).
In the included articles, 8 conducted the experiments just on male volunteers [33–40], 3 of them conducted on both genders [41–43], while 2 just on female volunteers [7, 44].
The physical characteristics of the volunteers in the selected studies
The physical characteristics of the volunteers in the selected studies
*M = males, *F = females, EC = Ethical committee approval, IC = Informed consent; **calculated BMI from the height and weight measurement results enclosed in the articles.
Type of working activity, meals and other measurements or requirements in the selected studies
Most of the articles gave the information on volunteer physical characteristics, BMI was given by 5 articles [7, 44], weight and height through which the BMI was calculated by 8 articles [33, 43].
In 3 articles [38, 43] it was assessed if volunteers were cigarette smokers. The medical control was conducted in one article [33]. Medicine taking was considered by one article [42]. The separation between tests was considered in 5 articles [34, 43]. Preconditioning time and air temperature was considered in 8 articles [7, 44], all of them considering comfort temperatures from 18 to 25°C, having 40% relative humidity on 25°C and 50% relative humidity on 20°C. Five of them used 20 minutes for the acclimatization period [7, 44]. Four of the included articles considered sitting [34, 42], four walking [35, 43], one cycling [33] and four order picking or loading type of working activity [7, 44].
The experimental conditions in the selected studies were thoroughly illustrated in the appendix Table 4. The most measured parameters were the skin temperature, recorded in 10 articles [33–42], and Tcore, also included in 10 articles [7, 44], and the heart rate in 7 articles [7, 44] and blood pressure in 4 articles [34, 42].
Metabolism/oxygen consumption was recorded in 6 articles [33, 44] and thermal sensation in 8 articles [33–35, 42]. In 6 of the included articles some other types of measurements were conducted [7, 44]. Type of working activity, meals and other measurements or requirements in the selected studies were thoroughly illustrated in the (Table 2). In total 8 articles considered the air movement velocity. Clothing insulations factors and clothes used in the selected studies were thoroughly illustrated in the appendix Table 5.
Several parameters influence the human response to severe cold thermal environment. Beyond the thermal environment conditions (air temperature, relative humidity and air movement velocity), there is the length of exposure, time of the day (morning/afternoon/night), type of activity (lighter or heavier exercise), physical characteristics of the human body (gender, age, height, weight, body fat), sleeping hours, consumption of alcohol, coffee, tea, to be a cigarette smoker, physical exertion previous to the exposure, the food and drinks consumption, illness history, medication currently taking, clothing insulation, acclimatization and other.
Blood pressure and heart rate
The blood pressure increases in all included studies, which is thoroughly illustrated in the appendix Table 4. One of the factors influencing this increase (both systolic and diastolic) is the air velocity [38]. It was also found that the average diastolic blood pressure is higher during the night compared with afternoon, while there was no change in the systolic blood pressure [34]. The heart rate was found to be increasing in 4 articles [7, 44] conducting order picking and walking activities, and decreasing in 2 articles [38, 42] conducting sitting and walking activities, illustrated in appendix Table 4. Strong effects on the sympathetic nervous system and its cardiovascular effect on organs were found with: cold exposure on face and with inhalation of cold air. Forehead cooling induces a stronger increase in muscle sympathetic nerve activity but it decreases heart rate. Thus, activation of muscle sympathetic outflow most likely coincides with parasympathetic activation of the cardiac autonomic nervous system [45]. Compared with cold preconditioning, comfort (thermo-neutral) temperature preconditioning result in higher increase of diastolic blood pressure during exposure to cold wind [38]. The protection of the head from cold was found to be an easy way to reduce the sympathetically mediated surge of blood pressure in young adults. Systolic and diastolic blood pressures increased more pronouncedly in normotensive individuals when a head protection (hat) was not used during cold exposure. Wearing hats also promoted faster recovery of forehead skin temperature and blood pressure during the recovery period [42].
Skin temperature
The mean skin temperature decreased with increasing exposure duration, increasing wind speed and decreasing the environmental temperature which is shown in appendix Tables 3 and 4. It started decreasing when the experiments started and continued decreasing until the experiments were completed. In Mäkinen (2001) experiment the decrease was highest after 60 min of exposure to – 10.0°C, with an air movement velocity of 5.0 m/s, decreasing the mean skin temperature to 26.4±0.3°C [35]. In the experiments with multiple cycles of exposure to cold, with recovery at room temperature, the mean skin temperature increased rapidly between the re-warming and the new period of exposure to cold, which ranged up to 3°C. No difference was found in its change from the beginning to the end of the experiment between the afternoon and night exposures [34].
However, peripheral skin temperature at night was found to be higher than that in the afternoon. So, the subjects were less likely to feel cold or pain sensation in the periphery at night, leading to an increased risk of both hypothermia and accidents for those who work in night period [34].
One of the included articles concluded that an optimization should be made in severe cold stores [7]. In the same direction four articles [7, 44] concluded that proper spacing and timing of work-rest periods were important for the optimization of the work in cold environments. One of them [36] found that an interval of 20 min at approximately +20°C during breaks was not sufficient to ensure a complete recovery of the skin temperature for all individuals. Therefore, warming-up breaks above 20 min at 20°C were suggested for subjects working in cold stores at – 24°C for more than 80 minutes [36]. This was in accordance with a previous research [15], which showed that after an exposure to – 24°C, a warming-up break of 20 min was not enough for the subjects to stop the cold sensation in some body parts. An appropriated work-load seems to be an effective way of maintaining the mean body temperature and the temperature of extremities in a cold environment [37, 46]. In addition, metabolic heat production should be maintained by at least a moderate level of physical activity over time as well as tasks planned in order to minimize the exposure of bared parts [47]. It is known that the thermal resistance is higher in active individuals [48]. It was also found that current protective clothing used at severe cold temperatures lead to a reduction of body and skin temperatures, especially in the extremities, and that gloves and boots should be improved [7, 49] in order to maintain adequate performance and comfort during long exposures.
As the extremities are found to be one of the main concerns in maintaining performance at low temperatures, some studies focused on that particular problem [33, 40]. In one of this studies [35] eight males were submitted for 1 hour at comfort environmental conditions (20°C, 0.2 m/s). No great difference between the toe (28.5±1.2°C) and foot (30.8±0.8°C) skin temperature was found. However, when they were submitted at severe cold environmental conditions (– 10°C, 0.2 m/s), the toe skin temperature (20.8±1.1°C) decreased much more compared with the foot (28.7±1.2°C) skin temperature [35]. Same reaction was found to be present in fingers compared with hand skin temperature, where, even being so close body parts, the finger temperature decreased from 29.7±0.5°C to 12.9±1.0°C while the hand skin temperature decreased much less, from 32.1±0.3°C to 23.8±0.6°C. Finger temperature was found to be an important indicator of hand and finger dexterity, leading to severely impaired manual performance when below 20°C [33] or as concluded by another research, below 14°C [40]. Nonetheless, two of the included articles concluded that manual dexterity tasks were not correlated with the mean body temperatures [37, 40]. The loading work was not found to increase the finger skin temperature, but the opposite, cooling and therefore a reduction in manual dexterity, while the mean body temperature increased, making the subjects feel less cold [37].
The Wind Chill Equivalent Temperature (WCET) were found to be a good indicator for manual performance decrease in combination with exposure duration for the WCET range of 1 to – 34°C and exposure time of up to one hour [40]. The WCET index might be used for evaluations in different industries with severe cold environments, where a reduced manual dexterity may decrease work performance and productivity, and increase the risk of accidents [37].
The limit criteria for extremity cooling should be introduced in further prediction models, in order to make the assessment of cold stress more complete and improve manual performance [39]. Indirectly, torso heating was found to be an effective way for maintaining toes and fingers temperature around 22–25°C for 3 h at a air temperature of – 25°C [48, 50–52] and at – 15°C [53]. Indirect heating was considered as a superior method of maintaining dexterity in the cold where the toes and deep body are kept warm, and tasks could be done comfortably barehanded. The primary drawback to indirect hand heating is a greater heater power requirement. As the toes, finger and hand temperatures where maintained high, the dexterity was better as concluded by all the mentioned articles.
Nose skin temperature was significantly higher in exercising subjects when compared to resting subjects, even though there was no significant difference in face temperature (excluding the nose) between conditions. Therefore, this finding suggests that acral regions of the face, such as the nose, are more sensitive to changes in the thermal state of the body, and hence will stay warmer compared with other parts of the face during exercise in cold [43]. Facial pain was reported when facial skin temperature decreased down to 0°C, reported after 30 minutes exposure to – 10°C on wind speed 1–5 m/s [38] after the preconditioning period. The face temperature increased when the environmental temperature increased, however when wind speed increased, the percentage of subjects showing a facial cold-induced vasodilatation decreased.
Wetting the skin during 10°C exposure significantly decreased the mean facial skin temperature to a value similar to the facial skin temperature observed during the 0°C exposure [43].
Mean body temperature
The mean body temperature was found to decrease below 35°C after 60 min of walking at – 10°C with 0.2 m/s air movement, and decreasing faster by increasing the air velocity [35]. It was also found to decrease below 35°C after 4 consecutive 30 min exposures to – 25°C, with re-warming periods of 20 min at 20°C. The current literature has described the mean body temperature decreasing to 32–35°C as mild form of hypothermia (general freezing), and to appear with shivering, tachycardia, tachypnea and slowness of ideation and compensated dysarthria [30, 54].
Nevertheless human thermoregulatory responses can be modified after a period of exposure to cold conditions. It was observed that subjects had developed a hypothermic general cold adaptation characterized by a decreased Tre (– 0.5°C), a decreased Tsk (– 0.5°C) with no changes in the metabolic heat production [16]. The author concluded that through three indicators (changes in the metabolic rate, rectal and skin temperature) it is possible to quantify the adaptation level, including local cold adaptation of the extremities [16]. Cold exposures increase cold tolerance and prevent cold injuries [17].
Core temperature
When exposed to cold, the core temperature decreased in 6 studies (7 articles) [7, 44] and to increased in 3 studies [35, 43] which is shown in appendix Tables 3 and 4. In the studies where the working activity was sitting, order picking or loading, the core temperature was decreasing, while in studies where the working activity was walking on a treadmill, the core temperature was increasing. As the core temperature in the “increasing core temperature articles” was measured rectally, the explanation might be found in the production of heat from the local muscles, for which Tre is directly affected, and therefore it is higher when the work is performed with the legs than when it is carried out exclusively with arms [55]. By several included articles it was concluded that the rectal temperature was highest when the working activity was heavier [35, 43]. The elevation of heat production by a heavier exercise level retained both core and skin temperatures at a higher level in comparison to a lower exercise level (especially in the hands and fingers), but the metabolic rate was not found to be an important factor to take in consideration for calculating the Wind Chill Index by one of the included articles [35]. When exposed to cold, the core temperature was found to decrease more in older than in younger subjects, as the core temperature decreased much more in male compared to female subjects [7, 44]. However, conclusions on the difference between genders should be done with caution, as the phase of the menstrual cycles was not considered in articles with female volunteers. During the night, the work should be avoided as it was noticed a decrease in the rectal temperature, manual performance and an increase in diastolic blood pressure [34]. Nevertheless, both rectal and tympanic temperatures were found not to be relevant for the assessment of thermal strain in cold thermal environment [55], therefore there is still no relevant knowledge on the influence of severe cold thermal environment on human core temperature throughout the exposure to SCE.
Limitations of the review and from the found studies
The searching for articles was limited to the used keywords and to the articles in the references of the selected ones. Further limitations of this systematic review lay in bias factors which were not considered in the included articles. A number of included studies didn’t consider if volunteers were cigarette smokers (n = 10), didn’t conduct a medical control (n = 12), didn’t consider if the volunteers were taking medications (n = 12). Only one of the included articles considered if the volunteers consumed alcohol [56], coffee [57] or tea [58] prior to participating in the experiments, what was their physical exertion, sleeping hours, which might have influenced the results of the experiments. The included articles which conducted experiments on female volunteers (n = 5) didn’t consider the follicular phase of the menstrual cycle, for has been found to influence the results [59]. Information on physical characteristics of the included volunteers, were not give in 6 articles for body fat and 8 articles for body surface, which is crucial for any kind of conclusions. Separation between tests is another important factor as different exposure air temperatures might lead to the acclimation of the volunteers, therefore should be considered in further experiments of this type. In the included articles, the core temperature was measured just by using measuring techniques which were found not to be relevant for the assessment of thermal strain in cold thermal environments [55].
Conclusions
Exposure to severe cold environment is and will remain a significant risk factor in working environments. Further studies should include working activities present in real life conditions exposed to severe cold thermal environment, both for outdoor (e.g. standing, walking, running) and indoor (in the industry or conducting laboratory simulations with real working movements and activities). Studies should be conducted with well specified volunteer physical characteristics with all of the mentioned (if possible) bias factors, taking in consideration both genders, differently aged people, acclimatized and non-acclimatized, exposed to different air temperatures, air velocities and time of exposure, specifying clothes used for their protection and the physical exertion needed for the task accomplishment. Further, core temperatures should be measured through oesophageal or intra-abdominal temperature, as the rectal, oral, tympanic, auditory canal and urine temperature were found not to be relevant for the assessment of thermal strain in cold thermal environment. All present studies conducted in cold thermal environment used rectal and tympanic measurements, where some show a decrease and some increase in core temperature.
Further studies should be conducted in laboratory and industrial severe cold thermal environment on acclimatized and non-acclimatized subjects, in order to measure core and skin temperature variations and consequent recovery periods. Future studies should measure oesophageal or intra-abdominal core temperature and skin temperatures on at least 8 points of the body, and consider different physical exertion activities.
Conflict of interest
None to report.
Footnotes
Appendix
Clothing insulations factors and clothes used in the selected studies
| Ref Nr | Clothing insulation |
| 1. | Thermo underwear, pullover, trousers, cold-protective suit (thick jacket and long trousers), thick hat, thermo gloves, cold-insulating boots |
| 2. | shirt, trousers and a winter coat (1.3 clo) |
| 3. | 1) normal training clothing sufficient for each particular temperature; 2) wearing 1, 2 or 3 layer clothing, respectively. The estimated thermal insulation of the clothing was 0.8 (20°C), 1.18 (0°C) and 1.82 clo (– 15°C) |
| 4. | Described thoroughly in the article, with clothing insulation values 1.18 (22°C), 2.49 (5°C), 2.72 (– 5°C), 4.2(– 15°C) and 4.27 (– 25°C) |
| 5. | Finnish military winter clothing ensemble ‘M91’ (long-legged underpants, long-sleeved undershirt, fibre pile pants, shirt, socks, trousers, outer jacket, fibre pile inner mittens, nylon outer mittens, knee-high rubber boots with linings, insulated hat with earflaps basic insulation approx. 2.2 clo. |
| 6. | Shorts and the Finnish Army outfit “M91” (total insulation: 0.415 K m2 W–1), which includes cotton long-legged underpants, long-sleeved two-rib undershirt (50% cotton/28% polychal/22% polyester), fibre pile pants and shirt (80% polyamide/20% polyester), trousers and jacket (weave, 60% cotton/40% polyamide), ankle socks (wool/synthetic fibre mix), rubber knee-high boots with wool felt-linings, fibre pile inner mittens, nylon outer mittens and cap with earflaps. |
| 7. | During 10°C dry and 10°C wet: uninsulated ski pants, wool socks, hiking boots, long, tight-fitting, cotton, honeycomb shirt; a thin, wind-resistant nylon shell; an acrylic ski hat (if requested by the subject), and a thin pair of gloves (if requested by the subject). The objective was to allow the subject to add or remove clothing as they more comfortable in all of thermal environments |
| 8. | The standard winter work clothing of the Royal Netherlands Air force consisted of: thermal underwear, battle dress, warm overall, dickey, warm socks, work shoes, fur hat with ear flaps, leather gloves and ‘trigger finger’ mittens. Goggles were used to prevent freezing of the eyes. ‘Camaches’ were put around the ankles to prevent excessive air movement through the trousers. |
| 9. | In the chill room warm underwear, a thermo shirt, a cold-protective vest, a pair of trousers, a wool hat, knitted gloves and thermo-insulated safety shoes were used. The gloves worn were primarily provided for occupational safety reasons rather than for keeping the hands warm. In the cold store the same underwear was used, but additionally a pullover, a pair of trousers and, more importantly, a special cold protective suit were worn. This suit consisted of a thick jacket and long trousers. Furthermore, a thick wool hat, thermo socks, special thermo gloves – normally made of fleece – and cold-insulating boots were worn. |
| 10. | Trunks (86 g), long underpants (563 g), a long-sleeved shirt (304 g), socks (60 g), a pair of gloves (118 g), a hood (195 g), cold-protective trousers (888 g), and a cold-protective jacket (1227 g). The total clothing mass was 3.491 kg, and the total insulation value estimated from this mass was about 3.4 clo. The subjects also wore cold-protective boots (1293 g) |
| 11. | Trunks, long underpants, a long-sleeved sweatshirt, socks, cold-protective trousers, a cold-protective jacket, a pair of gloves, and a hood. The total clothing mass was 3.26 kg, and the total insulation value estimated from this mass was about 2.3 clo. The subjects also wore cold-protective boots 1.5 kg |
| 12. | The subjects were dressed in a multi-layer cold-weather clothing ensemble with a basic insulation value (I#–) of 2.23 clo (0.346 K m2 W–1). The thermal insulation of the clothing ensemble was measured on a static thermal mannequin (ISO/DIS-9920, 1988). The ensemble comprised briefs (100% polypropylene), long-legged and long-sleeved underwear (100% polypropylene), knitted socks (wool/polyester), fibre pile jacket and trousers (100% polyamide), coverall and jacket (cotton/polyester), knitted cap, heavy insulated leather glove and fibre pile mitten, scarf and boots. A parka, providing additional insulation of 0.7 clo, was added to the original clothing ensemble for the last 50 min of the exposure at the lowest temperature. |