GB2336617A - Height safety system - Google Patents

Abstract

A height safety system comprises a flexible element (2) eg a wire, to which a lanyard is attached, supported by a number of spaced apart support brackets (10). The support brackets (10) can absorb loads along the flexible element (2) up to a predetermined limit, whereafter any excess load is transmitted along the flexible element (2) to an adjacent support bracket (10). The system is intended to reduce the 'shock' loading on each bracket (10) and hence on the structure to which the system is mounted. The flexible element (2) may move relative to the support bracket (10) when the load exceeds the pre-determined limit. The load exceeding the pre-determined limit may cause a portion (14) of the particular support bracket (10) to deform.

Description

1 BEIGRT SAFETY SYSTENS 2336617 The present invention relates to height

safety systems and, in particular, to a personnel fall arrest system.

Personnel fall arrest systems generally comprise a cable hung across an area of interest and having its ends secured to a. pair of brackets supported by the building or other support structure. Personnel operating in the area of interest attach themselves to the cable by safety lanyards or lines and in the event of a f all, the saf ety lanyard pulls on the cable so that the fall is safely arrested and the loads passed to the end bracket.

In known systems, unless the cable is very short, it is supported along its length between the two end brackets 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 preset limit.

A personnel fall safety lanyard is attached to a slider able to travel along the wire. When the f all occurs, the fall loads are transmitted through the lanyard and slider to the wire. The wire then pulls through the intermediate brackets until the fall loads are absorbed by the end brackets. The intermediate brackets limit the distance through which a person f alls bef ore f all is arrested, because, as is well known for geometric reasons, for given cable and end support characteristics the maximum distance f allen before the f all is arrested is dependent upon the cable length or the distance between support brackets.

Further, f or geometric reasons the load transmitted along the wire is greater than the fall arrest load on the lanyard and this increase in load is dependent upon the catenary angle formed by the wire so that the increase in the load along the wire relative to the fall arrest load along the lanyard also 2 increases in dependence upon the distance between the support brackets.

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

Finally, the support brackets limit the unsupported length of the wire, limiting the extent of wire movement in high winds so that the wire cannot rub against or strike a building structure, with possible damaging effects to both the wire and building.

The problem with systems of this type is that when a f all arrest occurs, high peak loads are applied to the end brackets and in turn these high peak loads must be transferred to the building structure as localised loads at the end bracket locations. This can cause problems in providing a f all saf ety system because many building designs, although having ample overall strength to absorb the f all 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 f acade so that the main load bearing structural members of the building are not easily accessible to be used to support the end brackets of the f all arrest system.

This invention was intended to provide a f all arrest system overcoming these problems, at least in part.

This invention provides a height safety system comprising a flexible elongate element supported by at least three spaced apart support brackets, the support brackets being arranged to absorb load transmitted along the elongate element and at least some of the support brackets being arranged to absorb load up to a prearranged limit and then allow any excess load to be transmitted along the elongate element to another support bracket, the flexible elongate element not being of the type having a primary track formation providing a continuous path for an attachment means and a secondary track 3 formation independent from the first, providing attachment points for the support brackets and being pre-tensioned.

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

Height safety systems according to the invention will now be described, by way of example only, with reference to the accompanying diagrammatic figures in which:

Figure 1 shows a first height safety system according to the invention; Figure 2 shows a second height saf ety system according to the invention; Figure 3 shows a third height safety system according to the invention; Figure 4 shows a first bracket suitable f or use in a height safety system according to the invention; Figure 5 shows a second bracket suitable f or 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 f ourth bracket suitable f or use in a height safety system employing the invention; and Figure 9 shows a f if th 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 supporting structure (1) such as a building.

A wire (2) is suspended across a part of the structure (1) from a first end anchor (3A) through a plurality of intermediate anchor brackets (4) to a second end anchor 4 bracket (3B). The end anchor brackets (3A, 3B) are identical and all of the intermediate anchor brackets (4) are identical.

In use, a slider (5) secured to a safety lanyard (6) is arranged to slide along the wire (2). As is well known in the field of height safety systems, the slider (5) and intermediate support brackets (4) are arranged to mutually cooperate so that the slider (5) can pass along the wire (2) through the intermediate support brackets (4) without the attachment of the slider (5) to the wire (2) or the support of the wire (2) by the intermediate support brackets (4) being released at any time. The lanyard (6) is attached to a personnel safety harness 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), as in conventional height safety systems of this type.

In a conventional system of this type, the intermediate support brackets (4) allow free movement of the cable (2) through the brackets (4) so that when a fall arrest takes place, all the loads are transferred along the wire (2) to the end anchor brackets (3A and 3B).

In the system according to the present invention, each of the intermediate support brackets (4) are arranged to absorb loads transmitted along the wire (2) up to a prearranged limit and then if the load goes beyond the prearranged limit, the wire is allowed to slip through the bracket (4) so that the excess f orce can be applied to and will be absorbed by the next bracket.

In Figure 1, the wire (2) is substantially straight. The wire (2) could of course be arranged to turn a corner at one or more points along its length by appropriate positioning of the end and intermediate support brackets (3 and 4).

The wire (2) can be arranged horizontally, vertically or at some angle in between, as required.

Although a height saf ety system in which all of the intermediate brackets (4) are capable of absorbing f orces f rom the wire (2) up to a prearranged limit and then allowing the wire (2) to slide through the bracket (4) is preferred, it would be possible to have some of the intermediate brackets be of the known type which allow the wire (2) to pass through the intermediate bracket.

A second height safety system according to the invention is shown in Figure 2. This is similar to the first example in that a wire (2) is attached to a structure (1) by a plurality of brackets. In the second example, the end support brackets (4A) and the intermediate support brackets (4) are all identical support brackets each able to absorb tensile energy transmitted along a wire up to a prearranged limit. If the tensile load on the wire (2) exceeds this prearranged limit, the brackets (4) acting as intermediate supporting brackets and spaced out along the length of the wire (2) allow the wire (2) to pass through the bracket (4), allowing the excess tensile load to be passed along the wire (2) to an adjacent bracket (4). In-line load absorbers (7) are placed adjacent the brackets (4) acting as end support brackets to ensure that the peak loading in a fall arrest situation passed along the wire (2) to the brackets (4A) will not exceed the pre-selected limit. In such a system, it would be necessary to limit the movement of the slider (5) to the length of a wire between the in-line load absorbers (7) rather than the full extent of the wire (2) between the end anchor brackets (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 provide a length of unsupported spare wire (2) beyond each end support bracket (4A), the length of spare wire (2) being sufficient that when a fall arrest event generated a tensile load on the wire (2) at an end support bracket (4A) which exceeded the prearranged limit, the spare wire (2) can pass through the end support bracket (4A) for a long enough period for suf f icient of the f all arrest energy to be absorbed by the end support bracket (4A) to reduce the tensile load below the prearranged limit and stop the spare wire (2) passing through the end support bracket (4A).

A third height safety system employing the invention is shown in Figure 3. This system is similar to the system of 6 Figure 2 in that all of the support brackets (4) are identical support brackets (4) arranged to absorb tensile load along a wire (2) to a prearranged limit and then to allow any excess tensile load to be transmitted along the wire (2) to another support bracket (4). Only one end of the third height safety system is illustrated in Figure 3.

In the third height safety system, a pair of support brackets (4B and 4C) act as an end anchor. The wire (2) passes through both brackets (4B and 4C) forming the end anchor but the movement of the slider (5) attached to the safety lanyard is limited to travelling along the wire (2) between the first bracket (4B) forming the end anchor assembly and the corresponding first bracket (4B) at the opposite end of the wire (2) and cannot travel on the section of the wire (2) between the respective two support brackets (4B and 4C) which form each end anchor assembly. As a result, the tensile load applied on the wire (2) to the second support bracket (4C) forming each end anchor assembly will only be the part of the tensile load transmitted along the wire (2) which exceeds the prearranged limit and has been passed through the first support bracket (4B) making up the end anchor assembly. Thus, it can be ensured that the loading applied to the second support bracket (4C) of each end anchor assembly is always less than the prearranged limit. In fact if necessary, three or more support brackets (4) could be chained together to form the end anchor assembly 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 and maintenance of the height safety system.

A fourth embodiment, not illustrated, would be to have the wire (2) extending in a loop right around the top of a building supported by a plurality of identical support brackets (4). In such a system, all of the brackets (4) would be able to transfer excess load to an adjacent bracket along the wire (2) if required and no end anchor assembly or specialized end anchor bracket would be needed.

7 In the second and third embodiments, it is preferred to provide an end stop on the end of the wire (2) to ensure that even if the height saf ety system is overloaded the wire (2) cannot be entirely pulled through the end anchor assembly or bracket and be released.

In all the described embodiments, it would of course be possible to employ additional conventional intermediate anchor brackets which allow the wire (2) to pass freely through them if desired, but it is believed that it will normally be advantageous to use only intermediate support brackets of the type able to absorb tensile load up to a preset limit and then allow a wire to slip to transmit any excess load along the wire to another bracket.

Height safety systems according to the invention in which the tensile forces generated in a wire during a fall arrest incident are absorbed by the intermediate support brackets up to a prearranged limit and the excess force is allowed to travel along the wire to another bracket provide the advantage that the peak loads passed to the supporting structure by the end brackets can be greatly reduced without increasing the amount of load applied to a 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, in prior art fall arrest systems, and in the system according to the present invention, the intermediate support brackets must be constructed and attached to their supporting structure sufficiently strongly to sustain and pass on to the support structure all of the load produced by a personnel fall arrest incident with the slider within the bracket, generally approximately 5 - 6 M. As a result, even though the load applied to a prior art intermediate support bracket allowing the wire to be pulled through it freely when a f all 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 M, the intermediate support brackets must be constructed

8 and secured to the support structure sufficiently to deal with the 5 - 6 M shock load of this worse case event. In systems according to the present invention, where the support brackets are arranged to absorb tensile load transmitted along the elongate element up to a prearranged limit and then to allow any excess tensile load to be transmitted along the wire to another support, the prearranged 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 f irst intermediate support bracket (10) is shown. The intermediate support bracket (10) comprises a first substantially Cshaped element (10A) and a second substantially C-shaped element (10B). The first and second C-shaped elements (10A and lOB) are sized so that the sides of the C-shaped element (10A) fit within the sides of the C- shaped element (10B) and corresponding slots (10C and lOD) are formed in the sides of the respective C-shaped elements (10A and lOB) so that the first and second C-shaped elements (10A and lOB) can be secured together by bolts (11A) and nuts (11B) passing through the slots (10C and lOD).

The first C-shaped element (10A) includes a further slot (10E) allowing the support bracket (10) to be bolted to some additional support structure (not shown).

The second C-shaped element (10B) bears a pair of semicircular projections (12), each of which supports a respective co-linear tubular sleeve (13). The wire (2) passes through the two co-linear sleeves (13) and a swage element (14) is 9 secured to the wire (2) between the two sleeves (13). The sleeves (13) are sized to restrain sideways movement of the wire (2) but to provide little resistance to longitudinal movement of the wire (2) through the sleeves (13).

The semi-circular projections (12) provide a gap between the second Cshaped element (10B) and the sleeves (13) in order to allow a slider moving along the wire (2) to pass between the tubular members (13) and the C-shaped member (10B).

When a tensile load is applied to the wire (2), the swage (14) located between the ends of the two tubular members (13) will prevent the wire (2) from moving relative to the bracket (10) so that the tensile load will be transmitted through a respective one of the tubular members (13) and semi-circular projections (12) to the second C-shaped member (IOB) and then through the first C-shaped member (10A) to the supporting structure. This transmission of the tensile load on the wire (2) to the supporting structure continues until the tensile load on the wire exceeds a preset limit at which time the wire (2) slips through the swage element (14). The tensile load limit at which the wire (2) begins to slip through the swage element (14) can be set to a predetermined value by use of appropriate swage and the wire dimensions and materials.

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

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

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

The second support bracket (20) comprises first and second substantially C-shaped elements (10A and lOB) linked by nuts and bolts (11A, UB) similarly to the first support bracket (10) and a pair of semi-circular projections (12) are mounted on the second C-shaped element (10B) as before.

A single cylindrical tubular member (23) is secured to the two semicircular elements (12) 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 f irst support bracket (10). The cylindrical member (23) is sized so as to restrain sideways movement of the wire (2) but provide little resistance to longitudinal movement of the wire (2) through the cylindrical member (23).

A swage element (24) is secured to the wire (2) spaced apart from the end of the cylindrical element (23) when the wire is in the rest position.

When a load is placed on the wire (2) pulling the swage element (24) towards the support bracket (20), the wire (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 wire (2) is transmitted through the swage element (24) into the cylindrical tubular element (23) and then through the semicircular projections (12) and first and second C-shaped members (10A and lOB) to the support structure.

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

A second swage element (24) is attached to the cable (2) on the opposite side of the support bracket (20) to allow limited movement followed by load absorption for tensile loads on the wire (2) in both directions.

A bracket of this type in which some movement of the wire (2) is possible will generally be easier to assemble and maintain than a system in which no free movement of the wire (2) is possible. This is because the forces acting on the wire (2) at rest can balance naturally by small movements of 11 the wire (2) so no pre-tensioning of the wire (2) is required. Further, if pre-tensioning of the wire (2) is desired, carrying out and checking the pre-tensioning is simplified.

The second support bracket (20) could of course be used with a single swage element (24) only on the wire (2) so that the bracket allows free movement of the wire (2) in one direction and absorbs tensile loading of the wire in the opposite direction. Similarly, the support bracket (20) could be arranged to allow no free movement of the wire (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 wire (2) is in its normal 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 (31A, 31B) linked by a planar section (31C) to give a substantially dumb bell shaped cross- section. The first and second cylindrical sections (31A, 31B) each have a respective bore (32A, 32B) running along their length. Note that bore 32B is not visible in Figure 6.

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

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

As is well known in the field of height safety systems, a slider with a break in it can be arranged to slide along the wire (2), the break being wide enough to allow the slider to pass over the bracket (30) with the bracket body passing through the break, and narrow enough that the wire (2) cannot pass through the break.

When a tensile load is applied along the wire (2), this will be transmitted through one of the swage elements (34) and through the bracket body (31) to a support structure so long 12 as the tensile load is below the predetermined load limit of the respective swage element (34). When the tensile load on the wire (2) exceeds the predetermined load limit of the swage element (34) carrying the load, for example during a fall arrest event, the wire (2) will pull through the swage element (34) while a part of the tensile load will continue to be transferred by friction between the wire (2) and the swage element (34) through the support bracket (30) to the support structure.

An alternative employment of the third design of support bracket (30) is shown in Figure 7. The third support bracket element (30) is arranged as before except that one of the swage elements (34) is secured to the wire (2) spaced apart from the respective end of the second element (31B). The other swage element (34) is secured to the wire (2) in contact with the other end of the second element (31B).

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

It would of course be 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 wire (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 allowed free movement of the wire (2) in one direction.

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

The swage elements can be crimped or otherwise permanently deformed to attach them to the wire (2) or 13 alternatively, the swage elements could include bearing surfaces loaded against the wire (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 wire (2) is preferred to ensure that the swage cannot become loosened, altering its load limit and so compromising the performance of the height safety system. However, in situations where a height safety system must be assembled and dismantled, the use of releaseably attached swage elements may be preferred, particularly where a height safety system is only temporarily required at a given location and it is undesirable to discard the wire after a short period of use.

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

In the above described embodiments, the elongate element carrying fall arrest loads in a height safety system is a wire. The present invention can also be applied to height safety 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 with reference to Figures 1 to 3 but with the wire (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 (41A) with a cylindrical bore therethrough, a bifurcated central section comprising a pair of planar elements (41B, 41C) substantially in parallel and a gripping portion (41D). The gripping portion (41D) is arranged to wrap around an elongate track member (42) and is broken by a slot (41E). The two clamping elements (41B, 41C) are secured to the gripping member (41D) 14 on opposite sides of the slot (41E) and the clamping element (41B) is attached to the first member (41A). A bolt (45) is passed throughthe 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 (41B, 41C) bears a pair of coinciding holes (41F) so that bolts (43) can pass through the holes (41P) to cooperate with nuts (not shown) to urge the clamping members (41B, 41C) together. A disc spring (41P) is placed on each bolt (43).

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

Similarly to the third bracket, a broken slider is used having a break wide enough to pass around the central section of the bracket (40), but too narrow to pass around the track member (42).

When a linear load, which may be tensile andlor 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 (41D). When this occurs, the track element (42) slides through the gripping portion (41D) 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 reduces below the frictional forceapplied by the gripping portion (41D) to the track, movement of the track (42) through the gripping portion (41D) stops and the linear load is again 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 (51A) and a serrated region (51B) adjacent the guide member (51A) and extending along the length of the elongate track element (51).

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

A second clamping element (SOE) is opposed to the first clamping element (SOD) 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 (SOA) and the central bore of the cylindrical member (50C) and secured in place with a nut (53B).

The opposed clamping elements (SOD, 50E) each define a partially cylindrical bearing surface shaped to fit around the guiding element (51A) of the elongate track member (51) and a plurality of projections (not shown) shaped to fit into the recesses in the serrated region (51B). The opposed clamping elements (SOD, 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 so onto the support structure (1) by friction between the guide element (51A) and the semi-cylindrical bearing surfaces of the clamping members (SOD, 50E) and by the projections of the clamping members (SOD, 50E) bearing against the serrations of the serrated region (51B).

When the linear force applied along the elongate track member (51) exceeds a preset level determined by the force with which the opposed clamping members (SOD, 50E) are urged together by the spring washer (54), the elongate track member (51) will pull through the bracket (50) allowing the excess 16 linear force to be transferred along the elongate track member to another bracket or brackets. When the applied linear f orce drops below this preset level, movement of the elongate track element (51) will stop and the applied linear f orces will again all be carried by the support bracket (50).

It is preferred that serrated regions (51B) are formed on both sides of the elongate track element (51) and that cooperating sets of serrations are f ormed on both clamping members (50D, SOE). However, the serrations could be formed on only one side of the elongate track element (51) and on a corresponding one of the clamping elements (50D, SOE) only or the clamping elements (50D, SOE) could be formed with one or more projections rather than a cooperating set of serrations.

Alternative constructions are also possible for both wire and track based systems. For example, the support brackets could be arranged to be controllably deformable so that linear loading up to a preset level would be carried from an elongate support element through the bracket to a support structure and the bracket would plastically deform if the loading went above this preset level, 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 to allow a load to be transferred along the support element to the other brackets.

In such a def ormable 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 so that no relative 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 by 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 to limit loads applied to the support structure and to allow movement of the elongate 17 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, limiting the period for which excess tensile load can be transferred along the elongate support element, or in other words, 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.

An alternative combined system would be one in which the primary load limiting mechanism was by movement of the elongate support element through the support bracket and having a limit stop, such as a rigidly attached swage on a wire or a f lange on a solid track, stopping movement of the elongate support element relative to the bracket at a preset distance. once this limit on movement of the elongate support element relative to the bracket was reached, the support bracket could then deform to contain and limit loads applied to the support structure. Such an arrangement could provide a useful margin of safety to allow for a situation where a height safety system is overloaded so that a safe limit of movement of the elongate support element relative to the support bracket is reached.

Height safety systems similar to some of those described above are disclosed in co-pending British Patent Application No. 9702855.9 and PCTIGB98100435 which relate 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 18 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 elements without obstructing said primary track formation wherein the elongate element has a cross-section with a centre portion of at least two lobes protruding therefrom, at least one of the loads constituting the second track formation and arranged for engagement by intermediate support brackets which grip the secondary track formation with the previous clamping force to allow the elongate element to fall 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.

Although the invention has been partially described 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.

19

Claims (11)

1. A height safety system comprising a flexible elongate element supported by at least three spaced apart support brackets, the support brackets being arranged to absorb load transmitted along the elongate element and at least some of the support brackets being arranged to absorb load up to a prearranged limit and then allow any excess load to be transmitted along the elongate element to another support bracket, the flexible elongate element not being of the type having a primary track formation providing a continuous path for an attachment means and a secondary track formation independent from the first, providing attachment points for the support brackets and being pre-tensioned.

2. A height saf ety 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 prearranged limit.

3. A height saf ety system as claimed in Claim 1 or Claim 2, in which at least some of the support brackets are arranged to def orm when the load exceeds the prearranged limit.

4. A height saf ety 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 prearranged limit and are arranged to def orm when the load exceeds a second prearranged limit.

5. A height safety system as claimed in Claim 41, in which the first prearranged limit is smaller than the second prearranged limit.

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 wire.

8. A height saf ety 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.

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