Patent Application
20190323801
This invention relates to explosive blast absorption. In particular it relates to a system comprising a barrier absorbing the effects of blast waves.
It is a requirement to protect structures and buildings against the effects of blast waves caused by an explosion, for example. Typically methods of achieving this include hardening or strengthening the structure or using techniques to deflect the blast waves. All of these techniques can work reasonably well to protect the buildings and structures themselves, and often to protect persons within them. However, all hardened structures tend to reflect the blast wave and the reflective wave will then continue propagating until it meets another structure. This other structure might not be so well protected and the reflected wave may cause considerable damage and possible loss of life to and within the structure. Thus, if a particular building, say a Government building, is hardened to protect that building then an explosion occurring in the vicinity of that building may not harm the persons within that building but the reflective shockwave may harm persons in an unprotected building across the street for example.
In addition, extreme hardening of the walls of a structure, which will typically be a nationally or politically significant building, will tend to leave the windows as the most vulnerable component. This facilitates the likelihood of their failure with the potential for lethal shards of glass to pass into the building and, due to the negative phase produced by the blast, also to the surrounding exterior environment.
The present invention arose in an attempt to provide a system which absorbs rather reflects a blast wave.
In a first aspect the invention provides an explosive blast absorption barrier, comprising a plurality of layers, including a front layer and at least one further layer which comprises a recess forming layer providing a plurality of tapered recesses, each tapering from a wider opening at a surface distal from the front layer to a narrower end, each tapered recess being at least partially filled with a mixture of particulate matter and a gel.
The particulate matter is most preferably sand. The gel may be formed from a gelling agent such as gelatine and water or be a synthetic material.
The mixture is typically such that the particles are held within the gel material and set within each tapered recess.
The tapered recesses are most preferably conical or square pyramidal shapes.
The recess-forming layer may be of a pulped paper material. Typically, in the UK, material of this type is used for the formation of containers for storing eggs for consumption.
In preferred embodiments, at least two recess-forming layers with the particulate matter/gel mixture are included.
Each recess-forming layer may be mounted upon a support layer. This might typically be a corrugated card material.
The barrier may comprise two or more such recess-forming layers, each separated by a support layer, typically with at least one air gap between layers. A sacrificial trim or external panel may form part of the barrier, positioned at a point that is likely to be closest to the blast centre.
In elements of the invention, the recess-forming layer in effect forms a tray or containment element for the sand/gel mixture. It is therefore shaped to attempt to modify a pressure wave which propagates to it. The angle of incidence of a blast wave to the recesses may be around 42°. Preferably it is made of a material such as pulped paper and other material and may contain a flame retardant such as Borax which will allow it to be substantially non-combustible. It may therefore be formed from a slurry of paper and water in the same way as an conventional egg box. Other components may also have flame retardants.
The gel material most preferably contains water mixed with a gelling agent such as gelatine. In addition to being a material for retaining the sand particles it is also an important element in its own right and can absorb heat generated from an explosive event, converting this to steam and water vapour under heat and pressure and thus serves to dissipate some of the energy of the blast as well as acting as a retardant. It forms into a gel and provides for a mixture, with the sand or other particulate matter, that is malleable in order to take on the form available from the profile of the substraight.
The sand or other particulate material is moulded with the gel material and will be compressed with this into the recesses within the recess-forming layer. Each particle has a mass and requires energy to be moved and separated but also acts as a retardant. When mixed with the water/gelatine mixture this becomes malleable and can be formed into the recesses in the substraight as described.
Thus, in embodiments of the invention, the effect of a blast is to act on each of the many particles in each recess. Each of these absorbs a small part of the total blast wave power. Whilst the particles themselves may be ejected, relatively small particles of less than 2 mm, preferably less than 0.9 mm in diameter, have minimal lethal impact and, if coming into contact with a human body, are unlikely to lead to more than superficial damage or perhaps non-permanent scratching of eyes etc. Sand is generally defined as between 2 mm and 0.0625 mm in diameter so is a suitable and convenient material.
Clearly, the more particles in each recess the better, as each one absorbs a small amount of blast energy.
In a further aspect the invention provides a method of protection, a structure comprising mounting a barrier as described between the structure and a region where a blast may originate from, such that the barrier provides a sacrificial blast absorption barrier.
Embodiments of the invention will now be described, by way of example only, with reference to the schematic accompanying drawings, in which:
The system of
It comprises a first layer which is generally a sacrificial trim/exterior panel and which may be flooring.
The next layer may be a non-flammable foam filing layer 3.
The next layer comprises a first one of two layers 4 which each form a plurality of tapered recesses (e.g. pyramidal or cone shaped), or triangular or other shaped channels, which are arranged to have wider openings further from sacrificial trim 2 and narrower ends (typically closed ends) which are closer thereto. They are therefore termed “recess-forming layers”). This may conveniently be formed, as is shown in the schematic
These recess-forming layers each have a plurality of elements shown as 5 which are formed by a mixture of sand or other particulate matter, a gel (e.g. gelatine) and water. The gelatine and water forms a gel which, when mixed with the sand, form a malleable paste which can be pushed into the recesses 4a of each layer 4. This may be done by inverting layer 4, filing each recess with the mixture and then allowing this to dry, when it will partially set to a sufficient level that when the layer is upturned, each pyramidal cone 5 is retained in place and does not fall out.
This component, when filled with sand/gel mixture 5, is then placed upon element 6, which is a support panel and which may be formed of corrugated card or otherwise. By making it of corrugated structure this provides further resilience and thus further blast absorption.
Note that the layer 4, which holds the conical elements 5, may have a substantially planer or otherwise formed upwards surface and may preferably just have the recesses formed in its lower surface. This is shown in
Underneath panel 6 is a further typically similar panel 6′. However this need not necessarily be identical to panel 6. The two panels 6 and 6′ are separated by spacers which allow an air gap to be formed between them. The air gap is shown at 7 in
Note that where the term “underneath” is used this is relative and applies when the barrier is used as a flooring. Clearly, if it is used other than “horizontally”, e.g. as wall material, or as a roof material, then the panels will not be relatively underneath each other in the same way.
Note that, however apart from at least one layer with the particle/gel mixture in recesses of this, the other components may be optional or any combination of them may be used in different embodiments.
The sacrificial layer and/or sand/gel layer (otherwise known as a containment tray) may be formed of sand or other particulate matter itself. Thus, that it may be made from said particles which are adhered together using a relatively strong adhesive and which can deconstruct under high pressure without causing lethal shrapnel. It may be formed of non-flammable fibrous elements such as nylon, resin materials or otherwise, most preferably of non-sharp elements. In addition, the sacrificial layer 1 may be made to have focused weak points to guide the pressure wave towards the centre of the system. This may be done by radially strengthening the layer from the centre, i.e. providing radial thickening ribs or otherwise or by making the layer stronger at its edge and weaker or progressively weaker towards its centre. Alternatively, a weaker portion can be formed at its centre and radially outermost parts will be strengthened. The strengthening can be done by making the strengthened part thicker, using a stronger adhesive on this, or otherwise.
If the tray is made of an adhesive sand it might be able to be formed in one forming operation with the conical inserts 5, by using with two types of sand, a first type which is more firmly bonded together to form the trays themselves and a second type which is mixed with the gel to form the pyramidal inserts.
Note that although sand is a preferred material, any particulate material can used. It is preferably one which is smaller than around 0.9 mm. Particles of greater than this size (coarse sand) might be liable to cause injuries such as eye injuries, so although usable, might be less preferred so that damage to a person, caused by the particles themselves being acted upon by the blast wave and impinging upon a person, is minimised and non-lethal.
The system, according to the present invention, forms a light weight, potentially portable, blast mitigation/absorption system. As described, the most significant components are the mixture of sand (or other particles), gelatine (or other gel forming agent) and water (or other liquid) which are formed in tapered recesses in recess-forming layers or trays and which will generally be mounted between support panels. An external sacrificial layer provides a surface upon which a person may walk, or forms the visible surface of a wall or other covering.
The system allows the destruction of its constituent parts in order to absorb energy from a blast wave. The system is designed to deconstruct by the blast loading, returning as far as possible to its constituted particles, e.g. sand particles, which are essentially inert and will not fragment into a form that is dangerous to persons or damaging to structural components. Thus, the energy of the blast is used in undergoing destruction of the barrier in a multi/micro ergonomic manner and thereby absorb the blast.
Referring again to the drawings and now to
As shown in the figures, a barrier B is placed above, or protecting a structure 11 to be protected so it may be stood off from this by a region 10 which may be a foam region, to provide more protection or which may be an air gap, in which case suitable spacers will be used (not shown) to space the barrier from the structure 11. Alternatively, it may be placed directly upon the structure.
As one example, each recess 4a (otherwise known as a cell) may contain approximately 2.5 cc of a sand/gel mix. The recesses need not be filled totally to the “brim” with the sand/gel mix. If we assume 8,000 grains of sand per cubic cm (cc) then each cell contains around 20,000 grains of sand. Each grain will have an average 4 points of adhesion, giving 80,000 micro breeches of adhesion for the blast wave to overcome per cell. In one example, 540 cells are provided per square metre in tray/substraight 4 and this equates to 43.2 million micro breeches per square metre. Each cell weighs around 0.020 Kg which is equal to about 11 Kg per square metre in the system. If the barrier is in total 100 mm thick from layers 1 to 9 then an explosive blast wave, normally travelling at say 6,000 m per second, will complete the traverse in 6 milli-seconds.
In one test a 100 mm deep barrier system achieved an approximate reduction of 80% of blast pressure using the parameters described above.
The embodiments shown in
Note that instead of the non-flammable form filing layer another air gap may be provided.
The tapered recesses may have curved closed ends rather than coming to a point. They may also have flattened closed edges (generally frustoconical). However, having a sharp angle at the other end helps to improve blast absorption.
Sand is generally defined by geologists as having particle size (diameter) between about 0.0625 mm ( 1/16 mm) to 2 mm. However in some embodiments gravel (size>2 mm) or silt (<0.0625 mm) may be used. Sand is preferred however.
Instead of conical or pyramidal shapes, the tapered recesses may be elongate channels having tapered sides, eg having a triangular cross-section.
