Avalanche triggered by explosives
When an avalanche is triggered by explosives , pressure is built up on an unstable snow cover by detonating an explosive in order to trigger an avalanche artificially and in a controlled manner (see: Artificial triggering of avalanches ). Avalanches can be triggered by detonation of an explosive using permanently installed equipment or mobile.
The triggering of avalanches by explosions is very important in practice. Since the end of the 1980s, avalanche triggering by gas mixture ignition has also been increasingly used.
Trigger effect
The additional pressure of the detonation on the unstable snow cover is supposed to cause a chain reaction to cause a small avalanche before a large avalanche can develop through accumulation of snow, which is uncontrolled and can cause great damage.
The effect of igniting a gas mixture is similar to the detonation of an explosive (depending on the gas volume and gas mixture).
Trip point height
The best effect of the detonation is achieved when the trigger pressure is built up about 0.5 to 3 (4) meters above the snow cover:
| Explosion point height | Cargo size |
Radius zone of action: |
|---|---|---|
| Over-snow blasting (approx. +3 to 3.5 meters) |
4 to 5 kg of explosives | 120 to 130 meters |
| Over-snow blasting (approx. +1 meter) |
1.5 to 2.5 kg of explosives | 60 to 70 meters |
| Over-snow ignition | 0.8 m³ propane gas - oxygen mixture |
30 meters |
| Over-snow ignition | 1.5 m³ propane gas-oxygen mixture |
40 meters |
| Over-snow ignition | 3.0 m³ propane gas-oxygen mixture |
50 meters |
| Surface bursting (snowpack) |
4 to 5 kg of explosives | 50 to 60 meters |
| Surface bursting (snowpack) |
1.5 to 2.5 kg of explosives | 35 to 40 meters |
| Release with 12 cm mine thrower (snow surface) |
3 kg of explosives | 40 meters |
| Triggered with rocket tube 80 (RAK) 8.3 cm (snow surface) |
0.7 kg of explosives | 20 to 25 meters |
| Blasting under the blanket of snow |
1.5 to 3 kg of explosives | 10 meters |
Blasts in the snow cover lose part of their energy by creating a crater in the ground and are therefore largely limited in their effect to this crater area, whereby ground vibrations can also occur, which can have positive effects on the triggering of avalanches. Small charges that detonate in a thick blanket of snow usually do not even create a crater and thus do not generate an air pressure wave. The effect of explosions is increased by reflections on rock faces. With dry, fresh snow, the greatest explosive effect is practically only achieved by blasting over snow. With over-snow blasting and large loads, up to 90% positive blasting can be achieved, with surface blasting an average of 60% and with blasting in snow less than 50%.
The correct trigger point height and effectiveness of the blast can also be determined from the blasting noise ( bang ) and the blasting fountain triggered by the detonation:
- the brighter the audible bang , the larger the zone of action,
- the duller the audible bang , the smaller the zone of action,
- the smaller the snow fountain, the larger the zone of action,
- the larger the snow fountain, the smaller the effective zone.
For the right time to trigger an avalanche, see: Artificial avalanche triggering - triggering time .
Explosives and amount of explosives
The explosive used commercially for the purpose of avalanche detonation in Europe is selected and suitable for these purposes, particularly with regard to handling safety even at low temperatures and insensitivity to moisture. The explosive should trigger the strongest possible shock wave, which is why, as a rule, only highly explosive explosives that have a high detonation speed are used. Explosives that have a high detonation speed but also a high blasting oil content (e.g. Knauerit-Alpinit etc.) are unsuitable because of the low ambient temperatures, because blasting oil solidifies at around −6 ° and the explosive loses its handling safety. In Germany, only powder explosives (e.g. sytamite ) that do not contain explosive oil but are sensitive to moisture may be used. Frequently used explosives in Austria and Switzerland are z. E.g .: Riomon T1 (formerly: Sytamit ) or Emulex . The previously used Lawinit of Austin Powder is no longer manufactured.
As a rule, explosives with a mass of 2 to 2.5 or 4 to 5 kg and a cartridge diameter of around 80 to 95 mm are used. If a 2.5 kg explosive cartridge detonates, around 4000 liters of gas volume is generated in about 7 ms .
In contrast to rock mining by blasting, an exact calculation of the loading amount is not required for avalanche blasting. The load amount between 2 and 2.5 kg or 4 and 5 kg is suitable in practice for almost all areas of application. Under- or over-dimensioning of the cargo cannot cause any damage.
In certain special cases, an avalanche can also be triggered with a detonating fuse .
Transportation of explosive charges
Appropriate carrying devices must be used when carrying explosives and detonators. There may be special provisions governing how much explosives a person can carry alone (in Austria e.g. 26 kilograms).
The transport of explosives on public roads must be carried out in accordance with the relevant statutory provisions and the European Agreement on the International Carriage of Dangerous Goods by Road (ADR).
Special regulations apply in cable cars and aircraft, and special permits may be required in order to transport explosives or detonators.
When transporting explosives and detonators, they must always be kept in separate containers.
Ignition of the explosives
Time fuse
The explosive is ignited advantageously via a time fuse cord (also: safety fuse cord ) with a previously defined burning time (in Austria: between 110 and 130 sec./m). The existence of this burning time must be checked with a test fuse before using it for avalanche blasting (in Austria at least monthly and documented, since moisture and aging can cause an impermissible change in the burning time). The time fuse with a minimum length is required to give those authorized to blast and helpers the opportunity to get to safety after the detonation of the explosive charge.
In Austria, the use of a time fuse less than one meter in length is therefore fundamentally prohibited (= around 2 minutes of burning time). Exception, e.g. B. in so-called avalanche watchdogs or avalanche detonators, if the blasting party already ignites electrically from cover or from the valley.
Ignition means
As an ignition means of the time fuse z. B. electric bridge igniter , tear-off igniter or firing pin igniter can be used. Ignition with electrical bridge detonators is, after purchasing an ignition device, the cheapest and safest option for igniting a time fuse and, subsequently, the explosive charge.
In the past, defective products were repeatedly delivered in the case of firing pin igniters and detonators, which prevented the explosive charge from being reliably ignited.
Systems
A fundamental distinction can be made between permanently installed and mobile systems or measures to trigger avalanches by detonating explosives.
Permanently installed systems
A permanently installed system such as B. a detonating cable car , an avalanche monitor , avalanche detonation mast , sometimes also artillery etc. are shot in , so that it is possible to operate such a system even in the dark or without visual contact and trigger the detonation.
Mobile systems or measures
Mobile avalanche triggering is used where there is a permanently installed system such as B. an avalanche guard, does not carry it economically or has to react quickly to special weather conditions. The mobile assets are helicopters flown to the destination or the blasting from a helicopter or manually made or are located on slopes equipment, snowmobiles etc. (z. B. avalanche pipe ) and be moved to the vicinity of the location. When an avalanche is triggered from the helicopter, the explosive charge z. B. dropped during a hover (see: Avalanche release by helicopter ).
The detonation of explosives with mobile release of avalanches can be initiated by hand, by means of a fuse with a detonator or electrical ignition with bridge detonators , impact detonators or with HU detonators .
For some years, Hamberger AG (Switzerland) offered a system with solid rockets ( avalanche rockets ) with a range of about 600 to 700 meters. Similar to anti-hail missiles , but with a charge of explosives. These avalanche missiles have not established themselves permanently on the market. They should have been too imprecise in reaching the set goal.
commitment
Permanently installed systems can also be used in poor visibility and in the dark. Mobile systems can usually only be used when visibility is good.
A special permit is required in Austria and Switzerland for the use of explosives to trigger an avalanche. Due to the varied training, accidents when avalanches are detonated by explosives are very rare.
Authority to issue orders and liability
The order for the use of explosives to trigger an avalanche for a specific area is usually made by the avalanche commission or a similar institution. A person authorized to blast is generally not authorized to carry out avalanche explosions. However, after the authorization to carry out the blasting work has been granted, the person authorized to blast alone is responsible and authorized to issue orders. It determines how the explosives and detonators will be transported by whom, how much explosives will be used, from where the corresponding charge will be detonated, how the locking and security measures are to be implemented, who will accompany him and who will detonate the explosive charge, etc.
Detection
In the case of permanently installed devices, a geophone or microphone installed in the device measures and displays or documents whether the detonation and the success of the blasting occurred . In the case of mobile systems, a visual inspection and manual documentation in advance to determine whether an avalanche has occurred or not.
Failure elimination
In order to be able to find failures ( duds ) more easily, the explosives are often equipped with a RECCO strip. Failures are to be recovered as quickly as possible. However, a minimum waiting time must be observed (in Austria e.g. 15 minutes after ignition until recovery).
The time fuses attached to an explosive charge must be cut off near the explosive immediately after recovery in order to reliably prevent re-ignition.
See also
- List of avalanche accidents , list of avalanches and landslides, landslides and list of disasters
- Search for avalanche victims , avalanche shovel and avalanche cord
Web links
- Avalanche explosions at Nebelhorn , video BR-Mediathek 5:13
Individual evidence
- ↑ Lukas Stoffel: Artificial Avalanche Release , Tec 21, Volume 131, 9/2005, p. 6.
- ↑ Christoph Skolaut, Florian Rudolf-Miklau: State of knowledge about the application of artificial avalanche triggering in Austria in State of the Art for Artificial Avalanche Triggering , July 2014, p. 9.
- ↑ The effective zone is the circular area around the detonation point within which the additional pollution generated has a certain minimum size. Effective zones are used for assessing negative explosions (“Which area was tested by the explosion?”) And for developing safety concepts (Lukas Stoffel [1] ).
- ↑ According to Lukas Stoffel: Davos Artificial Avalanche Release: Blasting Effect , Methods, Benefits, Problems , WSL Institute for Snow and Avalanche Research SLF, Innsbruck 2010, the mixture of the company Gasex: Propane: Oxygen = 18%: 82%.
- ↑ The percussion fuse must be fine-tuned accordingly so that it is triggered as far as possible on the surface of the snow.
- ↑ Christoph Skolaut, Florian Rudolf-Miklau: State of knowledge about the application of artificial avalanche triggering in Austria in State of the Art for Artificial Avalanche Triggering , July 2014, p. 8.
- ↑ Lukas Stoffel: P Artificial Avalanche Release , Tec 21, Volume 131, 9/2005, p. 6.
- ↑ a b § 14 no. 1 Blasting Work Ordinance, Federal Law Gazette II No. 13/2007.
- ↑ § 14 no. 4 Blasting Work Ordinance.
- ↑ See also: Kampf den Avalanche - A new type of avalanche launching device in: Schweizer Soldat: Monthly magazine for army and cadres with FHD newspaper , Volume 32, 1956–1957, Issue 12, p. 227, for a small rocket system with about 1.2 kg of active ingredient for triggering avalanches. This system also did not get beyond the test phase for triggering avalanches.