Abstract:
A safety net ( 1 ) for an opening ( 11 ), eg. an open stairwell in a construction site, where the safety net ( 1 ) comprises a plurality of straps ( 2 ) in a grid arrangement. The straps ( 2 ) consist of seat belt webbing or a similar material. The safety net ( 1 ) also comprises adjustable anchoring means ( 4, 14, 25 ) for anchoring ends of the straps to the perimeter ( 10 ) of the opening ( 11 ).

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to a safety net for use during building construction or the like, and more particularly, but not exclusively, relates to an improved safety net for the prevention of builders or workers falling through an opening in a multiple storey construction site.  
         BACKGROUND OF THE INVENTION  
         [0002]    Safety nets for use in the building industry are known and generally comprise a mesh net of relatively thin cords or the like attached at its perimeter to a metal frame. These types of nets are commonly used on the exterior of buildings underneath scaffolding to catch falling workers or building materials. Similar nets may be used inside buildings to cover openings in the floors, such as stairwells, whereby the metal frame is required to be securely attached adjacent the edges of the opening.  
           [0003]    The metal frame of these nets prohibits the net being universally adaptable to openings of different sizes and configurations. Furthermore, the metal frame bordering the perimeter of the safety net can be bulky, difficult to install and provide an obstruction which workers may trip over.  
           [0004]    Where the safety net comprises a mesh net bordered by a guide cable which is anchored to the metal frame, several problems arise. Firstly, a worker falling into the net may be injured by the metal attachments, which project into the space of the aperture and secure the guide cable to the metal frame. Secondly, where the guide cable breaks or fails, the safety net is rendered useless as there is nothing to support the safety net. Finally, a closely spaced mesh net may lead workers to believe that the net is safe to be walked across. Upon attempting to walk across the net the worker may fall or trip and be injured.  
           [0005]    Similarly important is the inadequacy of current safety nets to provide means by which the net may be adjusted to accommodate differently sized openings. Safety nets which comprise a metal frame require the frame and/or guide cable to be adjusted, which is time consuming and difficult, in order to fit the dimensions of different apertures. Alternatively, construction companies may require a range of metal frame safety nets of predetermined size. However, this is costly.  
           [0006]    Furthermore, current safety nets also fail to provide a means for the passage of workers and building materials through a portion of the net while the safety net remains in place and retains full structural integrity.  
           [0007]    It is therefore desirable to provide a safety net which can be adapted to various aperture sizes and retains significant strength upon failure or release of one or more support attachments.  
         SUMMARY OF THE INVENTION  
         [0008]    According to one aspect of the invention there is provided a safety net for an opening, said safety net comprising a plurality of straps in a grid arrangement, said straps consisting of seat belt webbing or similar material, and anchoring means for anchoring the ends of the straps to the perimeter of said opening.  
           [0009]    Preferably, the anchoring means for the straps are adjustable to allow the net to be adjusted to fit openings of different sizes. In a preferred embodiment, the anchoring means may comprise a metal plate having a first anchor portion adapted to be secured around the opening by fixing means, such as screws or bolts, or the like, and a second portion which includes spaced slots through which the end of a strap is threaded, thereby providing a secure adjustable fastening. In one preferred embodiment, the second portion is hingedly connected to the first anchor portion of the anchoring plate.  
           [0010]    In a further embodiment the anchoring means comprises a quick-release anchor in which the first and second portions are formed separately as first and second parts adapted to be releasably locked together. The second part may include an integrally formed lug. The first anchor part may include an aperture adapted to receive and releasably lock the lug of the second anchor part. Preferably, the lug and the aperture of the first anchor part are T-shaped. Furthermore, the first and second anchor parts may be adapted for substantially flush alignment when the first and second anchor parts are releasably locked.  
           [0011]    The safety net may also include a gap in one corner or along one side of the safety net to permit the transmission of building materials or workers, e.g. via a ladder, between adjacent levels of a building or construction site. This gap may be enlarged without substantially affecting the strength and integrity of the net due to the use of seat belt webbing to form the safety net and the use of separate anchor points on the ends of each strap. The construction of the invention also assists to maintain an adequate strength of the safety net where some of the straps or anchors fail. 
       
    
    
       [0012]    A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0013]    [0013]FIG. 1 is a plan view of a safety net, without the anchors, in accordance with the invention;  
         [0014]    [0014]FIG. 2 shows the intersection points of orthogonally arranged straps;  
         [0015]    [0015]FIG. 3 shows one form of an anchor plate attached to a floor surrounding an opening with the end of a strap threaded through the anchor;  
         [0016]    [0016]FIG. 4 is a plan view of the anchor plate of FIG. 3;  
         [0017]    [0017]FIG. 5 is a plan view of the components of another form of anchor plate;  
         [0018]    [0018]FIG. 6 shows the anchor plate of FIG. 5 in use;  
         [0019]    [0019]FIG. 7A and 7B are plan view of the components forming a quick release anchor;  
         [0020]    [0020]FIG. 8 is a side elevational view of the quick release anchor of FIGS. 7A and 7B in the locked position; and  
         [0021]    [0021]FIG. 9 shows the safety net anchored in position across an opening, such as a stairwell in a building. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    The safety net shown in FIGS.  1  to  9  comprises a plurality of straps  2  in a substantially orthogonal grid arrangement whereby the straps are connected at their intersection points  3  e.g. by stitching and anchor plates  4 ,  14 ,  26 ,  27  are attached to the ends of the straps.  
         [0023]    As shown in FIG. 1, the safety net  1  may generally define a rectangular section. However, it should be appreciated that the number of straps  2  comprising the safety net  1  may vary depending on the size of the safety net  1  manufactured. The straps  2  comprising the safety net  1  are preferably formed from an industrial webbing material of the type which is used to make seat belts in vehicles. This may be polyester or nylon, but may equally be formed from other appropriate materials. The webbing is cut into lengths which are appropriate for making a safety net  1  of the desired size.  
         [0024]    The ends of each strap  2  may extend beyond the outer perimeter of intersection points  3  by up to about 1 m but preferably by no less than 800 mm.  
         [0025]    [0025]FIG. 2 shows the intersection points  3  of four straps  2 . According to the preferred embodiment, intersecting straps  2  are attached to each other by sewing no less than 3 mm from the edge of the straps using heavy duty thread. According to a preferred embodiment, this thread is formed from a strong synthetic material, such as nylon. However, it is envisaged that other appropriate synthetic and non-synthetic materials may be used. Such means of attachment permanently fixes the straps in a substantially orthogonal grid arrangement, whereby the distance between any two parallel straps  2  is preferably no more than 250 mm. This construction provides the safety net  1  with substantial strength to support the weight of a worker falling on the net. It also allows the workers to see through the safety net  1  and providing a disincentive to workers considering walking over the safety net  1 . If a worker attempts to walk over the safety net, it is likely that one leg will pass through the net, but the spacing between straps should ensure that he does not fall completely through the net, with the weight of the worker supported by the net.  
         [0026]    Independent strength tests have been carried out on a safety net system in accordance with the invention and the ultimate tensile strength of the weakest link of the system was found to be about 6.7 kN. A free fall drop test was also conducted on the system by allowing a 120 kg sand bag to fall freely from 1.8 m. Even under these severe operating conditions, the tension produced at the most critical location was 4.0 kN, significantly less than the ultimate tensile strength of the weakest component (6.7 kN). Therefore, based on tests performed and under extreme conditions, the safety net system is only expected to be subjected to 60% of its ultimate tensile strength.  
         [0027]    [0027]FIG. 3 shows the way in which an end of a strap  2  engages with one form of anchor plate  4 . The anchor plate  4  shown in FIGS. 3 and 4 comprises a metal plate having a generally triangular-shaped anchoring portion  5  with fixing holes  8  for receiving fixing members and a strap-securing portion  7  having a plurality of elongate apertures or slots  9 .  
         [0028]    In a preferred embodiment, the anchor plate  4  is formed from a plate of stainless steel 3-4 mm thick, approximately 105 mm long and 70 mm wide. The width of the apertures or slots  9  is preferably 3-4 mm and the distance between the slots is preferably at least 9 mm. It will, however, be appreciated that the form and dimensions of the anchor plate  4  may be varied for different strength requirements.  
         [0029]    In use as shown in FIG. 3, the anchoring portion  5  is secured, e.g. by fixing screws  6 , to the floor  10  surrounding an opening  11  in a building, such as a stairwell, and the end of a strap  2  of the net is threaded through the slots  9  to secure the strap to the anchor plate  4 . The threaded engagement of the strap  2  with the apertures in the anchor  4  allows the distance between the anchor and the outermost intersection point  3  of the net to be adjusted and, therefore, allows the safety net  1  to be configured for openings of varying sizes.  
         [0030]    The members for securing the anchor plate  4  to the floor of a building, are preferably removable members such as screws  6 , as shown in FIG. 3. However, alternative methods of fixing other than screws may be used. The manner in which the anchor is fixed results in a shear force being placed on the means of securing the anchor to the building and the hinge  9  and  10  in the anchor when tension is placed on the straps  2 .  
         [0031]    When the safety net is to be used for a stairwell opening  11  in a multi-storey building as shown in FIGS. 6 and 9, the strap ends on at least one side of the opening  11  may be required to be attached to an expansion joint  12  of the building structure rather than to the floor  10  surrounding the opening  11 . For this purpose a hinged anchor plate  14  such as shown in FIGS. 5 and 6 is preferably provided.  
         [0032]    The anchor plate  14 , as depicted in FIG. 5, comprises a first anchoring portion  15  hingedly connected to a second strap-securing portion  17 . The first anchoring portion  15  includes two laterally spaced apart fixing holes  18  for use in fixing the anchor plate  14  to the expansion joint  12  of the building. The holes  18  are of sufficient size and shape to allow screws, or other means of attachment, to fix the anchor plate  14  to the expansion joint  12 . The second strap-securing portion  17  preferably incorporates three spaced apart laterally extending elongate apertures or slots  19 .  
         [0033]    The anchoring portion  15  and the strap-securing portion  17  are joined by a hinge  20  comprising three tubular sections  21 ,  22 ,  23  alternately welded to the first and second portions  15  and  17 , through which a rod  24  is inserted to form the hinge  20 .  
         [0034]    Preferably, the anchor plate  14  is about  70  mm in width and about 80 mm in length. The holes  18  in the first portion  15  are approximately 7 mm in diameter and the slots in the second portion  17  are preferably 50 mm long and 4 mm wide, with the slot closest the hinge  20  being 3 mm wide. It is further preferable that the first and second hinged portions  15  and  17  are formed from 3-4 mm thick stainless steel. However, it will be appreciated that the form and dimensions of the hinged anchor plate  14  and its holes and slots may be varied for different strength requirements.  
         [0035]    In use, as shown in FIG. 6, the anchoring portion  15  of the hinged anchor plate  14  is secured, e.g. by fixing screws  16 , to the expansion joint  12  at one side of the opening  11  and the end of a respective strap  2  is threaded through the slots  19  to secure the strap  2  to the anchor plate  14 . The hinged anchor plate  14  is specifically designed for anchoring the ends of straps  12  to a relatively narrow member such as an expansion joint  12  with the hinge  20  of the plate  14  relieving possible shear forces on the plate when heavy items fall on the safety net, placing tension on the straps  2 . While the anchoring portion  15  is illustrated in FIG. 6 as being secured to a horizontal surface, the anchor portion  15  is equally adapted to be secured to a vertical surface.  
         [0036]    One or more of the anchor plates  4 ,  14  may be substituted with a quick release anchor  25  formed in first and second parts  26 ,  27  as depicted in FIGS. 7A and 7B. The quick release anchor  25  provides a secure anchor point for straps  2  of the net, whilst also being readily releasable to create a gap in a corner or side of the net for workers or materials to pass through, without having to undo the threading of the strap through the second part  27  of the quick release anchor  25 .  
         [0037]    As shown in FIG. 7A, a first part  26  of the quick release anchor  25  includes a substantially triangular-shaped anchoring portion  34  integrally joined with a substantially rectangular-shaped receiving portion  35 . The anchoring portion  34  includes two apertures  28  for receiving therethrough fixing means in the form of screws, bolts or the like, whereby the first part  26  may be fixed to the floor  10  surrounding an opening. The receiving portion  35  includes a receiving aperture  29  in the form of a T-shape, however, other shaped apertures may be equally applicable.  
         [0038]    A second part  27  of the quick release anchor  25  comprises a substantially square or rectangular-shaped portion  36  with three parallel slots  9  for threadedly receiving a strap  2 . A lug  30  is provided on the second part  27 . The lug  30  preferably has a central body portion  31  joined at one end to the portion  36  and having end portions  32  at its other end which extend transversely of the body portion  31  to thereby define a T-shaped lug  30 .  
         [0039]    Preferably, the first and second parts  26 ,  27  are 3-4 mm thick and about  70  mm wide. The T-shaped aperture  29  may be 48 mm in width across the cross-bar and  35  mm in height. The slots  9  are preferably 4 mm in width and 50 mm long with the slot  9  closest the T-shape lug  30  being 3 mm in width. The slots  9  may be spaced 9 mm apart. Preferably the body portion  31  of the lug  30  is 16 mm wide and 20 mm long, while the cross-bar of the T-shaped lug  30  may be 12 mm high and 45 mm wide. Furthermore, the apertures  28  are preferably 7 mm in diameter.  
         [0040]    In operation, the first part  26  will be secured to the floor  10 , for instance, of a building via fixing means through apertures  28 . The end of a strap  2  is adjustably threaded through the slots  9  in the second part  27 .  
         [0041]    The first and second parts  26 ,  27  are locked together by firstly aligning the T-shaped lug  30  of the second part  27  with the T-shaped aperture  29  in the first part  26 . The end portions  32  are then passed through the cross-bar portion of the T-shaped aperture  29  so the end portions  32  move below the level of the T-shaped aperture  29 . The first and second parts  26 ,  27  are then moved away from each other so the end portions  32  of the lug  30  move behind the shoulders  33  defined by the T-shaped aperture  29 , while square portion  36  of the second part  27  remains on top of the first part  26 .  
         [0042]    The first and second parts  26 ,  27  are finally locked when shoulder portions  38  on the T-shaped lug  30  abut the bottom extremity  37  of the T-shaped aperture  29 . Performing the above process in reverse unlocks the first and second parts  26 ,  27 .  
         [0043]    Preferably, the first and second parts  26 ,  27  are shaped to provide flush alignment while in the locked position as shown in FIG. 8. As shown in FIGS. 7A, 7B and  8 , this may be achieved by contouring a portion of the first part  26  intermediate the anchoring portion  34  and receiving portion  35 . The body portion  31  of the T-shaped lug  30  may be equally contoured, so in the locked position the end portions  32  are substantially flush with a rear surface of the first part  26 , while the second part  27  is also substantially flush with a front surface of the first part  26 .  
         [0044]    The quick release mechanism  26 ,  27  is preferably retained in the locked position by the weight of the net so that additional locks or latches are not required. Accordingly, the quick release anchor  26 ,  27  may be easily released by sliding the T-shaped lug  30  out of engagement with the T-shaped aperture  29 . Equally, re-engagement effects locking of the quick release anchor. In this manner, temporary gaps in the safety net  1  may be quickly created and closed to ensure that the safety net  1  remains covering the opening  11  to a maximum extent, rather than have a gap ever present in the safety net  1 .  
         [0045]    [0045]FIG. 9 depicts the preferred embodiment of the safety net in use where the straps  2  in an orthogonal grid arrangement are disposed over an opening  11  in the floor  10  of a building under construction. The end of each strap  2  comprising the safety net overlaps the perimeter of the aperture  11  and is anchored to the floor  10  or expansion joint  12  of the building by separate anchor plates  4 ,  14  or  26 ,  27 .  
         [0046]    Where the frequency of movement of workers or materials between adjacent floors of the building through the net is high, the safety net may be constructed to include a gap  25 , instead of, or in addition to, the use of quick release anchors  26 ,  27 .  
         [0047]    The gap  25  may provide access for workers via a ladder (not shown) to the floor of the building below the safety net  1 . The construction of the safety net in the manner described above preferably allows for the ends of the straps  2  to be released from the anchor points (marked A in FIG. 6) such that a larger gap in the net can be provided. This larger gap allows workers to pass large or bulky building materials, or the like, through the opening while the remainder of the safety net  1  remains in place guarding against people or objects falling through the remainder of the opening  11 .  
         [0048]    A safety net provided with anchor plates  4 ,  14  and  25  on the ends of each strap has the capacity to catch heavy items falling onto the net and still retain its structural integrity and strength where some anchors or straps fail or are released. Further, the anchor plates  4 ,  14  and  25  provide adjustable anchor points for the straps  2  enabling the effective size of the safety net to be varied for different sizes or openings.  
         [0049]    It will be appreciated that various modifications may be made to the preferred embodiment described above without departing from the scope or spirit of the invention.