FR2988389A1 - Composition, useful in an explosive charge and projectile to release avalanches on terrestrial target e.g. winter sports stations, comprises potassium perchlorate and aluminum powder - Google Patents

Abstract

Explosive composition comprises potassium perchlorate and aluminum powder. Independent claims are included for: (1) an explosive charge to release avalanche comprising 900 g to 3 kg of the explosive composition; (2) projectile to release avalanche comprising the explosive composition and an initiation system connected to the explosive charge; and (3) avalanche release method comprising providing the explosive charge, and initiating the explosive charge so as to explode at a predetermined distance with the top of the terrestrial target.

Description

The invention relates to an explosive composition for triggering avalanches and a method for triggering avalanches. State of the art Several devices are currently used to artificially trigger avalanches at risk sites such as ski resorts where ski areas and private and public infrastructures must be periodically secured.

Sites likely to constitute an avalanche departure zone are generally avalanche corridors where snow has accumulated. The avalanche triggering then makes it possible to dislocate the snowpack of the valleys and to minimize the risks of avalanches.

The known avalanche triggering devices generally use explosive charges and are distinguished according to whether they are grounded or mobile. Since fixed avalanche triggering devices are expensive and unable to follow the movements of snowpack over-thicknesses as weather conditions change, it is preferable to use mobile devices.

Mobile avalanche trigger devices require the manipulation of an explosive projectile by an operator. Known explosive projectiles are hand grenades consisting of a dynamite stick initiated by a slow-wicking pyrotechnic detonator or an electric detonator. Hand grenades are set up on sites to be secured or launched from a fixed or mobile launch platform. The mobile launch platform is, conventionally, a helicopter flying over the site to be secured, to allow a vertical drop of the explosive charge over the avalanche corridor. These mobile avalanche triggering devices present significant risks for operators who are usually either fireworks or trackers. Indeed, handling explosive charges is the main cause of accidents during these operations because the handling of explosive charges is often performed in unstable climatic conditions and in dangerous areas.

Other remote avalanche triggering devices have been proposed from launch platform to reduce such risks. US-A-5872326 discloses an air gun which launches an explosive projectile fired by an impact rocket. The launch is carried out by a pneumatic launching tube delivering a gas under pressure to project the projectile which explodes in the vicinity or the impact of the snow. Document FR-A-2771168 proposes to constitute the explosive projectiles before firing, by producing a two-component explosive charge. The device inflates a balloon with an explosive oxidant / fuel mixture just before firing.

There may also be mentioned a fixed avalanche triggering device described in document FR-A-2765321. The avalanche triggering device comprises a base anchored to the ground and a gun that propels a detonating gas directed towards the area of the snowy corridor to be secured. Although these fixed avalanche triggering devices exhibit good performance, they require a heavy installation and maintenance infrastructure and remain extremely expensive. In order to follow the evolution of the snowpack as climatic conditions, it is still necessary to use dynamite in a conditioning able to be sent by an individual moving ski. However, the effectiveness of the latter method is not optimal because dynamite is an extremely controlled explosive product and it is necessary to send a large amount of explosive on the snowpack to obtain an avalanche trigger.

OBJECT OF THE INVENTION The object of the invention is to overcome the drawbacks of the prior art. In particular, the present invention aims to provide an explosive composition for more effective avalanche triggering.

According to the invention, this object is achieved by the fact that the explosive composition essentially comprises potassium perchlorate and aluminum powder.

Another object of the invention is to provide an avalanche triggering device that is more efficient.

According to the invention, this object is achieved by the fact that the avalanche triggering device comprises the explosive composition and a priming system connected to the explosive charge.

Another object of the invention is to provide an avalanche triggering method that is more efficient. According to the invention, this object is achieved by the fact that the avalanche triggering method comprises: - predicting the explosive charge, - initiating the explosive charge so as to explode at a predetermined distance above a terrestrial target Summary description Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given by way of non-limiting example and represented in the accompanying drawings, in which: FIGS. 1 to 3 represent , schematically and in side view, the various steps of the method of using an avalanche trigger projectile according to a particular embodiment of the invention. - Figures 4 to 6 show, schematically and in section, the various steps of the method of using an avalanche trigger projectile according to a particular embodiment of the invention. Description of particular embodiments. It has been discovered that an explosive composition essentially comprising potassium perchlorate (CIK04) and aluminum powder makes it possible to obtain, during its explosion, a breath sufficient to trigger an avalanche. An explosive composition comprising essentially potassium perchlorate (CIKO4) and aluminum powder is a composition in which the sum of these two constituents represents at least 50% by weight of the total composition.

In comparison with a dynamite charge conventionally used in the field of avalanche triggering, it has been found that the explosive composition indicated above makes it possible to obtain a result that is almost similar with a mass of product that can be divided substantially. In this way, the user of the explosive composition manipulates a lighter explosive charge which allows him to better target the target area. It is also possible to work with the same mass of explosive charge as in the past but to obtain an avalanche trigger on a much larger surface.

Various tests have shown that the explosive composition has an explosive power particularly well suited for the triggering of avalanches when the potassium perchlorate represents at least 50% by weight of the final explosive composition and the aluminum powder represents at least 30% by weight. weight of the final explosive composition. Advantageously, the chemical composition also comprises magnesium which makes it possible to slow down the reaction.

Particularly advantageously, very good deflagration results have been obtained for an explosive composition containing at least 60% by weight of potassium perchlorate and at least 35% by weight of aluminum. In a particular embodiment, in comparison with dynamite, the explosive composition comprising 60% by weight of potassium perchlorate, 38% by weight of aluminum and 2% by weight of magnesium made it possible to halve the mass of embedded explosive product for a substantially identical result on the avalanche trigger.

In a preferred embodiment that can be combined with the preceding embodiments, the aluminum powder used is "dark pyro" quality powder which makes it possible to have the best explosion power on the snowpack. The explosive composition may be in the form of a powder, but it is also possible to associate it with a binder so as to form an explosive material in the form of a paste, a gel or an emulsion . The explosive composition is then incorporated into the explosive material. Advantageously, the paste, the gel or the emulsion may comprise oxygen bubbles which promote the reaction of the deflagant composition and increase the explosive power. In a particular embodiment, the explosive composition may be devoid of materials generating an explosion color effect other than magnesium. The explosive composition is introduced into an explosive charge which comprises at least 900 g of the explosive composition. This mass of charge makes it possible to obtain a deflagrant effect sufficient to trigger an avalanche in the majority of the configurations. Advantageously, the explosive charge does not comprise more than 3 kg of explosive composition in order to maintain an effective explosive charge. Even more preferably, the explosive charge comprises between 1kg and 2kg of explosive composition so as to have the best relationship between the size of the load (weight, volume) and its effectiveness in triggering an avalanche. In a particular embodiment, the explosive charge comprises 1.4 kg of explosive composition to obtain the triggering of the avalanche in the majority of configurations without deteriorating the soil supporting the snowpack.

Since the chemical composition has essentially an explosive power and not a breaking power, it is particularly interesting to detonate the chemical composition at a distance from the snowpack so as to promote the triggering of the avalanche.

In this way, the triggering of an avalanche can be simply decomposed as follows: Predict the explosive charge indicated above, prime the explosive charge so that it explodes at a predetermined distance above the target. The explosion above ground can be achieved in different ways. For example, the explosive charge is thrown over the target and explodes in flight. It is also possible to use a projectile equipped with a rangefinder or a proximity detector so that the explosion takes place at a controlled distance above the target. It is also possible to use a load suspended by a wire above the target. In order to facilitate its use, the explosive composition is advantageously embedded in an avalanche trigger projectile which comprises a system for priming the explosive composition and therefore the charge.

With reference to FIGS. 1 to 3, preferably, the avalanche release projectile 1 is intended to be released, vertically, from an airdrop station 2, above a terrestrial target 3. terrestrial target 3 means an area of the territory likely to constitute an avalanche departure zone and to be secured by the elimination of at least part of the snowpack. The terrestrial target 3 can be delimited beforehand according to the detonating power of the avalanche triggering projectile 1 used. The aerial station 2 can advantageously be a piloted or unmanned aircraft (in English "unmanned aerial vehicle", UAV) commonly called drone. The aerial station 2 is preferably a helicopter. According to a particular embodiment shown in FIG. 4, the projectile for avalanche release 1 is formed by a casing 4 containing the explosive charge 5 and a pyrotechnic primer 6. The pyrotechnic primer 6 is preferably electric primer. The explosive charge 5 comprises the explosive composition in order to have an explosive or explosive power which makes it possible to limit the impact of the blast on the hard surface supporting the snowpack.

In a particular embodiment that can be combined with the foregoing embodiments, the projectile firing system is configured to trigger the charge explosion at a predetermined distance, di, above the earth target. The projectile for triggering avalanche 1 also includes a rangefinder 7. The function of the rangefinder 7 is to detect the terrestrial target 3 at a predetermined distance, di, corresponding to the range of detection of the rangefinder 7.

The rangefinder 7 may consist of one or more telemetric optical, acoustic or radio sensors. The rangefinder 7 is preferably an infrared (IR) rangefinder.

As shown in FIG. 1, in one particular embodiment, the use of the projectile for triggering avalanche 1 consists in putting the projectile 1 in the release position and then in jettisoning it in this position, vertically, above the terrestrial target 3 so that the rangefinder 7 and, more precisely, the sensors of the rangefinder are oriented facing the terrestrial target 3. The projectile for triggering avalanche 1 is released from a release point 8 of the Air Station 2.

As shown in FIG. 1, the projectile 1 falls towards the terrestrial target 3. During the fall, the avalanche triggering projectile 1 is held in a detection position corresponding to a position where the rangefinder 7 is directed towards the terrestrial target 3.

When the rangefinder 7 detects the terrestrial target 3 at the distance d1 (FIG. 2), the projectile for triggering avalanche 1 explodes above the snowpack (FIG. 3). The explosion creates a shock wave that causes a snowfall in the avalanche corridor. While in the devices of the prior art, the shock wave is generated when the projectile encounters a hard surface, this configuration of the device generates the shock wave above the snowpack. The shock wave achieves the weakening of the snowpack from its upper face instead of achieving embrittlement from inside the snowpack or even from the ground disposed under the snowpack. The weakening of the snowpack from its upper face helps to maintain the integrity of the soil which is particularly interesting during the summer period to reduce the risk of falling stones.

As shown in FIG. 4, the envelope 4 preferably has a necked balloon shape. The envelope 4 may, for example, be constituted by a neck 9 attached to a balloon 10 having an upper portion 11 and a lower portion 12. The neck 9 has a tubular shape and opens at the bottom (bottom in Figure 4 ) on the upper part 11 of the balloon 10 (at the top in FIG. 4). The lower portion 12 of the balloon 10 is fixed integrally to the upper part 11 according to any known method, for example, by gluing or with the aid of an adhesive. The upper and lower portions, respectively 11 and 12, of the balloon 10 thus provide a housing 13. The casing 4 is advantageously formed by a rigid material having a thickness that can vary between 1 mm and 5 mm, preferably between 2 mm and 5 mm. . The envelope 4 is preferably made of at least one rigid biodegradable material such as cardboard, card stock or corn material. The neck 9 and the upper and lower parts, respectively 11 and 12, may be constituted by the same material or by different materials. The rangefinder 7 is integral with the casing 4 and is advantageously arranged on the lower part 12 of the casing 4 so as to face the terrestrial target 3 in the release position and / or in the detection position. As represented in FIG. 4, the projectile for avalanche release 1 comprises a control module 14 for firing the pyrotechnic primer 6 and electrical supply means 15 placed in the housing 13 of the envelope 4. The explosive charge 5 is also placed in the housing 13.

The explosive charge 5 is advantageously packaged in a rigid, semi-rigid or flexible packaging and placed under this packaging in the housing 13. By way of example, the explosive charge 5 is in the form of a plastic bag containing the pyrotechnic composition marketed by the applicant. The control module 14 for firing the pyrotechnic primer 6 is connected to the rangefinder 7 and the pyrotechnic primer 6 by a communication circuit 16. In addition, the control module 14 is electrically connected to the power supply means The control module 14 may be a microcontroller which interprets and processes the data coming from the rangefinder 7 and manages the firing of the pyrotechnic primer 6. The control module 14 is parameterized to transmit a firing order to the pyrotechnic primer 6 upon detection of a terrestrial target 3 by the rangefinder 7. The rangefinder 7 is electrically connected to the power supply means 15 by a second electrical circuit 18.

The power supply means 15 are connected to an electrical connector 19 provided with a light indicator 20 indicating the level of charge of the power supply means 15. The electrical connector 19 is fixed to the wall of the casing 4 in such a way that to be able to be connected to a source of electrical energy (not shown). The electrical connector 19 connects the power supply means 15 to a source of electrical energy and allows the electrical charging of the power supply means 15. The indicator light 20 indicates when the maximum load of the power supply means 15 is reached.

The power supply means 15 are preferably constituted by one or more electrical capacitors or supercapacitors, for example, by three capacitors 2,3V having an electrical capacitance of 10 farads, marketed by Goldcap.

As shown in FIG. 4, the pyrotechnic primer 6 can be placed outside the envelope 4, possibly fixed to the wall of the envelope 4 according to any known method. An orifice 21 passing through the wall of the balloon 10, preferably the lower part 12 of the balloon 10, allows the introduction of the pyrotechnic primer 6 for contact with the explosive charge 5. The projectile for triggering avalanche 1 is preferably provided with a delaying means 22 for putting the control module 14 and / or the rangefinder 7 into operation. The delaying means 22 is triggered during the release of the projectile 1 from the air station 2. delay means 22 constitutes a safety which delays the activation of the control module 14 and / or the rangefinder 7. The delaying means 22 is preferably mechanical and comprises at least one power switch 23 intended to close the first electrical circuit 17 connecting the power supply means 15 and the control module 14. The power switch 23 is actuated when the projectile for avalanche release 1 is at a predetermined distance, d2, the release point 8. The delay means 22 comprises, advantageously, an additional power switch 24 for closing the second electrical circuit 18 connecting the power supply means 15 and the rangefinder 7. The additional power switch 24 is actuated when the avalanche release projectile 1 is at a predetermined distance, d3, from the release point 8 (FIG. 2).

According to a preferred embodiment shown in FIG. 4, the delaying means 22 comprises a three-strand wound wire 25 having first, second and third ends, respectively, 26, 27 and 28. The first end 26 of the coiled wire 25 is provided with anchoring means 29 intended to be fixed to a fixed release point 8 located in the air station 2. The anchoring means 29 are, for example, constituted by a loop made at the end of the coiled wire 25 and the release point 8 by a hook in which the loop can be crooked.

The second and third ends, 27 and 28, are provided, respectively, with the power switch 23 and the additional power switch 24.

As represented in FIG. 4, the retarding means 22 is arranged inside the casing 4 so as to place the majority of the wound thread 25 in the neck 9 while passing the anchoring means 29 of the neck 9 as well as the second and third ends, 27 and 28, in the housing 13. The second and third ends, 27 and 28, opening into the upper part 11 of the balloon 10 actuate, respectively, the power switch 23 and the switch 24. Starting from the first end 26, the coiled wire 25 is uniformly and circularly wound inside the neck 9. The wire 25 separates into two strands from a certain length of the wire 25. at a fork. The two strands have different lengths and end, respectively, at the second and third ends, 27 and 28. The length d2 of the wire 25 coiled between the first end 26 and the second end 27 is less than the length d3 of the wound wire 25 between the first end 26 and the third end 28. By way of example, the length di is preferably between 6m and 8m and d3 between 7m and 9m.

The method of using an avalanche trigger projectile 1 according to the particular embodiment described above comprises a first charging step. This step consists in charging the power supply means 15 until the indicator light 20 comes on, guaranteeing the presence of a reserve of sufficient energy for the operation of the projectile 1. As represented in FIG. The pyrotechnic primer 6 is then brought into contact with the explosive charge 5 by introducing the pyrotechnic primer 6 into the orifice 21. The projectile for triggering avalanche 1 is stowed by the anchoring means 29 at the release point 8 of the 2. This operation can be carried out indifferently, before or after, the steps of charging and setting up the pyrotechnic primer 6. Before the release, the power switch 23 and the additional power switch 24 maintain respectively, the first and second electrical circuits, 17 and 18, in an open circuit position. The control module 14 and the rangefinder 7 are not electrically powered and, therefore, are inactive. The next step is to drop the projectile for avalanche release 1 in the release position. Ditching position means a position in which the lower portion 12 is oriented towards the terrestrial target 3 and the neck 9 to the air station 2 drop. The center of gravity of the envelope 4 is situated at the lower part 12 of the envelope 4 because of its wider shape at the level of the upper part 11 and the lower part 12 than at the neck 9 The particular shape of the envelope 4 promotes the holding of the projectile 1 in the detection position. In the detection position, the rangefinder 7 is oriented facing the terrestrial target 3 and the neck 9 to the air station 2 drop. This stabilizing effect is accentuated by the aerodynamic shape of the projectile for triggering avalanche 1 and by the presence of the explosive charge 5 in the housing 13. The explosive charge 5 weighs the lower part 12 of the envelope 4 and creates a difference of weight between the balloon 10 and the neck 9, promoting the setting detection position during the fall of the projectile for triggering avalanche 1.

The projectile for triggering avalanche 1 may also include stabilizers 30 which aim to stabilize the projectile 1 in the detection position, during its fall. The stabilizers 30 are preferably tapes attached to the inner wall of the neck 9 of the envelope 4 and regularly distributed around the neck 9. After the drop and during the fall of the projectile 1, the tapes 30 unfold towards the outside the neck 9 by the effect of gravity. During the entire fall, the ribbons 30 thus stabilize the projectile for triggering avalanche 1, to maintain it in a suitable detection position.

As shown in FIG. 6, the wire 25 coiled in the neck 9 takes place during the fall of the projectile for triggering avalanche 1. When the distance traveled by the projectile 1 is equal to the length d2 of the wire 25 between the first end 26 and the second end 27, the second end 27 is detached from the first electrical circuit 17, releasing the power switch 23. The power switch 23 is thus actuated and closes the first electrical circuit 17. The control module 14 is then powered and active while the rangefinder 7 remains inactive.

As shown in Figures 7 and 2, the fall continues, the second strand of the wire 25 is in turn to the third end 28.

When the distance traveled by the projectile 1 is equal to the length d3 of the wire 25 between the first end 26 and the third end 28, the wire 25 is stretched and the third end 28 is detached from the second electrical circuit 18, releasing the switch additional power 24.

The additional power switch 24 is thus actuated and closes the second electrical circuit 18. The control module 14 and the rangefinder 7 are then powered and active. The wire 25 is released from the projectile 1 at a distance d3 from the release point 8. The projectile 1 is then no longer connected to the release point 8 (Figure 2).

As shown in FIG. 3, the control module 14 is parameterized so as to trigger the ignition of the explosive charge 5 at a predetermined distance, d1, from the terrestrial target 3 detected by the rangefinder 7. Thus, when the projectile for avalanche release 1 is at a distance d1, preferably between 0.6m and 1.5m, advantageously 0.8m, from the terrestrial target 3, the rangefinder 7 transmits the information via the communication circuit 16 to the control module 14 which triggers the ignition of the explosive charge 5 by activation of the pyrotechnic primer 6 (Figure 7). A rangefinder 7 having, advantageously, a detection range of between 0.6m to 1.5m, preferably 0.8m, is chosen. For example, the rangefinder 7 is an IR rangefinder marketed by the company under the name Sharp. According to a variant not shown, the upper part 11 and the neck 9 of the balloon 10 are constituted by the same material thicker than the material constituting the lower part 12 of the balloon 10. By way of example, the upper part 11 can be made with a material having a thickness of 5mm and the lower part 12 with the same material having a thickness of 2mm. Thus, the upper portion 11 opposes a greater resistance to the explosion than the lower part 12. The blast of the explosion is thus oriented, advantageously, downwards, that is to say towards the terrestrial target 3. L shock wave then propagates mainly in the direction of the terrestrial target 3, thus optimizing the detonating power of the explosive charge 5. According to a particular preferred embodiment, the control module 14 may advantageously comprise a safety relay 31 equipped with diagnostic means for providing a state on the integrity of the energy reserve of the power supply means 15. Thus, if the power supply means 15 are discharged to reach a capacitance value threshold Cs predefined without the projectile 1 has exploded, the safety relay 31 is self-destruct by welding, causing the triggering of the explosion of the projectile 1. For example, the rela The security system 31 is an AX100M 5V relay marketed by Sharp. The safety relay 31 is activated when the additional power switch 24 is actuated and the second electric circuit 18 closed. This operation is an additional security ensuring the neutralization of the projectile for triggering avalanche 1 in case, for example, of failure of the detection of the rangefinder 7.

According to another particular embodiment not shown, the aerial station 2 is a drone dropping. Several projectiles for avalanche release 1 can be stored in a rack and connected to an automated remote controlled release device according to any known method. The method of using the projectiles for avalanche release 1 differs from the method of use described above in that the contacting of the pyrotechnic primers 6 with the explosive charge 5 by introduction into the orifice 21 and the loading of the power supply means 15 are made before the release.

Although the avalanche release projectiles 1 described have a collar-shaped envelope 4, the invention is not limited to these particular embodiments which are given for illustrative purposes only. In particular, it is possible to envisage other forms of aerodynamic envelope ensuring the holding of the projectile for avalanche release 1 in the release position and / or in the detection position.

Unlike the devices of the prior art, the projectile for avalanche release according to the invention is efficient and economically viable while ensuring the safety of operators and the environment. The avalanche triggering device according to the invention is remarkable in that it comprises at least four safety devices. Indeed, the risk of explosion during the storage and transport of explosive projectiles is minimized or non-existent, because prior to any use, the steps of loading and contacting the pyrotechnic primer with the explosive charge are steps required to operate the projectile.

In addition, the projectile for avalanche release has a delaying means that activates the projectile only when a safety distance separates the operator of the projectile. This characteristic is a second safety preventing any risk of explosion when handling the projectile before release. Finally, the projectile for avalanche release according to the invention self-destructs in case of malfunction, which avoids the presence of explosive projectile activated in the field.

In addition, the projectile for avalanche release according to the invention respects the environment because it can be made in part of biodegradable material.

Claims (10)

REVENDICATIONS1. Explosive composition for avalanche release comprising essentially potassium perchlorate and aluminum powder. 2. Explosive composition according to claim 1 characterized in that the aluminum powder is of "dark pyro" quality. 3. Explosive composition according to one of claims 1 and 2 characterized in that it comprises at least 50% by weight of potassium perchlorate and 30% by weight of aluminum powder. 4. explosive composition according to claim 3 characterized in that it comprises at least 60% by weight of potassium perchlorate and 35% by weight of aluminum powder. 5. Explosive composition according to any one of claims 1 to 4 characterized in that it comprises magnesium. 6. explosive composition according to claim 4 characterized in that it comprises 60% by weight of potassium perchlorate and 38% by weight of aluminum powder and 2% by weight of magnesium. 7. Explosive charge (5) for avalanche release characterized in that it comprises between 900g and 3kg of the explosive composition according to any one of claims 1 to 6. 8. Projectile for avalanche release (1) characterized in that it comprises the explosive composition according to claim 1 and a priming system connected to the explosive charge (5) according to claim 7. - 2988389, 20 9. Projectile for avalanche triggering according to claim 8, characterized in that the priming system of the explosive composition is configured to detonate the explosive charge (5) at a predetermined distance (di) above a target terrestrial (3). 5 10. A method of triggering an avalanche characterized in that it comprises: - providing the explosive charge (5) according to claim 7, - prime the explosive charge (5) so as to explode at a predetermined distance 10 above a terrestrial target (3).