EP1073497A1

EP1073497A1 - Height safety system

Info

Publication number: EP1073497A1
Application number: EP99918157A
Authority: EP
Inventors: Peter Robert Flux
Original assignee: Latchways PLC
Current assignee: Latchways PLC
Priority date: 1998-04-23
Filing date: 1999-04-23
Publication date: 2001-02-07
Also published as: WO1999055425A1; GB2336617A; GB9808788D0; AU3618999A

Abstract

A height safety system comprises a flexible element (2) supported by spaced apart brackets (4) arranged to absorb load transmitted along the flexible element (2) up to a predetermined limit and then allow any excess load to be transmitted along the flexible element (2) to another support bracket. Each support bracket (4) allows the flexible element (2) to move relative to said support bracket (4) and/or each support bracket (4) deforms, when the load exceeds a predetermined limit.

Description

1 HEIGHT SAFETY SYSTEMS

The present invention relates to height safety systems and, in particular, to a personnel fall arrest system.

Many personnel fall arrest systems comprise a cable suspended along a walkway or across an area to be protected. The cable has its ends secured to a pair of terminal anchors supported by a fixed structure, such as a building or the like. Personnel operating in the protected area wear a personal safety harness which is attachable to the suspended cable by a safety lanyard or line and, in the event of a fall, the safety lanyard pulls on the cable so that the fall is arrested. The fall arrest loads are transmitted to the terminal anchors. In known systems, unless the cable is very short, it is supported along its length between the two terminal anchors by a number of spaced-apart intermediate brackets, the number of intermediate brackets being selected so that the maximum length of cable between any two brackets does not exceed a predetermined distance. In some systems, the user's safety lanyard may be attached to a mobile fastening device adapted to travel along the cable. If a fall occurs, the fall loads are transmitted through the lanyard and the mobile fastener to the cable. The cable then pulls through the intermediate brackets until the fall loads are absorbed by the terminal anchors. The intermediate brackets limit the distance through which a person falls before the fall is arrested because, as is well known for geometric reasons, for given cable and terminal anchor characteristics, the maximum distance travelled before the fall is arrested is dependent upon the cable length or the distance between support brackets.

Further, for geometric reasons, the load transmitted along the cable is greater than the fall arrest load on the lanyard, the increase in load being dependent on the catenary angle formed by the cable. Thus, the increase in load along the cable relative to the fall arrest load along the lanyard also increases in dependence upon the distance between the intermediate support brackets. 2

The intermediate support brackets also act as brace points at which the cable can change direction, allowing a single cable to pass around corners instead of being limited to a linear span.

In addition, the intermediate support brackets restrict the unsupported length of the cable, limiting the extent of cable movement in high winds so that the cable cannot rub against or strike the fixed structure to which it is attached, with possible damaging effects to both the cable and the fixed structure.

One disadvantage with systems of the type described above is that, when a fall arrest occurs, high peak loads are experienced at the terminal anchors which must be transferred to the fixed structure as localised loads at the terminal anchor locations. This can cause problems in providing a fall arrest system because many building designs, although having ample overall strength to absorb the fall arrest loads, are not designed to take high peak loads at localised positions. This is a particular problem where a fall arrest system has to be attached to a building facade which may be largely ornamental rather than structural. In such circumstances, the main load- bearing structural members of the building may not be easily accessible for attachment of the terminal anchors of the fall arrest system. It is therefore an object of the present invention to provide a fall arrest system which overcomes the aforementioned problems, at least in part. The invention is a

A height safety system according to the invention provides the advantage that any loads applied to the elongate element greater than the predetermined limit can be transferred from the elongate element to a fixed support structure through two or more support brackets, thereby limiting the peak loads applied to the fixed support structure by any one of the support brackets to the predetermined limit. 3

The invention will now be described, by way of example only, with reference to the drawings, in which:

Figure 1 shows a first height safety system according to the invention; Figure 2 shows a second height safety system according to the invention; Figure 3 shows a third height safety system according to the invention; Figure 4 shows a first bracket suitable for use in a height safety system according to the invention;

Figure 5 shows a second bracket suitable for use in a height safety system according to the invention; Figure 6 shows a third bracket suitable for use in a height safety system according to the invention; Figure 7 shows an alternative arrangement of the third bracket;

Figure 8 shows a fourth bracket suitable for use in a height safety system according to the invention, and Figure 9 shows a fifth bracket suitable for use in a height safety system according to the invention.

A first height safety system incorporating the present invention is shown in Figure 1 .

The height safety system is anchored on and supported by a fixed supporting structure ( 1 ) such as a building. An elongate support element in the form of a multiple strand metal cable (2) is suspended across a part of the fixed structure ( 1 ) from a first terminal anchor (3A), through a plurality of intermediate brackets (4), to a second terminal anchor (3B) . The terminal anchors (3A, 3B) are identical and all of the intermediate brackets (4) are also identical. 4

In use, a mobile fastening device such as a slider (5) secured to a safety lanyard (6) is arranged to slide along the cable (2) . The slider (5) and intermediate brackets (4) are arranged to co-operate in a known manner so that the slider (5) can travel along the cable (2), past the intermediate brackets (4), without detachment of the slider (5) from the cable (2) and without the cable (2) being released from the intermediate brackets (4) at any time. The lanyard (6) is attached to a personal safety harness of a user and, in the event of fall, the fall will be arrested by the lanyard (6) being supported by the support brackets (3 and 4) through the cable (2), in much the same way as a conventional height safety system of this type.

In a conventional system of this type, the intermediate support brackets (4) allow unrestricted longitudinal movement of the cable (2) through the brackets (4) so that, when a fall arrest situation occurs, all the loads are transferred along the cable (2) to the terminal anchors (3A, 3B) . In the system according to the present invention, such unrestricted longitudinal movement of the cable is not possible. Each of the intermediate support brackets (4) is arranged to absorb loads transmitted along the cable (2) up to a predetermined limit and then, if the load exceeds the predetermined limit, the cable is allowed to slip through the bracket (4) so that the excess force can be applied to and will be absorbed by the next bracket.

In the embodiment depicted in Figure 1 , the cable (2) is substantially straight. The cable (2) could, of course, be arranged to turn a corner at one or more points along its length by appropriate positioning of the terminal anchors and intermediate support brackets (3 and 4) . The cable (2) can be arranged horizontally, vertically or at some angle in between, as required.

Although a height safety system is preferred in which all of the intermediate brackets (4) are capable of absorbing forces from the cable (2) up to a predetermined limit before allowing the cable (2) to slip through the bracket (4), it is possible to use some intermediate brackets of a known type which allow the cable (2) to move longitudinally through the intermediate bracket in unrestricted fashion. Thus, a hybrid system could be installed, using 5 a mixture of conventional and controlled-slip intermediate brackets. The main criterion for an effective installation of this type is that the loads experienced at the terminal anchors, in a fall arrest situation, should not be excessive.

A second height safety system according to the invention is shown in Figure 2. This is similar to the first example in that a cable (2) is attached to a structure ( 1 ) by a plurality of brackets. In the second example, the terminal anchors (4A) and the intermediate support brackets (4) are all identical support brackets, each able to absorb tensile energy transmitted along a cable up to a predetermined limit. If the tensile load on the cable (2) exceeds this predetermined limit, the brackets (4) acting as intermediate supporting brackets and spaced out along the length of the cable (2) allow the cable (2) to pass through the bracket (4), allowing the excess tensile load to be passed along the cable (2) to an adjacent bracket (4) . In-line load absorbers (7) are placed adjacent the brackets (4A) acting as terminal anchors brackets to ensure that the peak loading in a fall arrest situation passed along the cable (2) to the terminal anchors (4A) will not exceed the predetermined limit. In such a system, it is necessary to limit the movement of the slider (5) to the length of the cable (2) between the in-line load absorbers (7) rather than the full extent of the cable (2) between the terminal anchors (4A). An alternative arrangement of the height safety system as shown in

Figure 2 would be to omit the in-line load absorbers (7) and to provide a length of unsupported spare cable (2) beyond each terminal anchor (4A) . The length of spare cable (2) is such that, when a fall arrest event generates a tensile load on the cable (2) at a terminal anchor (4A) which exceeds the predetermined limit, the spare cable (2) passes through the terminal anchor (4A) for a sufficiently long period for the fall arrest energy to be absorbed by the terminal anchor (4A) to a tensile load value below the predetermined limit. This prevents the spare cable (2) passing through the terminal anchor (4A) completely. A third height safety system employing the invention is shown in

Figure 3. This system is similar to the system of Figure 2 in that all of the support brackets (4) are identical support brackets (4) arranged to absorb 6 tensile load along a cable (2) to a predetermined limit and then to allow any excess tensile load to be transmitted along the cable (2) to another support bracket (4). Only one end of the third height safety system is illustrated in Figure 3, but it will be understood that the end which is not illustrated has a corresponding layout and construction.

In the third height safety system, a pair of support brackets (4B and 4C) act as a terminal anchor. The cable (2) passes through both of the brackets (4B and 4C) forming the terminal anchor, but the movement of the slider (5) attached to the safety lanyard (6) is restricted to that portion of the cable (2) between the bracket (4B) forming an inboard member of a first terminal anchor assembly and its counterpart (not illustrated) forming an inboard member of a second terminal anchor assembly at the opposite end of the cable (2) . The slider (5) cannot travel on the section of the cable (2) between the respective inboard and outboard support brackets (4B and 4C) which form each terminal anchor assembly.

By virtue of the foregoing arrangement, the tensile load applied on the cable (2) to the outboard support bracket (4C) in each terminal anchor assembly will only be that part of the tensile load transmitted along the cable (2) which exceeds the predetermined limit and which has been passed through the respective inboard support bracket (4B) . Thus, it can be ensured that the loading applied to the outboard support bracket (4C) of each end anchor assembly is always less than the predetermined limit. If necessary, three or more support brackets (4) could be linked together to form a terminal anchor assembly in the manner described above, to divide the load between them.

The advantage of the third embodiment over the first and second embodiments is that only a single type of bracket is required, simplifying assembly, maintenance and stock control for the height safety system.

A fourth embodiment, not illustrated, uses a cable (2) extending in a loop right around the top of a building, said cable being supported by a plurality of identical support brackets (4) . In such a system, all of the brackets (4) are able 7 to transfer excess load to an adjacent bracket along the cable (2), if required. No terminal anchor assembly or specialised end anchor bracket is necessary. In the second and third embodiments, it is preferred to provide an end stop on the end of the cable (2) to ensure that, even if the height safety system is overloaded, the cable (2) cannot be entirely pulled through the terminal anchor assembly or bracket and thereby become released.

In each of the embodiments described above, it is possible to employ additional conventional intermediate anchor brackets that allow the cable (2) unrestricted longitudinal movement through them, if desired. However, it is believed that it will normally be advantageous to use only intermediate support brackets of the type which absorb tensile load up to a predetermined limit and then allow the cable to slip, thereby transmitting any excess load along the cable (2) to an adjacent bracket.

Height safety systems according to the invention, in which the tensile forces generated in a cable during a fall arrest situation are absorbed by the intermediate support brackets up to a predetermined limit and in which excess force is then transmitted along the cable to an adjacent bracket, provide the advantage that the peak loads experienced by the supporting structure through the terminal anchors can be greatly reduced without increasing the amount of load applied to the supporting structure by the intermediate brackets.

It is possible that a fall may occur when the slider of the personnel fall safety system is passing through one of the intermediate support brackets. As a result, the intermediate support brackets must be constructed and attached to their supporting structure sufficiently strongly to sustain and pass on to the support structure the entire load produced by the fall arrest incident with the slider within the bracket, generally approximately 5 - 6 kN. This is a requirement, not only of the present invention, but also of prior art systems.

As a result, even though a prior art intermediate support bracket (one which allows the cable to be pulled through it freely when a fall arrest incident occurs) would normally only have to sustain and pass on to the support structure a peak load in the range of 1 .5 to 3 kN, these intermediate support brackets must be constructed and secured to the support structure in such a 8 way that they are capable of dealing with the 5 - 6 kN shock load that might occur in a "worst case" event. By contrast, in systems according to the present invention, in which the intermediate support brackets are constructed to absorb tensile load transmitted along the elongate element up to a predetermined limit before allowing any excess tensile load to be transmitted along the cable to an adjacent bracket, the severity of the "worst case" event can be alleviated. The predetermined limit can be set so that the maximum load on the intermediate support bracket which must be transferred to the support structure is equal to the loading applied to the support bracket by a fall arrest where the slider is located in the intermediate support bracket. Thus, the intermediate support brackets in a height safety system according to the present invention can be arranged to absorb some of the forces and energy involved in a fall arrest situation without increasing the maximum force which the bracket must be designed to withstand and to transfer to the support structure.

Intermediate support brackets suitable for use in systems as described above are illustrated in Figures 4 to 9.

In Figure 4, a first intermediate support bracket (10) is shown. The intermediate support bracket ( 10) comprises a first substantially C-shaped element ( 10A) and a second substantially C-shaped element ( 1 0B) . The first and second C-shaped elements (10A, 10B) are dimensioned so that the sides of the C-shaped element (10A) fit within the sides of the C-shaped element (10B) . Corresponding slots (10C, 10D) are formed in the sides of the respective C-shaped elements ( 10A, 10B) so that the first and second C-shaped elements ( 10A, 10B) can be secured together by bolts ( 1 1 A) passing through the slots ( 10C, 10D), said bolts (1 1 A) having associated nuts ( 1 1 B) threaded thereon.

The first C-shaped element (10A) includes a further slot (10E) allowing the support bracket ( 10) to be bolted to a fixed support structure (not shown) . The second C-shaped element ( 10B) bears a pair of semi-circular projections ( 1 2), each of which supports a respective co-linear tubular sleeve ( 13) . The cable (2) passes through the two co-linear sleeves ( 1 3) and 9 a swage element ( 14) is secured to the cable (2) between the two sleeves (1 3) . The sleeves ( 13) are dimensioned to restrain sideways movement of the cable (2) but provide minimal resistance to longitudinal movement of the cable (2) through the sleeves ( 13). The semi-circular projections (1 2) provide a gap between the second

C-shaped element ( 10B) and the sleeves ( 1 3) in order to allow a slider moving along the cable (2) to pass between the tubular members ( 1 3) and the C-shaped member ( 10B).

When a tensile load is applied to the cable (2), the swage ( 14) located between the ends of the two tubular members ( 13) will prevent the cable (2) from moving relative to the bracket ( 10) so that the tensile load will be transmitted through a respective one of the tubular members ( 1 3) and semicircular projections ( 1 2) to the second C-shaped member ( 10B) and then through the first C-shaped member ( 10A) to the supporting structure. This transmission of the tensile load on the cable (2) to the supporting structure continues until the tensile load on the cable exceeds a predetermined limit, whereupon the cable (2) slips through the swage element (14) . The tensile load limit at which the cable (2) begins to slip through the swage element ( 14) can be set to a predetermined value by use of appropriate swage and cable dimensions and suitable materials.

As the cable (2) slips through the swage element ( 14), friction between the two continues to transfer a predetermined part of the tensile load on the cable (2) through the bracket (10) to the support structure.

When the tensile load on the cable (2) falls below the predetermined value, the cable (2) stops slipping through the swage element (14).

A second support bracket according to the invention which allows controlled movement of the cable is shown in Figure 5.

The second support bracket (20) comprises first and second substantially C-shaped elements ( 10A, 10B) linked by nuts and bolts ( 1 1 A, 1 1 B), in similar fashion to the first support bracket ( 10) . A pair of semi-circular projections ( 1 2) is mounted on the second C-shaped element ( 10B), as before. 10

A single cylindrical tubular member (23) is secured to the two semicircular elements (1 2) so that the cylindrical member (23) is spaced from the second substantially C-shaped member ( 10B) to allow passage of a slider, as in the first support bracket ( 10) previously described . The cylindrical member (23) is dimensioned so as to restrain sideways movement of the cable (2) but provide minimal resistance to longitudinal movement of the cable (2) through the cylindrical member (23).

A swage element (24) is secured to the cable (2), spaced apart from the end of the cylindrical element (23) when the cable is in the rest position. When a load is placed on the cable (2) pulling the swage element (24) towards the support bracket (20), the cable (2) will move freely through the support bracket (20) until the swage element (24) is brought into contact with the end of the cylindrical tube (23). When the swage element (24) contacts the cylindrical tube member (23), the tensile load on the cable (2) is transmitted through the swage element (24) into the cylindrical tubular element (23) and then through the semi-circular projections ( 1 2) and first and second C-shaped members (10A, 10B), to the support structure.

Accordingly, if the tensile load is below the predetermined load limit of the swage element (24), the movement of the cable (2) then stops. However, if the tensile load is (or becomes) greater than the predetermined load limit of the swage element (24), the cable (2) is pulled through the swage element (24), applying a predetermined load to the support bracket (20) .

It will be understood that a second swage element (24) is usually attached to the cable (2) on the opposite side of the support bracket (20), though it is not shown in this view. This arrangement allows limited movement followed by load absorption for tensile loads on the cable (2) in both directions.

A bracket of this type, in which some movement of the cable (2) is possible, will generally be easier to assemble and maintain than a system in which no free movement of the cable (2) is possible. This is because the forces acting on the cable (2) at rest can balance naturally by small movements of the cable (2) so that no pre-tensioning of the cable (2) is required . Further, 1 1 if pre-tensioning of the cable (2) is desired, carrying out and checking the pre-tensioning is simplified.

The second support bracket (20) could, of course, be used with only a single swage element (24) on the cable (2) . This would allow free movement of the cable (2) in one direction and absorption of tensile loading in the cable in the opposite direction. Similarly, the support bracket (20) could be arranged to allow no free movement of the cable (2) in one or both directions by having one or both of the swage elements (24) in contact with the end of the cylindrical tubular member (23) when the cable (2) is in its rest position. A third support bracket according to the invention is shown in Figure 6.

The third support bracket (30) comprises a support element (31 ) comprising a pair of parallel cylindrical sections (31 A, 31 B) linked by a planar section (31 C) to give a substantially dumbbell-shaped cross-section. The first and second cylindrical sections (31 A, 31 B) each have a respective bore (32A, 32B) running along their length. Note that bore 32B is not visible in Figure 6.

A bolt may be passed through the first bore (32A) through the first cylindrical element (31 A) to secure the support bracket (30) to a support structure (not shown) .

A cable (2) passes through the second bore (32B) through the second element (31 B) and two swage elements (34) are secured to the cable (2) on opposite sides of the support bracket (30) in contact with the ends of the second element (31 B) .

As is well known in the field of height safety systems, a slider with a longitudinal slot in its body portion can be arranged to slide along the cable (2) . The dimensions of the longitudinal slot are such that it is wide enough to allow the slider to pass the bracket (30) by virtue of the planar section (31 C) being received through the slot, but too narrow to permit detachment from the cable (2).

When a tensile load is applied along the cable (2), this will be transmitted through one of the swage elements (34) and through the bracket body (31 ) to a support structure provided that the tensile load is below the predetermined load limit of the respective swage element (34) . When the tensile load on the 1 2 cable (2) exceeds the predetermined load limit of the swage element (34) carrying the load, for example during a fall arrest event, the cable (2) will pull through the swage element (34) . Meanwhile, a part of the tensile load will continue to be transferred to the support structure through the support bracket (30), by means of friction between the cable (2) and the swage element (34).

An variation in use of the third design of support bracket (30) is shown in Figure 7. Here, the third support bracket element (30) is arranged as before except that one of the swage elements (34) is secured to the cable (2) at a position which is spaced apart from the respective end of the second element (31 B) . The other swage element (34) is secured to the cable (2) in contact with the other end of the second element (31 B) .

This arrangement allows free movement of the cable (2) through the support bracket (30) in a first direction only until the respective swage element (34) contacts the second element (31 B) .

It is, of course, possible to arrange the third bracket (30) with both swage elements (34) spaced apart from the bracket member (31 ) to allow a controlled amount of free movement of the cable (2) in both directions.

Similarly to the second support bracket, one of the swage elements (34) could be omitted so that the third support bracket allows completely free movement of the cable (2) in one direction.

The features of the first to third support brackets can be exchanged. For example, the second member (31 B) of the third support bracket (30) could have a cut-out portion to divide it into two separate members with bores therethrough. The cable (2) could be passed through these bores and a swage element could be held between the two parts to pick up loads on the cable (2) in either direction .

The swage elements may be crimped or otherwise permanently deformed to attach them to the cable (2) . Alternatively, the swage elements may include bearing surfaces loaded against the cable (2) by relative rotation of two parts of the swage element. In general, use of a swage element crimped or otherwise permanently deformed to secure it to the cable (2) is preferred to 13 ensure that the swage cannot become loosened. Such loosening would alter its load limit and so compromise the performance of the height safety system. However, in situations where a height safety system must be assembled and dismantled, for example in a temporary installation, the use of releasably attached swage elements may be preferred .

In the above described embodiments, the elongate member carrying fall arrest loads in the height safety system is a single cable. The invention is equally applicable to height safety systems employing multiple cables. Brackets according to the present invention can be used with one, some or all of the cables.

In addition to cable-based height safety systems, the present invention can equally be applied to systems involving an elongate flexible track element to carry fall arrest loads.

Such systems will be similar to the first to third embodiments of the invention as described above with reference to Figures 1 to 3 but with the cable (2) replaced by an elongate flexible track element.

A suitable intermediate support bracket (40) for use in such a track- based height safety system is shown in Figure 8.

The fourth support bracket (40) includes a support element (41 ) comprising a cylindrical portion (41 A) with a cylindrical bore therethrough, a bifurcated central section comprising a pair of planar elements (41 B, 41 C) substantially in parallel and a gripping portion (41 D) . The gripping portion (41 D) is arranged to wrap around an elongate track member (42) and is broken by a slot (41 E). The two clamping elements (41 B, 41 C) are secured to the gripping member (41 D) on opposite sides of the slot (41 E) and the clamping element (41 B) is attached to the first member (41 A) . A bolt (45) is passed through the cylindrical bore in the cylindrical portion to attach the support element (41 ) to a C-shaped bracket (46) which is, in turn, secured to a supporting structure (not shown). Each clamping member (41 B, 41 C) bears a pair of coinciding holes (41 F) so that bolts (43) can pass through the holes (41 F) to co-operate with nuts (not 14 shown) for urging the clamping members (41 B, 41 C) together. A disc spring (41 F) is placed on each bolt (43).

The degree of grip exerted on the track element (42) by the gripping member (41 D) can be set by adjusting the force with which the bolts (43) urge the two clamping members (41 B, 41 C) together and this clamping force is set by the properties of the disc spring (44) selected .

Similarly to the third bracket described above with reference to Figures 6 and 7, a longitudinally-split slider is used having a slot wide enough to pass around the central section of the bracket (40), but too narrow to allow detachment from the track member (42).

When a linear load, which may be tensile and/or compressive, is applied along the track, this load passes through the support bracket (40) into a support structure until the linear load exceeds the predetermined gripping force of the gripping portion (41 D). When this occurs, the track element (42) slides through the gripping portion (41 D), allowing a predetermined load to be transferred by friction from the track member (42) to the support bracket (40) and the excess linear load to pass along the track member (42) to one or more adjacent brackets. When the linear force applied along the track (42) again falls below the frictional force applied to the track by the gripping portion (41 D), movement of the track (42) through the gripping portion (41 D) is stopped . Only the residual linear load is carried through the support bracket (40) to the support structure.

A fifth design of support bracket for a height safety system is shown in Figure 9. In this embodiment, the elongate track member (51 ) includes a substantially cylindrical guide member (51 A) and a serrated region (51 B) adjacent the guide member (51 A) extending along the length of the elongate track element (51 ) .

The support bracket (50) comprises a substantially C-shaped attachment (50A) including a slot (50B) to allow the bracket (50) to be bolted to a support structure and bearing a pair of coaxial holes (not shown) . The 1 5 second substantially cylindrical element (50C) has a central bore and has a first clamping element (50D) attached thereto.

A second clamping element (50E) is opposed to the first clamping element (50D) and secured thereto with a bolt (52) . The securing element (50A) is attached to the cylindrical member (50C) by a bolt (53A) passing through the two bore holes of the securing member (50A) and the central bore of the cylindrical member (50C) and is secured in place with a nut (53B) .

The opposed clamping elements (50D, 50E) each define a partially cylindrical bearing surface shaped to fit around the guiding element (51 A) of the elongate track member (51 ) and a plurality of projections (not shown) shaped to fit into the recesses in the serrated region (51 B) . The opposed clamping elements (50D, 50E) are urged together by the bolt (52) with a force controlled by a spring washer (54). When a linear load, which may be tensile or compressive, is applied along the elongate track member (51 ), this is transferred into the support bracket (50) and thence on to the support structure by friction between the guide element (51 A) and the semi-cylindrical bearing surfaces of the clamping members (50D, 50E) and by the projections of the clamping members (50D, 50E) bearing against the serrations of the serrated region (51 B) .

When the linear force applied along the elongate track member (51 ) exceeds a preset value determined by the force with which the opposed clamping members (50D, 50E) are urged together by the spring washer (54), the elongate track member (51 ) will pull through the bracket (50), allowing the excess linear force to be transferred along the elongate track member to another bracket or brackets. When the applied linear force drops below this preset level, movement of the elongate track element (51 ) will stop and the applied linear forces will again all be carried by the support bracket (50).

It is preferred that serrated regions (51 B) are formed on both sides of the elongate track element (51 ) and that co-operating sets of serrations are formed on both clamping members (50D, 50E) . However, the serrations may be formed on only one side of the elongate track element (51 ) and on a 1 6 corresponding one of the clamping elements (50D, 50E) only. Alternatively, the clamping elements (50D, 50E) could be formed with one or more projections rather than a co-operating set of serrations.

Alternative constructions are also possible for both cable and track based systems. For example, the support brackets may be arranged to be controllably deformable so that linear loading up to a predetermined level would be carried from an elongate support element through the bracket to a support structure. If the loading exceeds this predetermined level, the bracket plastically deforms, thereby limiting the amount of load transferred to the supporting structure and allowing the elongate support element to move relative to the other brackets in the system. This allows a load to be transferred along the support element to the other brackets.

In such a deformable bracket arrangement, in which the loads applied to the support structure are limited by deformation of the intermediate support brackets, the elongate support element can be rigidly attached to the support brackets. Thus, no movement of the elongate support element relative to the support bracket is possible, movement of the elongate support element relative to the other support brackets and the support structure being allowed only by virtue of deformation of the support bracket. Alternatively, the two concepts could be combined to allow both deformation of the support bracket and movement of the elongate support element relative to the support bracket. This would limit loads applied to the support structure and allow movement of the elongate support element relative to the support structure and other support brackets. The advantage of such a combined approach is that there is, inevitably, a physical limit to the amount of deformation of the support bracket which can occur. This restricts the period for which excess tensile load can be transferred along the elongate support element, thereby limiting the total amount of energy which can be transferred along the elongate support element to other brackets. Accordingly, it may be useful to allow for the possibility of overload of the fall safety system by allowing for movement of the elongate support element relative to the bracket once the limit of bracket deformation is reached. 1 7

One alternative combined system is one in which the primary load limiting mechanism uses movement of the elongate support element through the support bracket up to a limit stop, such as a rigidly attached swage on a cable or a flange on a solid track. This stops movement of the elongate support element relative to the bracket at a preset distance. Once this limit on movement is reached, the support bracket could deform to contain and limit loads applied to the support structure. Such an arrangement could provide a useful margin of safety in a situation in which a height safety system is overloaded, when a safe limit of movement of the elongate support element relative to the support bracket is reached but the system is capable of absorbing further energy without catastrophic failure.

Height safety systems similar to some of those described above are disclosed in the Applicants' International Patent Application No. WO 98/35724, which relates to a height safety system comprising a flexible elongate element, said element being pre-tensioned/stressed between support brackets at intervals to stiffen its linear form, and shuttle means coupled to said elongate element adapted for movement therealong, said shuttle means including attachment means for receiving a suspended load or a personal safety line; the element having primary and secondary track formations independent from each other, said primary track formation providing a continuous path along which said shuttle means is able to traverse without interruption, and said second track formation providing attachment points for said support brackets at any point along the extent of the element without obstructing said primary track formation, wherein the elongate element has a cross-section with a centre portion and at least two lobes protruding therefrom, at least one of the lobes constituting the second track formation and being arranged for engagement by intermediate support brackets which grip the secondary track formation with a predetermined clamping force to allow the elongate element to pull through the intermediate support brackets in response to an applied tensile load exceeding the predetermined clamping force, until the tensile load equals the predetermined clamping force, whereby said tensile load is partially transferred to an adjacent span of the elongate element. 18

Although the invention has been particularly described above with reference to specific embodiments, it will be understood by persons skilled in the art that these are merely illustrative and that variations are possible without departing from the scope of the claims which follow.

Claims

19 CLAIMS

1 . A height safety system comprising a flexible elongate element supported by at least three spaced-apart support brackets, said support brackets being arranged to absorb load transmitted along the elongate element; characterised in that at least some of said support brackets are arranged to absorb load up to a predetermined limit and then to allow any excess load to be transmitted along the elongate element to an adjacent support bracket, and further characterised in that said flexible elongate element is not of a type having primary and secondary track formations wherein said primary track formation provides a continuous unobstructed path for a mobile fastening device adapted to travel therealong and said secondary track formation, independent from said primary track formation, provides attachment points for said support brackets and being pre-tensioned.

2. A height safety system as claimed in Claim 1 , in which at least some of the support brackets are arranged to allow the flexible elongate element to move relative to the support bracket when the load exceeds the predetermined limit.

3. A height safety system as claimed in Claim 1 or Claim 2, in which at least some of the support brackets are arranged to deform when the load exceeds the predetermined limit.

4. A height safety system as claimed in Claim 2 and Claim 3, in which at least some of the support brackets are arranged to allow the flexible elongate element to move relative to the support bracket when the load exceeds a first predetermined limit and are arranged to deform when the load exceeds a second predetermined limit.

5. A height safety system as claimed in Claim 4, in which the first predetermined limit is smaller than the second predetermined limit. 20

6. A height safety system as claimed in any preceding claim in which the load is a tensile load .

7. A height safety system as claimed in any preceding claim, in which the flexible elongate element is a cable.

8. A height safety system as claimed in any one of Claims 1 to 7, in which the flexible elongate element is a track.

9. A height safety system substantially as shown in or as described with reference to Figure 1 of the accompanying Figures.

10. A height safety system substantially as shown in or as described with reference to Figure 2 of the accompanying Figures.

1 1 . A height safety system substantially as shown in or as described with reference to Figure 3 of the accompanying Figures.