A VERTICAL CONVEYOR The invention relates generally to a vertical conveyor and more particularly to a vertical conveyor which is driven only by the weight of passengers mounting or goods placed on the platforms of the conveyor. Whilst the invention will be described in the following principally in relation to a passenger lift adapted for use as a fire escape, the invention is not limited to this application. There are clearly many problems associated with fire in a building. Some of these problems are further aggravated if a fire breaks out in a tall building since the structure of a tall building will often form a chimney fanning the flames and accelerating the hot gases upwards. Thus, hot gases can rise at great speed through the building and percolate upwards therethrough, finding all voids and exits as they rise. In particular, lift shafts and stair wells can quickly become impassable as hot gasses and smoke will rapidly fill these voids.

This quickly makes escape down interior stairways difficult or impossible for persons on the upper floors of the building. In particular the elderly, young children or disabled people are likely to find themselves trapped on upper floors of the building.

Moreover, internal lifts are normally designed to shut down when a fire is detected by way of a safety- mechanism which trips a fire switch to shut down the system once the lift doors have opened at the nearest available floor, thus removing an alternative route of escape for the less agile occupants of the building.

Accordingly, it would be desirable to provide an efficient route of departure for use when a building catches fire, which route is external to the building and is powered independently of any power source which may be available in the building.

According to the present invention in one of its aspects there is provided a gravity driven vertical conveyor having passive means associated therewith for limiting the speed of descent of the conveyor. As employed herein the term passive denotes the absence of any power supplies, whether electric, hydraulic or whatever, associated with the speed limiting means and upon which the speed limiting means is dependent for operation. By virtue of this arrangement, the operation of the conveyor is made independent of the continuity of power supplies to the conveyor installation which is advantageous since in the event of a building fire power supplies commonly fail. According to another aspect of the invention there is provided a gravity powered vertical conveyor

comprising a continuous chain extending between upper and lower wheels; a number of platforms supported by the chain for transporting a load downwardly; and a hydraulic braking system associated with at least one of the wheels for limiting the speed of descent of the platform.

In the practice of the invention a preferably passive, hydraulically operated disc brake may be employed to absorb energy generated by the weight of a passenger or passengers descending on the conveyor and a hydraulic speed control may be used to maintain a substantially constant rate of descent regardless of the number or weight of the passengers. In order that the invention may be well understood, exemplary embodiments will be described hereinbelow, with reference to the accompanying drawings in which:

Figure 1(a) shows a bottom portion of a first embodiment of a vertical conveyor;

Figure 1(b) shows a top portion of the vertical conveyor;

Figure 2 is an exploded schematic view of an articulated platform and associated components; Figure 3 is a schematic drawing showing components of a platform arrester mechanism;

Figure 4 is a schematic sectional view showing the platform arrester mechanism cooperating with a platform;

Figures 5(a) and 5(b) show the operation of an obstruction latch arrangement provided on a platform; Figures 6(a) to 6(e) illustrate how an articulated platform collapses to pass under a lower wheel;

Figure 7(a) is a schematic diagram of one hydraulic braking system which can be used to control descent of the platforms;

Figure 7(b) is a schematic diagram of another hydraulic braking system which can be used to control descent of the platforms; Figure 8 shows a lever arm used to actuate hydraulic brakes to stop the conveyor;

Figure 9 is a schematic drawing showing features of an emergency mechanical brake;

Figure 10 shows a partial view of a chain in a guide channel;

Figure 11 is a schematic view of two chain links; Figure 12 shows a second embodiment of the conveyor as used on an offshore oil rig; and

Figure 13 shows an arrangement for use with the second embodiment for lowering an escape vessel.

Referring generally to Figures 1(a) and 1(b), the

vertical conveyor indicated at 1 comprises a base frame 2 housing a lower pair of notched wheels 3,4, a tower superstructure 5, an upper wheel housing 6 in which are mounted an upper pair of notched wheels 7,8 and a continuous chain 9 supporting a plurality of passenger platforms 10, two of which are shown in Figures 1(a) and 1(b).

The tower superstructure 5 is of square section and is constructed from vertical members 11 spanning the distance between horizontal members 12 which form the square section of the tower. An axle 13 passing though the upper pair of notched wheels 7,8 is supported at its ends by respective journals 14 ^" provided on horizontal supporting members 15 defining the boundary between the superstructure 5 and the upper wheel housing 6. Similarly, the axle 16 passing though the lower wheels 3,4 is supported at its ends by journals 17 provided on horizontal members 18. The notched wheels 3,4 and 7,8 each have notches 21 provided in the outer surface thereof at regular intervals and are arranged to receive end portions of chain pins 19 which extend between elongate chain links 20 on either side of the conveyor tower. The angular spacing between the notches 21 of the wheels and the corresponding length of the chain links

20 should be such as to minimise sinusoidal oscillations in the links which occur as the links 20 pass over the wheels. In the drawing the notches are shown as having a 60° spacing around the wheels, and it is believed that this represents the maximum spacing possible before the abovementioned oscillations make operation of the conveyor practically impossible. Advantageously the spacing between the notches 21 should be 30° or less to ensure that said oscillations are minimised.

The conveyor is gravity powered. That is to say, the only source of energy used to drive the platforms downwards is the weight of the passenger. Gravity is used as a prime mover in order to make the conveyor totally independent of power supplies which could fail in the event of a building fire.

Each passenger will have his own potential energy related to his weight and height above the ground. When the passenger steps onto a platform his potential energy tends to drive the platform downwards. Since the potential energy of the passenger is likely to be relatively small (the passengers weight is substantially less that the mass of the chain, wheels, platforms etc. of the conveyor) the inertia of the conveyor is designed to be as small as possible. However, as the potential energy of the passenger

overcomes the low inertia of the conveyor, the kinetic energy of the passenger and platform will increase.

Thus, the passenger and platform will accelerate towards the ground and if this acceleration was not restricted in some way the passenger could be seriously injured upon impact with the ground.

Clearly this would be highly unsatisfactory and the embodiment therefore .includes a number of features which limit the rate of descent of the passenger to an acceptable level, stop platforms descending to ease the task of passengers joining and leaving the conveyor, and stop the platforms in the event of a passenger or other .obstructions lying in the path of a descending platform. As will be described in greater detail hereinafter, the embodiment includes a hydraulic braking system which regulates the speed of descent of passengers. The braking system is arranged to vary the braking force in relation to the load passengers on the platforms so as to achieve a substantially constant rate of descent. Platform arrester levers accessible at the points of entry may be used to mechanically arrest the conveyor by actuating a buffer bar which cooperates with a platform arrester mechanism on the next vacant platform thereby to stop the platform so that the passenger can join the

conveyor. The weight of the passenger stepping onto the arrested platform will disengage the arrester mechanism from the buffer so that the platform can continue its downward journey. Further levers accessible at the points of entry and exit from the conveyor may be used to stop the conveyor for longer periods by actuation of the hydraulic braking system. Each platform is also provided with an obstruction latch arrangement which upon detection of any obstruction in the path of a descending platform, mechanically locks the conveyor to prevent further descent of the platform until such time as the obstruction is removed. Means are also provided for stopping the platform in the event of a passenger failing to leave the platform for whatever reason.

Referring now to Figure 2 it will be seen that the platform 10 comprises a major deck plate 22 and a minor deck plate 23. The major deck plate 22 which is the outermost plate of the platform 10, ie. the plate further from the tower superstructure 5, is secured along each side to main support brackets 26 and the minor deck plate is similarly secured to a substantially L-shaped transmission support link 27 which substitutes for the previously identified chain links 20 where a platform 10 is located. The L-shaped link extends between an upper ring 28 and a lower ring

29 of the chain. The main support bracket 26 and the L-shaped link 27 are pivotally connected at pivot holes 30 and 31 respectively to form an articulated platform. In order to enable the conveyor to be stopped so that a passenger can more easily step onto a platform, the conveyor is provided with a platform arrester 32 on the uppermost rung 28 which cooperates with the minor deck plate 23 to stop an unoccupied platform when a holding brake mechanism, to be explained hereinafter, is actuated by the user.

Furthermore, in order to stop a platform in the event of an obstruction, such as an earlier passenger ^• who has for example collapsed across his platform, an obstruction latch arrangement is also provided on the platforms. The obstruction latch arrangement comprises a pair of detecting arms 33a, 33b secured to a detecting arm link 33 hanging freely from the outermost edge of the major deck plate 22, a pair of latch pegs 34a, 34b at both ends of the lower ring 29 with an elongate synchronising bar 35 extending therebetween, and connecting wires 36a, 36b connecting the ends of the elongate synchronising bar 35 to respective detecting arms 33a, 33b. The conveyor 1 is intended for use as an escape route under emergency conditions. As such, intended

users of the conveyor, who may be of any age or ability, will not generally be familiar with the operation of the conveyor and indeed may well be in a less than coherent frame of mind if there is perceived imminent danger. Accordingly means are provided in the form of a platform arrester to ensure that users can step safely onto a vacant platform and subsequently away from the conveyor once they have been lowered to the ground. Platform arrester levers are provided at suitable intervals on the conveyor superstructure, for example at intervals corresponding to the spacing between floors of the building on which the conveyor is to be used. As shown in Figure 3, the platform arrester lever 37 is connected to a buffer bracket 38 pivoted about pivot blocks 39 at each end. The pivot blocks 39 are secured to vertical members of the superstructure 11 shown in ghost. Actuation of the arrester lever in the direction D causes the buffer bracket 38 to pivot forwards in the direction F toward the path of arrester wheels 40 at the ends of arrester arms 41 on the platform arrester 32. When the arrester wheels 40 of the next unoccupied platform come into contact with the buffer bracket 38 the platform will stop so that the passenger can mount the platform.

Of course, all other platforms will stop as well since they are all linked by the continuous chain 9. However, the delay to other passengers should not be too long since the platform arrester mechanism is arranged to disengage as soon as the waiting passenger steps fully onto the conveyor. Springs 42 on the upper surface of the platform arrester 38 are arranged to cooperate with the undersurface of the minor deck plate 23. As may be seen from Figure 4 the springs are arranged such that when a passenger P steps onto the arrested platform the arrester wheels 40 are conveyored clear by pivoting in direction B of their points of contact with the buffer bracket 38 so that the platform can continue on its way. It should be appreciated that when the platform arrester lever 37 is actuated and an occupied platform is the next platform to pass, the arrester arms 41 will be in a position where the wheels 40 can pass uninhibited by the buffer bracket 38. Thus, the platform arrester mechanism is arranged such that only .unoccupied platforms can be stopped, thereby in order to expedite evacuation of the building.

If for any reason a passenger collapses across the path of the platform, the obstruction latch arrangement on the following platform will automatically stop the conveyor so that said passenger

is not crushed by the next descending platform. Referring now to Figure 5(a) the wire 36 normally extends substantially horizontally between the free ends of the detecting arm 33 and the latch peg 34. It will be appreciated that an obstruction latch arrangement is provided on both sides of the platform but that only one side is shown and described for the sake of clarity.

When an obstructing object such as the object 43 in Figure 5(b) obstructs free movement of the wire 36 downwards, continued movement of the platform will cause the wire 36 to become distorted. Distortion of the wire 36 simultaneously urges the free ends of the detecting arm 33 and the latch peg 34 inwardly in relation to the obstruction causing the latching end 44 of the latch peg 34 to project outwards. The superstructure of the conveyor is provided with a plurality of notches (not shown) with which the latching end 44 will engage thereby causing the conveyor to stop. The conveyor will remain stopped by the latching pegs 34 until such time as the obstruction 44 is removed. When the obstruction is removed the obstruction latch arrangement can be disengaged by pulling the latching end 44 out of the notch so that the latch arrangement reverts back to the position shown in Figure 5(a) .

The obstruction latching arrangement also serves to control articulation of the platform during its passage under the lower wheels 3,4. Figure 6 shows the passage of a platform around a lower wheel 3 as it rotates in the direction of arrow 12. As can been seen from Figure 6(a), once the rungs 28 and 29 at either end of the transmission support link 27 are both engaged with notches 21 in the wheel 3 the platform 10 begins to collapse. The minor platform deck 23 remains substantially perpendicular to the support link 27 and, as the lower rung 29 moves under the wheel 3, the major deck plate 22 pivots about joint 45 whilst the detecting arm 33 moves under the major deck plate 22 under the influence of the wire 36. When the uppermost rung 28 lies directly below the axle (not shown) of wheel 3 the platform 10 will have collapsed to its minimum height so that it can pass through the base frame 2 (not shown) under the lower wheel 3, as can be seen from Figure 6(c). Further rotation of the wheel 3 will pull the collapsed platform through the base frame until the major deck 22 emerges from below the wheel 3 as shown in Figure 6(e). The major deck 22 remains hanging substantially perpendicularly to the minor deck 23 as it passes up the outside of the conveyor superstructure, ie. the major deck 22 hangs vertically

downwards during its passage to the upper wheel housing 6 (not shown) .

Energy to drive the conveyor is derived solely from the weight of passengers on the conveyor. In order to convert as much as possible of the passengers potential energy into kinetic energy the above described wheels and journals are arranged to generate only a low frictional loss through the use of suitable bearings. Roller bearings can be used to support the wheels, but if the conveyor is to remain inactive for long periods, as would be the case ^" when the conveyor is installed as a fire escape, bearings such as nylon sleeves lubricated with silicon oil are preferred since nylon sleeves are less likely to be flattened during periods of inactivity by the weight of the wheels. Furthermore, the chain links are arranged to pivot freely about their respective rungs. However, it would clearly be unsatisfactory for the conveyor to be entirely free-running since any passenger stepping onto a platform would rapidly accelerate towards the ground which could quite possibly result in injury to the passenger.

An hydraulic braking system is therefore included to regulate the speed of descent of passengers. Since at any given time the conveyor can be carrying anything from a small child or one platform to several

heavy adults on several platforms, the hydraulic braking system is arranged to vary the braking, force in relation to the load on the conveyor to achieve a substantially constant rate of descent. One hydraulic braking system for use in controlling the descent of platforms is indicated generally at 50 in Figure 7 and comprises a hydraulic fluid pump 51 driven by drive shaft 52 which is connected to the lower axle 16 (not shown) of the lower wheel pair, and a pair of caliper brakes 53 which cooperate with a disc brake 54 secured at one end of the lower axle 16 to regulate the speed of rotation of the lower wheels. Alternatively, several disc brakes may be secured to the lower axle 16. When a passenger steps onto a platform his weight will start movement of the platform downwards causing the lower wheels, and hence the drive shaft 52, to rotate. The pump 57 is preferably a multicylinder pump which provides a high fluid flow at low speed. Pumps similar to those used as marine steering pumps have been found to be particularly suitable in this respect. As the pump shaft 52 rotates, the pump outputs fluid at outlet 55 at a rate proportional to the speed of rotation of the shaft and the brake calipers 53 apply pressure to the discs 54 to restrict the speed of rotation of the wheels and thereby to

limit the speed of descent once a steady state has been reached. When a passenger steps from a descended platform the total load on the conveyor will be reduced and accordingly, the rate of descent of the other platforms will tend to fall. This fall in speed results in the pump 51 delivering less fluid from the outlet 55 to the caliper brakes 53 thereby reducing the pressure applied, to the discs 54 and increasing the speed of descent until a steady state is again reached.

The braking system 50 also includes an accumulator 56 connected to the hydraulic outlet 55 via a return valve 57 which allows fast fluid flow from the accumulator 56 but only slow fluid flow to the accumulator. The accumulator and valve are thus arranged to absorb sudden surges in pressure which occur for example when a passenger steps onto or away from the conveyor, thereby providing a smoother ride

_* for the passengers. A flow control valve 58 is also provided between the outlet port 55 and the inlet port 59 to provide a return path for fluid output from the pump 51. The flow control valve 58 is adjusted when the system is installed to provide the desired rate of descent. A pressure gauge 60 is optionally installed to assist in the adjusting of the flow control valve by providing

a reading proportional to the pressure applied by the hydraulic fluid. The desired rate of descent can be obtained by adjusting the flow control valve 58 to achieve a desired pressure reading when a predetermined load is on the conveyor The flow control valve also assists in absorbing surges in pressure by providing a feedback path to the pump.

A pressure release valve 61 is provided in parallel with the flow valve 58 to open a relief path for fluid in the event that excess fluid pressure is generated within the system. Similarly, hose burst valves 62 are provided in-line with the caliper brakes 53 to shut off the line to prevent the system from failing entirely in the event of hydraulic failure of one of the caliper brakes.

A shuttle valve 13 connects the pipes 64 from the pump outlet 55, the return valve 57, etc., to the pipes 65 leading to the hose burst valves 62. The shuttle valve is also connected to a brake master cylinder 66 and normally the path from the pipe 64 to the pipe 65 is open so that the hydraulic system operates in the above described manner. However, when the brake master cylinder 66 is actuated, the shuttle valve moves to close the path between pipes 64 and 65 and open the path from the master cylinder 66 to the pipe 65. Thus, actuation of the master cylinder 66

results in pressure therefrom being applied directly to the brakes 53.

The master cylinder is actuated by a lever arrangement (not shown) which connects to several locations in the conveyor. The lever arrangement serves several different functions, as will now be described. A lever arm 67 such as is shown in Figure 8 is provided in the base frame 2 at a position whereat the lever arm 67 co-operates with the undersurface of the platform 10. That is to say, when an unoccupied platform passes into the base frame 2, the undersurface of the platform will pass over the lever arm 67 unimpeded. However, if for any reason a passenger has failed to leave the platform by the time that the platform enters the base frame 2, the underside will push down on the lever wheel 68 against the force of spring 69 to actuate the master cylinder 66. The lever arm 67 is arranged such that gradually increasing pressure is applied thereto by an occupied descending platform to bring the conveyor gradually to a halt.

It will be appreciated that actuation of the master cylinder 66 in this way is a safety feature provided in addition to the obstruction latch arrangement described in particular with reference to Figure 5. Thus, if a passenger remains on a platform

in a position where he would be undetected by the obstruction latch arrangement, he will not be in danger of being dragged through the base frame 2 since the master cylinder will be caused to be activated by his weight on the platform.

Under normal operation, an unoccupied platform will be held in position until a passenger steps onto the platform when the passengers weight will act to free the platform from the buffer bracket 38. Under most circumstances this is a satisfactory arrangement which minimises the time in which the conveyor is stationary. However, special account has been taken of the needs of injured or disabled passengers who may have to be assisted onto a platform. In such circumstances the platform may have to remain in a stopped position whilst the injured or disabled passenger is manoeuvered onto the platform and it would be unsatisfactory for the platform to start moving as soon as the weight on the platform is sufficient to release the platform from the buffer bracket 38. Accordingly, a rod arrangement running the length of the superstructure and connected to the master cylinder is provided to enable the master cylinder to be activated. The rod arrangement is accessible from each floor of the building and may be activated by the passenger or other users, for example

members of the emergency services supervising evacuation of the building, before the passenger wants a platform. Access of the rod arrangement at ground level allows the platform again to be stopped so that the injured or disabled passenger can be helped off the platform.

A modified form of the above described hydraulic braking system is shown in Figure 7(a). The layout and general operation of this modified hydraulic braking system is in many respects very similar to that of the above described system and hereinafter only the differences between the two will be described with reference to Figure 7(b) of the drawings.

It should be noted from the above that an hydraulic braking system is included in the vertical conveyor to regulate the speed of descent of platforms on the conveyor and is arranged to vary the braking force in relation to the load on the conveyor to achieve a substantially constant rate of descent. In the previously described system there is a lag in the response of the pump to a change in load on the conveyor, when for example a passenger steps onto a platform. This lag results from the fact that when a passenger wishes to join the conveyor the whole system is stopped by the application of pressure to the brake from a hydraulic master cylinder. When the pressure

from the master cylinder is released, the conveyor will start to descend and this drives the pump. Initially the pump will not be driven fast enough to apply sufficient pressure to the brake. Until the pump reaches the required speed the conveyor and passengers thereon will fall rapidly. Whilst perfectly safe, this initial rapid increase in speed can be disconcerting for passengers both joining and already on the conveyor. Referring now to Figure 7(b) of the drawings, the other hydraulic braking system indicated generally at 80 includes a pressure compensating control valve 81 in place of the above disclosed flow control valve, a pressure check. valve 82 in line between the flow line from the pump 85 and the calipers 83, and a nominal return valve 84 which provides a return path for fluid past the pressure check valve 82 and back to the inlet line to the pump 85. As in the above described system, the pump delivers fluid at a rate proportional to its speed of rotation and this results in pressure being applied through the calipers 83 to a disc brake 86. The pressure applied to the disc brake 86 limits the rate of descent of the loaded conveyor.

When a passenger wishes to join the conveyor the lever 87 associated with the master cylinder 88 is actuated to apply sufficient pressure to the disc

brake 86 via the calipers 83 to stop the conveyor. Once the passenger has joined the conveyor the lever 87 is deactuated so that the master cylinder 88 no longer applies pressure to the calipers 83. The pressure check valve 82 is arranged to maintain the pressure applied to the calipers at the level it was at when the lever 87 was actuated whilst the speed of the pump 85 increases. Thus, the pressure check valve 82 in effect isolates the calipers 83 from the pump whilst the speed of the pump increases. The load on the pump is reduced to only that of the pressure compensating valve 81 and so the pressure of the fluid output from the pump quickly reaches the required level. In general, pressure compensating valves will only operate above a predetermined pressure threshold and the pressure check valve 82, in isolating the pump 85 from the calipers, also enables the pressure compensating valve 81 to be primed to its pressure threshold by the pump more quickly than it otherwise could be. A pressure compensating valve with a pressure threshold of greater than about 80 psi is preferred.

In order to enable some of the pressure to be released from the brake 86 to allow the conveyor to start descending, a nominal return valve 89 is

provided in line between the pressure check valve 82 and the calipers 83. When the lever 87 is released, pressure at the calipers 83 is bled by the nominal return valve 89 to the outlet side of the pump 85. The nominal return valve 87 is placed between the calipers 83 and the pressure check valve 82 to provide a return path for fluid from the calipers to the outlet from the pump to enable the conveyor to start moving initially. As the pressure from the pump 85 increases above that on the caliper side of the pressure check valve 82, the pressure check valve 82 opens to provide a path from the pump 85 to the

^• calipers 83 and the pump thereby applies pressure directly to the calipers to control the rate of descent of the conveyor.

In the event of a total hydraulic failure, a mechanical emergency brake independent of the hydraulic system is brought into effect. The emergency brake is a standard elevator speed brake connected to the lower axle 16 and arranged to operate at speeds above a predetermined maximum. When the speed of the axle exceeds said maximum, a cantilever weight (not shown) is released driving a pair of catches 70 into the path of the ascending chain U as shown in Figure 9. The catches can be disengaged manually by way of a lever 72 to release the chain

therefrom such that the platforms are lowered a rung at a time.

The chain used to connect the upper and lower wheel pairs and to support the platforms includes a number of features which help to reduce friction between the chain links and between the links and the guiding channels of the superstructure within which channels the chain travels.

Figure 10 shows a partial detail of the chain 9 in which a number of chain links 20 are located in a guide channel 75 formed in the vertical member 11. A platform 10 and its associated transmission link 27 are also shown. In an ordinary chain when a weight P is placed on the outer edge of the platform 10 the force will be transmitted through the platform about ring 28 thereby causing the lower end of link 27 to move in the direction Z. The length of the platform 10 will be considerably greater than that of the link 27 and accordingly the force asserted at Z will be larger than that from weight P. In extreme cases the force at Z can result in the link 27 jamming in the guide channel 75. This has long been a known problem with all types of vertical conveyors which rely on chains to form part of the drive mechanism. One way of overcoming this problem is simply to provide bearings such as wheels at the ends of the links in

order to reduce friction between the links and the channel. However, this solution does not fully address the problem since the force applied at 2 through the fitted wheel will still be of the same magnitude.

Because the problem is one of mechanical advantage (the platform acts as a lever to drive the end of the link into the channel) it is possible to provide a solution to the problem which takes advantage of this fact. According to a further aspect of the invention therefore a vertical conveyor comprising platforms attached to an endless moving chain is formed so that the chain is able to bend in one direction transverse to its length but, by virtue of interactions between adjacent links of the chain, cannot bend in the opposite direction. In the described embodiment of the invention as can be seen from Figure 11, the chain links 20 are provided with stop tabs 76 which project away from the main surface of the link to engage with the next link in the chain.

Provision of the stop tabs 76 on each chain link in the manner shown in Figure 11 allows the chain 9 to bend around the wheel 3 in the normal way, as illustrated in Figure 10, but prevents the chain 9 from bending significantly in the opposite direction.

A significant result of this unidirectional bending is

that when a weight P is placed on the platform 10 the force will be transmitted through several links before emerging as a force S at link 20(a) for example. Thus, the mechanical advantage of the platform/link lever is significantly reduced and the force S at link 20(a) will be less than the force from weight P at the end of the platform 10. Accordingly, there will be less likelihood of the chain jamming in the guide channel 75. The above conveyor has been described broadly without reference to suitable dimensions in order to facilitate a broad understanding of the concepts underlying the invention. The dimensions of a prototype conveyor manufactured in accordance with the invention will now be discussed briefly in order to further enhance the readers understanding.

In a prototype constructed by the inventors the tower 5 is of 4 ft square section and is made from vertical members 9 ft in length bolted between horizontal members which form the square section. Each wheel 3, 4, 7, 8 is made as a single casting and is one yard in diameter. Notches spaced at 30° intervals around the circumference of the wheel support the continuous chain 9. The chain comprises a plurality of 1 inch diameter pins 19 at 9 inch intervals connected by chain links 20 formed of 1%

inch steel plates tested to 24,000 lbs. The passenger platforms 10 are secured to the chain 9 by way of the links 27 at approximately 9 ft intervals and the detecting arms 33 on each platform are 9 inches long. The overall platform length is approximately 3 feet, 9 inches of which is provided by the minor deck plate 23.

The braking system 50,80 • is pre-adjusted to restrict the speed of the wheels to between 4 and 5 rpm and this gives a descent speed of between 36 and

45 feet per minute when there is at least one passenger on a platform. The emergency speed brake is preset to trip out if the speed of the wheels exceeds

6 rpm. At these speeds, the braking system must be capable of absorbing a large amount of energy; calculations have shown that the energy generated during use is typically of the order of 300W per passenger, so with a typical load of 10 passengers the braking system must be capable of dissipating typically 3kW and the discs 54, the calipers 53 and other components of the braking system are dimensioned accordingly.

When the conveyor is used as a fire escape secured to the outside of the building, it will normally be enclosed within a housing to protect the workings of the conveyor and to give a greater sense

of security to escapees when using the conveyor. Typically the housing will be clad with steel sheeting.

Housing the conveyor in this way could cause problems in the event of a fire since the structure would act as an external chimney sucking in hot gasses and smoke. However, by providing brushes along the edges of the platforms, which brushes co-operate with the inner walls of the housing, a positive air pressure will be created within the housing to hold back the hot gasses and smoke.

A water tank may also be advantageously provided at the top of the tower to supply a continuous wall of water down the inner walls of the housing to cool the housing. Moreover, illuminated signs powered by an independent battery for example, along with instruction notices etc. may be advantageously provided within the housing at strategic locations to aid escapees in their escape from the building. Recent incidents on offshore oil rigs have made it apparent that to increase the likelihood of survivors emerging from a fire for example on an offshore oil platform the time taken to evacuate workers should be minimised. A second embodiment shown in Figure 12 of the accompanying drawings is adapted for use on an

offshore oil rig for example. Many features of this embodiment are common to those described in relation to the first embodiment and to avoid unnecessary repetition, only those features that differ will be identified in the following description.

As is shown in Figure 12, the conveyor 100 can be provided at or near one or more of the supporting legs 101 of the platform 102. The hydraulic braking system 50 is preferably provided at the top of the superstructure 103 along with the necessary controls to stop vacant conveyor platforms so that the next passenger can climb thereonto.

Since the relative distance from the platform A02 is variable depending on tides, wave heights, etc., it is impractical to provide a conveyor which lowers passengers all the way to sea level. Instead a staging platform 104 is provided at an intermediate position 0-n the supporting leg 101. Passengers are lowered to the staging platform 104 by the conveyor and escape to the sea is made via a flume 105.

Advantageously self-inflating survival dinghies are provided to facilitate escape down the flume 105. The staging platform 104 and the conveyor 100 may be enclosed in a mesh safety cage 106 to protect the occupants from falling debris and the like from the burning platform 102.

It has been calculated that an evacuation rate of about 25 mn per minute or grater can be achieved, if vacant platforms are not stopped by the escapees.

The above described second embodiment is adapted for use as an emergency escape route for an offshore oil rig. In inclement weather conditions such as those often found in the North Sea for example, the need for personnel to dress in clothing designed to protect against such conditions may introduce an unacceptable delay to the evacuation time thereby putting life at risk. Escape from an oil rig has conventionally been by way of life boats launched from boat launch areas on the rig. These boats are lowered or dropped vertically from the launch areas into the sea. Under storm conditions, strong winds will introduce a high yaw and the effect of wave troughs at rising or descending swells will be naturally to incline the boat to go under the platform rather than away from it. In order to obviate the need to dress in clothing to protect against the hostile weather conditions we propose both the use of our conveyor to provide a relatively non-hostile environment for the transporting of evacuees from the oil rig platform to an escape vessel assembly point to enable all evacuees to join quickly the escape vessel and a new

arrangement for lowering the escape vessel both quickly and safely from the assembly point to the sea.

The arrangement for lowering the escape vessel is shown in Figure 13 of the accompanying drawings. Referring now to Figure 13, the arrangement comprises an escape vessel 111 coupled to an hydraulically tensioned submarine cable 112 by way of swivel latch mechanisms 113. The submarine cable 112 is secured to the sea bed by any suitable anchoring means via two in-line safety latch pressure release units (not shown) , and to the rig by way of a lifeboat davit release mechanism 114. A boat retaining clamp

115 is also provided to retain the escape vessel 111 in position. The vessel 111 is normally stored by way of the boat retaining clamp 115 at an assembly point on the rig. The assembly point or staging grid provides shelter from extremes of weather and to this end may be protected by a lattice screen shelter cage comprising Barry control E mounts built to admirally shock tool specification and, British aircraft corporation jet stream deflector rails.

The submarine cable 112 defines an angled descent path designed to take the boat over the effect of waves and provide an angle of attack of the vessel to the sea in accordance with the vessels requirements as defined by the manufacturer of the vessel. An

adjustable rear suspension stay enables the angle of attack to be changed as required and a very sharp angle of descent can be defined with the speed of descent of the vessel being controlled by a davit clutch, thereby reducing the angle of the davit head to the anchor point.

In order to ensure safe running of the arrangement under emergency conditions, marine growth on the suspension cable must be controlled to ensure unencumbered descent of the vessel when tensioned up from dormant to active position. Moreover, regular testing of the arrangement is necessary so as to conform to standard procedures and this gives rise to the need to recover the launched vessel after testing which can be readily provided for in practice. Similarly, safety ratios on all elements of the apparatus should be chosen to meet the requirements of the appropriate regulations.

The above described system inter-alia offers the advantage that the operation is dependent solely on gravity and requires no external power sources.

The invention having been described by way of example, it will be apparent to those possessed of the relevant skills that modifications are possible without departing from the ambit of the invention. For example, whilst the described embodiments are of

conveyors which operate in a vertical direction, it will be appreciated that some departure from the vertical might well be possible if the accompanying increased friction either causes no problems or causes no insuperable problems. The word "vertical" as employed herein is thus not to be read in a strict sense, but rather embraces other possibilities for transfer between different vertical levels.