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
being heavier than air, its injection from the bottom of the pipe fills it progressively without
loss before ignition
The various phases of the process led to different volumes of exploders depending on the
ground profile and avalanche path size. Another important evolution concerns the possible
simultaneous shots from two 0.8 m 3 and 1.5 m 3 exploders.
2. THE GAZEX® SYSTEM
The system is composed of a shelter, exploder tubes, pipelines and a radio control system.
The polyester shelter, placed on a wooden platform, houses the gas metering devices, the
propane bottles, the valves and the receiver unit. Oxygen is stored outside the shelter.
There are two types of shelters: one ‘’autonomous’’ dedicated to one to four exploders and the
classic shelter for maximum 8 exploders. The shelter is equipped with a Faraday Cage, a
lightning arrester, and meteo instruments. The receiver unit is powered by solar panel, with
storage batteries.
The steel exploder tubes are designed to withstand the explosions and exist in several models
i.e. volumes: 0.8 m 3 , 1.5 m 3 , 3 m 3 , 4.5 m 3 .
Firing is controlled by the opening of the valves which free a predetermined quantity of
oxygen and propane gas. Gases are stored in the shelter, and brought separately by pipelines
down to the exploder where the mixing of the gases happens. After closure of the valves, the
spark plugs of the exploder produce an electric arc which detonates the gas mixture. After
each shot, the system refills itself to the pre-adjusted tank pressure in preparation for the next
shot.
The different phases of the firing process with Gazex® are the following :
• Detonation of the gas mixture inside the exploder creating an overpressure in the
latter (for 2 milliseconds), CO2 and water steam are obtained.
• Ejection of gas at the open end of the exploder (20 millisecondes); ejection speed
towards the mantle of 1 200m/s (at the mouth of the exploder).
• The gases shock the mantle with a 30° incidence; the speed of gases at the level of
the snow mantle varies between 500 and 600 m/s.
• These gases expand after ejection and disturb the surrounding air which creates a
moving shock wave.
Bassetti , Desaulti, Ugnon-Fleury and Roux 121