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OCR for page 37
5
Avalanche Control
Control techniques used in the United States are comparable to those used in other
industrialized mountain countries. However, there is a growing disparity between the type
and extent of techniques used in the United States and those used in such countries
as Switzerland, France, and Austria where a long-term commitment to the reduction of
avalanche hazards has achieved greater progress in avalanche control ant! a higher orioritv
for public safety.
c' ~ ,
The objective of avalanche control is to reduce or eliminate the hazard from potentially
destructive avalanches Methods for accomplishing this include (~) active methods, which
involve systematic attempts to artificially trigger small nondestructive avalanches as a means
of reducing the hazard as well as to test the accuracy of avalanche hazard forecasts, and
(2) passive methods, which include anchoring or modifying the snow in avalanche starting
zones so as to eliminate the release of large destructive avalanches and the construction of
various structures to divert or dissipate the force of an avalanche in track or runout zones.
ARTIFICIAL RELEASE OF AVALANCHES
Avalanches may be initiated by detonating high explosives either in or above the
snowpack. When such artificial triggers produce avalanches, impressions about snow stability
can be ascertained, and options for avoiding the consequent hazards can be formulatecI.
When efforts to trigger avalanches fail, however, it should not be concluder] that the
snowpack is necessarily stable (Gubler, 1983; Pratt, 1984; Penniman, 1987~.
Mechanical shear loading to the snowpack in starting zones can be accomplished with
or without explosives. Explosives can be used to drop cornices or release smaller stuffs from
above onto large avalanche starting zones (McCarty et al., 1986~. This safe and effective
way of applying large shear loads to a slope is often helpful in determining the stability
of the snowpack and in triggering avalanches. Under certain conditions, cornices can be
safely kicked loose by experienced technicians to test the stability of lower slopes. Alter-
native experimental methods for releasing avalanches include gas detonated above buried
canisters (e.g., GAZ.EX), air-bag inflation, and "seismic exploration" air guns (LaChapelle,
37
OCR for page 38
38
1977, 1978; Penniman, 1989b; Tremper, 1990; D. Abromeit, U.S. Forest Service, written
communication, 1990~.
Since 1933 the most versatile and practical techniques for artificially triggering ava-
lanches utilize various forms of high explosives to induce a shock wave into the snowpack
(Fraser, 1966; Seligman, 1962~. Over 100,000 explosive charges are detonated annually
for avalanche control (PerIa, 197Sb). The equivalent of ~ kg (2.2 Ib) of TNT has been
established by tradition as the standard charge for testing snow stability, but larger charges
can and often are used when necessary, and smaller charges may be adequate for thin new
snow (PerIa, 197Sb). The best results with explosives are achieved from detonations that
occur I-2 m (3 - ft) above the snow surface or on rock surfaces near the target areas in
starting zones. Correct placement and correct timing of explosive detonations are critical to
their effectiveness (Gubler, 1977, 1983; LaChapelle, 1978) and are often a matter of local
experience.
Techniques that utilize explosives have been reasonably safe and effective for the ma-
jority of snow conditions when strict safety precautions are observed and generally accepted
control procedures are followed. However, with certain conditions, such as wet snow, ex-
plosives have often been unreliable. Some serious safety problems remain unresolved, as
will be noted later; liabilit~v issues are discussed by Fagan and Cortum (1986~.
A variety of delivery systems are currently in use, the most common of which is hand
delivery. This technique, widely used at U.S. ski areas, requires avalanche control techni-
cians to ski or walk to predesignated delivery sites and physically throw charges into known
avalanche starting zones. Costs are comparatively low when a large number of avalanche
Oaths are concentrated in easily accessible areas and the placement of explosives can be
. . .. . . . ~ · · . · · ~ · .
widely adjusted to achieve greater enect In various snow deposition patterns. L'~sadvanta~es
~ OF ~
Of hand charging are that the procedure cannot be readily performed at night or during ex-
treme storms and the avalanche control technician may be exposed to hazardous conditions.
Suspending the charge at the desired height above the snow surface or on rock surfaces
is also impractical without significantly increasing the cost and time necessary to conduct
operations. Experiments in Switzerland with booms that swing out over a starting zone to
suspend a charge have had some success; apart from the Alpental ski area in Washington,
none are in current use in the United States.
The hand charge is currently the predominant explosive system for avalanche control in
terms of the number of explosive charges. The hand-charge system, ignited with a pull wire,
seems to be relatively safe, as few explosive accidents have occurred despite wide variation
in the types of explosives used and the broad range of deployment conditions. Areas under
U.S. Forest Service (USFS) permit were, at one point, required to develop safety plans for
training personnel in the use of hand charges, but there has been reluctance among some
~ , ~ · ~
.. ~ ~ . . ~ . ~ , .. , ~ .~ '. . ~ ~ . ~ ~ r . '.
suppliers of explosives to be involved with hand-thrown applications due to a lack of studies
about the reliability of the assembled hand-charge configuration as well as distrust toward
departures from standard procedures used in normal blasting practices.
Two hand-charge accidents in 1973 at Mammoth Mountain, California, probably in-
volved some aspect of the pull-wire fuse igniter attachment and led to formal testing of the
hand-charge system by the Naval Weapons Center at China Lake, California, at the request
of the USES. Testing revealed that the system in use at the time could experience detonation
from electrostatic fields, thus indicating the need for a grounded or nonconductive fuse. The
primary cause of the accidents was apparently poor operational procedures. The test report
concluded that the USES should institute a procedure for certifying proficiency in handling
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39
of specific detailed safety instructions: "These must be specific, not broad, platitudes such
as 'the operation shall be conducted in a safe manner"' (Austin et al., 1974~. It is difficult to
prepare specific safety guidelines without referring to a specific hand-charge system (Peria,
197Sb).
Cable delivery systems are little used in the United States (Dombroski, 19~. These
systems are being installed throughout much of Europe (Gubler, 1983) and in some parts
of Canada. Of Austrian and German origin, over 120 cable explosive transport systems
are now used in France alone for ski areas and transportation routes (Brugnot, 1987, 1989;
Borrel, 1987; Rapin, 1989~.
Using manual or powerec} drives, cable delivery systems transport explosive charges to
avalanche starting zones on a cable tramway. Once in position, sophisticated remote-control
carriers automatically lower charges to the appropriate height above the snow surface and
then detonate them. Cable systems more than 6 km long sometimes require computer-
aidec! motor drive and radio-signaled explosive control (Brugnot, 1987~. These systems
can deploy several carriers at once, thereby saving time, and can be operated at night and
in poor visibility from a safe location with maximum electiveness, allowing inaccessible or
dangerous starting zones to be remotely accessed. Depending on their design sophistication,
cable systems can appear relatively expensive to build and to operate, yet they seem to be
cost-effective. To some, there are aesthetic problems the systems do not beautifier the
landscape. Regulations in France require the retrieval of explosive charges after a 30-
minute delay if firing has failed (Brugnot, 1987~. This creates operational difficulties but is
in the interest of public safety.
Helicopters can be used to deploy explosive charges by aerial bombing. They are also
used to transport control technicians to otherwise inaccessible terrain for hand-charging
operations. In the United States, Federal Aviation Administration regulations govern the
operation of helicopters for the transportation of explosives and for aerial bombing op-
erations. In the Uniter] States and Canada, helicopter delivery is commonly practiced by
helicopter ski companies and by mining and construction companies for short-term projects
(Gmoser, 1978; Peria and Everts, 1983~. The method allows a very accurate and fast inspec-
tion of starting zones and placement of charges. Helicopter flights are, however, limited to
favorable weather conditions, and explosive charges cannot be suspended above the snow
surface or placed on rock surfaces to achieve maximum effect. In fact, because helicopter-
droppecl charges penetrate deeply into the snow, heavier than normal charges must often be
used to gain the same effect as with a standard hand-thrown charge. Although the hazards
of hand charging do not exist with aerial bombing, flying in mountainous terrain can be
equally dangerous.
Preplanted explosives systems have not been used much in the United States and have
seen only limited use elsewhere. These systems have the advantage of being installed during
~1 summer weather and because they are detonated remote]v there is virtualiv no hazard
E, ~ ~ · _ ~ , ~ _ ~ ~ , ~ ~ ~ , , , _
~ · ' *= ?~ ·1 . ~ . · ~ . ~ ~ , ~ · · ·~ ~ . . -
to tecnnlclans. while the systems can provide control tar otherwise 1naccesslole starling
zones, they are very susceptible to mechanical failure due to stress on components buried
by snow Another disadvantage is that only a limited number of charges can be placed
and only in fixed positions. The relative cost of installing remote systems is high, and the
effectiveness of detonation in deep snow is questionable (Peria and Everts, 1983~.
In the United States the use of artillery is a predominant method of avalanche control.
The advantage of artillery is that it can be fired at any time of the day or night, regardless
of weather. Artillery rounds can also be fired into rock surfaces near target starting zones
OCR for page 40
40
of weather. Artillery rounds can also be fired into rock surfaces near target starting zones
for better effect. As with aerial bombing, rounds that must be shot into the snow usually
detonate below the surface and can be less effective in deeper snowpacks (Peria, 197Sb).
The resulting shrapnel can be a hazard, and overshooting is always a possibility, with the
accompanying threat of property damage and injury.
Both military-produced artillery and civilian-produced artillery are widely used by U.S.
ski areas, highway departments, and industry. Military artillery pieces include 75-mm and
105-mm recoilless rifles (RR), the 75-mm mountain howitzer, and the 105-mm howitzer.
Field tests of 106-mm recoilless rifles are scheduled for the 1989-1990 season (Penniman,
1989b; D. Abromeit, U.S. Forest Service, personal communication, 1990~. The explosive
content of ammunition for these weapons varies from about 0.7 to 3.5 kg (~.5 to S.0 Ib) of
high-speed explosive.
The supply of ammunition for the World War T 75-mm howitzers is limited, although in
the past, at critical intervals, ammunition supplies have been "discovered." Despite its age,
this weapon remains one of the more popular rifles in use, especially in places where high
accuracy and reliability are essential because of proximity to populated areas.
In 1950 recoilless rifles were made available by the U.S. Army, which helped recluce
dependence on the dwindling supplies of World War ~ ammunition and replacement parts
for the 75-mm howitzers (LaChapelle, 1956, 1962~. The recoilless rifles are lighter than
the howitzers, and because of their low recoil they allow lighter support structures and
permanent gun emplacements. Permanent gun emplacements in turn permit instrumental
alignment for blind firing during periods of poor visibility.
The recoilless rifle is the principal type of artillery currently used for avalanche control.
Some areas are using this weapon by choice because its shorter range reduces the chance
of overshoot into populated areas. Recoilless rifles require frequent vent inspection and
vent replacement. A shortage of adequate spare vents is considered to be a major problem
for some users. Once again, however, the major problem facing users is the possibility that
aging ammunition may be withdrawn from the program, as it was in the summer of 19SS
(Abromeit, 19~; D. Bowles, Utah Department of Transportation, personal communication,
1986~. Inspections by the U.S. Army of ammunition prior to shipment are made on a
lot-sample basis to ensure that the ammunition meets acceptable standards of use. To
avoid interruptions in critical avalanche control programs, users have tried to maintain large
ammunition inventories. While this provides a longer-term supply, it fails to address the
level of inventory control and inspection formerly guaranteed by Army military storage and
testing procedures.
Current (1989) estimates indicate that for users of the 105-mm RR there is at least
an S-year supply of serviceable rounds and an additional 6 to 7 years of "unusable but
repairable" rounds (Penniman, 1989b). Thereis only about a 4-year supply for the 75-mm
RR. For these reasons the U.S. Army has now relaxed its prohibition on civilian use of the
106-mm RR. However, this weapon is also out of production, and its use represents only a
temporary solution.
The only civilian artillery piece being used in this country, the "Avalauncher," is pro-
duced in California by R. C. Peters Avalanche Control Systems. This device is a compressed
air cannon that propels a I-kg, rocket-shaped projectile a distance of ~ km (Atwater, 1968~.
The projectile detonates on impact and throws no shrapnel. Its range and accuracy are
inferior to those of military weapons, but use of the Avalauncher could increase because
users have been warned that military ordnance will be depleted within a few years at current
OCR for page 41
41
than do conventional military weapons. However, there are safety concerns, and production
problems plague the manufacturer, leaving Avalaunchers and projectile parts in chronic
short supply. Other substitutes for military weaponry have been proposed, but none have
been developed (PerIa, 197Sb; Penniman, 1989b).
CONTROLLING THE USE OF EXPLOSIVES
Prior to Woricl War IT the USFS pioneered the use of explosives for avalanche control.
Subsequent efforts by the USFS to obtain military weapons for avalanche control came
shortly after World War Il:, when the first artillery tests for avalanche control were conducted
with French 75-mm howitzers at Berthoud Pass and soon after at Alta (Kalatowski, 1988~.
An immediate result of these successful tests was the development and acceptance of a
guideline "Memorandum of Understanding" between the U.S. Department of Agriculture
and the U.S. Department of Army hi. Herbert, U.S. Forest Service, personal communication,
1986; Kalatowski, 1988~. This memorandum defined the roles and responsibilities of the two
departments in what would become the weapons program. Under the terms of agreement,
the U.S. Army would supply surplus weapons and ammunition, with repair and training
support, to local USFS offices. The USFS would administer the program and assume
responsibility for training gun crews, operating the program, and maintaining public safety.
The memorandum had the effect of making the USFS and the U.S. Army partners in
selected areas and created a protective "umbrella" to spread the risks.)
During the early period, avalanche control artillery was fired by National Guard gun
crews, with target selection by USFS snow rangers. While the firing by National Guard
crews was highly professional, the leac! time for weapons deployment was immoderately
long compared to forecast lead time. By 1966 the roles were more clearly defined. In
areas having a high hazard, defined as Class A, the USFS would provide snow rangers
with avalanche forecasting and artillery control expertise. Areas with less serious avalanche
problems were ciassifiec! as Class B or Class C. Class B areas were monitored and assigned
direct USFS control if they failed to provide adequate avalanche protection for the public.
Class C areas did not require rifles or direct snow ranger supervision. Over time a gradual
shift was made to the employment of ski-area personnel as gun crews, and the USFS's role
was reduced to administrative monitoring with little hands-on gun time (D. Bowles, Utah
Department of Transportation, personal communication, 1986).
In some instances, weapons control programs have been developed by state agencies.
Highway departments in Alaska, California, Colorado, and Washington have developed
successful avalanche control programs similar to those of USFS-administered ski areas
(L~aChapelle, 1962). The state governments entered into local agreements, usually involving
both their National Guard and the U.S. Army, to supply weapons and support.2 Generally,
the resulting programs have faced problems similar to those encountered in USFS programs,
mainly in the areas of spare parts, ammunitions availability, dud disposal, and gun crew
training.
MAJOR PROBLEMS IN THE USE OF EXPLOSIVES
Unexploded charges (duds) represent one of the most serious operational problems
facing explosives control programs, particularly for the artillery program (Abromeit, 19~).
Self-destruct capabilities are not normally built into military warheads.
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42
In many areas dud rates of 2 to 5 percent are common (D. Bowles, Utah Department
of Transportation, personal communication, 1986~. In most instances the rounds are fully
armed but fad] to explode on contact with the snow. Armor-piercing rounds are less sensitive
and generate a larger percentage of duds. Rounds of high explosive plastic tracers (HEPT)
have shown a dud rate up to 30 percent ED. Abromeit, cited by Penniman (1989b)~. Also,
recoilless rifles yield a substantially increased dud percentage when used at over half the
maximum range (Peria, 197Sb). This increase is due to the influence of trajectory; with
flat-trajectory grazing shots into soft powder, some projectiles sup back into the air and
continue their flight to some other landing site. Unexploded rounds have been found at
the maximum range for the weapon, which for the 105-mm recoilless rifle and the 75-mm
howitzer is over ~ km (5 miles). Most duds fall into remote and inaccessible areas, but
despite a low encounter probability many are found each year (Perla, 197Sb).
Military ordnance experience suggests that 10 percent of duds detonate spontaneously
(D. Bowles, Utah Department of Transportation, personal communication, 1986~. The
remaining 90 percent remain fully armed in some unknown state of sensitivity. Because
military ammunition is well constructed and sealed to withstand long-term exposure to
extreme environmental conditions, duds may remain operational for years. Most areas
using weapons have had this problem since the inception of weapons programs in the early
19SOs, and the cumulative number of lost, fully armed, and sensitive explosive charges is
probably in the thousands.
Immediate retrieval of unexploded charges is generally impossible, and therefore dud
control is included in the spring cleanup operations for area gun programs. The recovery
rate is no more than about 50 percent. If an average dud rate of 3 percent is assumed for
an average annual national projectile expenditure of about 6,000 rounds (cf. Peria, 197Sb),
a recovery rate of 50 percent implies 90 lost rounds per year (D. Bowles, Utah Department
of Transportation, personal communication, 1986~. Since artillery has been used for over
30 years, perhaps 3,000 unexploded rounds could exist in the U.S. backcountry, threatening
recreationists. The current tendency for 105-mm RR users to switch to the more abundant
HEPT rounds should exacerbate the dud problem (Penniman, l989b; D. Abromeit, U.S.
Forest Service, personal communication, 19904. Similar problems may arise with the 106-
mm RR. With increased urbanization and use of backcountry areas, the probability of dud
encounters is expected to increase.
A second major problem is related to the Avalauncher, toe only civilian artillery in
use in the United States. Designed to meet a specific avalanche control problem, the
Avalauncher provides short shots with low fragmentation and has the further advantage that
Tufts are rapidly reduced to an inoperative condition by the open case design. Its initial
development was supported by the USES (Atwater, 1968), and further refinements have
been made by the manufacturer. The projectile has a finned plastic case that can be loaded
with any type of explosive, from cast primer to dynamite. Arming is achieved by air flow,
removing an arming disk and safety pin as the projectile exits the barrel, and a magnetically
retained firing pin initiates base detonation on impact. Ranges up to 1,500 m and beyond
are possible, although the longer distances require a stronger projectile case to prevent case
collapse in the barrel. English and French versions (Avalancheurs) are capable of distances
up to 4,000 m (12,000 ft) (Brugnot, 1987~; neither is used in the United States.
The Avalauncher has been widely accepted for avalanche control, despite little official
recognition by such branches of the government as the Federal Alcohol, Tobacco, and
Firearms Agency. The USES lost interest in its development, though its view has been one
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43
of benign neglect, neither approving nor disapproving its use. Avalaunchers are used today
at many ski areas under USES permit. The history of its use is further obscured by scant
documentation by either the manufacturer or users (however, see Ream, 1990~.
Users have long recognized the Avalauncher's inherent defects, both in operational
safety and quality control of the weapon and its design. Many users have implemented
special operating procedures to resolve some of these problems and make its use somewhat
safe (e.g., Marier and Fink, 1986~. Because the Avalauncher is not a fail-safe system, the
mechanism watt fire with component failure in the firing or drive mechanism. As a result,
air leakage can cause the mechanism to fire.
A fatal accident in Chile involving an Avalauncher led to an analysis of the device by
the USES San Dimas Laboratory (Spray, 1983), which concluded that the fusing system
then used did not conform to standard ordnance practice. Such flaws in design would
not be tolerated in military systems, which are under tight administrative control, with
crews thoroughly trained and obedient to specific operating documents. No such control or
documentation is guaranteed for civilian operation, and this represents a serious problem
that should be addressed.
MECHANICAL COMPACTION AND DISRUPTION
In the United States the stabilization of snow in avalanche starting zones through
compaction is performed primarily by recreation facilities personnel such as at ski areas.
The process densities the snow, adding strength and reducing the tendency for future slope
weakening through temperature gradient metamorphism. Compaction is accomplished by
"boot packing," skiing, or machine methods. Boot packing is performed by a group of
individuals walking down a known avalanche path in early season. Though usually requiring
only a single pass down the slope, this method is labor intensive, and in the United
States has been limited to small, easily accessible avalanche paths. Ski compaction can
be accomplished cheaply by skiing patrollers and by the public. Effective in breaking
up cohesive snow slabs, the method is widely used in the United States and throughout
the world. Machine compaction utilizes the weight of over-snow vehicles to density the
snowpack. The effect is similar to skiing but can be accomplished faster and with more
uniform results. Nevertheless, machine compaction is not widely used, chiefly because of
the inaccessibility of many starting zones and the current high costs of vehicles and cable
belay systems.
STRUCTURAL CONTROL OF AVAI^NCHES
Structural avalanche control includes the natural or artificial anchoring of the snowpack
in starting zones, structure-influenced redistribution of the snowpack in starting zones, and
the structural protection of lives and property located in known or suspected avalanche
paths.
Destructive avalanches may be prevented by retention structures that anchor the snow
in starting zones. Such structures are most commonly used where avalanches threaten per-
manent facilities, towns, or roads. Provided snow depths do not exceed design parameters,
such structures have proved effective, although their reliability may be questionable when
snow cover is deep and poorly cohesive (Brugnot, 1987~. The most common retention struc-
tures in use include snow rakes, snow bridges, and nets (Thomman, 1986; Lazard, 1986~.
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44
Earthen terraces and rock-fi~led steel baskets (gabions) have been used in the past but are
seldom used now. Steel or earthen retention structures are usually designed as permanent
structures, while wooden retention structures (rakes and bridges) are temporary and are
used in conjunction with reforestation (Fraser, 1966; Iaccard, 1986; Montagne et al., 1984~.
In the latter case the maturing trees are expected to take over the job of anchoring the
snow, and the wooden structures are either left to disintegrate over time or are removed.
While retention structures and avalanche path reforestation programs are used quite
extensively in Europe and elsewhere, few have been instituted in the United States. Where
snowpacks more than 4 m (12 ft) deep are common, as in the mountains of the Pacific
coastal states, retention structures would have to be of massive proportions and are not
economically feasible. In the Intermountain and Rocky Mountain states, however, where
snow is less deep, retention structures could be installed more economically, but they would
still be expensive ant! might encounter resistance on aesthetic grounds. In Switzerland
structural control is subsidized by federal funds provided that building sites are selected in
regard to avalanche zoning plans (Frutiger, 1972~.
Under certain conditions the size and frequency of avalanches can be reduced through
structures that alter storm wine! patterns ant] thereby alter the deposition patterns of snow in
starting zones. Such devices are usually used in conjunction with supporting structures and
are not intended to eliminate the threat of avalanches, but rather to influence the amount
and pattern of snow that accumulates in the starting zone. They are currently being used in
a few parts of the United States.
One redistribution structure, called a "jet roof," acts as a "venturi" at the ridge line
above avalanche starting zones (Peria and Martinelli, 1976~. It reduces cornice buildup and
causes wind-borne snow to deposit farther down the lee slope where inclinations are more
gentle. Installation and maintenance may be expensive. Other redistribution structures
include snow fences, which are usually located on flat ridge crests above starting zones or on
windward ridges (Norem, 19784. Fences trap blowing snow in fetch areas before the snow
can reach the starting zones or cornices above the starting zone. Redistribution structures
are relatively inexpensive to build but have limited application. Their major disadvantage is
that they are less effective when winds deviate from their prevailing directions or are absent
altogether.
Retarding or catchment structures, such as mounds, ditches, terraces, and dams can be
designed to foreshorten runout distances of avalanches. Mounds and terraces usually are
used to stop, divert, confine, or slow moving avalanche debris in the lower track or the
runout zone of avalanche paths; some have been used in Colorado and Alaska (LaChapelle,
1962; Mears, 1981; YanIong et al., 1980~. Dams are usually designed to stop debris and are
normally located in runout zones. Numerous mounds and terraces may also be positioned
above the dams to decrease the impact force on the main structure.
Retarding structures may be permanent, of earth, rock, and concrete construction, or
may be large temporary berms of snow. An advantage of permanent retarding structures is
their capacity to withstand tremendous impact forces. They require little maintenance once
in place. A disadvantage is the short-term expense and the major visual transformation
imposed on the landscape. Temporary structures made of snow are inexpensive to build
and they disappear each summer, but they are not as strong as permanent structures, and
maintenance is required after impact with major avalanches. Few permanent retarding
structures have been built in the United States, but in Japan, Europe, and even in parts
of South America they have been built with favorable results (Fraser, 1966; Mears, 1981;
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45
Jaccard, 1986~.
Temporary structures built of snow have been successfully employed in
California to reduce avalanche runout.
Other structures can be designed to protect permanent facilities, such as sheds, gal-
leries, and tunnels to protect railroads and highways; berms of earth, concrete, or snow to
deflect avalanche debris; and wedge-shaped walls that divert moving debris around specific
structures or facilities (Fraser, 1966; Mears, 1981~. In the United States, railroad galleries
and tunnels have had success in reducing the number of avalanche incidents involving trains,
but few structures have been constructed to protect highways from avalanches (LaChapelle,
1962; Mears, 1986~. Dependence has been placed on active control. A proliferation of other
types of diversion structures can be found in Europe and other parts of the world (Fraser,
1966~. In populated areas the possibility of avalanche debris being diverted to the benefit
of some but the detriment of others must always be considered in their design.
Other protective measures that make a structure more resistant to impact forces may be
integrated into existing or proposed facilities; such measures include reinforcement, angled
walls and roofs, and an assortment of protective shutters and doors for buildings located
in avalanche paths. These adaptations can be more aesthetically pleasing than retarding
or diversion structures, and their cost can be more easily amortized over the long term.
Although a safe haven may be created, no protection is provided to people and property
located outside the structures. The hazard of access into or out of reinforced structures
remains unchanged unless diversion devices are also installed.
New structures built in avalanche paths in the United States may have reinforcing fea-
tures designed into their construction. Some local building codes require design considera-
tions for inhabited buildings in avalanche paths (Mears, 1980), though uniform engineering
standards do not exist. Questions may arise concerning appropriate engineering criteria and
liability in the event of design failure.
COMMENTS
I. No system providing accountability ant] effective channels for information transfer
exists for developing and implementing safe procedures and transmitting related technolog-
ical developments. In the early years of U.S. avalanche control, procedures for technology
transfer were developed by a small group involving the USFS, USFS permittees, and the
National Ski Patrol System. No such formal system exists now, although an ad hoc com-
mittee on weapons use, established in 1989 (Penniman, 1989b), after this report had passed
review, represents a step in the right direction. A follow-up meeting was held in Seattle in
May 1990 (D. Abromeit, U.S. Forest Service, written communication, 1990~.
2. Improvements are needed in the handling of explosives. A development program
is needed to test alternative weapons delivery systems, including other types of surplus
artillery. There is still a need for an accurate and reliable short-range weapon with a large
supply of ammunition. Accurate inventories of ammunition are needed, and crew training
procedures should be reviewed and improved.
3. A formalized certification procedure should be established, and information and
training should be widely available. Present training programs appear to be derived from
the original Memorandum of Understanding and involve U.S. Army and USFS instructors.
Areas with military weapons have each developed their own weapons training programs,
and in most cases have retained crews for long periods of time. This has developed a local
expertise that is stable if slightly ingrown. But the loss of crews through attrition or age, and
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46
the need for additional weapons programs, will inevitably require additional training. There
appears to be justification for a uniform nationwide weapons training program to include
all explosive systems. Such a program might include
a. careful development of instruction manuals;
b. basic training in weapons handling to persons lacking experience;
c. continued education in training and safety for personnel at all levels of experience;
d. development of certification standards based on both written tests and weapons
handling ability;
e. training in procedures for weapons maintenance and ammunition storage and
transportation; and
£ training in the documentation, location, and disposal of duds.
4. The problem with duds is important and is increasing in severity, but despite some
efforts to find a replacement for military ordnance, adequate solutions have not been devel-
oped. Indeed, use of HEFT rounds wall likely exacerbate the problem. Alternatives include
the development of a new projectile with self-destruct capabilities, increased emphasis on
dud location, and more sensitive fusing. Explosive-carrying cable lift systems enable explo-
sive loads to be retrieved if firing has failed (indeed this is compulsory in France; Brugnot,
1987~. Therefore, one possible solution to the problem is to replace artillery with cable
delivery systems.
5. Cable deliver~v systems offer some potential for U.S. industrial entrepreneurship,
but developments in the United States substantially lag those in Europe.
6. The chief problem with structural control of avalanches is cost. The massive
structures needed to stabilize deep snow on steep slopes are expensive to construct and
must be regularly inspected and repaired. Yet routine maintenance is difficult to fund.
7. European experience on structural control procedures may be more or less directly
transferred to the United States, if proper site evaluation is conducted prior to design and
installation.
NOTES
I. Apparently, the governing statute is 10 USC 4655: "When required for the pro-
tection of public money and property, the Secretary of the Army may lend arms and
ammunition to federal agencies upon request by agency head" (D. Abromeit, U.S. Forest
Service, written communication, 1990.) The latest Memorandum of Agreement with the
USES is dated JuIv 1989~ affecting 13 ski areas in 7 states.
Issue
~ , ~
2. Memoranda of Agreement exist between the U.S. Army and state government
agencies in Alaska (March 1987), California (November 1989), Colorado (October 19S7),
Washington (February 1989), and Wyoming (June 1989) (D. Abromeit, written communica-
tion, 1990~.
Representative terms from entire chapter:
starting zones
