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Keywords: avalanche accident,avalanche rescue
ABSTRACT
Avalanche balloonsareconsideredas rescuedevices to
prevent avalanche burial.Based onalimitednumberof
test results and field experience the effectiveness ofava-
lanche balloons is preliminarily assessed. The results sug-
gest that the avalanche balloon is effective in reducing the
frequencyand extent of burial in avalanches.However, the
limits of effectiveness could not be determined and many
questions remain unresolved.
INTRODUCTION-DEVELOPMENT OF THE
AVALANCHE BALLOON
Different means for detection and rescueof avalanche vic-
tims were intensively discussed in the late 1960'sand the
early 1970's during the meetings of the International Foun-
dation VanniEigenmann andthe International Committee
forAlpineRescueSystems(IKAR).AproposalbyRuth
Eigenmann in 1970 was the wearingof a ski jacket that can
be inflated by means of compressed airorgenerated gas.
Around the same time Josef W. Hohenesterpresented his
invention:the avalancheballoon.Both systemswere con-
sidered asbuoyancy elements supposed to keep the victim
closertothesnowsurface,and werepartlyseenasim-
provement of the avalanche cord(de Quervain, 1975). The
avalancheballoon invented by Hohenester was further de-
veloped in the late eighties and offered forsale byPeter
Aschauer, a German manufacturer. By the summer of 1996
more than 3000so-called ABS backpacks were manufac-
tured andsold on the premise that burial can be prevented
byhelpingthevictimtostayontopoftheflowing
avalanche.During travel in avalancheterrainthe avalanche
balloonisfoldedandcarriedinaspeciallydesigned
backpack. In caseof avalanche involvement, the skier trig-
gers the balloon by pulling a rip-cord and releasing pres-
surizedgas from the cartridge. Thegas passesat high speed
through jets drawing in outside air(Venturi effect) toin-
flate the balloon within 2 - 3 seconds.
Thisarticlerepresents asummaryandupdateofthe
original work described in Tschirky et al. (1995). For addi-
tional details the reader is referred to this article.
THEORETICAL CONSIDERATIONS
Theoreticallytheavalanche balloonshouldhelptopre-
ventburialbytwoeffects:bydecreasingtheapparent
weight of the victim in the flowing snow and, in particular
byincreasingthevictim'svolumewhichsupportsthe
process of inverse size segregation in a flowing avalanche.
By this dynamic process of inverse grading, largeparticles
rise throughthe surroundingsmaller particles to thesurface
layer, where, dueto the higher velocity at the surface, they
move on to the frontof the granularavalanche.Inlaboratory
granular-avalancheexperiments,largeparticleswere
frequently moved to the front and top of the accumulation
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(Savage, 1993).
The unequal distribution of density between the balloon
and the person howevermeans that the balloon tends to
locate above the person.
Static buoyancy alone cannot explain the proposed ef-
fect of the avalancheballoon, since flow densities are typi-
cally less than 400 kg/m 3(approx.density of victim with
inflated balloon).
KNOWN ANDDOCUMENTED AVALANCHE INCIDENTS WITH
AVALANCHE BALLOONS
As of 15 March 1996 we only know about seven incidents
involving a total of 11 skiers equipped with the ABS back-
pack.Allvictimssurvived.Two balloonsdidnotinflate
due to human errorortechnical malfunction.These two
skiersgotcompletelyand partlyburied,respectively. Of
the 9 people with inflated avalanche balloons,6 were not
buriedoronlypartlycoveredwith snow;3were buried
critically1 ,i.e.theirheads were underthe snow, butthe
balloon was visible on the surfaceof the avalanchedeposit.
Definitionofcriticallyburied: Avictimisconsidered
as critically buried,if most of the body,in particularthe
head andthe thorax are substantially buried with snow, so
that the person cannot freehimself andis in mortal danger.
Partsofthe bodyorthe equipment maybevisible.This
type of burial was previously described as totally buried.
PREVIOUS PRACTICAL TESTSOF THE
AVALANCHE BALLOON
Hohenester intensivelytestedhisinventionat theZugspitze
(Germany) during 1975-79. One test by Allianz Technology
Centre in 1978 is documented as well as two testsby the
Canadian Parks Service from Banff National Park (Canada)
in 1980-81. Some tests were also done with the further de-
veloped, ABS-AvalancheAirbagSystem, using video shots
for documentation. As far aswe know, in all previous tests,
the balloon was not completely buried, but was visible on
the avalanchedeposit.
TESTS BY SFISAR WINTER 1994-95
The Swiss Federal Institute forSnow and Avalanche Re-
search (SFISAR)at Weissfluhjoch/Davos carried out pre-
liminary tests with the ABS avalancheballoon during the
winterof 1994-95.The objective was to examine whether
the avalancheballoon folded into a skier's backpack, trig-
gered and inflated in time could effectively prevent a per-
sonfrombeingburied ina slabavalanche. Product-spe-
cific characteristics such as technical reliability and ease
of handling of the ABS avalanche backpack were not the
main objective of the tests.The test equipment included
18 different life-size dummies (mass: 65-85 kg) and 10 ABS
avalanche backpacks,6ofwhich were equipped witha
radio forremote triggering of the balloon.
The dummies fully equipped as skiers,with and with-
outtheavalanche balloon,were placed in pairsbyheli-
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