The present invention relates generally to a unit for absorbing impact and particularly to a unit intended to prevent injury of individuals or damage to articles resulting from a fall.

The present invention finds particular, although not exclusive, utility on building construction sites. Recent legislation introduced for the construction industry demands that it must be insured that an individual cannot fall more than two metres onto a hard surface. As the height of a construction increases scaffolding is used on its exterior to reduce the chances of a fall. However, for example, whilst individuals are working on roofing timbers they can potentially fall into the interior of the building and land on what will most likely be joists, which will carry the floorboards of the upper most level of the construction. The distance between the roofing timbers and the joists will be greater than two metres such that there is a need for some method of preventing injuries from a fall, and indeed in any situation where it is likely that a individual may fall from a distance greater than two metres onto a hard surface.

It is known, for example from GB 2 367 877, to provide impact-absorbing units in which an outer casing contains a loose fill of compressible particles, for example expanded polystyrene. In such systems, however, part of an impact is absorbed by movement of the particles and this can result in an uneven distribution of particles within the outer casing. Because the compressible particles are loosely filled within the outer casing they will not automatically return to a predetermined position. In particular where the distribution of the particles has become uneven due to movement of the unit or following an impact, a subsequent impact in an area of the unit in which particles have previously been displaced may result in a reduced capacity to absorb a subsequent impact.

According to a first aspect of the present invention there is provided a fall arrest unit comprising an outer casing and inner cushioning means comprising one or more flexible envelopes housing a fluid.

The unit may be formed so as to be capable of being placed together in a closely adjacent relationship with one or more further such units to define a substantially continuous impact surface.

The use of one or more compressible volumes of fluid as an impact absorbing means gives the potential for a fall arrest unit which will absorb impact and thereafter return to a required shape and fluid distribution.

The or each envelope may comprise an enclosed volume which is sealed at the point of manufacture so that it is permanently inflated. Fluid is therefore permanently resident within the envelope/s, and the fall arrest unit is thereby self- contained and requires no further processing before being ready for use.

The cushioning means may comprise a plurality of independent and unconnected envelopes. Alternatively, some or all of the envelopes may comprise one or more partitions defining plurality of connected fluid-containment volumes. Where a plurality of envelopes are present at least some of the envelopes may intercommunicate with one another and allow movement of fluid therebetween.

In view of its intended use to absorb impacts and shocks, the or each envelope is preferably made of a material sufficiently resistant to tearing or rupture so as to be substantially non-rupturable in use.

The or each envelope may be formed as part of the structure of the outer casing. In some embodiments part of the or each envelope may be defined by the outer casing.

The cushioning means may be of an elongate form. For example, the cushioning means may comprise a plurality of flexible envelopes arranged in a linear array and connected to each other at opposite ends. In particular where the elongate cushioning means is longer than the outer casing, the cushioning means may be formed into a folded configuration within the outer casing. A folded configuration of an elongate cushioning means could be used to produce a multi-layer cushioning structure in which the cushioning medium will not be dispersed upon experiencing an impact.

The folded configuration of an elongate cushioning means could be a regular or irregular sinuous configuration. The fluid envelopes may be inflatable and deflatable such that a fall arrest unit could be transported to a site in an uninflated, and significantly reduced size, and inflated once in situ for ease of transport and/or storage.

The fluid housed by the or each flexible envelope may comprise a gas, such as air. Of course, where there are a plurality of flexible envelopes, the fluids housed in the envelopes may be the same or different to each other.

The fluid may comprise a gel which may be any semi-solid colloidal solution or jelly. In one embodiment the gel may exhibit inverse thixotropic properties upon experiencing shock-loading.

The fluid of choice and the nature of the envelope may be chosen to provide different impact-absorbing properties. That is to say that the resistance to the falling object could be varied with judicious choice of the structure of the envelope and the fluid. With suitable choices of envelopes and fluids, the resistance to a falling object could be varied within a single unit so that, for example, the resistance to a falling object could be increased gradually from the upper surface of fall arrest unit downwards.

The outer casing may be perforated so as to allow the passage of air through the fall arrest unit. Therefore as an object impacts the unit air can be displaced from the interior of the outer casing to improve the efficiency with which impact energy is dissipated. The fall arrest unit may be provided with connection means so that the unit can be connected to other such units to form the impact surface. The connection means may be adapted to allow connection of adjacent surfaces of respective units when they are stacked one on top of the other. For example the connection means may be arranged to allow interconnection of adjacent upper and lower surfaces of respective units whereby to allow stacking of units to increase the absorbent capacity of the impact surface.

The connection means may comprise a zip, clasp, strap or the like.

Whilst in theory any size of fall arrest unit could be created it may be preferable for each unit to be sized to as to be easily portable and for interconnection means to be provided on each unit to allow formation an impact surface of sufficient dimensions.

In order to allow manipulation of the fall arrest unit it may further comprise a handle portion. The clasps or the like may be positioned at the free ends of external straps secured to the outer casing to form handles.

The outer casing may comprise at least one substantially flat surface to facilitate the placement of the unit in closely adjacent relationship with another such unit.

The outer casing may be formed from a plurality of panels. The panels may be formed to assume a naturally convex shape when assembled to form the outer casing. In such embodiments once the inner cushioning means is added to the outer casing the panels will be pushed outwardly from their initial convex form to give substantially flat surfaces rather than concave surfaces as could be the case if the panels were initially flat.

The selection of materials for and the form of such a fall arrest unit is of particular importance if it is to function as required. For example, if the fall arrest unit is intended to be used on a building construction site the unit will likely be subjected to a large amount of wear and tear. An outer casing formed from a substantially wear-resistant material would therefore be advantageous.

The unit may be required to absorb impact indefinitely and in this case would preferably retain a predetermined shape. The outer casing panels may be secured together at their peripheries in such a way that the peripheral connections serve to assist in retaining a predetermined shape. The predetermined shape may comprise substantially flat faces. The panels may be secured edge to edge to form a projecting ridge in the form of a stiffened rib. The panels may be secured together by stitching; and the thread used for stitching is preferably high strength, typically 5000 denier, 7 grams per denier polypropylene.

It is noted that stitching can usefully be employed other than for purposes of sealing panels together. For example, if stitching is used at corners and along edges of a unit regardless of whether this is required for sealing the stitching also serves a protective function. This function may be enhanced by judicious choice of the stitch type; overlock chain stitch is preferred. The unit may be of substantially parallelepiped form. Such a unit may comprise an outer casing formed from two major panels each defining two adjacent major surfaces of a parallelepiped, and two opposing rectangular end panels.

The outer casing may be formed from or treated with a water-resistant material. This is particularly useful if the fall arrest unit is intended for use on a building construction site. Alternatively or additionally the outer casing may be formed from or treated with a fire-resistant material to enable its use in a wide range of circumstances.

The outer casing may be formed from woven polypropylene.

The unit may have dimensions of a multiple of approximately one third of a metre as this is a standard measurement in the building industry and will allow the unit to fit easily within the dimensions of a construction.

The present invention also provides an impact-absorbing surface comprising a plurality of fall arrest units as described above.

The present invention also provides a method of construction of a fall arrest unit as described above comprising the steps of: providing an outer casing; providing cushioning means comprising one or more flexible envelopes housing a fluid; and introducing the cushioning means into the outer casing. The cushioning means may be elongate and accordingly can be introduced into the outer casing in such a way as to form a plurality of folds, thereby providing a multi-layered cushioning structure.

The present invention also provides a method of cushioning the fall of a person in the construction industry comprising the steps of providing a plurality of fall arrest units as described above and arranging the units together in a closely adjacent relationship to define a substantially continuous impact surface on which to receive a falling person.

The plurality of fall arrest units may be arranged in a single layer, or may be arranged in stacked layers in order to increase the absorbent capacity of the impact surface.

The present invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a prospective view of a fall arrest unit according to a first embodiment of the present invention;

Figure 2 is a diagrammatic side view of the fall arrest unit of Figure 1;

Figure 3 is a diagrammatic side view of a fall arrest unit according to an alternative embodiment; Figure 4 is a diagrammatic side view of a fall arrest unit according to an alternative embodiment;

Figure 5 is a diagrammatic section of a linear array of fluid-containment volumes according to an alternative embodiment of the present invention;

Figure 6 is a diagrammatic section showing a linear array of fluid-containment volumes according to an alternative embodiment;

Figure 7 is a diagrammatic section of a fall arrest unit incorporating a folded linear array of fluid-containment volumes;

Figure 8 is an exploded perspective view illustrating the constituent parts of an outer casing formed according to an embodiment of the present invention;

Figure 9 is a magnified view of the region of a join between two panels forming part of an outer casing according to the present invention;

Figure 10 is a diagrammatic transverse section of an outer casing formed according to the present invention prior to insertion of fluid-containment volumes;

Figure 11 is a transverse section of the outer casing of Figure 10 shown following insertion of fluid-containment volumes; Figure 12 is a plan view of a fall arrest unit according to an embodiment of the invention;

Figure 13 is a magnified perspective view of one and of a fall arrest unit according to an embodiment of the present invention;

Figure 14 is a magnified view of an end of a fall arrest unit formed according to an alternative embodiment;

Figure 15 is a perspective view of an impact surface formed from the interconnection of a plurality of fall arrest units according to the present invention; and

Figure 16 is a perspective view of an impact surface formed by stacking fall arrest units according to the present invention one on top of the other.

Referring first to Figures 1 and 2 there is shown a fall arrest unit generally indicated 1. The unit 1 comprises an outer casing 10 formed from a wear-resistant material, and inner cushioning means in the form of an envelope 20 housing a volume of air 21. The outer casing is formed from 1700 Denier woven polypropylene having a tensile strength of 1.7MNm'2 and a weight of approximately 0.1KGm"2. The inner envelope 20 is formed from a stress-resistant and resilient material such as a plastics material. In this embodiment the inner envelope 20 is formed from 50 micron thick polypropylene. The outer casing 10 protects the inner envelope 20 from damage in use. The enclosed volume of air 21 functions to arrest the fall of an object striking the unit 1. The level of inflation of the envelope 20 can be selected to provide a desired level of resistance against the falling object and a required level of energy dissipation.

Referring now to Figure 3 there is shown an alternative embodiment in which a fall arrest unit 101 comprises an outer casing 110 and eight fluid-containment envelopes 120 arranged in two stacks of four envelopes one on top of the other. Each of the envelopes 120 houses an enclosed volume of air 121 under pressure. The envelopes 120 are not interconnected with each other and are not connected to the outer casing 110.

Referring now to Figure 4 there is shown an alternative fall arrest unit generally indicated 201. The unit 201 comprises an outer casing 210; and in this embodiment the energy-dissipating fluid is housed in two types of containment envelopes. The first type comprises a plurality of semi-circular section envelopes 220 arranged around the interior periphery of the casing 210. The envelopes 220 are formed onto the outer casing 210 and the outer casing 210 forms the outer wall of the envelopes 220. The second type of envelope comprises a generally tubular envelope 225 which is placed in the interior cavity of the outer casing 210. In this embodiment the envelopes 220 house volumes of air 221, and the tubular envelope 225 houses a volume of gel 226 selected to exhibit reverse thixotropic properties upon experiencing impact. Referring now to Figure 5 there is shown a linear array of fluid-containment volumes 320, in this embodiment housing argon gas. Each of the envelopes 320 is generally elliptical and is connected to other such envelopes at either end to form the linear array. The array may be formed either by interconnecting a plurality of separate envelopes or by forming the array as a single super-structure with integral divisions.

Referring now to Figure 6 there is shown an alternative linear array of envelopes 420 similar to that shown in Figure 5, except that the envelopes 420 are not completely separate in that ports 423 are formed at the interface between adjacent envelopes 420. The ports 423 allowed the envelopes 420 to intercommunicate with each other and therefore fluid can be displaced from one part of the linear array to another.

Referring now to Figure 7 there is shown a fall arrest unit generally indicated 501. The unit 501 comprises an outer casing 510 and inner cushioning means in the form of an array of fluid-containment envelopes 520 of the same general type as that shown in Figures 5 and 6. In this embodiment the envelopes 520 are formed as a linear array and connected to each other by connection strips 524. The linear array of envelopes 520 is introduced into the outer casing by folding it into place and forming a fall arrest structure with a regular sinuous configuration in which a plurality of fall arrest envelopes are arranged in stacks. Referring now to Figure 8 the construction of an outer casing 10 suitable for forming a fall arrest unit according to the present invention is shown. The casing 10 is formed from two major panels 30, 35 and two rectangular end panels 40, 45. The casing 10 may be formed by joining the panels 30, 35, 40, 45 to form an open- sided enclosure allowing insertion of one or more fluid-containment envelopes before the opening is closed along the remaining edge between the panels 30 and 35. Alternatively, the panels 30, 35, 40 may be first be joined to form an open- ended sack before one or more fluid-containment envelopes are inserted before the rectangular end panel 45 is used to close the casing 10.

Referring now to Figure 9 there is shown a magnified view of the region of the join between two panels 30, 40. Where the edges of the panels 30, 40 meet they are pressed together to form two lips 31, 41 and stitched over the join; a chain overlock stitch 47 is preferred as this type of stitching serves to secure earlier stitches which results in a strong join. In this way a rigid upstanding rib 37 is formed at the periphery of the panels 30, 40 and likewise along the longitudinal edges of the panels 30, 35 which helps to maintain the shape of the units. If the stitches are close together the result is a substantially continuous sheeth which helps to protect the most vulnerable part of the fall arrest unit.

Referring now to Figure 10 there is shown a diagrammatic transverse section of a fall arrest unit 1 formed in part by panels 30 and 35. It will be noted that the two opposite corners of the structure are secured together by stitches 47 as discussed in relation to Figure 9. Each of the panels 30, 35 comprises first and second sub- panels 31, 32 and 36, 37 which are joined at respective folds 33, 38 to formed generally L-shape panels 30, 35 in which the sub-panels 31, 32 and 36, 37 are generally orthogonal to each other. The panels 30, 35 are formed such that the sub-panels 31, 33 and 36, 37 all naturally assume a generally convex shape. The benefit of this convex configuration is that when the fall arrest unit casing 10 thus formed is filled with one or more fluid-containment envelopes (not shown) the convexity of the sub-panels is removed and the outer faces of the panels 30, 35 become substantially flat (shown in Figure 10) to enable the unit to be easily placed against similar formed units.

Referring now to Figure 12 there is shown the top surface 32 of the fall arrest unit 1, which comprises the sub-panel 32 of the panel 30. The surface 32 has three lateral interconnection modules 60 mutually spaces along its length, and a longitudinal interconnection module 65 at either end thereof. Referring now also to Figure 13, the lateral interconnection modules 60 comprise a lateral strap 70 secured at either end by stitching 71 and having a male 75 and female 80 portion of a clasp fastener at either end. The strap 70 is loose between the stitching 71 to form a handle for manipulating the unit 1. The longitudinal interconnection module 65 comprises a female or male (in this embodiment a female) portion of a clasp fastener. In some embodiments at each end of the unit 1 both the male and female clasp fastener portion is provided so that the orientation of units 1 with respect to each other is not important for interconnection purposes.

Referring to Figure 14 there is shown an alternative arrangement of a lateral interconnection module 160. The strap 170 is secured at either of its ends by stitching along or adjacent to the respective longitudinal edges of the panels 130, 135. Male and female connectors 175, 180 are in this embodiment threaded onto the strap using respective aperture eyelets 176, 182 which allows movement of the connectors along the strap to effect adjustment of their position.

Referring now to Figure 15 there is shown a protective impact surface formed from the interconnection of a plurality of units 601. In this embodiment the interconnection means comprise longitudinal and lateral hook and loop fastener panels 690, 695 stitched onto adjacent panels of the outer casing 610 and allowing the units 601 to be placed in a closely adjacent relationship to form a substantially continuous impact surface.

Referring now to Figure 16, units 701 are shown provided with hook and loop fastener panels 796 on adjacent upper and lower surfaces of the units 701. The panels 796 allow the unit 701 to be securely staked one on top of the other. A combination of the panels 796 shown in Figure 16 and the panels 690, 695 shown in Figure 15 could be used to produce a multi-layered extended impact surface from a plurality of fall arrest units.