Ann. occup. Hyg., Vol. 47, No. 1, pp. 7-16, 2003
© 2003 British Occupational Hygiene Society
Published by Oxford University Press
Cold Exposure During Helicopter Rescue Operations in the Western Alps
1 Institute for Aerospace Medicine, Faculty of Medicine, Technical University of Aachen; 2 Department of Nephrology and Rheumatology, University of Göttingen; 3 State Institute for Occupational Safety and Health of North Rhine Westfalia, Düsseldorf, Germany
Received 19 July 2002; in final form 3 October 2002
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Objective: The study evaluates exposure to the cold of personnel involved in helicopter rescue operations in an alpine environment. Methods: Rescue operations over a period of 15 months in the Oberwallis region (Switzerland) were analysed with special regard to the weather conditions, the locality and its altitude, and the duration. The equivalent chill temperature was estimated with two independent models. ‘Mean exposure’ as well as the ‘worst-case situation’ (based on maximum windspeed) were calculated. The results were evaluated according to the ‘classic’ Siple–Passel model, the more recent model of Danielsson, ISO 11079, ISO 9920, the German industrial standard DIN 33403.5, and the German government regulations for work in cold environments (‘G21’). Results: The temperature models showed only marginal differences in chill temperature. Assuming ‘worst-case conditions’, the Siple–Passel model showed that 87.1% of the operations occurred at chill temperatures > –30°C, 12.1% in the range of –30 to –45°C, and 0.8% at <–45°C. The lowest temperature was –54.6°C. The Danielson model resulted in 77.6% without the risk of frostbite, 20.1% with >5% risk, 6% with >50% risk and 1.8% with >95% risk. According to DIN 33403.5, 1.5% of the operations were performed at chill temperatures higher than cold class 1: 2.3% are class 1, 13.3% class 2, 34.7% class 3, 34.6% class 4 and 13.7% class 5. The maximum exposure times of DIN 33404.5 are exceeded in at least 0.5% of the missions. According to ISO 11079, clothing with 2.0 clo is sufficient in 40.2 and 23.9% of the operations [summer, required clothing insulation (IREQ) min. and IREQ neutr., respectively]. In winter the corresponding results are 0.3 and 0.0%. Duration of limited exposure is exceeded in 9.1 (IREQ min.) and 19.8% (IREQ neutr.) of the operations in summer and in 10.3 and 19.8% in winter. According to ISO 9920, ICL min. as well as ICL neutr. is exceeded in 100% in summer and winter operations. Conclusions: Alpine rescue operations are typical of a place of work in a cold—sometimes extremely cold—environment. Because of the limited time of exposure during the majority of the operations, the most important danger for rescue personnel is frostbite, although hypothermia cannot be excluded in cases of prolonged operations. Special advice to avoid the specific risks must be given to the crews and an examination by occupational medicine, e.g. according to ‘Working in cold environments, G21’ of the German Berufsgenossenschaften, is recommended. Recommendations for adequate clothing are given.
Keywords: helicopter rescue; alpine rescue; winch operations; cold injuries; hypothermia; mountain
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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In comparison to urban emergencies, those in alpine regions occur in an environment that exposes personnel to various conditions, above all cold and altitude (hypobaric hypoxia). The demands depend on the altitude of the mission and the actual weather conditions. Until now there were no data available which could be used for recommendations in occupational medicine, mainly because of technical problems with data acquisition during alpine helicopter rescue operations. In addition to other factors, such operations are characterized by extreme time pressure, the limited number of personnel involved, the limited space in the helicopter and the limited load it can carry at altitude. Therefore, it is impossible to carry additional persons just to obtain data during the mission. The use of automatic devices is also limited, because they cannot be mounted outside the helicopter due to two reasons: (i) every device mounted on an aircraft requires individual permission from the aviation authorities, and (ii) the nature of a helicopter itself makes correct data acquisition of temperature and wind impossible, especially when ‘hot-loading’, i.e. with the engine and the rotor running continuously during the mission or during winch operations (about 10% of all missions!). Putting devices somewhere near the site of the accident would absorb manpower (not available, see above) and would be of limited effect because the limited time of measurement would give purely accidental results in an environment with changing conditions.
The goal of our study was not to obtain exact physiological data about heat loss, a problem that has been well investigated by Siple, Passel, Danielsson, and many others (Siple and Passel, 1945; Danielsson, 1996). We wanted to appraise the risk to personnel exposed to cold environments during alpine rescue operations with their quickly changing conditions. Because it is not realistic to obtain meaningful data during such operations, we used an artificial (statistical) approach to estimate exposure to the cold, by combining the data of the accident’s locality with the time of exposure and the coincident meteorological data, primarily the air temperature and wind speed, which allow us to calculate the equivalent chill temperature. The approach was performed assuming mean conditions and as well as ‘worst-case conditions’.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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A retrospective analysis of 1082 rescue operations (January 1992–March 1993, n = 456 days) was performed to obtain data about the exact time when the mission was carried out, the altitude of the location and the duration of exposure at the rescue scene. The equivalent chill temperature at the scene was estimated using two different methods. The first one used the coincident air temperature of the next meteorological measuring point (Ulrichen, Canton Wallis) as follows: for missions between 7 p.m. and 8 a.m., the day’s minimum temperature; for those between 12 a.m. and 3 p.m., the day’s maximum temperature; and for other missions, the day’s mean temperature. With these data the air temperature at altitude was calculated using the ICAO standard atmosphere (ICAO, 1964; Ernsting and King, 1994). These temperatures were converted into equivalent chill temperatures according to Siple and Passel (Siple and Passel, 1945, 1999; Ernsting and King, 1994) and according to Danielsson (1996) using the wind speed measured at Ulrichen. The day’s average wind speed was used for ‘mean conditions’, the day’s maximum wind speed for ‘worst-case conditions’.
The second method used data obtained from the ascent of meterological balloons at Payerne (Canton Waadt, 75–100 km from the location of the rescue operations). The temperature corresponding to the altitude of the accident’s location was converted into the equivalent chill temperature as described above using the wind speed and the temperature of the same altitude measured by the balloon. All calculations were performed with dry air temperature because humidity has a negligible effect at subfreezing temperatures.
A difference between both methods of <5°C in equivalent chill temperature was defined as ‘identical’. In cases with a difference of >5°C, the lower temperature was used for final evaluation. The temperature regression of each of the series from the Payerne series was analysed for linearity. In case of an inversion with an irregularity of temperature of >±5°C, the method giving the lower temperature was used (in total on 9/456 days, i.e. 2.0% of the whole period investigated). The equivalent chill temperatures were classified according to the following systems: (i) the German authorities for occupational safety (Advice for medical examination: ‘Work in cold environments, G21’) (Berufsgenossenschaften, 1998) (> –25°C, –25 to –45°C, <–45°C); (ii) 5, 50 and 95% risk level according to Danielsson (1996); (iii) the ‘classic’ approach of Siple and Passel (1400 curve and > –30°C, –30 to –45°C, <–45°C) (Siple and Passel, 1945); and (iv) DIN 33403.5 (see Table 1). The Siple–Passel model was included for better comparison with other investigations because most authors in altitude medicine still use it.
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The insulation recommended was calculated according to ISO 11079 using the software of Nilsson and Holmer [required clothing insulation (IREQ) minimal and IREQ neutral] (DIN, 1993a; Nilsson and Holmer, 2002). The same program was used to obtain the duration of limited exposure (DLE) minimal and DLE neutral, and ICL according to ISO 9920. The calculations were based on typical alpine clothing which has an insulation of
2.0 clo (see table C1 in DIN, 1993a), and an air permeability of 10 l/m2/s; we assumed a metabolic energy production of 90 W/m2 (mean value in ISO 8996: DIN, 1993b), 0 W/m2 of mechanical work and a relative air humidity of 85% (DIN, 1993a).
To estimate the seasonal differences, two subgroups of all operations were evaluated. The first included missions in December, January and February (‘winter operations’, n = 385), the second included those from July to September (‘summer operations’, n = 329). Both subgroups were analysed with all the models described above. Statistics were performed by non-parametric tests (
2-test, Mann–Whitney U-test) using SPSS software. P < 0.05 was accepted as significant.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The altitude of the rescue operations is shown in Fig. 1: 7% of the missions took place at low altitude (<1500 m), 79.3% at moderate altitude (1500–3500 m) and 13.7% at high altitude (3500–4560 m). Most operations were performed at wind speeds of 3–6 Beaufort. For details about dry air temperature and wind speed, see Fig. 2. The temperature regression of the ascents at Payerne showed a distinct linearity with a decrease of –0.057°C/10 m (±0.0098, n = 446; Fig. 3), which follows almost exactly the regression of the ICAO standard atmosphere. Only 9 days of the 456 investigated (2%) showed an inversion of >5°C, mostly between 1400 and 2000 m (Fig. 4 shows an example of this).
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With the Siple–Passel model and ‘mean conditions’, 99.5% of all 1082 operations took place at chill temperatures above –30°C, 0.5% between –30 and –45°C. With ‘worst-case conditions’, in 87.1% the chill temperature was above –30°C, in 12.1% between –30 and –45°C, and in 0.8% lower than –45°C. The lowest equivalent chill temperature in our investigation was –54.6°C, the highest 28.6°C (Fig. 5). A wind-chill effect of >–5°C was calculated for 34.8% of the missions. There were significant seasonal differences (P < 0.01; Table 2, Fig. 5). As expected, most operations in summer took place at more comfortable temperatures, but the data show a wide range at all seasons with very cold conditions also occurring in summer (Fig. 5).
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With the model suggested by Danielsson and ‘mean conditions’, there was no or minimal risk of frostbite in 97.2% of all rescue operations, and in 2.8% a risk of >5%. In ‘worst-case conditions’, the corresponding results were 77.6% with no risk, 20.1% with >5% risk, 6.0% with >50% risk and 1.8% with >95% risk. For comparison, 85% of the operations show no risk according to the Siple–Passel 1400 curve, and 15.0% an increased risk (‘mean conditions’). Assuming ‘worst-case conditions’, the corresponding data were 72.9% for no risk and 27.1% for increased risk. As expected, there were significant differences between summer conditions and winter operations with the Danielsson model as well (P < 0.01; Table 3).
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The data classified according to DIN 33403.5 showed that 4.7% of all rescue operations occurred at temperatures above cold class 1, 5.0% class 1, 39.6% class 2, 38.5% class 3, 11.6% class 4, and 0.5% class 5 (‘mean conditions’). With ‘worst-case conditions’ the corresponding values are 1.5, 2.3, 13.3, 34.7, 34.6 and 13.7%. Again there are significant differences between summer and winter operations (P < 0.01; Table 4).
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Classified according to G21, 97.3% of all operations took place at temperatures > –25°C, and an additional 2.7% between –25 and –45°C (‘mean conditions’). Assuming ‘worst-case conditions’, the corresponding values were 78.2, 21.0 and 0.8% at <–45°C. Again there were significant differences between summer and winter operations (P < 0.01; Table 5).
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The mean time of exposure was 15.3 (±30.2) min but with remarkable variation up to 850 min (Fig. 6). This mission was performed at a chill temperature of –22°C at an altitude of 3500 m (Siple–Passel model, ‘worst-case’ calculation). There was no significant difference in the duration between summer and winter operations. According to DIN 33403.5, the recommended maximal exposure times were certainly exceeded in 0.5% of all missions (twice in cold class 3, twice in class 4 and once in class 5; Fig. 6). Additionally, there may be some further instances in cases when the following mission started shortly after the previous one was finished. This could be evaluated precisely by the flight reports, but it would be rare because the number of missions per day is limited: in 43.8% of all the days evaluated there was no mission, in 22.3% there was one mission, in 13.6% two, in 8.1% three, in 5.5% four, and only in 6.7% more than four missions (Zermatt; the data from the other base at Raron do not differ significantly). The mean duration of the missions was 64 min.
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The insulation recommended by ISO 11079 and ISO 9920 is shown in Tables 6 and 7. While the insulation is sufficient in 40.2% (IREQ min.) and 23.9% (IREQ neutr.) in summer operations, it is sufficient in only 0.3% (IREQ min.) in winter operations (0.0% for IREQ neutr.). In summer operations the DLE is exceeded in 9.1% (DLE min.) and in 19.8% (DLE neutr.) respectively. The mean duration of the summer operations is 61.9% (±277.8) of DLE min. and 75.8% (±279.2) of DLE neutr. The most by which the DLE was exceeded was 4722% when a climber fell ~100 m down a couloir on the Matterhorn. He was found at an altitude of
3500 m, and had a pelvis fracture, tibia fracture, thorax contusion, blunt abdominal trauma, hypovolemic shock and hypothermia. The whole team was blocked by bad weather with an ambient air temperature of –3.7°C and a wind speed of 11.3 m/s. In winter, DLE min. is exceeded in 10.3% of the operations, DLE neutr. in 19.1%. The mean duration is 57.9% (±42.2) and 67.3% (±51.5) of DLE min. and DLE neutr., respectively. The most by which the DLE was exceeded was 417% (DLE min.) and 556% (DLE neutr.) when a climber fell 30 m into a crevasse at an altitude of 3100 m. He suffered from a femur fracture and facial injuries. The ambient conditions were –1.1°C air temperature and 6.4 m/s wind speed. The difference in how much the DLE was exceeded between summer and winter was not significant (neither for DLE min. nor DLE neutr.). According to ISO 9920, a clothing with 2.0 clo is insufficient in all summer and winter operations (Table 7).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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During alpine rescue operations, personnel are exposed to a wide variety of environmental factors, such as hypobaric hypoxia, low temperatures, wind and radiation, as well as extreme helicopter noise and high workload. In contrast to most other professions, these factors change over a wide range depending on the location of the mission, the weather conditions and the situation on site. In addition, they often change very abruptly during the mission. Up until now there were no data available that quantify these impacts on the crews and which could be used for qualified advice and medical care by occupational medical staff. In our present study we quantified the amount of cold exposure during missions in the western Alps (typical altitude 3000–4000 m, maximum altitude 4659 m). Although current technology for measuring meteorological data directly at the site of an alpine accident during a rescue operation does not yet permit accurate data of cold exposure, and extensive measurement during rescue operations is impracticable and ethically questionable, it was none the less possible to get a rough appraisal of the cold exposure of the the personnel under these circumstances. This statement is based mainly on the fact that there were only minimal differences (only 2% of the days investigated) between two independent methods of estimation, which means that the risk appraisal was nearly independent of the method used.
Holmer (1993) discusses five principal cooling mechanisms: (i) whole-body cooling, (ii) extremity cooling, (iii) convective cooling (wind chill), (iv) conductive cooling (contact) and (v) airway cooling. With whole-body and extremity cooling being less important in an alpine rescue (mainly because of the limited exposure time during most operations), with conductive cooling being easily prevented by using adequate clothing (although conductive cooling is not avoidable in every situation), and with airway cooling actually being impossible to use because it depends mainly on the breathing volume for the workload, which is unknown for alpine rescue operations, we used the model of convective cooling for our estimations. As there is normally wind at the site of an alpine accident, the wind-chill models should work best.
The model of Siple and Passel has been widely discussed since it was introduced in 1945, mainly because it works exactly only if the skin exposed is unprotected (Siple and Passel, 1945, 1999; Kaufman and Bothe, 1986; Kaufman et al., 1987; Paton, 1999). Some authors also argue that the human’s thermal response depends not only on physical conditions and physiological state, e.g. metabolic rate, but also on past experience, how people perceive the environment and how weather conditions differ from the norm (Kaufman et al., 1987). Most authors criticize the Siple–Passel model mainly because the underlying model does not comply with modern heat transfer theory (reviewed in Brauner and Shacham, 1995). Therefore, other indicators such as exposed skin temperature and maximum exposure time, or, for conductive cooling, contact coefficient and maximum exposure time, have been suggested (Brauner and Shacham, 1995; Havenith et al., 1995). Another criticism is that the original model was limited to a wind speed of 12 m/s, although most authors accept extrapolation of the model above this limit, as do governmental and non-governmental recommendations (e.g. Danielsson, 1996; Anon., 1998).
Recently the Siple–Passel model was modified by Danielsson, who pointed out that the model in its original version underestimates the effect of wind speed, because the surface temperature of the cylinder they used was not, as they expected, similar to that of the freezing water (Danielsson, 1996). While the Siple–Passel model indicates a greater risk at higher temperatures and higher airspeeds than the 5% curve of Danielsson, it approaches Danielsson’s 50% curve at –20°C, which means that it gives a minor risk under these conditions (Danielsson, 1996). However, as Danielsson points out, at these low temperatures a change of the airspeed of 2–3 m/s can change the risk by >50%. All the risk curves should therefore be used with caution, because minor changes in the climatic, behavioral or physiological conditions can have a considerable effect on the risk of tissue freezing (Danielsson, 1996). In consequence, the differences between the models of Siple–Passel and Danielsson are of minor consequence for the question investigated in our study.
Nevertheless, the wind-chill index and the more widely used wind-chill equivalent temperature represent an attempt to combine several weather-related variables into a single index that can indicate human comfort. When no exact data are available for the situation, and the conditions are changing unpredictably over a wide range, this index describes the amount of cold exposure and the risk for cold weather injuries quite well (Sinks et al., 1987; Wyon, 1989; Anttonen and Virokannas, 1994; Virokannas and Anttonen, 1994; Candler and Ivey, 1997). Wyon (1989) demonstrated a good agreement of equivalent wind-chill temperature and heat loss for the full range of civilian outdoor clothing, although whole-body heat loss through clothing was lower than predicted by Siple’s model. Virokannas and Anttonen (1994) investigated heat loss in mild winter conditions (chill index 1050–1520 kcal/m2/h; 280–350 W workload, clothing insulation 1.7–2.4 clo) and documented the wind-chill index. They predicted the risk of cold injuries quite well, with local cooling of the face and the peripheral extremities the most serious problems. They confirmed these results in another investigation (Anttonen and Virokannas, 1994).
In our study, both approaches show similar results, caused by predominating weather situations with temperature regressions that are nearly identical to the data of the ICAO standard atmosphere of –6.5°C/1000 m (ICAO, 1964). Of course, differences between the standard atmosphere and reality are well known (e.g. table 1.3, p. 8 in Ernsting and King, 1994), but nevertheless it is well proven, for example, for statistical approaches in aviation physics and technology as well as in aviation medicine. Major differences between the two approaches in our study, which means ±5°C or more, are limited to only 2% of the whole period, so that they are of minimal influence on the general estimation of cold exposure. Therefore, the equivalent chill indices calculated for each mission included should be relatively correct, although some factors such as local winds or lee situations could not be considered.
In contrast to the best approach to describe cooling, the increase of the risk for cold weather injuries with strong winds and low temperatures is undisputed (e.g. Sinks et al., 1987; Holmer, 1993; Candler and Ivey, 1997). Candler and Ivey (1997) reported that 99.3% of all cold weather injuries to US soldiers (n = 273) were first- and second-degree frostbite; 71% of these happened at equivalent wind-chill temperatures of <–29°C. They confirmed that the risk also increased with factors well-known in mountaineering, e.g. inadaequate clothing, wet clothing, dehydration, inactivity, fatigue and previous cold weather injuries. Sinks et al. (1987) analysed 657 accidents and pointed out that the risk of cold weather injuries increases at significantly milder weather conditions than previously published cold hazard charts suggest. Their data show an increasing risk at –12°C resting air temperature and wind velocity >4.5 m/s (Beaufort 3). These conditions are within the range of most missions invesigated in our study. Therefore, and because cold stress reduces work ability by 70% (Anttonen and Virokannas, 1994), alpine rescue personnel should be given special advice to prevent cold weather injuries.
Our ‘mean conditions’ underestimate the real conditions of many operations. At –20°C, where the Siple–Passel 1400 curve approaches the Danielsson 50% curve, a minor change of the air velocity has a significant influence on the cold effect; 27.8% of the missions in our investigation took place within or below this range (Siple–Passel model, ‘worst case’). Therefore, and according to usual procedures in occupational medicine and safety, worst-case conditions should be used for risk evaluation. In DIN 33403.5, work in cold environment is defined as ‘work with air temperatures below +15°C and where humans show a negative heat balance in spite of the effects of workload and clothing’. With 34.7% of our rescue operations in cold (class 3) and 48.3% in very cold and extreme cold environments (class 4 and 5), our data show that exposure of personnel is surprisingly extreme. Although the recommended maximum exposure time is exceeded in only 0.5% of the missions, and the recommended rewarming time can be achieved in nearly 100% of the missions, it must be pointed out that these recommended limits of exposure time are based on adequate clothing.
The typical clothing during alpine helicopter rescue operations is a combination of pants, undershirt, shirt, trousers, jacket, anorak, boots, helmet, gloves and (sometimes) slipover trousers; this combination has an insulation effect of 2.0 clo (DIN, 1993a). Because most techniques in helicopter rescue do not require heavy workload, and workload data in these conditions have in any case not been available until now, we performed the calculations using the low metabolic rate (DIN, 1993b). The results show that the clothing is insufficient in a considerable number of operations. The differences between the results according to ISO 11079 and ISO 9920 are mainly caused by the fact that the influence of wind chill is more important in the ISO 9920 calculations. But in most cases the time by which the DLE is exceeded is limited, and therefore hypothermia should be mild. This corresponds to the feeling of the rescuers who often report shivering but rarely symptoms of moderate or severe hypothermia. But nevertheless it must be pointed out that in 1.4% (DLE min.) and 2.7% (DLE neutr.) of the summer, and 0.8 and 1.4%, respectively, of the winter operations, DLE is exceeded by >200%. In these cases, danger from hypothermia must be assumed for the rescuers, and of course even more so for the victim. In consequence, the content of the rescuers’ backpacks should be reconsidered, because normally no additional clothing or bivouac sack is included in the equipment of air rescue personnel. Especially for questionable or bad weather conditions, additional clothing should be a ‘must’.
One main problem during alpine helicopter rescue is finding clothing that can cope with the quickly changing conditions: +15 to +20°C (and more) in the helicopter’s cabin and –20°C (and less) only minutes later at the site of the accident—a difference of 40°C and more! This is even more pronounced during winch operations. Because most helicopters used for alpine rescue are too small to be re-entered in-flight at the end of any winch operation, the personnel as well as the patient stay outside until an intermediate landing area is reached. Our data show this period to range from 2 to 14 min, with a mean duration of 6.3 min (±2.53, n = 163). During this period, personnel are exposed to wind speeds of up to 160 km/h (and sometimes even more), resulting in extreme equivalent wind-chill temperatures and an extreme risk of frostbite. In contrast to the personnel, the risk to the patient is minimal, because normally he/she will be carried in the rescue bag (Fig. 7), which offers near-perfect protection against any weather conditions.
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There are, in fact, no representative data about cold weather injuries during alpine rescue operations available, mainly because most of these injuries are not reported as occupational accidents, e.g. the frostbite to three fingers of one of the authors, which happened during a mission in the Monte Rosa region at an altitude of
4200 m in cold weather and moderate wind (estimated equivalent chill temperature –30°C). However, our data indicate the need for preventive advice and care by occupational medicine, e.g. according to the medical check-up ‘Working in cold environments (G21)’ in Germany (Berufsgenossenschaften, 1998), to avoid cold weather injuries. Because of the wide range of equivalent chill temperatures throughout the year, it is not very useful to differentiate these recommendations between ‘summer’ and ‘winter’—although the differences in chill temperatures between summer and winter conditions are significant. Special regard should be given to persons with medical problems that cause increased risk for cold injuries. In most cases, these people need to be excluded from alpine rescue operations. The best prevention of cold weather injuries regarding the quickly changing conditions encountered during a mission is clothing with several insulating inner layers, and an outer layer that offers good wind protection. During winch operations, a simple trick is effective at reducing the risk of frostbite to the face: as soon as the rescuer is winched up and reaches the helicopter’s skid with his hands, he can turn around to expose his back towards the wind with his hood protecting his neck and head. It should also be pointed out that the victim is exposed to the conditions discussed above as well, and in most cases even longer than the rescue team. Although a mobile telephone is used for 50% of the emergency calls in the region (Jelk, 2000), and the helicopter base is in Zermatt, near to most of the mountains climbed, it still takes 27.9 ± 59.4 min (n = 1082) for the rescue crew to arrive. Therefore every mountaineer or skier must be well educated in protecting themselves from the cold. Acknowledgements—The authors would like to express their gratitude to the Swiss Meterological Institution and Air Zermatt AG, Zermatt / Swizerland for their support.
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FOOTNOTES |
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* To whom correspondence should be addressed. Am Botanischen Garten 15, 40225 Düsseldorf, Germany. Fax: 0049-211-1649111; e-mail: kuepper.cl.th{at}t-online.de
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REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Anon. (1998) Health aspects of work in extreme climates within the E&P industry. London: Oil Industry International Exploration and Production Forum. pp. 1–34.
Anttonen H, Virokannas H. (1994) Assessment of cold stress in outdoor work. Arctic Med Res; 53: 40–8.
Berufsgenossenschaften, H. d. g. (1998) Berufsgenossenschaftliche Grundsätze für arbeitsmedizinische Vorsorgeuntersuchungen. Stuttgart: Gentner Verlag.
Brauner N, Shacham M. (1995) Meaningful wind chill indicators derived from heat transfer principles. Int J Biometeorol; 39: 46–52.[Medline]
Candler WH, Ivey H. (1997) Cold weather injuries among US soldiers in Alaska: a five-year review. Mil Med; 162: 788–91.[ISI][Medline]
Danielsson U. (1996) Windchill and the risk of tissue freezing. J Appl Physiol; 81: 2666–73.
DIN. (1993a) ISO 11079: Bestimmung der erforderlichen Isolation der Bekleidung (IREQ). Berlin: Deutsches Institut für Normung.
DIN. (1993b) ISO 8996: Bestimmung der Wärmeerzeugung im menschlichen Körper. Berlin: Deutsches Institut für Normung.
Ernsting J, King P. (1994) Aviation medicine. Oxford: Butterworth-Heinemann.
Havenith G, Heus R, Daanen HA. (1995) The hand in the cold, performance and risk. Arctic Med Res; 54 (suppl. 2): 37–47.
Holmer I. (1993) Work in the cold. Review of methods for assessment of cold exposure. Int Arch Occup Environ Health; 65: 147–55.[Medline]
ICAO. (1964) Manual of the ICAO standard atmosphere. Montreal: ICAO.
Jelk B. (2000) Unfälle des Jahres 1999. Clubnachrichten SAC Zermatt; 25: 6.
Kaufman WC, Bothe DJ. (1986) Wind chill reconsidered, Siple revisited. Aviat Space Environ Med; 57: 23–6.[Medline]
Kaufman WC, Laatsch WG, Rhyner CR. (1987) A different approach to wind chill. Aviat Space Environ Med; 58: 1188–91.[Medline]
Nilsson HO, Holmer I. (2002) Calculation of required clothing insulation (IREQ), duration limited exposure (DLE), required recovery time (RT). Computer software IREQ 2002 v. 3.1a (http://www.niwl.se/tema/klimat/ireq2002alfa.htm).
Paton B. (1999) Paul Siple and the origin of windchill—a commentary. Wilderness Environ Med; 10: 174–5.[Medline]
Sinks T, Mathias CG, Halperin W, Timbrook C, Newman S. (1987) Surveillance of work-related cold injuries using workers’ compensation claims. J Occup Med; 29: 504–9.[Medline]
Siple P, Passel C. (1945) Measurements of dry atmospheric cooling in subfreezing temperatures. Proc Am Philos Soc; 89: 177–99.
Siple P, Passel C. (1999) Excerpts from: Measurements of dry atmospheric cooling in subfreezing temperatures. Wilderness Environ Med; 10: 176–82.[Medline]
Virokannas H, Anttonen H. (1994) Thermal responses in the body during snowmobile driving. Arctic Med Res; 53 (suppl. 3): 12–8.
Wyon DP. (1989) Wind-chill equations predicting whole-body heat loss for a range of typical civilian outdoor clothing ensembles. Scand J Work Environ Health; 15 (suppl. 1): 76–83.
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