THIS INVENTION concerns an access platform to support personnel, for example, to enable maintenance work to be carried out on a fixed column or other surface and is particularly intended to enable maintenance engineers to work upon the supporting legs or other structural members of an offshore drilling platform although it may be used in many applications where normally inaccessible parts of a structure require attention.

Safety regulations require that if a supporting cage or platform is to be lowered into a working position with personnel on board, then extreme safety standards must be met including the use of multiple suspension lines and winches in case the lines from one winch should fail.

Such regulations do not usually apply to self-lowering equipment which may be used by skilled personnel to descend from an elevated position to a work place therebelow.

It is therefore necessary to provide an access platform to support personnel and which may be lowered into position unoccupied and fixed in said position by an operator suspended on his own support lines. It is intended, that once the operator has fixed the access platform in position, he and/or others may then occupy same to carry

out maintenance work and afterwards leave the platform and disconnect it from the work site so that it may be recovered unoccupied.

In international patent application No. WO 92/00423 there is described an access platform comprising a rectangular base frame having upstanding vertical corner posts and a rectangular guard rail all suspended by four corner cables and a central suspension line. The platform is lowered into place without personnel on board, and a tie strap is then taken around the column and made fast by a ratchet handle on the base. Thus, the platform is made fast against the column. A leg pivotally attached to the rear of the base is tensioned by a line such that its forward edge is also braced against the column. Thus, the entire platform is supported by and braced against the column such that it cannot fall away in the event of failure of the suspension line. Once installed, the platform may be occupied by maintenance personnel.

One disadvantage of an access platform made in this way is the obstruction caused by the supporting cables extending upwardly from the four corner posts to a position where they are connected jointly to the single suspension line. In many applications, an operator on the platform must have unobstructed access to the work site before him.

Another disadvantage is the difficulty which may be experienced when bracing the platform against a surface which is other than vertically or horizontally disposed with respect to the

platform base.

It is therefore an object of the present invention to provide an access platform which meets the requirements of operational safety and at least substantially avoids the aforementioned disadvantages.

According to the present invention, there is provided an access platform to support personnel, for maintenance of a fixed structure, comprising a platform base, cable means for suspending same in a horizontal attitude, and at least one tie member adapted to pass around the fixed structure and having means whereby the tie member may be made fast on the platform to brace the latter rigidly against the structure sufficiently to support the platform and prevent it from falling away from the structure in the event of failure of the suspending cable means; characterised in that the suspending cable means is attached to at least one rigid member extending upwardly from a part of the platform base and located in use other than in front of personnel positioned on the platform base, thus to provide unobstructed forward access to a work site.

Preferably, adjustable oraciπg means are provided on a front portion of the platform base and adapted to en. : e the latter to be braced against a surface which is other than vertically or horizontally disposed with respect to the platform base.

An embodiment of the invention will now be described,

by way of example only, with reference to the accompanying drawings in which:-

Fig. 1 illustrates schematically, in elevation, an access platform made in accordance with the invention and made fast in contact with a fixed column;

Fig. 2 is a horizontal section taken along line II— II of

Fig. 1;

and Fig. 3 is a plan view of a part of the access platform.

Referring now to the drawings it is to be assumed that work is to be carried out on a fixed column 10 which may form part of the structure of an offshore drilling rig.

An access platform generally indicated at 11 is to be made fast on the column 10 such that it may be occupied by maintenance engineers to carry out work on the column. The platform consists essentially of a rectangular base frame 12, four upright corner members 13 and a rectangular guard rail 14 extending horizontally around the tops of the corner members 13.

Extending upwardly from the base frame 12 centrally at the rear thereof which is a rigid tubular mast 30, an upper part 31 of which being removably attached via a collar 32 and removable fixing pins. The vertical length of the upper part 31 is somewhat in excess of the height of the corner posts 13 and at its top it describes an

arc at 33 and terminates in a horizontal portion 34 extending forwardly over the centre of the platform 12. Reinforcing fillets 35 and 36 are attached by welding to the upper part 31 and a pair of suspension lines 17 are attached by fixed eye bolts 16 to the forwardly extending horizontal portion 34, a reinforcing plate 39 serving to distribute the load along the latter.

The parts 30 to 35 and 16 and 17 serve together to support the access platform in use.

A pair of diverging supporting struts 37 welded to the lower end of column 30 extend beneath the platform base 12 and are further welded thereto for additional support.

Extending forwardly from the rectangular part of the base frame 12 is a bracing frame 18 which, as can be seen in Fig. 2, is pivotally attached at 38 to the front member of the base frame 12. The forward edge of bracing frame 18 is V-shaped to encompass part of the circumference of column 10, and the whole frame 18 can pivot about a horizontal axis to enable the platform base to be braced against a surface which is other than vertically or horizontally disposed with respect to the platform base. The front edge of frame 18 may be provided with rollers which abut the surface of the column 10.

Still referring to Fig. 2, anchored at 19 to one side of the forward region of base frame 12 is a flexible ratchet strap or tie

member 20 which, in use, is taken around column 10 and made fast by a ratchet handle 21 attached to the opposite side front region of the base frame 12.

Pivotally attached (optionally) to the two rear corners 22 of the base frame 12 is a leg 23 which, as can be seen in Fig. 1, is adapted to extend downwardly and forwardly at an angle of approximately 30° into contact with the surface of column 10 beneath the bracing member 18.

The leg 23 is divided longitudinally into two parts which are joined pivotally at 24 on a swivel and the forward edge 25 of the leg is V-shaped to accommodate a part of the circumference of the column 10. Once again the swivel action of the forward part of leg 23 will accommodate a surface at an angle other than vertical or horizontal.

Extending upwardly from the leg 23 and attached at 24 thereto is a line 26 which is removably fixed to a jammer 27 and thus holds the leg 23 in tension against the column 10.

A toe board 28 surrounds the base of the platform to prevent tools and other equipment from being lost over the side.

The access platform is installed by being lowered initially to the required level whilst unoccupied. During descent, leg 23 may depend, at a greater angle, from the base frame 12 with line 26 extended. Once at the correct level, an engineer who has descended

to approximately the same level on his own descent lines, is able to manoeuvre to take strap 20 around column 10 and secure it by the ratchet handle 21 thus bracing the frame 18 against the column surface. The engineer will then draw line 26 upwardly through jammer 27 until the line is taut with leg 23 braced against the surface of the column at 25.

With the platform assembled in this way, little or no tension remains on main suspension lines 17, the entire device being largely supported by and braced against the column 10. In this condition the engineer and other personnel may enter the platform to carry out work on the column. Once the work is completed and the personnel have left the platform, it may be released from the column by reversing the installation procedure and moved, for example, to a different level whereat further work may be conducted.

It will be appreciated that the bracing frame 18 and the forward part of leg 23 may be interchanged with similar members having different front edge formations to match different work surfaces, and the adjustability of leg 23 enables it to be braced against, for example, a part of the column having greater or lesser dimensions than the part with which frame 18 is in contact.

The fixing of the access platform rigidly with respect to the column 10 satisfies safety regulations and provides a rigid and comfortable structure from which work may be carried out and in which tools and other equipment may be safely deposited within the

confines of the toe board 28. Forward access to the column is unobstructed since the suspension system is located behind the operator.

It is not intended to limit the invention to the details hereinbefore described. For example, the suspension mast consisting of members 30, 36 may be replaced by two upright members disposed at the two rear corners of the platform or slightly forward of the rear edge, and attached jointly or separate ly to two or more suspension lines. The requirement is that full unobstructed access to the work site forwardly of the platform should be available.

In a further embodiment the toe board 28 at the front of the platform and/or at one or both sides thereof may be replaced by upstanding walls pivotally attached along the bottom of the platform so that it may be lowered to a horizontal position and supported by chains or the like. With such an arrangement the access platform may be used as a diving platform from which divers may descend into the water. In the case of a forward diving platform this may, if required, rest upon the bracing frame 18.