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 AvalancheProbingRevisited
TimAuger1andBruceJamieson2
1 Banff Park Warden Service
Box900, Banff, Alberta T0L 0M0,Canada
2 Dept. of CivilEngineering,University of Calgary, Calgary, Alberta
Phone 403-220-7479, Fax 403-282- 7026, e-mail jbjamies@acs.ucalgary.ca
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Avalancheprobing is still required to searchavalanchede-
positswhen otherrescue means such as transceivers are
unavailable. For manyyears themost common method em-
ployed by organized rescue teams in western Canada has
beenthe techniqueknownascoarse probing. In coarseprob-
ingtherescuerslineupelbowtoelbowandprobethe
snowpackonceperstep astheline ofprobersadvance.
This technique producesa pattern of probe holes on a 75 x
70 cm grid. The probability of detection rangesfrom 20%
fora vertically oriented victimto 95% fora prone orsu-
pinevictim and is consideredto average76%(Schild, 1963,
1974).
Theideabehind coarse probespacing recognizes the
need to sacrifice some thoroughness to improve the speed
of probing and thus maximize the chances of recovering a
victimalive.Thedecision toemploycoarseprobingre-
flects the sort of trade-offs orrisk-management familiarto
themodernincident commander.Inavalanche searches
requiring manualprobing the problem, in simple terms, is
how to get as many holes into the snow as fast as possible.
This paper examines two possible means to improve the
speed and efficiency of probing in rescues where there is
stilla possibilityforlive recovery.Limiting the depth of
probing is discussed and several alternative probing tech-
niques are compared.
LIMITING DEPTH OF PROBING
The concept of restricting the depth of probing is not new.
Lacking sufficient burial statistics,Perla (1967)assumed
that avalanche victimswere distributed uniformly in the
top 3 m of an avalanchedeposit, and concludedthatlimit-
ingprobingdepth wouldnotincrease theprobabilityof
findingavalanchevictims alive. However, recentSwissand
US statistics on burial depth (Figure 1) representadequate
samples forre-consideration of optimum probing depths.
Itisclearthatsurvivalisrelatedtodepthofburial.
Deeper burial likely means more restricted respiration and
denser snow deposition containing less air.Deeper burial
often resultsfrom larger andthusmore violentevents. Since
deeper burial is more likely to mean the victim has already
succumbed, it makes sense to consider limiting the depth
ofprobingifitimprovestheoddsoffindingthevictim
whoismorelikelytostillbealive because ofshallower
burial.
If the depth of probing is limited,the speed of probing
should increase because the probe does nottravel as far.
Speed is furtherimproved if the probe itself can actually
be shortened making it easier forthe rescuer to manage.
Is there an optimum depth of probing? Both sets of sta-
tisticsshowthetotalnumberofvictimsburiedinava-
lanches decreases at depths below 1.5 to2.0 m.Perhaps
more significant is the sharp decline in the proportion of
survivors at depths greater than 1.5 to 2.0 m.
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If the rescue leader is faced with searching a vast area,
he may opt fora shallowerprobe depth not only to speed
up the rate of probing,but to focus the search on that part
of the debris mostlikelytocontain a victimwho isstill
alive.
Wechose 1.5 meters (close to 5 feet) as the test depth for
limiting probing.This depth would reach approximately
68% ofthe total victimsin the US database and 88% of
those recovered alive.Using the Swissstatistics,85% of
the victims,or95% of those recovered alive,were found
at depths less than 1.5 m.
Theeffectofshorteningtheprobes,and limitingthe
depth to 1.5 m is discussed in detail in the next section.
FIELD TESTS
Field tests ofvarious techniques were conducted at Rog-
er's Pass,B.C.on March 29,1996.An undisturbed snow-
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