International Symposium on Mitigative Measures against Snow ...

<strong>International</strong> <strong>Symposium</strong> on Mitigative Measures against Snow Avalanches
Egilsstaðir, Iceland, March 11–14, 2008
4. PERFORMANCE
The shape of the volume will direct the explosion vertically to the snow cover, creating a
detonation that will hit this cover. As shown in the figure 4, it is a typical profile of detonation
with first an overpressure front followed by a depression period: it has a double effect on the
snow cover; first to break its resistance and then to lift it and ease its move.
Measurements made with an air overpressure sensor on ground without snow give positive
results: the maximum overpressure obtained at a 12-meter horizontal distance reaches
80mbars for the wave reflected on the ground, which is equal to the 0.8m 3 Gazex® system.
The main difference is the duration of the detonation, which is twice shorter than the propane
detonation (Gazex® system). The influence of this parameter will be tested during the 2007-
2008 winter. A priori, Daisy Bell® would stand between the classical explosive and the
explosion of the propane-oxygen mixture, in terms of effects and wave speed.
mbars
100
80
60
40
20
0
‐20
‐40
‐60
‐80
0 0.01 0.02 0.03 0.04 0.05
temps
Time(s)
Gazex O.8 m3
Daisy Bell
Figure 4 Air overpressure obtained at a 12m horizontal distance for a fire at 3m above a
ground without snow and compared with the Gazex® system in similar conditions
NB: to improve the performance of the system, the introduction of a tightening (or sonic pass)
at mid-height inside the cone is planned. Preliminary tests show a gain of 20 to 30% on the
total amplitude of the wave. To date, no major limitation due to the air flow of the helicopter
has been seen.
5. CONCLUSION
Daisy Bell®, this new system of avalanche prevention release, transported by helicopter, has
many advantages to secure an important area after snowfalls. Its simplicity is the guarantee of
the reliability and its transport by helicopter ensures a great mobility and a rapidity of
treatment.
This first winter will be dedicated to validate performances and the use of the system with 10
devices. In parallel, the development is being validated and approved by INERIS, French
National Institute for industrial risks.
Berthet-Rambaud and others 95