1 SAFETY BARRIER TECHNICAL FIELD 5 This invention relates to elevated work platforms. The invention has particular utility with platform ladders having an elevated work platform, however the invention is not limited to this type of work platform. Platform ladders having an elevated work platform are often referred to as "order pickers" or "platform steps" and are used principally in maintenance, warehousing of stores or 10 retailing. BACKGROUND ART There is a growing awareness of issues relating to occupational health and 15 safety. One area of concern that has not been adequately addressed is the provision of a safety barrier to the access point of a platform with ladder access, commonly known as a platform ladder. Where no safety barrier is provided at the platform access point there is a resulting risk of a fall from height. 20 It is known to provide a safety barrier to the access point of platform ladders. In one known platform ladder a safety barrier has been provided at the platform access point. The barrier being a single bar spans the open face between fixed rails provided at each side of the platform. The bar is pivoted at 25 one end and inscribes an arc in the vertical plane to permit access to the platform. In other known mobile platform ladders a safety barrier is provided by means of a chain or gate. A common major drawback of these known barriers is that they require the 30 user to release a handhold from the ladder to actuate the barrier to allow passageway in order to gain access to the platform. DISCLOSURE OF INVENTION 35 This invention in one aspect resides in a mobile platform ladder including: A safety barrier displaceable between a position at which the platform is dismountable and a position at which dismount from the platform is barred; and 40 locking means for retaining the barrier in the dismount barred position, wherein when the locking means is released, the barrier means returns to the platform dismount enabled position; and 45 driving means for driving the barrier to the platform dismount enabled position when the locking means is released. Preferably, the barrier is pivotably mounted for horizontal movement.
2 5 Preferably, the locking means is pivotably mounted for vertical movement such that displacement of the locking means by the barrier means automatically locks the barrier in the platform dismount barred position. Preferably the barrier constitutes an L-shaped member such that pivoting of 10 the L-shaped member to displace the locking means locks one arm of the L shaped member and simultaneously urges the remaining arm through horizontal movement to bar dismount from the platform. Preferably the driving means includes a torsion spring however any other 15 driving means may be used. Preferably the barrier means is mounted to a channel section however other sections may be used. 20 BRIEF DESCRIPTION OF ILLUSTRATIONS In order that this invention may more easily be understood and put into practical effect, reference will now be made to the accompanying illustrations which illustrate preferred embodiments of the invention, wherein: 25 Fig 1 is a an overhead view of a platform ladder with the safety barrier according to the invention in the platform dismount barred position: Fig 2 is a an overhead view of the platform ladder of Fig. 1 with the safety 30 barrier according to the invention in the platform dismount enabled position: Fig 3 is a detail view of the locking means with the locking means released. Fig 4 is a detail view of the locking means with the locking means retaining 35 the barrier means in the platform dismount barred position. Fig 5 is a detail reverse side elevation of the locking means and channel section. 40 Fig 6 is a detailed view of the driving means. Fig 7 is a detailed view of barrier means at the pivot point. BEST MODE 45 With reference to the Figs Referring firstly to FIG 1, there is illustrated a platform ladder 10 with fixed safety railing to 3 sides of the platform and a barrier means 11 in the form of 50 an L-shaped member. Referring to FIGS 1 and 2, there is illustrated the mechanism whereby barrier means 11 may be displaced from a platform dismount barred position (FIG 1) to a platform dismount enabled position. (FIG 2) 3 5 Referring now to FIG 1, there is shown an illustration of the barrier means 11 in the platform dismount barred position. In this position arm A of barrier means 11 is locked to the channel section 12 at lock position 13 such that arm B of barrier means 11 bars dismount from the platform ladder. 10 Referring to FIG 3 and 4, there is shown the locking means. Locking means 14 is pivotably mounted to channel section 12, to allow rotational movement in a vertical plane and shaped such that a force applied to arm A of the safety barrier 11 to engage locking means 14 will cause locking means 14 to inscribe an arc in a vertical plane about the pivot point such that under force of 15 gravity the leading edge of locking means 14 will trace the shape of arm A of barrier means 11. It will be appreciated that in the lock position, channel section 12 provides a limit to the movement of arm A of the safety barrier 11 and is also configured to allow a tracing of the diameter of arm A of safety barrier 11 by locking means 14, such that locking means 14 will finally act 20 under gravity to retain arm A of barrier means 11 in the platform dismount barred position. Referring to FIG 5, channel section 12, is slotted to permit rotational movement in a vertical plane of locking means 14. The depth of the slot 15 is 25 dimensioned in relation to the shape of locking means 14 such that locking means 14 is limited in rotation in a vertical plane to ensure that locking means 14 will finally act under gravity to retain arm A of barrier means 11 (FIG 1) in the platform dismount barred position when a force is applied by the barrier means 11 to engage locking means 14. 30 Referring now to FIG 2, there is shown an illustration of the barrier means 11 in the platform dismount enabled position. On release of the locking means 14 (FIG 3), barrier means 11 will automatically be driven to the platform dismount enabled position in which arm B of barrier means 11 permits dismount from 35 the ladder platform. Referring to FIG 6, there is shown the driving means 16 whereby the barrier means 11 is driven to the platform dismount enabled position. Driving means 16 (that in the illustrated embodiment consists of a torsion spring) acts about 40 pivot 19 (FIG 7) and is also attached to barrier means 11 at 17 and to channel section 12 at 18. Displacement of barrier means 11 to the platform dismount barred position (FIG 1) will load driving means 16 such that release of locking means 14 (FIGS 3 & 4) will cause driving means 16 to exert a force to return arm B of barrier means 11 to the platform dismount enabled position (FIG 2) 45 Referring to FIG 7, barrier means 11 is pivotally mounted to channel section 12 at pivot 19. It will be appreciated barrier means 11 is limited in rotation by contact with channel section 12 at the channel end 20 such that arm A of barrier means 11 will span the platform access point of the platform ladder 10 50 when barrier means 11 is urged to the to the platform dismount enabled position by the driving means 16 (FIG 6) 4 5 barred position and that such displacement mat be effected by body contact only without the need of manual displacement. It will be understood that the preferred embodiment of the invention provides a safety barrier that is displaceable between a platform dismount barred 10 position in which the platform may not be dismounted and a platform dismount enabled position at which the platform is dismountable. An additional benefit of the preferred embodiment of the present invention is that the ladder platform is safer to climb in that it does not require the user to 15 release a handhold from the ladder in order to displace the safety barrier to facilitate access to the platform. It should be noted that the platform dismount enabled position of the barrier means ensures body contact of the user when accessing the platform and 20 entry onto the platform will automatically urge the safety barrier towards the platform dismount barred position. Further, due to the driving means, the safety barrier will maintain body contact with the user until such time as arm A of the safety barrier is locked. Thus to allow free movement on the platform the user will be required to lock the safety barrier. 25 It will of course be realized that whilst the above has been given by way of an illustrative example of this invention, all such and other modifications and variations hereto, as would be apparent to persons skilled in the art, are deemed to fall within the broad scope and ambit of the invention as is herein 30 set forth. 35 40 45 50