Avalanche deaths in the United States: a 45-year analysis

Transcription

1 Wilderness and Environmental Medicine, 10, (1999) ORIGINAL RESEARCH Avalanche deaths in the United States: a 45-year analysis CHARLES E. PAGE, MD; DALE ATKINS, BA; LEE W. SHOCKLEY, MD; MICHAEL YARON, MD From the Denver Health Medical Center, Division Qf Emergency Medicine (Dr Page and Dr Shockley). Ihe Colorado Avalanche Information Center, Colorado Geologic Survey (Mr AIkins). and the University of Colorado Health Sciences Center, Division of Emergency Medicine, Colorado Emergency Medicine Research Cemer (Dr Yaron). Objective.-To describe the demographic characteristics and patterns of death of persons killed in snow avalanches over a 45-year study period. Methods.-The national avalanche database was the source of data in this retrospective, descriptive study. Results.-A total of 440 victims were killed in 324 fatal avalanches, of which 87.7% were fully buried, 4.7% were partially buried, and 7.6% were not buried. The average age was 27.6 :!: 10.6 years, and 87.3% were men. Victims who died included climbers (25.5%), backcountry skiers (22.7%), out-of-bounds skiers (10.0%), snowmobilers (6.8%), in-bounds skiers (5.2%), residents (4.5%), ski patrollers (3.6%), workers (3.6%), and motorists (3.0%). Over the 45-year study period there appear to be decreases in the deaths ofin-bounds skiers, highway workers, and motorists. Increasing fatalities were observed among out-of-bounds skiers, snowmobilers, ski patrollers, and backcountry skiers. Most deaths occurred in Colorado (33.0%), Washington (13.2%), and Alaska (12.0%). Conclusions.-Avalanche fatalities have increased over the last 45 years. Climbers, backcountry skiers, out-of-bounds skiers, and more recently snowmobilers constitute the majority of the victims. The decrease in deaths among groups that benefit from avalanche control programs supports the benefit of avalanche prevention strategies. Further study is needed to assess the impact of avalanche safety education for individuals who travel in remote and uncontrolled terrain. Key words: avalanche. trauma, wilderness medicine. skiing Introduction An avalanche occurs on a slope when the cohesive properties within the snowpack or between the snow and the ground fail to resist downward gravitational forces. Avalanches can occur spontaneously; they may also be triggered by the weight of a person or by explosives. Objects or humans in the path of an avalanche can be swept down the slope. As the avalanche comes to a stop, the snow consolidates rapidly as a result of the release of thermal energy. Previous studies have implicated asphyxia and blunt trauma as the leading causes of deaths in avalanches [1-5]. Although considerable knowledge has been gained in recent years regarding the mechanisms of avalanche activity, little has been published about the victims themselves. This study describes the demographics of avalanche victims in the United States, evaluates trends in the num- Direct correspondence to Division of Emergency Medicine; Mailcode #0108; Denver Health Medical Center; Denver, CO (Dr Page). ber of persons killed in avalanches over the past 45 years, and describes the type of activities in which victims were engaged at the time of the accident. This represents the largest cohort of avalanche fatalities published to date. Materials and methods Retrospective data were collected from the national avalanche accident database. Each accident entry in the database documents the number of people who were caught and killed in each avalanche. Additional information available about the victims includes their sex and age, and the time and date in which the accident occurred. We also recorded the duration of burial before retrieval from the snow, the depth in which the head was buried under the snow, and whether the person was fully buried or partially buried. We defined a partially buried victim as a person who had part of his or her body under the snow when the avalanche came to a halt, whereas a

2 Avalanche deaths in the United States 147 Table 1. Description of each activity Activity Backcountry skier Climber Guides Helicopter!snowcat Highway workers Hikers Hunters In-bounds skier Miners Miscellaneous Motorist Out-of-bounds skier Playing Rangers Rescuers Residents Ski patroller Snowboarder Snowmobiler Snowshoers Workers Description Skiing in the backcountry (uncontrolled or remote terrain); skimountaineer. Without skis or snowshoes. On-duty ski or mountain guide. Skiing in uncontrolled or remote terrain. Employees of highway department or operating snowplow. Not using snowshoes or skis. Hunting at the time of the accident. Within a ski area boundary in an area designated as "open". Invoved in a mining operation. Other recreational categories. In a vehicle. Enters a "closed"area or exits the outer boundary of a ski area. Children playing where an avalanche occurs. Paid or volunteer wilderness worker. Rescuing avalanche victims. Caught in a building or town; snow originating on rooftops. On-duty ski patroller. Riding a snowboard. Operating a snowmobile. Using snowshoes. Workers not otherwise specified. fully buried victim was one whose head was buried under the snow. Ratings of victims' avalanche education was known in 16.1% and backcountry experience was known in 25.5% of victims. These data were not analyzed. The type of preaccident activity is also recorded for each accident. Table 1 describes each activity category. In some cases, more than one category may describe a victim, but each victim was assigned only one category for the purposes of analysis. The type of employment takes precedence over the type of conveyance used. Hunters, ski patrollers, rescuers, climbers, unspecified workers, rangers, and guides are included in their respective categories, even if they were using snowmobiles, snowboards, or other means of transport. Snowboarders are not included in the in-bounds and out-ofbounds categories. The study population consisted of avalanche fatalities from January 1, 1950, through December 31,1994. The avalanche accident information was first assembled into a database in 1960 when the US Forest Service (USFS) Avalanche Program began in Fort Collins, CO. The data prior to 1960 was collected retrospectively from sources, such as ski areas, who were familiar with the accidents. After 1960, database information was reported to and collected by the USFS. Sources of reporting include rescue organizations, emergency medical providers, ski patrollers, law enforcement agencies, reports in the media, and avalanche forecasters. In 1972, the USFS Westwide Avalanche Network computerized the data. The database is currently maintained by one of the authors at the Colorado Avalanche Information Center in Boulder, CO. Colorado population data were collected from annually reported vital statistics published by the Colorado Department of Public Health and Environment [6-8]. Data were analyzed using Pearson correlation tests, and mean values are reported ± standard deviation. Results Four hundred forty victims died in 324 fatal accidents. The age was known in 252 (57.3%) of the victims. The mean age was 27.6 ± 10.6 years (range, 6-61 years). The sex of the victims was known in 315 (71.6%) of victims: 275 (87.3%) were men and 40 (12.7%) were women. The burial status was known for 319 (72.3%) victims; 87.7% were fully buried, 4.7% were partially buried, and 7.6% were caught but not buried. Duration of burial before bodies were uncovered was known in 198 (67.3%) of the 319 with a mean of 32.5 ± hours (range, 5 minutes to 60 days). Only 29.3% of victims were uncovered in the first hour; 79.3% were uncovered within the first 24 hours. Of the 407 victims who were partially or fully buried, the depth of burial was known in 211 (51.8%) and was 5.88 ± 5.29 feet. Figure 1 illustrates the increasing number of fatalities reported annually (r = 0.64), with the most deaths (33.0%) occurring in Colorado (Table 2). An average of 15.0 individuals were killed annually in last 20 years of the study period, during which 68.2% of the avalanche deaths in the study period occurred. The number of fatalities per capita in Colorado has not changed over this 45-year period, as suggested by the correlation of the estimated population of the state of Colorado with the number of persons killed by avalanches in Colorado (r = 0.667) (Fig 3). Table 3 lists the numbers of victims killed in each activity category. Deaths in the leading activity categories for IS-year periods are shown in Fig 2. Trends toward decreasing numbers of deaths are seen among highway workers, motorists, and in-bounds skiers. Increasing deaths are seen among out-of-bounds skiers, backcountry skiers, and snowmobilers. The month in which the avalanche occurred was known for all cas-

3 148 Page et al , a o 1! I i i ~! I ~..! ~ Fig 1. The number of fatalities in US avalanches annually (r = 0.643). Year es. Although avalanche deaths occurred in each month of the year, 88.0% of fatalities occurred between November and April, with February as the peak month (23.5%). The time in which the fatality occurred was known in 50.7% of victims. Most victims (88.3%) were killed between 0900 and 1600 hours. Discussion ty. Climber deaths initially increased, but then decreased compared with other activities during the last third of the study period. The work of snow scientists, ski patrollers, avalanche forecasters and other avalanche professionals has enhanced the understanding of the physical properties of snow, avalanche dynamics, and improved techniques for The number of persons killed in avalanches increased Table 3. Activities of victims (n = 440). over the 45-year study period. The greatest number of deaths occurred among climbers, backcountry skiers, Activity Killed % of total out-of-bounds skiers, and snowmobilers. Deaths among backcountry skiers, out-of-bounds skiers, and snowmo- Climber bilers have increased despite advances in avalanche safe- Backcountry skier Out-of-bounds Snowmobiler Table 2. Victims by state, In-bounds State Killed % for period Resident Ski patrol Worker Colorado Motorist Washington Highway worker Alaska Playing Utah Snowshoer California Hiker Idaho Rescuer Montana Snowboarder Wyoming Hunter Nevada Miner Oregon Helilsnowcat New Hampshire Miscellaneous recreation New Mexico Guide New York Ranger Maine Total

4 Avalanche deaths in the United States 149 m % 5% 10% 15% 20% 25% 30% 35% Fatality (% of 15 year total) Fig 2. Fatalities in leading activity categories expressed as a percentage of 15-year total deaths. avalanche hazard recognition and prediction. Preventive strategies designed to decrease avalanche morbidity now include decisions regarding road closure and active triggering of avalanches with explosives near highways and at developed ski areas. This type of avalanche control prevents the development of unstable layers in the snowpack and results in fewer and less severe avalanches. The marked decrease in fatalities among snowplow drivers, motorists, and in-bounds skiers resulted from these preventive measures. One-third of all avalanche deaths occurred in Colorado. The correlation between the general population of Colorado and avalanche deaths in the state suggests that the per capita rate of avalanche deaths in Colorado may have remained constant. If the percentage of the Colorado population that participates in these activities has increased, then the death rate among those at risk may have actually decreased. The only previous study of avalanche accidents in the United States is a descriptive study that reports the burial circumstances, diagnoses, and outcomes of 21 avalanche victims in the state of Utah [2]. Twelve fatalities and nine injuries are described during a 6-year study period. European studies have attempted to determine the relationship between burial time (time to extrication) and survival; these studies report that survival decreases with burial time and that the 50% mortality point occurs within approximately min [9-12]. The major limitation of these studies is that many persons who are caught and not injured or killed may be unreported. Climbers, backcountry skiers, out-of-bounds skiers, and snowmobilers represent 65% of all avalanche fatal ~ ~ ~~ ~ ~ 2.5 Population (millions) Fig 3. Correlation of Colorado population with Colorado avalanche deaths (n = 111; r = 0.667)

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6 Avalanche deaths in the United States 7. Colorado Department of Health, Health Statistics Section. Colorado Vital Statistics. Denver, CO: Colorado Department of Health; Colorado State Department of Health, Records and Statistics Section. Annual Reportof Vital Statistics. Denver, CO: Colorado State Department of Health; Falk M, Brugger H, Adler-Kastner L. Avalanche survival chances. Nature. 1994;368: Brugger, H, Falk M, Buser 0, Tschirky, EE L'arva: bilan 151 et perspectives [in French]. Neige et Avalanches. 1997;78: Brugger, H, Falk M, Adler-Kastner L. Der lawinennotfall neue aspetke zur pathophysiologie und therapie von lawinenverschiitteten [in German]. Middle Eur J Med. 1997; 109: Burtscher M. Avalanche survival chances. Nature. 1994; 371:482.