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Avalanche Notes |
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* use your back button to get back to the contents section Brevent uses a variety of control measures including Gaz Ex, Avalancheurs, Helicopter, hand charges, ski control and an experimantal Avalex system. Gaz Ex Gaz Ex is a permenant installation. It uses a large pipe (exploseur) with a curve at the end aimed down at the snowpack. Exploding gas in the pipe produces a pressure wave that "thumps" the snowpack. Supports for the pipe are drilled and then glued into the rock with a special epoxy. A mixture of oxygen and propane are released into the pipe and then ignited with a peizo-electric spark. The gas is stored in a shelter (abri) and can supply numerous exploseurs through pipes laid in the ground. The gas tanks get replaced by helicopter. The gas is released and mixed at the shelter by a system of valves and sensors controlled by a microprocessor and then fed to the appropriate exploseur. The two Brevent installations are initiated by a computer software which communicates via radio signal with the microprocessor at the shelter. A computer in the patrol director's office runs the software. With communication established between the computer software and the microprocessor the desired exploseur can charged and fired remotely. The microprocessor/software link reports pressure in the gas bottles, wind direction, speed and temperature and also reports whether the detonation was successful. This all relys on various sensors connected to the microprocessor. Power at the shelter comes from batteries charged by a solar panel. There have been a lot of technical problems with the two installations at Brevent so maintenance has been more or less continuous. The advantages are that the system can be fired remotely from a long distance, it can be fired blind and it can be fired often during storms to prevent buildup. Also, the explosive is inexpensive. There are about 30 Gaz Ex exploseurs in the Chamonix area. Most are at the ski areas but the community also has them in the starting zones of some of the large paths that can run out across the valley if left to build up. Avalancheur The Avalancheur is manufactured in Toulouse, France. It uses a two part explosive payload equilivant to about a 2kg charge. Both components are liquid. The arrow or fleche is an aluminum tube about 5 feet long with a tail piece and nose cone that each seal onto the tube with a rubber gasket to prevent the liquid from escaping. The tail piece contains the detonator which initiates a small piece of det cord upon impact. A safety pin is removed to arm the tail piece when the fleche is inserted into the Avalancheur. The explosive is suposed to become inert after two days so only the detonator remains a hazard in the case of a dud. The Avalancheur has a 12 ft. fiberglass barrel that is attached only for use and otherwise stored elsewhere in a plastic cover. The metal housing contains the pressure chamber and trigger mechanism. A nitrogen bottle is attached to the housing and a valve controls gas pressure for each shot. The vertical angle is always the same and distance is controlled by adjusting the gas pressure. The whole unit turns to aim the shot at different compass headings marked in degrees on the base. The compass heading and gas pressure for each shot are pre-recorded so the shot can be fired blind. To assemble, the explosive is mixed by pouring the contents of the smaller bottle into the larger one and then shaking. The tail piece is then inserted on the tube and the mixed explosive is poured into the top. The nose cone is inserted and the fleche is ready for insertion into the Avlancheur. Firing is done electrically with a battery powered detonation box attached to a fairly long cord. A key must be turned to activate the box and then a test button must give a green light before the shot can be fired. This seems to be a very good system. The shots are accurate and pack a good punch. The down side is the shots are expensive. Helicopter The Helicopter is fast and efficient but can only be used when visibility is good. It has been the preferred method at Brevent. It only takes 20-40 minutes to get most of the control work done once the charges have been made up. They use a private service, CMBH (Chamonix-Mont Blanc Helicopters). The charges are the same as used for hand charging, a 2.2 kg alumized gel in a plastic wrapping. They are double capped and fused and an igniter is crimped onto each fuse end. The two fuses are taped together. A special tool is used to pull both igniters at once. The charges are carried in an aluminum rack that holds 28 and there is room for two racks in the helicopter. During control work the blaster sits in front next to the pilot. An assistant is in back next to the charges. The assistant hands the charge forward and when the blaster is ready the assistant opens the door. The blaster then pulls the igniters and tosses the charge. A spotter on the ground verifies that all charges detonate. Avalex Avalex is an experimental system being tested on Pente de la Fouine. It resembles a small space station. The metal structure is bolted onto a concrete pad and can be installed or removed by helicopter. The structure holds 24 tubes that each contain an inflatable balloon. There are hydrogen bottles underneath. To fire, a radio signal is sent from a portable box to the Avalex. One baloon is inflated automatically with a mixture of hydrogen and air. Inflation pops the lid off the tube and allows the balloon to escape to the end of it's tether. In theory the balloon fills up and is then ignited electrically with wiring preinstalled inside. There have been problems and the system has only fired a few times in two seasons. We have been forced to shoot the slope with the Avalancheur and risk blowing up the Avalex. |