Abstract:
A safety anchor device for limiting movement of a person or arresting a fall of a person working at height, and in particular to an inflatable safety anchor device that may be positioned at a high point and then inflated with a liquid to provide a dead-weight anchor device. A dead-weight anchor device for securing a line to a person working at height comprises an attachment for a line that is provided on a top surface of a flexible-walled container. The container has an internal volume that may in use be inflated with a quantity of water to provide an anchoring dead-weight and subsequently deflated by letting water escape. The container has a plurality of flexible walls, including a pair of walls that are internally connected by drop threads that limit the separation between said pair of walls when the internal volume is inflated by water.

Description:
BACKGROUND 
       [0001]    a. Field of the Invention 
         [0002]    The present invention relates to a safety anchor device for limiting the movement of a person or arresting a fall of a person working at height, and in particular to an inflatable safety anchor that may be positioned on a roof or other high point and then inflated with a liquid such as tap water to provide a dead-weight anchor device. 
         [0003]    b. Related Art 
         [0004]    Dead-weight anchor systems, also known as anchor-weight systems, are used when people need to work at height, usually on a roof or a similar structure, and a preinstalled fixed anchor system is not available. A fixed anchor system might not be available because an anchor system has never before been needed at a work location or because there is some difficulty in installing a fixed anchor system or because access is only needed temporarily. A dead-weight anchor system therefore uses an anchor device that can be moved into position and then weighted down to provide a dead-weight anchor. 
         [0005]    Dead-weight anchor systems are ideal for flat roofs where no roof penetration is possible, but may be used on any flat or gently sloping surface where the slope is insufficient to destabilise the dead-weight anchor. Examples of other locations include lift-shaft housings on tower blocks, exposed balconies, large beams or sound areas of concrete and geological features. 
         [0006]    One type of dead-weight anchor system uses a metal frame with a central eye bolt anchorage point with a centre swivel in an upper surface of the frame. After positioning, the frame may be loaded with weights until the dead-weight anchor has sufficient mass to resist movement when limiting the movement of a person or when arresting a fall of a person working at height connected to the anchor by a safety rope or line. The relevant standard governing dead-weight anchor systems is BS EN 795:1997 and the Code of Practice for their use is BS 7883. 
         [0007]    The strength of the attachments to the dead-weight anchor device should at least equal the strength of the rope(s) attached to the safety anchor. 
         [0008]    Dead-weight anchor devices themselves should be unquestionably reliable. Wet conditions can significantly affect the frictional performance of dead-weight anchor systems. The frictional resistance of any dead-weight anchor device should be assured by being capable of not moving when subjected to a load of four times that which will be applied when limiting the movement of a person in a work positioning situation. A higher factor will be required if the dead-weight anchor system may be needed to arrest a fall of a person working at height. It may also be necessary to consider the possibility of rescue, which may involve the weight of two persons. 
         [0009]    One type of dead-weight anchor device uses an inflatable flexible anchor bag that is positioned for use when empty, and then filled with a liquid, which will normally be tap water, for example by means of a hose. When inflated with water the flexible anchor bag serves as a dead-weight anchor device. The bag may have an inlet to which the hose is temporarily connected when being filled with water. The inlet may also serve as an outlet to drain water when the device is not in use. It is important to have sufficient contact area and mass to provide sufficient friction between a lower side of the device and the supporting surface. To ensure that the lower side remains flat and to provide maximum weight, the flexible anchor bag has an approximately cubic form when inflated with water. 
         [0010]    The flexible bag necessarily has flexible walls so that the bag can be collapsed when not in use and expanded when filled with water. This causes a problem when the attachment point is provided on the top surface, as a pull on the bag can cause the anchor bag to roll as the flexible walls deform from the pulling force. To reduce this problem, the safety line or working line attachment are therefore preferably provided on a side of the bag, however, this results in a restriction in the working area that may be covered by a worker working at height, as the safety line or working line should always lead directly to the attachment point and should not be wrapped around the dead-weight anchor device. 
         [0011]    It is an object of the present invention to provide a more convenient dead-weight anchor bag for use on a roof or other exposed location at height. 
       SUMMARY OF THE INVENTION 
       [0012]    According to the invention, there is provided a dead-weight anchor device for securing a line to a person working at height, comprising a flexible-walled container with an internal volume that may in use be Inflated with a quantity of water to provide an anchoring dead-weight and subsequently deflated by letting said quantity of water escape from the container when not in use, the container having at least one attachment for said line, wherein the container has a plurality of flexible walls, including a pair of walls that are internally connected by drop threads that limit the separation between said pair of walls when the internal volume is inflated by said quantity of water. 
         [0013]    The attachment may include an eye bolt or other fixing means for attachment to a worker safety line or working line. 
         [0014]    In use, the drop threads provide a degree of internal rigidity to the inflated internal volume, so that the shape of the water inflated container resists deformation when pulled at the attachment, for example when arresting the fall of a worker connected to the attachment by a safety line. Because the inflated container substantially maintains its shape under such stresses, the dead-weight anchor device resists rolling and maintains frictional contact with a supporting surface. 
         [0015]    In a preferred embodiment of the invention, the drop threads extend across the internal volume, most preferably between the top and bottom sides or surfaces of the container. 
         [0016]    The walls preferably include a pair of flexible walls opposite each other. For example, in a preferred embodiment of the invention, the pair of walls includes a bottom wall that in use forms a base adapted to engage with a surface for supporting the weight of the device when inflated and an opposite top wall that forms an upper surface of the flexible container. The drop threads then extend between the pair of opposite walls with adjacent drop threads extending in a parallel direction when the internal volume is inflated with water. 
         [0017]    To provide maximum rigidity the drop threads are preferably provided over substantially the whole extent of the opposite portions of the pair of walls. In a preferred embodiment the drop threads are provided at a typical density of six threads per square centimetre. 
         [0018]    Because the dead-weight anchor device resists deformation of shape and rolling, the attachment may advantageously be provided on an upper surface of the container, for example in a central portion of the top wall. This then permits the worker to move in an arc around all sides of the dead-weight anchor device without the connecting line becoming wrapped around any portion of the device. A useful way of using the weight anchor is by stringing a line between two or more anchors to which the worker is attached with a sliding harness attachment line. 
         [0019]    In a preferred embodiment of the invention, the top and bottom walls are connected at their peripheries by one or more side walls that extend around the periphery of the device. 
         [0020]    The dead-weight anchor device may also comprise an inlet for admitting water to the internal volume of the container, this inlet being provided on a side wall that extends between the top and bottom walls. The inlet may be provided in an upper portion of said side wall and may comprise a spout that extends laterally away from the side wall, preferably extending in a direction directly away from the attachment on the flexible container for the safety line or work line. This helps to prevent the spout from being snagged by the connecting line as the worker moves about. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: 
           [0022]      FIG. 1  shows a plan view from above of a dead-weight anchor device according to a preferred embodiment of the invention; 
           [0023]      FIG. 2  is a cross-section through the dead-weight anchor device, taken along line II-II of  FIG. 1 ; and 
           [0024]      FIG. 3  is a view of a portion of the underside of the dead-weight anchor device of  FIG. 1 , showing a high friction strip that extends around the periphery of the base of the device. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIGS. 1 and 2  show a dead-weight anchor device  1  for securing a safety or work line  2  to a person working at height (not shown). The device  1  has a substantially square outline as seen from above in the plan view of  FIG. 1 , formed by a flexible-walled container  4  with an internal volume  6  that in use is filled with a quantity of water, indicated by diagonal dashes  8  in  FIG. 2 . 
         [0026]    The container has six main flexible walls  10 - 15  including a substantially flat bottom wall  10 , a substantially flat top wall  11  that is generally parallel with and opposite to the bottom wall, and four convexly curved side walls  12 - 15  that extend between the bottom and top walls  10 ,  11 . The container also has four convexly curved corner side walls  16 - 19  that extend between the bottom and top walls  10 ,  11  and which are angled at 45° to the adjacent main side walls. As seen in  FIG. 2 , each main side wall  12 - 15  has a semicircular profile. Together the walls  11 - 19  fully enclose the internal volume  6  of the container  4 . 
         [0027]    The internal volume  6  is filled with water  8  by means of one or more inlet spouts  20 ,  21 , provided on the side wall sections  19 ,  20  so that at least one spout will be conveniently located with respect to a water source. Each spout has an end cap or valve  22 ,  23  that can be opened and closed as required. In use a hose (not shown) is temporarily connected to one of the spouts  20 ,  21  when opened, and after the volume  6  has been substantially or completely filled, the hose is disconnected and end cap  22 ,  23  closed to seal in the water  8 . 
         [0028]    When the dead-weight anchor device  1  is no longer needed at a particular location, a drain cap  24  is opened so that water is let out of the volume  6 . 
         [0029]    The container  4  may optionally have a pressure relief valve (not shown) to prevent this from bursting by excessive water pressure. 
         [0030]    The walls  10 - 19  are flexible, being preferably made from polymer coated fabric in sections that are bonded together along seams  26  that run between adjacent sections  10 - 19 . The bond between wall sections is made in overlap regions along the seams shown by dashed lines  37 . 
         [0031]    Because the walls  10 - 19  are flexible, the container may be collapsed and folded or rolled (not shown) up when not in use. When the internal volume of the container is filled with water  8  the container walls become inflated and assume the shape shown in the drawings. 
         [0032]    As shown in  FIG. 2 , the internal volume  6  is crossed by multiple drop threads  28  that extend transversely between the bottom and top walls  10 ,  11 . The ends  25 ,  27  of each drop thread are woven within the thickness of the material forming the bottom and top walls, between outer and inner surfaces  29 ,  30  of the container  4 . 
         [0033]    The drop threads limit the expansion and ultimate separation between the bottom and top walls  10 ,  11  and so constrain the shape of the inflated container  4 , and hence also the amount of water  8  that may be put into the container. The ultimate quantity of water inside the container has sufficient mass to provide a dead-weight so that the line  2  is securely anchored. One advantage of the drop threads  28  is therefore to limit the amount of water  8  that may be put inside the container  4 , which avoids the problem of potentially overloading a supporting surface  32  on which the dead-weight anchor device  1  rests. The drop thread arrangement therefore predetermines the amount of liquid that may be put into the container  4  and therefore predetermines the anchoring mass of the device  1 . 
         [0034]    The main benefit of the drop threads however, is to provide a degree of internal rigidity to the container  4 . This is particularly beneficial as the container  4  has a squat profile, being about 200 mm high (H), and 1.5 m wide (W) and 1.5 m long (L). The low centre of mass relative to the container  6  provided by this arrangement is helpful in permitting the dead-weight anchor device to be used on gently sloping surfaces. 
         [0035]    The container  4  has in the centre of the top side  11  an attachment  36  with swivel  38  for connection to the safety or work line  2 . The attachment  36  may be an eye for an eye bolt or karabiner (not shown) or any other suitable attachment means. The forces from any lateral pull on the centrally located attachment  36  will be transmitted by the material of the top wall  11  and to the drop threads  28  and to the bottom wall  10 . Although the top wall may shift slightly in the direction of the pull, the drop threads  28  will restrain the movement and so the effect of the drop threads  28  is to substantially maintain the external shape of the filled container when pulled at the attachment  36 . Sudden tension at the attachment  36  causes a distortion of the bag and motion of the water inside which has a significant effect in absorbing the energy of a fall. This advantage is not experienced by rigid weight anchors which therefore need to have greater mass for the same level of security. 
         [0036]    As shown in  FIG. 3 , the bottom wall may have around an outer periphery or over the whole surface a friction material  40 , which may be a compliant and/or textured strip of rubber or other high friction material. In use, this will tend to engage the supporting surface  32 , thereby helping to anchor the device  1  to remain in place. 
         [0037]    The device has a substantially square outline as seen from above in the plan view of  FIG. 1 . The invention is, however, applicable to other outline profiles, for example round or rectangular. A round shape will provide the same anchoring effect from any direction with respect to a pull on a central attachment. A rectangular shape will provide a preferential restraint along the long axis of the rectangle, and may be appropriate where there are constraints on the positioning of the device or where the working angle of the line  2  is always close to the long axis of the rectangle. 
         [0038]    In the present example, the height or thickness (H) between the bottom and top sides  10 ,  11  is about 200 mm. The diagonal extent of the inflated anchor bag is about 2100 mm. The ratio of the thickness between the top and bottom sides to the diagonal extend of the dead-weight anchor device is therefore about 0.095. 
         [0039]    The invention is applicable to other shapes that are more or less squat, but preferably the ratio of the maximum separation between the top and bottom walls to the maximum extent in any direction of the base should be less than 0.5. Above this ratio, rigidity is progressively lost as the drop threads become longer relative to the size of the base. However, the preferred ratio of the maximum separation between the top and bottom walls to the maximum extent in any direction of the base is between about 0.05 and about 0.15. 
         [0040]    In the present example, the container is formed by first making a curved edge piece from eight pieces  12 - 19  of a polymer coated fabric. The fabric is waterproof and bondable to the drop thread material and to itself by adhesive, vulcanised or welded joints. 
         [0041]    This curved edge piece is then bonded to a square piece of the drop thread material, sometimes referred to as pile fabric, consisting of the bottom and top walls  10 ,  11  and the joining drop threads  28 . The base fabric for the drop thread material is high tenacity polyester  1100  Dtex with an external coating of polychloroprene (Neoprene) and the drop threads are made from double ply Nylon 470 Dtex. The weight of the drop thread material is 2400 g/m 2  (±10%). The tensile strength of the drop thread material is about 350 daN/5 cm (weft) and about 400 daN/5 cm (warp). 
         [0042]    In the event of a fall the dead-weight anchor device according to the invention will resist deformation or rolling and will act as an effective fall arrest device. 
         [0043]    The use of a drop thread material extending across the short dimension of the dead-weight anchor bag makes the bag a more suitable shape as compared with a simple water-filled bag. The result is that the dead-weight anchor device according to the invention can be used on a roof having a greater slope than would be possible with a simple water-filled bag. 
         [0044]    The invention therefore provides a dead-weight anchor device that has roll resistance to lateral forces imparted on a working line or on a safety line when braking the fall of a worker attached to the a safety line. 
         [0045]    It should be understood that the invention has been described above by way of example only and that modifications in detail may be made without departing from the scope of the invention as set out in the claims. For example, the side walls could be a single narrow strip of material, however this does not make best use of the drop thread material, which is relatively more expensive than the side wall material.