Ammunition and explosives – Blasting – Contained blasting charge
Reexamination Certificate
2002-06-07
2003-11-11
Nelson, Peter A. (Department: 3641)
Ammunition and explosives
Blasting
Contained blasting charge
C102S502000, C102S202120, C102S275120
Reexamination Certificate
active
06644203
ABSTRACT:
This invention relates to an explosive device and method of using such a device of particular, but not exclusive, application to triggering avalanches in a controlled manner.
Avalanches can present a serious danger to people and property when triggered in an uncontrolled manner, whether by a natural cause such as the weather conditions or unintentionally as a result of human activity such as skiing or climbing. It has therefore become an established practice in many mountainous areas to maintain continuous programs of avalanche control.
Control techniques can be separated into two main categories; passive and active. Two examples of passive control include a preventative approach, with the construction of terraced steel barriers high on the mountain slopes to pin the snow layers and prevent slippage, and a protective approach, where massive ground based deflectors are constructed on lower parts of the mountain to divert avalanche debris from specific structures considered to be at risk. Active avalanche control techniques form part of a carefully organized and continuous process of weather system surveillance, local condition forecasting and a range of practical procedures designed to induce controlled artificial avalanche releases.
This practice of regularly triggering small, controlled releases is intended to minimise the build up of snow in known start zones which, if left, would eventually release naturally. Such natural releases of large volumes of snow can cascade to develop massive slides invariably causing extensive damage to services, infrastructure, property and people. People are injured and killed by avalanches every year, world wide.
This invention supports active methods of avalanche control and in particular the use of explosives to stimulate artificial avalanche release. Explosives are used extensively in this role and a wide range of delivery methods are employed to suit the prevailing operational environment. Some of the more common delivery techniques are described below.
Where start zones are inaccessible, the explosive charge can be delivered to the slope in the form of a projectile fired from a gun or mortar system where the projectile explodes on or shortly after impact. Short ranges (2 to 5 km) can be covered by gas gun projector systems such as the nitrogen driven avalauncher, used extensively in the U.S., Canada and Europe. Longer ranges demand high performance systems and military artillery pieces typical of the 105 mm howitzer and 106 mm recoilless rifles have been used in this role for many years. Accuracy remains a problem for both systems at the limits of their range performance. However, the most significant problem with the military gun systems currently in use is that the ammunition is now obsolete and ageing.
Although older military ammunition fuzes detonate upon impact (but almost certainly well below the surface in the case of snow pack), in fact, proximity air bursts above the surface produce the most effective avalanche release performance. However, with gun fired projectiles this can only be achieved with electronic proximity burst fuzes. The cost of such fuzing is both inhibitive and notoriously unreliable against light, dispersed mediums such as surface snow, the use of impact fuzing therefore continues.
A more recent approach, developed primarily for protection of road and rail routes in remote areas, involves a fixed installation bolted into the mountain side in close proximity to an avalanche start zone. The apparatus, known by its commercial name as Gaz-Ex, consists of a large divergent funnel down which a charge of inflammable gas is injected and ignited using a remote ratio command fire management system. The resultant shock wave emitted from the mouth of the funnel then stimulates the controlled release of small avalanches, the frequency being dictated by a combination of local weather surveillance and avalanche forecasting techniques.
Where sites are particularly inaccessible, or have become so due to heavy snow fall or are unsuitable for the use of gun systems and/or the installation of Gaz-Ex systems, helibombing is often employed. Helibombing involves dropping a bag of commercial explosive composition, typically ANFO, into the avalanche start zone from a helicopter. The charge is detonated via a length of pyrotechnic delay fuze which is ignited in the helicopter before release.
US-A-4,817,529 discloses a method for automatically positioning a blast charge at a predetermined position end height above the snow surface to achieve an air burst from the explosive charge. The charge is suspended below a small host. The hoist and charge assembly are attached to a fixed steel cable winch system that traverses the hoist and charge assembly across the slope to the desired firing position. The small hoist is then issued with a command to lower the charge until a senses contact with the snow, and raise it back to a pre-determined height above the snow surface. The charge is fitted with a pyrotechnic delay fuze with a long burn time to allow for the overall positioning sequence to be completed prior to detonation. This fixed system is useful for slopes with a known line of trigger points.
Most areas in ski resorts are accessible, including the mountain peaks, and this accessibility enables explosive charges to be delivered or placed by hand. The practice of hand charge operations is probably the most cast affective and extensively used method of avalanche control in many ski resorts but is carries with it obvious hazards in poor weather conditions. The hand charge is a relatively simple device consisting of a lightly cased (cardboard) explosive charge detonated by a length of capped pyrotechnic delay fuze. The fuze can either be ignited and the charge thrown into a preferred position or the charge can be pre-positioned above the surface on a bamboo stick before the fuze is ignited. In both cases, within the delay time, the operator must retire to a safe position before detonation occurs.
Perhaps the most undesirable characteristic of a pyrotechnic delay fuze is that once the fuze has been ignited the only quick way to de-fuze the device is to attempt to cut the fuze beyond the flame front. This is not acceptable practice, but may be the only option when faced with an emergency. However, once ignited and abandoned, irrespective of circumstances, detonation of the charge cannot be evened. These characteristics together with the difficulty, in adverse weather conditions, of detecting if a fuze has been properly ignited have led to injury and fatalities in the past.
Not surprisingly, more appropriate firing systems have been adopted by the majority of explosive user communities world wide. It is important to recognize, however, that the particularly awkward range of environmental conditions associated with avalanche control operations impose the continued use of pyrotechnic delay fuzes pending identification of a satisfactory alternative.
The present invention focuses on avalanche control operations using hand charges. It seeks to provide an explosive device which will extend the convenience and versatility of hand charge control techniques.
The present invention, according to a first aspect, provides an explosive device comprising: an explosive charge body including an explosive charge and a detonator; a housing; and a length of non-pyrotechnic firing line having a first end and a second and, one end being operatively connected to the detonator, the majority of which line is stored within the housing so as to permit progressive removal from the housing on pulling one of the ends thereof; and in which movement of the non-pyrotechnic firing line is restrained so as to prevent the one end of the non-pyrotechnic firing line being pulled away from and operatively disconnected from the detonator when the non-pyrotechnic firing line is pulled from the housing.
The explosive charge of such a device can be launched towards a desired site while tethering the end of the non-pyrotechnic firing line not connected to the detonator. The non-pyrotechnic f
Nelson Peter A.
Nields & Lemack
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