GB2373015A - Roof truss safety system - Google Patents

Abstract

The safety system, for use during the construction of a building, comprises boards 1 with a central portion 2 that is dimensioned to fit between adjacent trusses 4 of a roof and support means 3 along two opposed edges with which the boards can be releasably secured to the trusses to provide a safety surface extending therebetween. The support means may be formed from support arms that are secured to opposite sides of the central portion or may comprise elements that extend underneath the central portion so that each element forms opposed arms on two sides of the board. The distal ends of the support arms are turned downwards so as to limit the lateral movement of the board relative to the trusses and the top portion of the arms may include apertures for receiving a fixing pin to enable the boards to be used with trusses positioned at different distances from one another. The system may also include secondary boards that can be positioned on top of and spanning between two adjacent boards positioned between the same two trusses.

Description

Safety System

The present invention relates to a safety system for providing a safety surface across roof trusses in a building under construction, and a method of providing a temporary safety surface across roof trusses using such a safety system.

During the construction of a building, workers fitting roof timbers on the building are exposed to a danger of injury through falling when the floor beneath them has not yet been boarded out. Several methods of reducing the risks have been tried, including placing nets, scaffolding, polystyrene blocks or inflated pillows beneath the work area, but these have not proved satisfactory, and in practice have proved expensive and/or time consuming.

Viewed from one aspect, the present invention provides a safety system for providing a safety surface across roof trusses, comprising a plurality of first boards, each first board having a central portion and support means on two opposite sides of said central portion, the support means being adapted such that in use, when said first boards are laid across said roof trusses, the support means support each of said first boards on adjacent roof trusses with said central portion positioned between said roof trusses, and each of said first boards is adapted to be releasably located in a lateral direction with respect to said roof trusses by co-operation with at least one of said roof trusses, wherein said first boards are liftable from said roof trusses for re-use to form a safety surface across roof trusses at another location.

In use, the first boards can be laid across the roof trusses of a building to cover the whole roof area whilst workers are fitting roof timbers, or to cover a smaller area of the roof trusses above which work is to

be carried out. Once work has been completed in an area above the boards, the boards can readily be lifted without damage to the boards or the roof trusses, and moved to a different location within the same building or a different building, where they can be re-used to form a temporary safety surface at the new location.

There is thus provided a simple, effective and cost efficient system of addressing the risks faced by workers operating above an area which has not been permanently boarded out.

The first boards are so formed that in use, the boards cooperate with the roof trusses to provide at least some lateral positioning for the boards. It is not necessarily intended that the boards are restrained from small lateral movements by the roof trusses, but rather that the lateral movement of the boards with respect to the trusses is restricted by the cooperation of the boards with the trusses to such a degree that the boards are safely retained on the roof trusses. This can simplify the procedure for laying the boards on the roof trusses and avoid the need for other securing means which might damage the boards.

The boards may be formed so as to cooperate with the roof trusses in any convenient manner. At least preferably, each of the first boards has locating means arranged to extend below the upper surface of the roof trusses in use so as to locate the board laterally against a side of roof trusses. Such locating means extend below support surfaces on the support means that are adapted to rest on the upper surfaces of the roof trusses.

In at least preferred embodiments, a plurality of first boards is provided, each of which is adapted by virtue of its configuration to form a stop means against inwardly or outwardly facing surfaces of one or both roof trusses on which said first board is supported.

In particularly simple arrangements, the first

boards are adapted to be located laterally with respect to the roof trusses by virtue of the central portion of the boards slotting between adjacent roof trusses and being laterally positioned by the inwardly facing walls of the roof trusses.

In such an arrangement, at least a lower part of the central portion of each first board extends below the support means, and in particular extends below support surfaces formed on the support means. In one convenient arrangement, the whole of the central portion of each first board is disposed within the vertical height of the roof trusses. Outwardly facing lateral sides of the central portion of each first board are opposed to inwardly facing sides of the roof trusses.

When the lateral width of the central portion is substantially the same as or slightly smaller than the spacing between inwardly facing sides of adjacent roof trusses, small lateral movements of the first board bring the central portion against an inwardly facing side of a roof truss so as to prevent further lateral movement in that direction.

The support means can have any appropriate form, including, for example, flanges extending along opposite sides of each central portion. However, preferably the support means comprise a pair of support arms extending from two opposite lateral sides of each central portion.

In a particularly strong arrangement which is well adapted to withstand large forces from above, such support arms are formed at the ends of a pair of support members which extend continuously under a central portion and protrude from opposite sides thereof. In a particularly stable arrangement each of the first boards has two support arms positioned so as to extend from each lateral side of the central portion, near the longitudinal ends of each central portion, but spaced from said longitudinal ends and from each other. In use, the support arms extending from a first side of the

central portion rest on the upper surface of a first roof truss and the support arms extending from a second side of the central portion opposite to said first side rest on a second roof truss adjacent to the first roof truss.

The first boards can be formed of any suitable material such as wood, metal or plastic. It has been found to be particularly convenient to form the central portions of a sheet of wood of uniform thickness and to form the support means of metal. The central portion can be strengthened by metal sections running along or underneath the lateral sides.

In one arrangement as described above, the central portion of each of the first boards is adapted to be laterally located by inwardly facing sides of adjacent roof trusses. Means of locating the first boards with respect to the roof trusses can alternatively or additionally be provided by the support means. Such locating means could include, for example, downwardly extending flanges, protrusions, channels, pins, bolts or the like on said support means.

For example support means extending from at least one lateral side of the central portion of each first board, such as each of a pair of support arms, may be provided with a downwardly extending portion at a distal end, which is adapted to position a first board by abutment against an outwardly facing wall of a roof truss. In one embodiment, support means such as support arms extending from both lateral sides of the central portion of each first board are provided with a downwardly extending portion such as a flange, for laterally locating the first board by abutment of said downwardly extending portions to form a stop means against the outwardly facing walls of a pair of adjacent roof trusses. First boards having such a construction are particularly straightforward to position on a pair of adjacent roof trusses with downwardly extending

flanges at the outer distal ends of the support means, e. g. support arms, on both sides of the central portion hooked over the outer sides of the adjacent roof trusses.

It is not always convenient to hook an end portion of a support arm over a roof truss, for example this can be awkward when laying a safety surface near the walls of a building or otherwise when there are obstructions near to a roof truss. In one embodiment, a safety system has been devised in which first boards are adapted to be laterally located by means of co-operation with a roof truss on only one side of the board. More specifically, the boards are configured or are otherwise provided with means suitable for positioning or acting as stop means against inwardly facing and outwardly facing sides of the same roof truss.

Positioning against a single roof truss can be achieved, for example, by positioning the central portion of a first board so as to be located by an inwardly facing side of a roof truss and providing a downwardly extending flange or the like at the distal end of a support arm, the downwardly extending flange being spaced from the central portion by a distance substantially equal to or slightly greater than a standard lateral width of a roof truss.

Alternatively, a second locating means can be provided on a support means for positioning a first board against an inwardly facing side of a roof truss, spaced from a first locating means such as a downwardly extending flange at a distal end of the support means for positioning a first board against an outwardly facing side of a roof truss. Such a second locating means could comprise a second downwardly extending flange, for example. However, in a particularly preferred embodiment, such a second locating means comprises a downwardly extending pin receivable in an aperture formed in a support means, the aperture being

formed at a location intermediate the central portion and a distal end of the support means. In use, when a first board having such an arrangement is laid on a pair of adjacent roof trusses, the downwardly extending flange positions the first board against an outside of one of the roof trusses and the pin positions the first board against the inside of the same roof truss. If desired, the support means on the other side of the central portion need have no means for locating the first board, but instead can simply rest on the adjacent roof truss. Furthermore, the central portion can have any suitable lateral width and need not be dimensioned to locate the first board so as to be retained on the roof trusses.

It is not uncommon for two roof trusses to be laid directly adjacent each other in some parts of a building and one of the reasons a locating means such as a pin is preferred at an intermediate location on a support means is to facilitate removal of the locating means from interference with an obstruction therebelow. Preferably a locating pin is slideable within its receiving means so as to be displaceable upwardly when an obstacle is contacted at the lower end of the pin. Even more preferably, such a locating pin may be resiliently biased into a downwardly extending position within a said receiving means. In some systems workers may be required to insert a locating pin into a receiving means as part of the process of laying a safety surface, and to subsequently remove said pin before lifting the first boards for use elsewhere, or the pin may be captured in the receiving means and may simply require to be raised or lowered by a worker laying or lifting the safety surface, as appropriate. However, arrangements are also envisaged in which a locating pin is adapted to be retained in said support means arranged to protrude downwardly from said support means at least in use, such that, as with other arrangements described herein, the

simple step of laying the first boards on adjacent roof trusses is sufficient, by virtue of their configuration, to position the first boards laterally with respect to the roof trusses, without workers being required to perform any other operations.

In the construction industry for building houses, roof trusses tend to have one or more standard spacings.

Preferably the first boards are adapted to co-operate with roof trusses having a standard spacing. In the UK, two standard spacings between the centre lines of adjacent roof trusses are 450 mm and 600 mm. A roof truss generally has a lateral width of approximately 35 mm, such that standard spacings between the inwardly facing sides of adjacent roof trusses are typically substantially 415 mm and 565 mm, and standard spacings between outwardly facing sides of adjacent roof trusses are substantially 485 mm and 635 mm. Thus, for example, first boards adapted to co-operate with roof trusses having a standard spacing of 450 mm between their centre lines might have a central portion with a lateral width of about 415 mm or slightly smaller (e. g. 400 mm) to slot between the roof trusses and be located by their inwardly facing walls.

In a particularly preferred system, first boards are adapted to co-operate both with roof trusses having a first standard spacing, for example by the central portion being positioned against inwardly facing walls of the roof trusses, and to co-operate with roof trusses having a second standard spacing greater than the first standard spacing, for example by virtue of downwardly extending locating means provided on the support means.

In one embodiment, the safety system further includes a plurality of second boards which are adapted to be supported on and extend longitudinally between pairs of first boards. Preferably the second boards are slideable with respect to the first boards. For example the second boards may be slideable between upwardly

extending portions of support arms provided on said first boards. Such an arrangement enables the first and second boards to be more easily lifted from roof trusses after cross pieces have been nailed over the trusses, by positioning the second boards in areas where cross pieces will be laid and then slidingly withdrawing the second boards from under the cross pieces.

Viewed from a second aspect, the present invention provides a method of providing a temporary safety surface across roof trusses, said method comprising providing a plurality of first boards, each first board having a central portion and support means on two opposite sides of said central portion, laying said plurality of first boards on said roof trusses with the support means of each said first board supported on adjacent roof trusses and the central portion positioned between said roof trusses, each of said first boards being releasably located in a lateral direction with respect to said roof trusses by co-operation with at least one of said roof trusses, and lifting said boards from said roof trusses for re-use to provide a safety surface across roof trusses at another location.

Such a method is simple and effective to operate and is capable of enhancing the safety of persons working in the construction of buildings.

In a preferred operation of said method there is further provided a plurality of second boards and the method comprises the steps of supporting the second boards on spaced first boards so as to extend longitudinally therebetween, and slidingly withdrawing said second boards with respect to said first boards prior to lifting the first boards from the roof trusses for re-use at another location.

Preferably there is further provided guide means adapted to co-operate with said support arms to facilitate stacking, and a method according to the invention further includes a step of stacking the first

boards in said guide means between uses.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings wherein: Figure 1 is a schematic perspective view of a first board for use in a safety system and methods in accordance with a first embodiment of the invention; Figure 2 is a schematic perspective view of the first board of Figure 1 in use, positioned on a pair of roof trusses; Figure 3 is a schematic end view of the arrangement shown in Figure 2; Figure 4 shows a section through a first board comprising part of a safety system according to a second embodiment of the of the invention; Figure 5 shows a section through a first board comprising part of a third embodiment; Figure 6 shows a section through a first board comprising part of a fourth embodiment; Figure 7 shows a perspective view of the first board illustrated in Figure 6; and Figure 8 shows a perspective view of two of the first boards shown in Figures 6 and 7 in use positioned on a pair or roof trusses with a second board extending between the first boards.

Figures 1 to 3 show a first board 1 which is one of a plurality of identical first boards 1 which form a safety system according to a first embodiment of the invention. The board 1 has a central portion 2 comprising a rectangular sheet of uniform thickness formed of wood. Four metal support arms 3 are affixed to the central portion 2, such as by means of screws (not shown) securing an underside of each support arm to the upper surface of the central portion 2.

In Figures 2 and 3, a board 1 is shown in the position it adopts in use, supported by the support arms 3 on an adjacent pair of parallel roof trusses 4.

The first board 1 is generally rectangular and is positioned in use so that its longer sides extend parallel to the roof trusses 4 on which the board 1 is supported. The shorter dimension indicated by the letter"x"in Figures 1 and 3 is slightly smaller than the spacing between the inner sides of the roof trusses 4 so that there is a slight gap between the long sides of the central portion 2 and the roof trusses 4. The vertical dimension or thickness of the central portion 2 is selected to give the board sufficient strength to withstand the force of someone walking or falling onto the board 1.

A pair of support arms 3 extend laterally from each of the two opposing long sides of the central portion 2, spaced slightly from the longitudinal ends of the central portion 2. The support arms 3 are dimensioned so that when the central portion 2 is fitted between a pair of adjacent roof trusses 4, the support arms 3 overlie part of the roof trusses 4. In the illustrated embodiment, the support arms 3 extend across approximately one half of the width of the roof trusses 4, to support the board 1 on the roof trusses and withstand normal loads.

The support arms 3 are located towards the upper part of the central portion 2, such as by screwing to the upper surface of the central portion 2, and when a board 1 is placed in position on a pair of roof trusses 4 as shown in Figures 2 and 3, the central portion 2 extends below the tops of the roof trusses 4.

The long vertical sides of the central portion 2 face the inner sides of the roof trusses 4 to limit the lateral movement of the board 1 with respect to the roof trusses 4.

It should be understood that the central portion 2 is not a close fit between the roof trusses 4 in this embodiment, although such would also be possible. More preferably, the lateral dimension of the central portion

2 is slightly smaller than the spacing between the inner sides of the roof trusses to permit some movement, for ease of installation and to allow for slight variations in the straightness and alignment of the roof trusses 4.

However, the lateral dimension of the central portion 2 is such as to restrict the lateral movement of the board 1 to a sufficient degree to ensure that there is always an overlap between the support arms 3 and the roof trusses 4.

A safety system comprising a plurality of first boards 1 as illustrated in Figures 1 to 3, is suitable for providing a safety surface across roof trusses having a spacing between their inner sides of approximately 415 mm. This corresponds to a pitch of approximately 450 mm between the centre lines of the roof trusses. Typically each of the trusses has a horizontal width of approximately 35 mm. The lateral dimension of the central portion 2 in the illustrated embodiment is approximately 400 mm.

In use, the first boards 1 can be laid across an area of roof trusses 4 where work is to be carried out, such as fitting roof timbers, tiling and so forth. This allows persons to work safely above the roof trusses 4 without a risk of injury through falling, or with a reduced risk. The boards 1 are simple and convenient to lay, with the central portion 2 of each board 1 slotting between a pair of adjacent trusses 4. The boards 1 are supported on the support arms 3 and are laterally retained in position by the sides of the central portion 2 of each board 1 being restricted in their movement by the trusses 4.

Once work in an area in which the boards 1 are laid is complete, the first boards 1 can readily be lifted from their position on the roof trusses 4. The boards 1 can be moved to a new area of roof trusses 4, in the same building or elsewhere, and re-used in the same manner to provide a safety surface in a new area. The

ease with which the boards 1 can be laid, and the ability to re-use the same boards on subsequent occasions, results in a very convenient and cost effective system for ensuring the safety of persons working in areas above the roof trusses of a building under construction.

It may not be desirable to re-use all of the first boards 1 immediately after they have been removed from a particular area, for example to make way for a permanent floor. The support arms 3 in the illustrated embodiment make the boards 1 particularly convenient for stacking between uses. More particularly, the support arms 3 are adapted to be engaged in guides (not shown) having recesses to receive the support arms 3. In one arrangement, the guides are in the nature of channels in which the support arms 3 can be slidingly engaged.

Figure 4 shows a first board 11 which is one of a plurality of identical first boards 11 that comprise a safety system according to a second embodiment of the invention. The board 11 illustrated in Figure 4 comprises a central portion 12 formed of a sheet of uniform thickness reinforced by two longitudinally extending square sections 15 underneath the lateral sides of the sheet. Two metal bands 16 (one only shown) extend laterally underneath the central portion 12 and up the outer sides of the central portion 12 to protrude above the upper surface of the central portion 12. The metal bands 16 are then turned through 90 degrees to form support arms 13 extending outwardly from two opposite sides of the central portion 12. The support arms 13 are located near, but spaced from, the longitudinal ends of the central portion 12. In use, a lower surface of the support arms 13 forms a support surface for supporting the first board 11 on an upper surface of adjacent roof trusses 4, whilst the central portion 12 is positioned between the roof trusses 4 to form a safety surface.

Each of the support arms 13 of the first board 11 illustrated in Figure 4 has a downwardly extending flange 17 at its distal end. In use, the flanges 17 extend below the tops of the roof trusses 4 on the outer sides of the roof trusses, such that an inwardly facing side of each flange 17 faces an outer side of one of the roof trusses 4 having a standard spacing x on which the first board 11 is supported. The first board 11 is positioned laterally with respect to the roof trusses 4 by virtue of the flanges 17 which are brought into contact against the sides of the roof trusses 4 by lateral movement of the first board 11 and provide a means of stopping further movement in that direction.

Figure 5 shows another type of first board 21 which is one of a plurality of identical first boards 21 comprising a safety system in accordance with a third embodiment of the invention. The first board 21 illustrated in Figure 5 is identical to the first board 11 shown in Figure 4, except that the support arms 23 of the first board 21 shown in Figure 5 are longer than the support arms 13 of the first board 11 shown in Figure 4 and extend further from the central portion 22.

Downwardly extending flanges 27 at the distal ends of the longer support arms 23 are adapted to restrict lateral movement of the first board 21 shown in Figure 5 when the first board 21 is supported on a pair of

adjacent roof trusses 4'having a second standard spacing y, which is larger than a first standard spacing x.

Conveniently, the first boards 21 illustrated in Figure 4 are also suitable for laying across roof trusses 4 having a standard spacing x which is narrower than the second standard spacing y. The position that a first board 21 adopts in use with respect to roof trusses 4 of a narrower standard spacing x is indicated by showing roof trusses 4 which are at a narrower spacing in phantom lines. The first board 21 is

positioned laterally with respect to roof trusses 4 at a narrower spacing by virtue of the inwardly facing sides of the roof trusses 4 restricting lateral movement of the central portion 22. The first boards 21 can therefore be used interchangeably over roof trusses 4, 4' having two different standard spacings x, y. In an embodiment for use in the United Kingdom, two standard spacings between the centre lines of adjacent roof trusses are 450 mm and 600 mm corresponding to a spacing x, y between inner sides of adjacent roof trusses of about x = 415 mm and y = 565 mm.

Figures 6 and 7 show another first board 31 which is one of a plurality of identical first boards 31 forming a safety system in accordance with a fourth embodiment of the invention. The first board 31 shown in Figures 6 and 7 is identical to the first board 21 shown in Figure 5, except that a downwardly extending flange 37 is only formed at the distal end of two support arms 38 on one side of the first board 31. The support arms 39 extending from the other side of the central portion 32 are flat at their distal ends, which enables them to be easily accommodated on roof trusses 4'near the walls of a building, or where there are other obstacles that might interfere with a downwardly extending flange. The two support arms 38 which are provided with a downwardly extending flange 37 at their distal end are each provided with an aperture 40 at an intermediate position along their length, which is adapted to receive a pin 41. When laid across adjacent roof trusses at a standard spacing y, the flanges 37 locate the first boards 31 against an outer side of one of the roof trusses 4'to restrict movement in a lateral direction to the left as shown in Figure 6, whilst the pins 41 locate the first boards 31 by providing a stop means against an inner side of the same roof truss 4'to restrict lateral movement in the opposite direction to the right as shown in Figure 6.

The pins 41 are captured in the apertures 40 by means not shown and are slideable within the receiving apertures 40. The pins 41 are spring biased by means not shown into a position protruding downwardly from a support surface on the underneath side of the support arms 38, where they act in use to restrict lateral movement of the first boards 31 by forming a stop means against the inside surface of a wall truss 4'. An advantage of arranging the pins 41 to be slideable within the receiving apertures 40 is that the pins 41 are able to retract upwardly if the first boards 31 are placed on an obstacle, thereby avoiding damage to the pins 41 and the obstacle. For example, the pins 41 may sometimes come into contact with an upper surface of roof trusses 4'as they are laid, or two roof trusses may occasionally be encountered directly adjacent each other, or there may be other obstacles next to a roof truss 4'on which a first board 31 is to be laid.

In an alternative embodiment (not shown), locating pins are removably engageable in receiving apertures on the support arms, or are slideable in receiving apertures without being spring biased into a downward position.

A pair of first boards 31 identical to the one shown in Figures 6 and 7 are shown in Figure 8 laid on a pair of adjacent roof trusses 4'. Each of the first boards 31 has two support arms 38 on one side supported on one roof truss 4', each having a distal flange 37 and a locating pin 41, and two support arms 39 on the other side, having no locating means, which are support on an adjacent roof truss separated from the first roof truss 4'by a standard spacing. The pair of first boards 31 shown in Figure 8 are separated from each other in the longitudinal direction of the roof trusses 4'.

A second board 50 shown in Figure 8 is supported at its longitudinal ends on the first boards 31 so as to extend longitudinally between the pair of first boards

31. The second board 50 is a rectangular sheet of uniform thickness, made of the same material as the first boards 31 e. g. wood. In the illustrated embodiment the second boards 50 have a length of 2m and the first boards 31 have a length of 1.5m. The second board 50 does not have any support arms and is supported between the roof trusses 4'solely by its end portions resting on the first boards 31.

The lateral width of the second board 50 is substantially the same as the lateral width of the central portion 32 of the first boards 31 and the second board 50 fits slidingly between vertically extending portions of the support arms 38,39 which protrude above the upper surface of the central portion 32. In operation, when it is desired to lift the first and second boards 31,50 for re-use at another location, the second boards 50 can be slid over the first boards 31 by grasping handles 51 cut in the second boards 50 at each end. This facilitates removal of the second boards when the positioning of cross pieces or other obstacles across the roof trusses above the second boards 50 would make it difficult for the second boards to be raised vertically from their in-use position. It will be noticed that the upper surface of the second board 50 is positioned in use below the level of the upper surface of the roof trusses 41.

Thus, an embodiment of safety system described with reference to Figure 8 includes a plurality of first boards 31 and a plurality of second boards 50, and a method of providing a temporary safety surface in accordance with an embodiment of the invention described with reference to Figure 8 includes the steps of laying a plurality of second boards 50 supported on and extending between first boards 31.

Claims (32)

Claims

1. A safety system for providing a safety surface across roof trusses, comprising a plurality of first boards, each first board having a central portion and support means on two opposite sides of said central portion, the support means being adapted such that in use, when said first boards are laid across said roof trusses, the support means support each of said first boards on adjacent roof trusses with said central portion positioned between said roof trusses, and each of said first boards is adapted to be releasably located in a lateral direction with respect to said roof trusses by co-operation with at least one of said roof trusses, wherein said first boards are liftable from said roof trusses for re-use to form a safety surface across roof trusses at another location.

2. A safety system as claimed in claim 1, wherein the support means of each of said first boards have support surfaces for positioning in use on upper surfaces of said roof trusses, and wherein each of said first boards has a locating means arranged to extend below a said support surface when said first board is laid across said roof trusses for providing a stop means against a side surface of a said roof truss so as to restrict lateral movement of said first board with respect to said roof truss.

3. A safety system as claimed in claim 1 or 2, wherein in use at least a lower portion of said central portion of each first board extends below a portion of said support means adapted to be supported on said roof trusses.

4. A safety system as claimed in claim 2, wherein said central portion of each first board is disposed in use

below said support surface.

5. A safety system as claimed in claim 4, wherein said arrangement is such that in use, an upper surface of each said central portion is disposed below an upper surface of a roof truss on which said first board is supported, and a lower surface of said central portion is disposed above a lower surface of said roof truss.

6. A safety system as claimed in any preceding claim, wherein a dimension of said central portion of each first board in said lateral direction is substantially equal to, or slightly smaller than, a standard spacing between roof trusses.

7. A safety system as claimed in claim 6, wherein said dimension of said central portion of each first board in a lateral direction is about 400 mm.

8. A safety system as claimed in any preceding claim, wherein said support means comprise a pair of support arms extending laterally from each of said two opposite sides of said central portion.

9. A safety system as claimed in claim 8, wherein said support arms are formed at the ends of a pair of support members which extend continuously under said central portion and protrude from opposite sides thereof.

10. A safety system as claimed in claim 8 or 9, wherein said support arms are positioned two near each longitudinal end of a said central portion, spaced from the longitudinal ends thereof.

11. A safety system as claimed in any preceding claim, wherein a said support means on at least one side of said central portion of each of said first boards has a

downwardly extending portion such as a flange or the like at its distal end.

12. A safety system as claimed in any preceding claim, wherein a said support means on at least one side of said central portion of each of said first boards has a downwardly extending locating means spaced from a distal end thereof.

13. A safety system as claimed in any preceding claim, wherein said support means on at least one side of said central portion of each of said first boards is provided with a means for receiving a locating means for engaging a side of a roof truss.

14. A safety system as claimed in claim 13, wherein said receiving means comprises an aperture adapted to receive a pin.

15. A safety system as claimed in claim 13 or 14, wherein said support means has a downwardly extending portion at its distal end and said receiving means is spaced from said distal end of said support means by a distance corresponding substantially to a standard lateral width of a roof truss, such that in use a said first board is laterally locatable by means of a said downwardly extending portion engaging against an outside surface of a roof truss and a said locating means engaging against an inside surface of said roof truss.

16. A safety system as claimed in any of claims 12 to 14, further comprising said locating means being slideably received in said receiving means, and means for resiliently biasing said locating means towards a downwardly extending position with respect to said receiving means.

17. A safety system as claimed in any preceding claim, wherein a lateral dimension of said central portion of each first board corresponds substantially to a first standard spacing between roof trusses, or is slightly smaller than said first standard spacing, and a locating means such as a downwardly extending flange, or a receiving means for receiving a locating means such as a locating pin, is adapted to laterally locate a said first board on adjacent roof trusses of a second standard spacing.

18. A safety system as claimed in any preceding claim, further comprising a plurality of second boards adapted to be supported on and extend longitudinally between pairs of said first boards.

19. A safety system as claimed in claim 18, wherein said second boards are slidingly supportable on said first boards.

20. A safety system as claimed in claim 19, wherein in use said second boards are laterally located by, and slideable with respect to, said support means on opposite sides of said first boards.

21. A safety system as claimed in any preceding claim, further including guide means arranged to co-operate with said support means to facilitate stacking said first boards between uses.

22. A method of providing a temporary safety surface across roof trusses, said method comprising providing a plurality of first boards, each first board having a central portion and support means on two opposite sides of said central portion, laying said plurality of first boards on said roof trusses with the support means of each said first board supported on adjacent roof trusses

and the central portion positioned between said roof trusses, each of said first boards being releasably located in a lateral direction with respect to said roof trusses by co-operation with at least one of said roof trusses, and lifting said boards from said roof trusses for re-use to provide a safety surface across roof trusses at another location.

23. A method of providing a temporary safety surface as claimed in claim 22, wherein said method includes a step of laying said first boards on said roof trusses such that said central portion of each first board slots between adjacent roof trusses of a first standard spacing so as to be located in a lateral direction by engagement of the central portion against the inner surfaces of said roof trusses.

24. A method of providing a temporary safety surface as claimed in claim 22, wherein said method includes a step of laying said first boards on said roof trusses such that a downwardly extending locating means on at least one of said support means locates each of said first boards laterally by engagement of said downwardly extending locating means against a side of a said roof truss.

25. A method of providing a temporary safety surface as claimed in any of claims 22 to 24 wherein said support means comprise a pair of support arms extending laterally from each of said two opposite sides of said central portion.

26. A method of providing a temporary safety surface as claimed in claim 24 or 25, wherein said method includes a step of providing a releasable locating means in a receiving means provided on a said support means of each first board, so as to locate said first board laterally

with respect to said roof trusses, and releasing said releasable locating means prior to lifting said first boards from said roof trusses.

27. A method of providing a temporary safety surface as claimed in any of claims 22 to 26, further comprising providing a plurality of second boards and supporting said second boards on spaced pairs of said first boards so as to extend longitudinally and slideably therebetween.

28. A method of providing a temporary safety surface as claimed in claim 27, further comprising a step of sliding at least some of said second boards with respect to said first boards so as to remove said second boards from under cross-pieces extending between said roof trusses, prior to lifting said first and second boards from said roof trusses.

29. A method of providing a temporary safety surface as claimed in any of claims 22 to 28, further comprising the step of stacking said first boards between uses.

30. A method of providing a temporary safety surface as claimed in any of claims 22 to 29, utilising a safety system having the features of any of claims 1 to 21.

31. A safety system for providing a safety surface across roof trusses substantially as hereinbefore described with reference to the accompanying drawings.

32. A method of providing a temporary safety surface across roof trusses substantially as hereinbefore described with reference to the accompanying drawings.