GB2278627A - Tethering system for workmens safety lines - Google Patents

Abstract

A safety tethering system for use by workmen working on high buildings or the like, comprises an elongate channel 10 fixed to the side of the building or the like and having a channel mouth in the form of a longitudinal slot of restricted width as compared with the interior of the channel. The system further comprises a retaining block 24 slidable in the channel but held captive by the channel, the block carrying a lever 36 pivotable in the block and having an end portion extending from the channel and adapted to receive a shackle connected with a workman's safety harness. The lever 36 has a toe portion 36b at its other end which, when the outer end portion of the lever is lowered projects through one of a series of slots formed in the base of the channel to prevent the block sliding down the channel. When the workman using the system is climbing upwardly or climbs downwardly in a controlled fashion the lever 36 is maintained in a raised position in which the toe portion 36b is retracted into the block, away from the base of the channel, so that the block can slide freely to follow the workman's movements. A turntable system may be provided allowing transition of the block from vertical to horizontal rails and vice versa. <IMAGE>

Description

DESCRIPTION OF INVENTION Title: "Safety Tethering System" THIS INVENTION relates to a safety tethering system, whereby, for example, a workman working on a high building or holes in ground pits etc. or structure or on the side of a deep pit or shaft in the ground, can secure a body harness to the structure in such a manner that, should the workman slip, he will be prevented from falling, which system nevertheless will allow the workman to move normally about the structure being worked on without undue impediment and with exposure of the workman to the hazard of being unsupported being reduced to the minimum.

According to the invention there is provided a safety tethering system comprising at least one elongate channel having a longitudinal slot or opening into the channel which is of restricted width, as compared with an interior part of the channel, said slot or opening being defined between opposing edges of opposing lateral flanges of the channel, a retaining block held captive by said opposing flanges but slidable longitudinally along the channel, a tethering member in the form of a lever pivotally mounted in said block having a first arm extending from the block and having a free end outside said channel with a formation adapted to receive a connector for a workman's harness, said channel having, extending along its base wall, opposite said longitudinal slot or opening, a longitudinally extending series of slots, said lever having a second arm which can be extended from said block on the side thereof opposite that from which the first arm extends and capable of projecting into any slot of said series, the arrangement being such that in one angular position of said lever in said block said second arm is retracted from the base of the channel and from said series of slots but that, in another angular position of said lever in said block said second arm is projected from the block towards the channel base to project through whichever of the slots of said longitudinally extending series of slots is for the time being aligned therewith, to prevent sliding of the block along the channel.

The block may carry rollers rotatably mounted therein and projecting from the block for engagement with the inner surfaces of the channel in order to reduce friction.

Alternatively, the block may itself be made of a low-friction material, such as nylon, PTFE or PET (polyethylene terephthalate), or may carry shoes of such low-friction material engaging the opposing surfaces of the channel.

Embodiments of the invention are described below by way of example with reference to the accompanying drawings, in which: FIGURE 1 is a perspective view from below of a metal channel member used in the tethering system of the present invention, FIGURE 2 is a view in cross section showing the channel of Figure 2 with a locking trolley engaged therein, FIGURE 3 is a side elevational view showing a channel member in accordance with Figure 1 with the locking trolley fitted therein and attached by a connector to a workman's harness (not shown), FIGURES 4a and 4b are side elevation views of the locking trolley, FIGURE 5 is a side view of an alternative form of retaining block and locking lever, FIGURE 6 is a view corresponding to Figure 5 but in longitudinal section in the plane of the locking lever, FIGURE 7 is a plan view, from the back of the retaining block and lever of Figure 5, FIGURE 8 is a view, in cross-section, through the channel in which the retaining block of Figures 5 to 7 operates, showing, in end view, the block and lever of Figures 5 to 7, and FIGURES 9a to 9d are schematic views showing operation of a transfer system.

Referring to Figures 1 and 2, a channel member 10 comprises a base wall 12, opposing side walls 14 and flanges 16 which extend towards one another, parallel with the base wall 12 from the edges of the side walls 14 remote from the base wall 12 to define therebetween a longitudinal gap or slot 18 of reduced width as compared with the spacing between the opposing side walls 14. Extending centrally along the base wall 12 is a series of elongate slots 20, the series and the individual slots, extending longitudinally with respect to the channel member 10. The channel member 10 is conveniently formed as rolled sheet steel section of constant cross section (apart from the slots 20) throughout its length.Such a channel member 10 may, for example, be firmly secured in a vertically extending orientation to the side of the building on which workman are to carry out repairs or maintenance duties, or to a sloping roof, or to other high structures, such as bridges, pylons, etc.

Mounted within the channel 10 and slidable longitudinally therein, is a body 22 which is relatively elongate in the direction of elongation of the channel 10 and is, in cross section, of a size and shape to fit freely within the channel 10 but to be incapable of being withdrawn through the channel 10 via the slot 18 or of rotating within the channel 10. In one embodiment of the invention, as described in more detail below, the body 22 comprises a generally rectangular block 24 which carries, rotatably mounted therein, rollers which engage the interior surfaces of the channel base, the interior surfaces of the flanges 16 and the interior surfaces of the side walls 14, so that the body takes the form of a trolley which is guided for smooth easy sliding movement longitudinally of the channel 10.As shown in Figures 4a and 4, the block may carry a pair of rollers 26 (one on either side) at its upper end projecting slightly from the block for engagement with the channel base, a pair of rollers 28 (one on either side) at its lower end, projecting slightly from the block for engagement with respective ones of the flanges 16, a single roller 30 at its upper end, rotatable about a central axis perpendicular to the channel base 12, the roller 30 projecting from the block on either side and fitting with clearance between the side walls 14. Thus the roller 30 is able to engage either side wall 14 depending upon whether the block is displaced slightly to the right or slightly to the left in the channel. A similarly configured and arranged single roller 32 is mounted at the lower end of the block.An aperture or slot 34 extends entirely through the block 24 in the middle thereof, from the face of the block which adjoins the flanges 16 to the face of the block which adjoins the channel base 12. A lever 36 extends through this slot 34 and is mounted for pivoting on a shaft 38 which extends parallel with the plane of the base 12 and perpendicular to the longitudinal direction of the channel 10, said shaft 38 passing through a transverse bore in the block 24, which bore intersects the slot 34, the shaft passing through a complementary transverse bore in the lever 36.As shown in Figures 4a and 4b, the form of the lever 36 and the position of its pivot shaft 38 with respect to the block 24 are such that, in a normal, working position of the lever 36 with respect to the block 24, as shown in Figure 4a, a longer arm 36a of the lever extends generally horizontally from the vertical channel 10 (i.e. perpendicular to the longitudinal extension thereof) through the slot 18, whilst a shorter arm 36b of the lever lies entirely within the confines of the block 24. However, when the lever arm 36a is pivoted downwardly relative to its position in Figure 4a, the arm 36k is swung outwardly to project beyond the face of the block 24 which is closer to the base wall 12 of the channel. The extent to which the arm 36b thus projects in this position is sufficient to extend the arm 36b through an adjoining slot 20 in the base wall 12. Thus, assuming that the channel 10 extends vertically, if a workman tethered to the lever arm 36a should slip and fall, the lever 36 will be pivoted towards the position shown in Figure 4b. If, at the time the lever is so pivoted, the lever arm 36b is aligned with one of the slots 20, the lever arm 36b will extend through such slot 20 and downward movement of the block 24, and thus of the workman suspended from the lever arm 36a will be arrested by engagement of the arm 36b with the lower edge of the slot 20.If the arm 36b, during the initial fall, should first engage a land between adjacent slots 20, either the resulting friction will arrest the block 24 or, if it does not, the block will slide until the arm 36b moves into the next lower slot 20.

As shown in Figure 4b the lever 36 is biased towards its position in which arm 36b is projected from the block to engage in slots 20, by a plunger 38 accommodated in a bore 40 in the block and urged into engagement with the lever 36 by a compression spring 42 in the bore 40.

Normally, at least when working on a structure on which the channel extends vertically, the workman will be substantially level with the block 24 so that a slight horizontal outward pull exerted by the workman on the lever 36 by way of his harness will serve to pivot the lever 36, against its spring bias, into the position in which the shorter arm 36k lies entirely within the block so that the workman is free to climb upwardly or downwardly.

Referring to Figures 5 to 8 these show an alternative form of retaining block.

The body 22 of Figures 5 to 8 is intended to fit in a channel 10' of a similar configuration to that described above except that the free edges of the strip from which the channel is formed are rolled over, as indicated at 50 in Figure 8, to form, in effect, flanges 16 of increased thickness. In the arrangement of Figure 8, the channel member 10' which receives the retaining block is welded to an identical channel member, along weld seams indicated at 52. In the arrangement of Figures 5 to 8, the retaining block 24E which corresponds in function to the block 24 of Figures 2 to 4b is again of elongate generally rectangular form and has a central through slot 34 of the same form as that in the block 24 to receive a similar lever 36 which is spring biased by a similar plunger 38 and spring 42, (Figure 6).The block 24E of Figures 5 to 8 differs from block 24 of Figures 2 to 4b principally in that no channelengaging rollers are mounted in the block. Instead, the block carries replaceable shoes or sliders 44 of low friction material such as Nylon, PTFE, or (and preferably), polyethylene terephthalate (PET), which are of the channelsection shown in Figure 8 and which fit snugly in respective longitudinal channels or grooves 46 extending along opposite sides of the block. In use, the rolled-over flanges 50 engage in the longitudinal channels 54 defined by the shoes 44, whereby the block 24E is guided for longitudinal sliding movement in the channel 10' but is held captive against separation from channel 10'. The shoes or sliders 44 are detachably secured to the block 24E by screws 48 passed through holes in the shoes, into threaded bores in the block 24E.

Whilst in the foregoing description it has been assumed that the channel 10 has been secured to a building or other structure so as to extend fully vertically, such channels may, for example, be mounted on the sloping roof surface of, for example, a pent roof of a high building, the longitudinal direction of the channel 10 in such a case following the slope of the roof, with the channel mouth or slot facing upwardly and outwardly.

Due to the change in orientation of the lever 36 and block 24, 24E with respect to the vertical in such a position, there is a greater tendency for the lever 36 to lock inadvertently than in the case where the channel extends vertically and to counter this tendency frangible plastics clips, (not shown) or light springs may be used to keep the lever 36 disengaged from the channel base 12 and slots 20 in normal working, the clips or springs being, however, weak enough to fracture should a workman tethered to the lever 36 slip, so that the lever 36 can pivot and lock the block 24, 24E in place in the channel, thereby supporting the workman. Alternatively, it is possible to use channels 20 without slots for those sections following the slope of a roof, or for sections extending horizontally.

It is contemplated that a structure to be worked on may have a network of interconnected horizontal and vertical sections of channel 10, 10', (and/or sections of channel extending at an angle to the vertical) with an arrangement similar to a railway turntable being provided at each junction between channel sections which are at an angle to one another, whereby a retaining block to which a workman is tethered may be transferred readily from one section to another without requiring even temporary disconnection from the system so that a workman is never exposed to the risk of a fall. Figures 9a to 9d illustrate such an arrangement, at successive positions during transfer of a retaining block 24, 24E from a vertical section 60 of a channel 10, 10' to a horizontal section.

In these drawings, reference 60 denotes the turntable, which incorporates a short section of channel 10' extending diametrally thereacross, 62 designates a fixed arcuate wall around the exposed periphery of the turntable, (except where the latter is bounded by the adjacent ends of the horizontal and vertical section of channel 10').

Thus, in Figure 9a the block 24E is being run up the vertical section into the turntable 60 (Figure 9b); the turntable is then rotated (Figure 9c) to bring its short channel section, carrying the block 24E, into alignment with the horizontal section, after which, as shown in Figure 9d, the block 24E can be run off along the horizontal section of channel.

It is further contemplated that a climbing structure might comprise a ladder the stringers of which are formed by channels having the form of the channel 10' in Figure 8 (including the identical channel section welded thereto) with the rungs being, for example, welded to the side walls of the channels, or passed through apertures in the side walls of the back channel. With such an arrangement, a workman climbing the ladder would have a safety harness tethered to a block, such as shown in Figures 5 to 8, sliding in the channel provided by one stringer, or possibly tethered to two such blocks sliding in the channels provided by respective said stringers.

It will be appreciated that, in some applications, a retaining block, corresponding to the block 24E and shoes 44 in combination may be made as an integral body formed ent-irely from an appropriate plastics material or fibrereinforced plastics material.

Claims (6)

1. A safety tethering system comprising at least one elongate channel having a longitudinal slot or opening into the channel which is of restricted width, as compared with an interior part of the channel, said slot or opening being defined between opposing edges of opposing lateral flanges of the channel, a retaining block held captive by said opposing flanges but slidable longitudinally along the channel, a tethering member in the form of a lever pivotally mounted in said block having a first arm extending from the block and having a free end outside said channel with a formation adapted to receive a connector for a workman's harness, said channel having, extending along its base wall, opposite said longitudinal slot or opening, a longitudinally extending series of slots, said lever having a second arm which can be extended from said block on the side thereof opposite that from which the first arm extends and capable of projecting into any slot of said series, the arrangement being such that in one angular position of said lever in said block said second arm is retracted from the base of the channel and from said series of slots but that, in another angular position of said lever in said block said second arm is projected from the block towards the channel base to project through whichever of the slots of said longitudinally extending series of slots is for the time being aligned therewith, to prevent sliding of the block along the channel.

2. A system according to claim 1 wherein said block has, on opposite sides thereof, respective longitudinal grooves which receive the opposing edges of said opposing lateral flanges whereby the block is held captive with respect to the channel.

3. A system according to claim 2 wherein said grooves are lined with linings of plastics material.

4. A safety tethering system substantially as hereinbefore described with reference to and as shown in Figures 1 to 4k of the accompanying drawings.

5. A safety tethering system substantially as hereinbefore described with reference to and as shown in Figures 5 to 8 of the accompanying drawings.

6. Any novel feature or combination of features described herein.