WO2014045052A1

WO2014045052A1 - Methods and systems for blast mitigation

Info

Publication number: WO2014045052A1
Application number: PCT/GB2013/052470
Authority: WO
Inventors: Jeremy Milton; Lawrence KILEY; John Martin
Original assignee: J. & S. Franklin Limited; Explosive Containment, Inc
Priority date: 2012-09-21
Filing date: 2013-09-20
Publication date: 2014-03-27
Also published as: GB201216918D0; GB2506588A

Abstract

A blast containment system comprises a cellular unit (20) for use in shielding a weapon or the intentional detonation of a UXO device. The unit (20) is formed of a plurality of interconnected open cells (3) of flexible fabric material. A larger cellular space (24), that is interconnected with one or more of the open cells (3), accommodates a weapon or UXO device in use. The system may comprise one or more further cellular units (2, 2') stacked next to and/or on top of the cellular unit (20). The open cells (3) may be filled in use with a fine aggregate material such as sand, earth or the like.

Description

Methods and Systems for Blast Mitigation

Unexploded ordnance (UXO) is any explosive weapon or military munitions (bullets, shells, grenades, bombs, projectiles, land mines, naval mines, etc.) that has been left primed or un-primed that did not explode when employed and poses a risk of unintentional detonation, potentially many decades after it was used or discarded. UXO can be found in many countries that have been exposed to war or bombing, for example in Belgium, France, Germany and the UK from World War II, in Laos from the American Vietnam War, and in the USA from bomb testing during World War II and even dating back to the American Civil War. In addition there is a large amount of UXO left over from army training exercises. As well as the danger of explosion and harm to civilians, buried UXO also entails a risk of environmental contamination. UXO clean-up costs are high, including the costs of surveying and mapping, manual detection e.g. with metal detectors, removing vegetation from the site, transportation of personnel and equipment to the site, digging out buried ordnance, and carrying out a controlled explosion.

UXO in the form of primed munitions that cannot be moved from its location has to be blown up in place. On-site personnel determine the need for engineering controls for any given intentional detonation. The use of sandbags, water mitigation systems and buried earth model are authorized as engineering controls for intentional detonations. The US Army Corps of Engineers has developed procedures to be followed for the sand bag method per "Use of Sand Bags for Mitigation of Fragmentation and Blast Effects due to Intentional Detonation of

Munitions", HNC-ED-CS-S-98-1 , dated 1998, to mitigate fragmentation and blast hazards to a maximum of 200 feet (60 m).

Building a barricade using sand bags requires a large number (e.g. 1000s) of sand bags to be transported to the detonation site. The sand bags are typically stacked in an offset configuration to increase the stability of the barricade. For small UXOs less than 70 mm in size, and for sub-munitions and grenades, a double wall thickness of sand bags is typically built to surround the UXO e.g. in a circular configuration. The sand bags are stacked to a height of at least one metre. For medium-sized UXOs such as missiles, rockets and projectiles up to 200 mm in size, and for large-sized surface munitions, a four- or five-wall thickness of sand bags are stacked to partially surround the UXO e.g. in a semi-circular configuration. The sand bags must be stacked to a height of at least 1.5 m. Large UXOs such as bombs are too large for a barricade to be built to surround them. Instead a wall barricade is built between the UXO and the nearest buildings etc. to be protected so as to be at least as tall as the buildings. The barricade may not be able to completely prevent damage from being caused by detonation, but it may lessen the effect of the blast and reduce the size of the evacuation area required. The use of sand bags to mitigate the effects of intentional detonation has multiple drawbacks. Building barricades from sand bags is very time consuming. For example, a wall barricade that is 4 m long, 2 m high and 3 sand bags thick would require around 700 sand bags. As the height of the barricades increases, it becomes difficult for the sand bags to be manually lifted into place. If the barricade is not built carefully then the sand bags can shift and the structure becomes unstable. For stability the sand bags must be stacked in a wedged configuration with each subsequent layer stepped back from the layer below. The sand bags have to be moved individually but they are heavy and cumbersome to handle. Furthermore, when the UXO is detonated at least some fragments of the exploded weapon may penetrate through the barricade due to gaps between the sand bags and the sand bags are often thrown several hundred metres by the pressure wave of the blast.

There remains a need for effective methods and apparatus for use in UXO clearance operations.

According to a first aspect of the present invention there is provided a method of mitigating the fragmentation and blast effects of an intentional detonation, comprising shielding an unexploded ordnance (UXO) device by: providing one or more cellular units formed of a plurality of interconnected open cells of flexible fabric material with the open cells spaced at a minimum distance D from the device; and filling the open cells of the one or more cellular units with a fine aggregate material such as sand, earth or the like. Optionally, the method further comprises the step of intentionally detonating the shielded UXO device.

It will be appreciated that shielding a UXO device using such cellular units has various advantages compared to standard procedures using sand bags. Construction of the shielding is much quicker than using sand bags, allowing more economical build and clear-up times. Each unit provides an integral cellular structure that can be opened out and filled in much less time than it takes to position individual sand bags. Moreover the cellular unit(s) can be easy to transport to the site of the UXO device, for example in flat-pack form, and then filled with locally available material (sand, earth, etc.). As each cellular unit is provided as an integral cellular structure, construction and connection of cells on-site is not required, as is the case with gabions for example. The units being split into multiple cells enables a greater compaction of the fill material, potentially leading to improved protection levels. As a particular unit or set of units can be designated for clearance of a given UXO device, the shielding can be built in a consistent manner with the same easily produced design, resulting in a reliable performance across multiple clearance operations, in turn leading to reduced risk. Safety distances can be minimised. Furthermore the method can easily be tailored for use with different kinds of UXO, the modular construction allowing simple scaling-up of designs and minimal use of skilled labour. If the height of the one or more cellular units is already greater than the height of the UXO device above the ground then it may not be necessary to stack any units on top of one another. Each filled unit can conveniently form a barricade to absorb the fragments and blast wave produced by detonation. A single unit may be provided as a wall-like barricade. The unit itself may comprise multiple rows of cells so that it replicates a wall that is several sand bags thick. Otherwise multiple units may be situated next to or adjacent one another, e.g. side-by- side or with adjoining corners, etc. to form a barricade extending over a desired distance. The cellular units may be positioned so as to at least partially surround the UXO device, for example in an L-shaped, U-shaped, semi-circular or circular configuration. Whatever the configuration of the barricade, the cells of each unit are always spaced at the minimum distance D from the device so as to provide an air space around the device, as will be discussed in more detail below.

While a single layer of one or more cellular units may be provided to shield the UXO device, the method preferably comprises stacking at least one cellular unit on top of another one. The units may be stacked and then all filled at the same time, but at least when building barricades that are several units high it is preferable to provide a lower unit and fill (or at least partially fill) the lower unit before stacking an upper unit on top. The shielding of a UXO device may further comprise the steps of: providing the one or more cellular units in a first layer; filling the open cells in the first layer with a fine aggregate material such as sand, earth or the like; providing one or more further cellular units in a second layer on top of the first layer; filling the open cells in the second layer with a fine aggregate material such as sand, earth or the like; and optionally repeating with subsequent layers. Methods according to embodiments of the present invention have the advantage of being flexible so that a user can select the number of cellular units and the way in which they are arranged so as to suit the type of UXO device to be detonated. The shielding of a UXO device may therefore further comprise the step of selecting the number of cellular units and/or the number of layers of cellular units depending on the UXO device to be shielded.

A benefit of stacking cellular units as opposed to sand bags is not only that high barricades can be built quickly, but also that the shielding structure can have at least one generally vertical side or end wall with greater stability than a barricade made of sand bags. To help stabilise such a vertical wall, and to substantially prevent or minimise the fine aggregate material escaping from between the stacked units, the method preferably further comprises the step of forming a seal between vertically juxtaposed units. The seal may be formed by a strip extending substantially horizontally around the periphery of the cellular units at the junction between vertically juxtaposed units. The strip may be provided separately from the units, or it may be provided by one of the units. For example, a skirting strip may extend substantially horizontally around the periphery of at least one of the units and depend upwardly or downwardly to seal across the junction between vertically juxtaposed units. The skirting strip may be a separate piece of material, e.g. attached to the unit, or it may be integrally provided by the material of the cellular unit, preferably by the outer perimeter wall(s) of the unit.

As has been described above, the UXO device may be shielded by arranging one or more of the cellular units with the cells at a distance D from the device. While multiple units may be arranged to substantially surround the UXO device, where adjoining units are only touching there may be a risk of the fragments and blast wave generated by detonation not being adequately shielded. The applicants have recognised that it is preferable for an interconnected cellular structure to extend around the UXO device. It is therefore preferred to arrange at least one cellular unit over the UXO device so as to house the UXO device in a space in the unit at a minimum distance D from one or more neighbouring cells. While the space that houses the UXO device could be filled with material, it is preferable to leave an air space around the UXO device while the neighbouring cell(s) are filled. An advantage of providing an air space around the UXO device over the distance D is that fragmentation travels in front of the pressure wave of the blast and hits the filled cell(s) before the impact of the blast wave. The larger the air space, the greater the dissipation of the blast wave. The fragments of the exploded device can be safely buried in the cells before the blast wave causes any damage to displace or disrupt the cellular unit.

A cellular unit that is designed to house a UXO device is considered novel and inventive in its own right, and thus when viewed from a second aspect the present invention provides a cellular unit for use in intentional detonation of UXO devices, the unit being formed of a plurality of interconnected open cells of flexible fabric material and further comprising a cellular space to accommodate a UXO device in use, the cellular space being interconnected with one or more of the open cells and larger than each open cell. The larger cellular space can provide an air space over a minimum distance D from a UXO device placed in the space and the neighbouring open cell(s). Such a cellular unit therefore provides a quick and easy way to shield a UXO device for detonation as one or more of the open cells can be filled, e.g. with a fine aggregate material such as sand, earth or the like, to absorb the resulting fragmentation and blast wave emanating from the device in the larger cellular space.

In the same way as is described above, such cellular units may be provided side-by-side and/or stacked on top of one another to form barricades substantially surrounding the larger cellular space that houses a UXO device in use. A cellular unit comprising a larger cellular space that can be used to house a UXO device may not necessarily have open cells

interconnected with the larger cellular space on all sides. In one set of embodiments the cellular unit comprises a larger cellular space that is interconnected with open cells on at least two sides. In another set of embodiments the cellular unit comprises a larger cellular space that is interconnected with cells on at least three, four or more sides. It will be appreciated that this may depend on the geometry of the cells and/or of the space. The cells may be triangular, rectangular, polygonal or substantially circular in shape. The larger cellular space may also be triangular, rectangular, polygonal or substantially circular in shape, and the same or different shape as the open cells.

It will be appreciated that what is meant by the open cells being interconnected, and the larger cellular space being interconnected with at least some of the open cells, is that they are fixed to one another, for example connected by shared material. This can be contrasted with individual sand bags that are not connected together but merely stacked adjacent one another. The interconnected open cells and/or larger cellular space may be at least partially formed from a continuous strip of material. The strip of material may be folded back and forth in a zigzag configuration to form the side walls of adjacent cells in a row. To form multiple rows of cells, the strip of material may be folded back and forth on itself with the folded layers bonded to each other at spaced apart locations such that the material can be opened out into a honeycomb-like cellular arrangement. In any embodiment, the cells at the perimeter of the cellular unit may be interconnected by a continuous strip of material that wraps around to form the outer walls of the unit. The material forming the outer perimeter walls of the cellular unit may be higher than the material forming inner walls of the cellular unit. The outer perimeter walls may therefore be provided with an integrally formed skirting strip that extends substantially horizontally around the periphery of the unit and depends upwardly or downwardly to seal across the junction between vertically juxtaposed units. Such a skirting strip not only prevents the escape of fill material when cellular units are stacked on top of one another, but also aids with locating and aligning the units when they are stacked. In other embodiment the skirting strip may not be integrally formed with the outer perimeter walls but provided by a separate strip of material instead, for example fastened around the outer perimeter walls to extend substantially horizontally around the periphery of the cellular unit.

As is mentioned above, the cellular unit may comprise one or more rows of open cells. If the cellular unit consists of a single row of open cells then the larger cellular space may not be interconnected with open cells on all sides. However other cellular units may be placed adjacent to the unit, e.g. in a side-by-side arrangement, so that there are open cells (that can be filled) surrounding the larger cellular space that accommodates a UXO device in use. When the device is detonated, the fragments and blast wave will travel out in all directions to be intercepted by filled cells of the units. For smaller explosive devices it may be adequate for one or more single-row units to be arranged around the larger cellular space holding the device.

However, the Applicant has appreciated that it may be beneficial for the larger cellular space to be surrounded by interconnected open cells so as to increase the strength and resistance of the unit to a blast. Thus in one set of embodiments the cellular unit comprises a larger cellular space that is substantially surrounded by interconnected open cells. This can improve the efficacy of the unit in mitigating fragmentation and blast effects from the intentional detonation of a UXO device.

It will be understood that the interconnected open cells of a cellular unit are generally minimised in size, being large enough for ease of filling but small enough that compartmentation of the unit provides benefits in terms of strength and blast resistance. Meanwhile the larger cellular space is made larger than each open cell so that it can accommodate a UXO device in use and provide an air space extending over a minimum distance D from the device. The air space provides room for a blast wave to spread so that it becomes temporally separated from the faster-moving fragments when the device is detonated. The fragments will therefore hit the surrounding cells that have been filled and be absorbed before the blast wave hits. So as to optimise this effect, the larger cellular space may be made at least as large as two, three, four, five, six or more of the open cells in the unit. In practice the size of the larger cellular space depends on the UXO device to be detonated. It is preferable for the open cells to be spaced at a minimum distance D from the device that is at least 150-300 mm.

As a blast will travel in all directions, it is preferable for one or more cellular units to be stacked on top of a unit comprising a larger cellular space that accommodates a UXO device in use. Any cellular units that surround and/or cover a cellular unit for use in intentional detonation of UXO devices may be formed of interconnected open cells but without a larger cellular space. The cells are filled in use, for example with a fine aggregate material such as sand, earth or the like. When a cellular unit extends over the top of a larger cellular space that accommodates a UXO device, it is desirable that the fill material does not fall down into the larger cellular space below and interfere with the air space discussed above. It is therefore preferable for a cellular unit for use in intentional detonation of UXO devices to be provided with a cover for the larger cellular space. The cells in a vertically juxtaposed unit can therefore be filled while the cover prevents material from dropping down into the larger cellular space below.

This is considered novel and inventive in its own right, and thus when viewed from another aspect of the present invention there may be provided a blast containment system comprising a lower cellular unit comprising a cellular space to accommodate a UXO device in use, a cover over the cellular space, and at least one upper cellular unit, formed of a plurality of interconnected open cells of flexible fabric material, arranged on top of the cover. The open cells of the upper unit may be at least partially filled, in use, with a fine aggregate material such as sand, earth or the like. The lower cellular unit may further comprise a plurality of

interconnected open cells of flexible fabric material that are interconnected with the cellular space. In addition, or alternatively, the lower cellular unit may be arranged adjacent to one or more other cellular units formed of a plurality of interconnected open cells of flexible fabric material. Any of the open cells in the lower layer may also be at least partially filled, in use, with a fine aggregate material such as sand, earth or the like.

As is described above, the blast containment system may further comprise a skirting strip that extends substantially horizontally around the periphery of the upper and lower cellular units to form a seal across the junction there between. The skirting strip may be integrally provided by the material of one of the cellular units or provided as a separate piece of material.

The step of providing a cover may be applied not only to those methods that provide a cellular unit comprising a larger cellular space to accommodate a UXO device in use, but also to any method where one or more cellular units are arranged to substantially surround a UXO device and one or more further units are stacked on top to cover the device. In embodiments of the methods described above, the shielding of a UXO device may further comprise the steps of: providing a cover that extends over the device and the distance D; and providing one or more further cellular units in a second layer on top of the cover. The open cells of a unit in the second layer on top of the cover can therefore be filled without material falling onto the UXO device and the surrounding space extending over a minimum distance D. Not only does this maintain an air space around the device, but also the risk of falling material disturbing the device and causing an unintentional explosion is removed.

There will now be described some general features of a cellular unit formed of a plurality of interconnected open cells of flexible fabric material, whether or not the unit further comprises a cellular space to accommodate a UXO device in use.

It is advantageous for each cellular unit to be made exclusively of a fabric material, so that there is no secondary fragmentation associated with the system. The use of a flexible fabric material ensures that the units are relatively light and easy to handle before being filled. Each unit can be flat-packed so that it is relatively compact to transport. The system may therefore be suitable for air freight and helicopter delivery to remote areas. The fabric material may also enable more eco-friendly disposal of units after use.

The cells may be formed of any suitable fabric material exhibiting strength and flexibility, including woven, knitted and nonwoven fibrous webs. However the flexible fabric material preferably comprises a flexible nonwoven material. Nonwoven materials have very good tensile strength, stiffness, puncture resistance and tear resistance, combined with flexibility. It is further preferred that the nonwoven material is polypropylene-based. A particularly preferred material is a nonwoven fabric made from bi-component fibres. One such suitable material comprises 70% polypropylene and 30% polyethylene. The cellular units may be manufactured from thermally bonded strips of a suitable flexible nonwoven material. Although methods and apparatus according to embodiments of the present invention have been discussed above in the context of the intentional detonation of UXO devices, the applicants have recognised that the invention may also find use in mitigating the effects of other types of weapons, for example chemical and/or biological weapons. According to a further aspect the present invention therefore extends to a method of mitigating the effects of a weapon, comprising shielding a weapon by: providing one or more cellular units formed of a plurality of interconnected open cells of flexible fabric material with the open cells spaced at a minimum distance D from the weapon; and filling the open cells of the one or more cellular units with a fine aggregate material such as sand, earth or the like. Optionally, the method further comprises the step of activating the weapon. When viewed from a yet further aspect the present invention provides a cellular unit for use in shielding a weapon, the unit being formed of a plurality of interconnected open cells of flexible fabric material and further comprising a cellular space to accommodate a weapon in use, the cellular space being interconnected with one or more of the open cells and larger than each open cell. When viewed from a yet further aspect the present invention provides a weapon shielding system comprising a lower cellular unit comprising a cellular space to accommodate a weapon in use, a cover over the cellular space, and at least one upper cellular unit, formed of a plurality of interconnected open cells of flexible fabric material, arranged on top of the cover. Any of the features described above may be provided in association with these further aspects of the invention. The weapon can be any weapon for which physical shielding provides protection, including e.g. bombs, mortar rounds, explosive shells, firearms, grenades, incendiary devices, missiles, rockets, etc. as well as chemical and/or biological weapons.

Some preferred embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 illustrates the stacking of two small cellular units;

Figure 2 shows an embodiment of a blast containment system made of small cellular units for use with mortar rounds and small shells;

Figure 3 shows another embodiment of a blast containment system for use with larger shells;

Figure 4 illustrates the stacking of two large cellular units; and

Figure 5 shows another embodiment of a blast containment system made of large cellular units for use with large bombs.

There is seen in Fig. 1 a cellular unit 2 sold as DefenCell ® DT1 that is formed of a plurality of interconnected open cells 3 of flexible fabric material. Further details of such cellular units are described in WO 2008/037972, the contents of which are hereby incorporated by reference. The unfilled unit 2 can be folded flat to fit in the same space as a full sand bag with a weight of only 4.1 kg. The unit 2 is therefore compact and easy to carry to the site of a UXO device or other weapon. Or the unit 2 can be dropped from a height with no likelihood of damage, making it ideal for remote locations. Once the unit 2 is opened out and the cells 3 filled with material 8, as shown in Fig. 1 , it forms a barricade that is 4.9 m long, 0.6 m high and

0.7 m wide, equivalent to about 160 sand bags. The unit 2 can be filled with locally available earth or sand, the fill material 8 being compacted simply by treading on top. The open cells 3 of the unit 2 have a height of 0.5 m except the outer perimeter wall 4 of the unit 2 is provided with an upstanding skirt 6 that is 0.1 m higher than the internal cell walls. As can be seen from Fig.

1 , when another cellular unit 2' is stacked on top of the lower unit 2 it nests inside the skirt 6 so as to be retained in position without leakage of the fill material 8. Any number of such cellular units 2, 2' can be placed alongside each other and/or stacked on top of one another to build a force protection system. The cellular units 2, 2' are each one cell wide and eight cells long.

Fig. 2 shows how a blast containment system can be formed from the cellular units 2 seen in Fig. 1 together with a cellular unit 20 specifically designed for use in the intentional detonation of UXO devices. The cellular unit 20 in the middle of the lower layer 22a has a conventional cellular unit 2 placed either side and/or an upper layer 22b of conventional cellular units 2' stacked on top. The cellular units 2, 2', 20 are each one cell wide and four cells long (half as long as shown in Fig. 1). Like the conventional cellular units 2, the cellular unit 20 is formed of a plurality of interconnected open cells 3 of flexible fabric material. However it can be seen that the cellular unit 20 further comprises a cellular space 24 designed to accommodate a UXO device (not shown) in use. The cellular space 24 is interconnected with the open cells 3 of the unit 20 but is larger than the conventional cells 3. The cellular space 24 can therefore provide an air space around the UXO device (not shown).

There is also seen in Fig. 2 a pipe 26 passing out from the cellular space 24 and through the adjoining cellular unit 2 to the outside of the system. The pipe 26 is used to run a detonator cable to the UXO device. The pipe 26 can be run through, or under, the cells as required. Over the top of the cellular space 24 there if provided a cover 28. The walls of the cellular space 24 are lower than the neighbouring cell walls so as to enable the cover 28 to be recessed and lie flush with the top of the unit 20. The cover may be made of plywood or any other suitable material.

The build sequence for a blast containment system as seen in Fig. 2 is as follows. The cellular unit 20 and two conventional cellular units 2 are placed side-by-side to form a lower layer 22. If the weapon is already in position then it is ensured that the cellular space 24 locates over the weapon with a sufficient air space between the weapon and the nearest cell walls. All of the open cells in the lower layer 22 are filled with aggregate material 8 (such as earth or sand), the fill material being compacted by foot and topped up until level with the internal cell walls. The cellular space 24 is left empty. Next two further conventional cellular units 2 are stacked on top of the left and right cellular units 2 in the lower layer 22, and filled. If the weapon is not already in position then it is placed inside the cellular space 24. A detonator cable is led out through the pipe 26. To finish the build, the cover 28 is placed over the cellular space 24. Another conventional cellular unit 2' is then placed on top of the cover 28 and filled. Once all personnel have cleared the area then a controlled explosion of the weapon can be carried out.

The blast containment system seen in Fig. 2 has been designed for use with 60 mm and 81 mm mortar rounds or 105 mm shells. In order to contain the blast from a larger shell, such as a 155 mm shell, a design as seen in Fig. 3 may be employed. There is again a cellular unit 20 in the middle of the lower layer 32a that comprises a cellular space 24 designed to accommodate a UXO device (not shown) in use. Either side of the cellular unit 20 there is placed a wider cellular unit 30 that is two cells wide and eight cells long (sold as DefenCell ® DC2). Stacked on top of the cover 28 there is a conventional DT1 cellular unit 2' (one cell wide and eight cells long) and two more DC2 cellular units 30 are positioned either side to form a third layer 32b. In addition, a third layer 32c is provided by another DC2 cellular unit 30 placed on top of the central units 20, 2'. It will be understood that additional cellular units, whether

DT1 , DC2 or otherwise, may be stacked next to and/or on top of the units shown, as required.

There is seen in Fig. 4 a cellular unit 40 sold as DefenCell ® DC4 that is four cells wide and eight cells long. As before, the cellular unit 40 is provided with a 0.1 m skirt 46 that extends around the periphery of each unit. The internal cell walls are 0.5 m high. The interconnected open cells 43 of the unit 40 and filled in use with material 8 such as sand or earth.

Such cellular units 40 can be used to build a blast containment system, as seen in Fig. 5, which is designed e.g. for a 100 lb bomb. In this system the central cellular unit 40' in the lower layer 42 comprises a cellular space 44 designed to accommodate a bomb (not shown) in use. A detonator cable is led out through a pipe 46. A cover 48 is positioned over the space 44 to prevent fill material falling in from the upper layers. The lower layer 42 is formed by placing a cellular unit 40 either side of the central unit 40'. Four further layers 52a- 52d, each formed of three of the units 40, are stacked on top of the lower layer 42 and filled one by one. For larger systems such as this a digger may be used rather than relying on manual filling. Each unit 40 is equivalent to 600 sand bags when filled.

Examples

A series of demonstrations, using cellular units as substitutes for sandbags, were conducted to demonstrate their suitability as a confinement and mitigation measure with selected munitions. The munitions used were 60 and 81 mm mortars, a 105 mm shell, and a 100 lb air-delivered bomb. Test Procedures

Evidence of the effectiveness of each blast containment system was collected through the use of witness screens and other means. The suitability of each blast containment system for mitigation with the selected munitions was to be judged on a simple pass or fail criteria. Specifically, if witness screens showed any perforation by fragmentation from the munitions then the demonstration would be judged a failure. If there was no perforation by fragmentation then the demonstration would be judged a success.

Evidence was collected through several means, specifically: aluminium witness screens, photography, video, examination of the structures and debris in the surrounding area post-blast, pressure gauges and surrogate window structures at specific ranges. Aluminium witness screens were placed against one side wall, one end wall and the top of each blast containment system. They were held in place using duct tape (roof screens also had lightly filled sandbags on them because of high winds). Two digital video cameras (12 m away) recorded each blast. One camera covered an end wall which did not have a witness screen attached, the other camera covered a side wall that did not have a witness screen. Five pressure gauges were positioned around the blast containment system. Surrogate window structures were placed at given stand-offs to provide physical evidence of potential pressure damage and were co-located with the pressure gauges.

Examination of the structures, post-blast, for the throw distance of components and debris, and any perforation of the outer walls of the blast containment system was carried out. Within 6 m of the blast house the area was checked for anything that could be confused with blast debris and was removed. Within the 6 m area a fresh sheet of geotextile was placed on the ground to provide a clean surface for the easy identification of debris from the blast.

Table 1 below summarises the post-blast evidence gathering procedures and which blast containment systems they were applied to.

Action 60 mm 81 mm 105 mm 100 lb

Examination of external witness plates for Yes Yes Yes Yes

perforation.

Examination of outer cell walls of units for Yes Yes Yes Yes

perforation.

Examination of window structures for any Yes Yes Yes Yes

damage.

Off-site analysis of blast pressure data. No - Yes Yes Yes

readings

not

taken

Recovery of representative fragmentation Yes Yes Yes Yes from seat of site of each detonation.

Examination of cleared area covered by Yes Yes Yes Yes geotextile within 6 m of each blast

containment system for evidence of any

fragmentation.

Examination of post-blast photography. Yes Yes Yes Yes

Examination of post-blast videos. Yes Yes Yes Yes

Table 1

The munitions were detonated through the employment of pipe perforators. It is understood that one perforator per munition would normally be used. During this demonstration, to reduce the risk of malfunction and the consequential requirement to dig out the munition, two perforators were used on each munition. This is recommended as standard practice when using blast containment systems for an intentional detonation.

Results: Blast containment system for 60 mm mortar rounds

A blast containment system was built according to the design shown in Fig. 2. The effect of detonation on the blast containment system was limited. Some minor shifting and collapse of the fill material in the middle top unit took place as the fill (sand) fell back into the cavity created by the detonation. The area covered in geotextile around the blast house was inspected. There was no debris from the blast house spread onto this area.

Witness Screen Results: There were no perforations of the witness screen due to fragmentation from the munition. There was some minor damage to the side witness screen from the placement of the detonation cord.

Perforation: The exterior walls of the units were examined and no perforations from

fragmentation were observed.

Window Frame Results: There was no damage to the windows.

Overpressure Gauge Results: No pressure readings were taken during this blast due to a combination of time and Burn Index constraints. Results: Blast containment system for 81 mm mortar rounds

A blast containment system was built according to the design shown in Fig. 2. The effect of detonation on the blast containment system was limited. Some minor leaning of one side wall took place and a seam in one wall section, alongside the munition, was split, leading to a small spill of fill material (sand). On one end wall another minor spill of fill material was apparent - this was due to the placement of the PVC pipe in this area and the damage caused by the detonation cord, rather than damage from the main detonation. Fill in the area directly above the detonation fell back into the cavity created.

fragmentation were observed.

Window Frame Results: There was no damage to the windows.

Overpressure Gauge Results: 4 of the 5 signals triggered. The sensor on the radial side at 120' did not trigger as the signal was below threshold.

Gauge Location Maximum Peak Comments

Overpressure (psi)

Axial 40^' 0.321/0.311

Axial 80' 0.132/0.131

Radial 40' 0.509/0.460

Radial 80' 0.178/0.179

Radial 120' Less than threshold Did not trigger Results: Blast containment system for 105 mm shells

A blast containment system was built according to the design shown in Fig. 2. The effect of the 105 mm munition was more pronounced. Both side walls collapsed outwards, the top cell unit sliding off the bottom one. A significant cavity was created in the centre of the structure but with the end sections of the middle cell units staying in place. Some fill (sand) spilt out from the side walls about 3 m either side of the structure and at the end where the detonation cord and pipe entered there was a further minor spill of about 1 m. The area downwind, to a distance of about 5-6 m, had a smattering of ejected fill on it. This appeared to be fill that had been ejected from the top and then taken by the wind. Witness Screen Results: There were no perforations of the witness screen due to fragmentation from the munition. There was some minor damage to the side witness screen from the placement of the detonation cord.

fragmentation were observed.

Window Frame Results: There was no damage to the windows.

Overpressure Gauge Results: All 5 signals triggered. The signal at Radial 120' triggered early due to wind.

Gauge Location Maximum Peak Comments

Overpressure (psi)

Axial 40' Less than threshold

Axial 80' Less than threshold

Radial 40' 0.535/0.518

Radial 80' 0.220/0.219

Radial 120' <0.1/0.1 Triggered early due to

wind Results: Blast containment system for 100 lb bomb

A blast containment system was built according to the design shown in Fig. 5. This blast containment system suffered considerable damage and was not left standing after the detonation. Some of the units were pushed over and fill material spilled out. However, the blast itself was effectively absorbed.

Witness Screen Results: There were no perforations of the witness screen due to fragmentation from the munition. As before there was some minor damage to one of the side witness screens from the placement of the detonation cord.

Perforation: The North side of the structure, which remained standing, was examined and no perforations from fragmentation were observed. Where possible the exterior surfaces of the other cell units that had collapsed were also examined and showed no signs of perforation. Window Frame Results: There was no damage to the windows.

Overpressure Gauge Results: Only 2 signals at both gains were recorded, these were both on the Radial axis.

Gauge Location Maximum Peak Comments

Overoressure fosiV

Axial 40' Less than threshold

Axial 80' Less than threshold

Radial 40' 0.752/0.744

Radial 80' 0.328/0.326

Radial 120' <0.2/0.123 Results Summary

During the demonstrations:

- There was no perforation of witness plates by fragmentation.

- There was no damage to the surrogate window structures.

- Pressure data indicated a significant effect in mitigating blast effects.

- Spread of debris was effectively controlled.

- No fragmentation was found to have perforated the outer cell walls, and no fragmentation was found on the cleared geotextile area surrounding each blast containment system.

The test results are summarised in Table 2 below.

It was concluded that the blast containment system designs for 60 mm and 81 mm mortars, 105 mm shells and a 100 lb. air-delivered bombs were effective.

Claims

1. A cellular unit for use in the intentional detonation of UXO devices, the unit being formed of a plurality of interconnected open cells of flexible fabric material and further comprising a cellular space to accommodate a UXO device in use, the cellular space being interconnected with one or more of the open cells and being larger than each open cell.

2. A cellular unit as claimed in claim 1 , wherein the larger cellular space is interconnected with the open cells on at least two sides.

3. A cellular unit as claimed in claim 1 or 2, wherein the interconnected open cells and the larger cellular space are at least partially formed from a continuous strip of material.

4. A cellular unit as claimed in claim 1 , 2 or 3, wherein a continuous strip of material wraps around the open cells and/or the larger cellular space to form the outer perimeter wall(s) of the unit.

5. A cellular unit as claimed in any preceding claim, comprising a skirting strip that extends substantially horizontally around the periphery of the unit and depends upwardly or downwardly to seal across the junction between vertically juxtaposed units.

6. A cellular unit as claimed in claim 5, wherein the skirting strip is integrally formed with the outer perimeter wall(s) of the unit or is provided as a separate piece of material.

7. A cellular unit as claimed in any preceding claim, wherein the larger cellular space is substantially surrounded by interconnected open cells.

8. A cellular unit as claimed in any preceding claim, wherein the larger cellular space is at least as large as two, three, four, five, six or more of the open cells.

9. A cellular unit as claimed in any preceding claim, wherein the open cells are filled in use with a fine aggregate material such as sand, earth or the like.

10. A blast containment system comprising a cellular unit as claimed in any preceding claim, and further comprising one or more further cellular units formed of a plurality of interconnected open cells of flexible fabric material.

11. A blast containment system as claimed in claim 10, wherein the further cellular units are stacked next to and/or on top of the cellular unit comprising the larger cellular space.

12. A blast containment system as claimed in claim 11 , further comprising a cover for the larger cellular space.

13. A blast containment system comprising a lower cellular unit comprising a cellular space to accommodate a UXO device in use, a cover over the cellular space, and at least one upper cellular unit, formed of a plurality of interconnected open cells of flexible fabric material, arranged on top of the cover.

14. A blast containment system as claimed in claim 13, wherein the lower cellular unit further comprises a plurality of interconnected open cells of flexible fabric material that are

interconnected with the cellular space.

15. A blast containment system as claimed in claim 14, wherein the cellular space is larger than each of the plurality of interconnected open cells.

16. A blast containment system as claimed in claim 14 or 15, wherein the cellular space is substantially surrounded by interconnected open cells.

17. A blast containment system as claimed in any of claims 13-16, wherein the lower cellular unit is arranged adjacent to one or more other cellular units formed of a plurality of

interconnected open cells of flexible fabric material.

18. A blast containment system as claimed in any of claims 10-17, wherein the open cells are filled in use with a fine aggregate material such as sand, earth or the like.

19. A blast containment system as claimed in any of claims 10-18, further comprising a skirting strip that extends substantially horizontally around the periphery of the upper and lower cellular units to form a seal across the junction therebetween.

20. A blast containment system as claimed in claim 19, wherein the skirting strip is integrally provided by the material of one of the cellular units or is provided as a separate piece of material.

21. A method of mitigating the fragmentation and blast effects of an intentional detonation, comprising shielding an unexploded ordnance (UXO) device by:

providing one or more cellular units formed of a plurality of interconnected open cells of flexible fabric material with the open cells spaced at a minimum distance D from the device; filling the open cells of the one or more cellular units with a fine aggregate material such as sand, earth or the like; and

optionally, intentionally detonating the shielded device.

22. A method as claimed in claim 21 , comprising:

positioning multiple said cellular units next to or adjacent one another to form a barricade.

23. A method as claimed in claim 21 or 22, comprising:

positioning said one or more cellular units so as to at least partially surround the device.

24. A method as claimed in claim 21 , 22 or 23, comprising:

stacking at least one said cellular unit on top of another said cellular unit.

25. A method as claimed in any of claims 21-24, comprising:

providing said one or more cellular units in a first layer;

filling the open cells in the first layer with a fine aggregate material such as sand, earth or the like;

providing one or more further cellular units in a second layer on top of the first layer; filling the open cells in the second layer with a fine aggregate material such as sand, earth or the like; and

optionally repeating with subsequent layers.

26. A method as claimed in claim 24 or 25, comprising:

forming a seal between vertically juxtaposed cellular units.

27. A method as claimed in claim 26, comprising:

providing a skirting strip to extend substantially horizontally around the periphery of the vertically juxtaposed cellular units and form a seal across the junction therebetween.

28. A method as claimed in any of claims 21-27, comprising: selecting the number of said one or more cellular units and/or the number of layers of said one or more cellular units depending on the UXO device to be shielded.

29. A method as claimed in any of claims 21-28, comprising:

arranging at least one said cellular unit over the device so as to house the device in a cellular space in the unit at a minimum distance D from the interconnected open cells.

30. A method as claimed in claim 29, comprising:

filling only the open cells of the one or more cellular units so as to leave an air space around the device in the cellular space.

31. A method as claimed in any of claims 21-30, comprising:

providing a cover that extends over the device and the distance D.

32. A method as claimed in claim 31 , comprising:

providing one or more further cellular units in a second layer on top of the cover.

33. A method of mitigating the effects of a weapon, comprising shielding a weapon by: providing one or more cellular units formed of a plurality of interconnected open cells of flexible fabric material with the open cells spaced at a minimum distance D from the weapon; filling the open cells of the one or more cellular units with a fine aggregate material such as sand, earth or the like; and

optionally, activating the weapon.

34. A cellular unit for use in shielding a weapon, the unit being formed of a plurality of interconnected open cells of flexible fabric material and further comprising a cellular space to accommodate a weapon in use, the cellular space being interconnected with one or more of the open cells and being larger than each open cell.

35. A weapon shielding system comprising a lower cellular unit comprising a cellular space to accommodate a weapon in use, a cover over the cellular space, and at least one upper cellular unit, formed of a plurality of interconnected open cells of flexible fabric material, arranged on top of the cover.