GB2303400A

GB2303400A - Safety line support

Info

Publication number: GB2303400A
Application number: GB9514958A
Authority: GB
Inventors: Leonard John Feathers
Original assignee: Barrow Hepburn Sala Ltd
Current assignee: Sala Group Ltd
Priority date: 1995-07-21
Filing date: 1995-07-21
Publication date: 1997-02-19
Also published as: GB9514958D0

Description

SAFETY EQUIPMENT This invention relates to safety equipment for use by those who are exposed to the risk of a fall from a tall structure, and has particular reference to such equipment for use by workers at or near the top of a tall, flat-topped structure such as a high-rise building having a flat roof.

It is well known to provide safety equipment comprising a track support and a safety track which is attached to such support and carries one or more runners for attachment to a safety line connected to a safety harness worn by a worker.

Examples of such apparatus are described in Barrow Hepburn Sala Limited's Patent Specifications Nos EP 0 273 673 B and EP 0 585 268 A (WO 92/20407).

Known apparatus of this sort is designed with special reference to its use during the construction phase of some civil engineering project, and the safety track, which may take the form of a steel cable is usually located in an overhead position. The resulting apparatus is secure and effective, but it is somewhat cumbersome and takes some time to install. This is no real disadvantage where it is to remain on site for moderate to long periods of time such as may be involved in construction, but it does present a considerable inconvenience if the safety equipment is only required for short term use, for example as may be required when servicing equipment mounted on a flat roof of a building, or indeed when carrying out maintenance work on such a roof itself.There is also a possible risk that if the time required for erecting proper safety equipment in order to carry out some task is too long, for example greater than the time required for actually carrying out the task, then safety standards may be skimped with attendant risk to life.

It is an object of this invention to provide a safety track and support therefor which can be erected rapidly and is therefore particularly adapted for use in situations where a temporary requirement exists.

According to this invention, there is provided safety apparatus comprising a safety track and a support therefor, which support comprises a central body having a plurality of legs radiating generally horizontally therefrom, said legs having downwardly extending, outwardly splayed, distal portions (called "lower legs") terminating in feet, the safety track being secured to those lower legs.

Such an apparatus can be erected extremely rapidly, and it can be surprisingly effective as a fall arrest device. The device is particularly suitable for use in providing security to persons working on, or from, a flat roof.

To provide proper support for the safety track, it is preferable that there should be at least six legs. The use of an excessive number of legs will simply add to the weight of the apparatus and its cost, and there is no need for more than twelve legs. In fact we have found that the optimum number of legs for the purpose in view is eight, and it is accordingly appropriate to refer to the support for the track as a spider.

It is preferred that the safety track be secured at a rather low level, for example below 50 cm above the feet. If the apparatus is located centrally on a flat roof, a worker's safety line may be attached thereto and be of such a length as to disallow too close approach to the edge of the roof, assuming of course that this is consistent with the task to be performed. In the event of a fall from the roof, the worker's safety line will then exert a force on the spider at an angle slightly below the horizontal, the drop being due to the difference in height between the roof edge and the level of the safety track, and this force will exert a turning moment on the spider about a notional line ("the turning axis") joining the pair of feet closest to the position of the safety line which will tend to lift the body and other feet of the spider.This turning moment will be greater as the height of the safety track is greater, and we have found that the optimum height for such track is below 40 cm.

It is also desirable that there should be a minimum height above the feet for the safety track. The track is preferably at a level of at least 20 cm above the feet.

A level of about 30 cm is particularly suitable. The aim is that in the event of a fall, the projection of the taut safety line should pass above the centre of mass of the spider. The result would be a turning moment about the centre of mass tending to pull the feet nearest the safety line into ever firmer contact with the roof. This in combination with the outward splaying of the lower legs tends to promote resistance of the spider against being dragged across the roof. The feet may be provided with rubber soles further to promote grip.

Some lifting of the far legs of the spider as a fall is arrested can be tolerated, but this should be kept within limits so as to obviate any risk of the spider toppling. There are three particular properties of the spider which will affect the moment about the turning axis which is due to its mass which acts in opposition to the moment due to the fall. These are: 1 The size of the spider. The greater the size, the greater will be the resistance to lifting in the event of a fall: but its portability will be reduced with increase in size.

2 The mass of the spider. The greater the mass, the greater will be the resistance to lifting in the event of a fall: but its portability will be reduced with increase in mass.

3 Any articulation of the limbs of the spider. For a given size and mass, the resistance to lifting will be increased with an increase in the rigidity of the structure. This need have no effect on its portability.

To promote rigidity, it is preferred that the lower legs of the spider be braced by struts. Alternatively, or in addition, it is preferred that stringers be provided to act between successive legs towards their distal ends and maintain them in constant, and preferably equal, spaced relation.

It is desirable that the moment about the turning axis due to the mass of the spider should be at least about 900 N.m. This can readily be achieved with a total spider mass of 50 kg and a total diameter of about 4 m. If the legs of the spider are demountable from the body, as is preferred, then the legs need be no longer than 2 m. Such legs may easily be transported from site to site even in a rather small vehicle, and they can easily be transported in a standard passenger lift or elevator within a building.

If required by regulation, the body of the spider may be secured to a fixing point using a short length of rope or chain.

A preferred embodiment of the invention is shown by way of example only in the accompanying drawings in which Figure 1 is a partial plan view of that embodiment, Figure 2 is an elevation of a distal end of a leg of that embodiment, and Figure 3 is an elevation of the proximal end of the leg of of Figure 2.

In the drawings, safety equipment for securing persons against a fall comprises a spider having legs 1 connected to a body 2. The legs 1 are bent at knees 3, and feet 4 are connected to lower leg portions 5 extending upwardly and inwradly to the knees. Upper portions 6 of the legs are also bent for attachment of the body 2. The upper 6 and lower 5 portions of the legs are interrupted by internal tension tee-joints 7 which serve to secure ends of struts 8 which brace the legs. Stringers 9 are provided between those struts 8 and fixed by angle clamps 10.The upper portion 6 of each leg 1 is secured to the body 2 by means of pair of flange clamps 11, one on each side of the respective strut 8, and similar flange clamps 11 are provided on the lower leg portions 5 for the attachment of a safety track, for example a safety track such as that described in EP 0 585 268 A ('NO 92/20407).

The legs 1, struts 8 and stringers 9 may suitably be formed of commercially available 50 mm aluminium alloy scaffold tubing, and the angle and flange clamps and the tee-joints may also be such as those used in scaffold systems.

Such a spider support for a safety track may be located substantially centrally of a flat roof, for the support of a safety track to which a worker's safety harness may be connected by means of a safety line. The safety line may be of appropriate length, for example to limit the worker's approach towards the edge of the roof, thus preventing him from falling over that edge. If desired, and if the size of a roof permits, two or more such supports may be used for supporting a single safety track.

Claims

1 Safety apparatus comprising a safety track and a support therefor, which support comprises a central body having a plurality of legs radiating generally horizontally therefrom, said legs having downwardiy extending, outwardly splayed, distal portions (called Ulower iegs") terminating in feet, the safety track being secured to those lower legs.

2. Safety apparatus according to claim 1, wherein such apparatus comprises at least six legs.

3. Safety apparatus according to claim 1 or 2, wherein the safety track is secured at a level not more than 50 cm above the feet.

4. Safety apparatus according to any preceding claim, wherein the safety track is secured at a level between 40 and 20 cm above the feet.

5. Safety apparatus according to any preceding claim, wherein the lower legs of the support are braced by struts.

5. Safety apparatus according to any preceding claim, wherein stringers are provided to act between successive legs towards their distal ends and maintain them in constant, and preferably equal, spaced relation.

6. Safety apparatus according to any preceding claim, wherein the moment about a turning axis defined by a line joining any successive pair of feet of the support and due to the mass of the support is at least 900 N.m.