WO1993011524A1 - Fire escape system - Google Patents

Abstract

Methods and apparatus for providing visible indication of an escape route through an enclosed smoke obscured area are disclosed. In preferred embodiments one or preferably two laser beams are directed into the system from an exit and are housed in shrouding. The shrouding has windows through which the beam can be seen when smoke particles are present in the air. Preferably the two beams are housed in juxtaposed shrouds one of which has large holes for access of smoke, giving early warning of a smoke condition. The early warning shroud communicates with the other shroud via restricted access so that smoke only penetrates into this shroud and reveals its beam in severe smoke conditions but the beam in this shroud is not extinguished until much later than the early warning beam.

Description

"FIRE ESCAPE SYSTEM"

The present invention relates to systems for assisting escape from enclosed areas in which there is an uncontrolled fire. Apart from the risk of death due to burning a frequent cause of death in fires is inhalation of smoke. Whilst smoke inhalation can cause death rapidly depending on the nature of the materials which are burning the risk of death is increased the longer a person is exposed to smoke. Fires in underground railway systems have demonstrated the need to make it possible to find ones way through smoke-filled passages to an exit. The present invention is' concerned with providing visible indication of an escape route through an enclosed smoke obscured area. It has been developed with the problems which arise in fires in underground railway systems in mind and will be described with particular reference to such systems. It is however applicable to indicating an escape route from any enclosed location e.g. a room to the outside atmosphere where a multiplicity of routes are available or large rooms have to be traversed, having a remote exit or exits which have to be found to continue the route and which will be liable to be obscured by smoke. Examples of such other locations include hotels, conference centres, buildings with atria, shopping centres or malls, public buildings e.g. multistory public buildings, theatres, cinemas, entertainment complexes, mines, sports centres, oil rigs and oil rig accomodation, ships, and blocks of flats. Domestic housing is not excluded. Ordinary incandescent or neon lights and signs which have individual discrete locations rapidly become obscured in smoke quite apart from being more liable to fail when the temperature rises. In the Kings Cross fire of 1987 the lighting system proved inadequate to enable escapers as well as rescuers and firefighters to find their way around in the smoke. Fire officers followed the walls by touch, there being no indication of any route to platforms where passengers needing to escape might be located. The present invention is based on the realization that a highly collimated beam of light which tends to have low visibility in clean dust-free air becomes visible in smoke because the smoke particles diffuse the light in the beam. The most readily available current form of such a beam is a beam of laser light, which, as is well known, is a monochromatic (i.e. single wavelength) coherent (i.e. all waves in phase) beam of radiation. Laser beams may be generated by exciting the electrons in material enclosed in a space bounded by opposing mirrors one of which has an exit aperture so that photons emited by electrons decaying from an excited state can emerge from the aperture an do so as the said coherent monochromatic beam. This may be a continuous wave or pulsed mode laser beam. The laser may be a gas laser e.g. helium-neon, argon-kryptron, or helium-cadmium, a solid state laser or a dye laser or other effective laser. When the term laser beam or laser light is used herein it is to be taken to include any light beam having the highly collimated properties of a laser beam however the beam is generated. Beams actually generated by a laser are currently much preferred. Our earlier case published GB Application No. 221 685A contemplated that the power rating of the laser should be chosen to be such as to penetrate the anticipated maximum smoke particle density whilst being of low enough power and so located to be such as not to cause eye damage. The said earlier case postulated that even if the beam was such as eventually to be obscured by the smoke at the very height of the smoke intensity of a fire, it would still perform a very useful function by remaining visible much longer than other light sources. If the laser was located at a position where only deliberate efforts would enable a person to achieve direct intra-beam viewing i.e. to place their eye in the laser beam and look at the laser source then higher power ratings could be used. EP 352336 (Seidenko) , filed before GB 2214685 was published, failed to perceive even that the smoke particles could be used to reveal the beam and merely used the laser light by digitally scanning to write or project the word EXIT on the inner face of a door giving outlet from a space. Seidenko entirely failed to realise that even a laser beam will become rapidly extinguished in the smoke from a fire. Thus quite apart from there being no discussion of this problem, Seidenko do not advocate the use of a laser beam as a continuous sign denoting an escape route and leading the escaper along the said route. The inventor has now realized that attenuation by smoke even of a laser beam is more rapid than previously thought and that an unshrouded beam will lose its signalling capability before the most dense smoke conditions are reached, and before any useful effect can be made from this phenomenon. Seidenko manifestly failed to recognise that this problem existed. The present invention still relies on the ability of a laser beam to travel long distances in unattenuating or only slightly attenuating conditions and to reveal a smoke condition by illuminating the individual smoke particles thus revealing its own location, becoming visible and performing a signalling function. The present invention is based on the recognition that the most dangerous fires will be those where the seat of the fire is closest to the beginning of an exit route. This is because this will result in the laser beam being extinguished furthest from the outlet. The problem is to ensure the integrity of the laser beam for the longest possible part of the route wherever the seat of the fire is located along the exit route. One solution to this problem which the inventor has now perceived is to originate the laser beams from both the start of the escape route and the exit, preferably with the ingoing and outgoing beams parallel to each other but slightly spaced apart so that they do not interfere with each other. However this will require more careful alignment of components and a single beam arrangement is preferable. A further perception which the inventor has now made is that if the laser beam is directed into the system from a location at or near the outlet or exit from the system, extinction will only be liable to occur right at the fire and if that fire is near the start of the escape route much less of the escape route will be at risk. Another option is to have beams directed both inwardly from the exit and outwardly from the beginning of the escape route with the beams meeting and been appropriately stopped or absorbed at an appropriate location, referred to as the handover point, intermediate the ends of the escape route, e.g. just beyond the outlet to a platform in a subway or underground system. However such arrangements will require extra lasers and decisions on where to locate the handover point. The inventor has now observed from laboratory tests that advantages can be obtained by causing an airstream to flow along the exit route around the laser beam. This gives an appearance of directionality - variations in smoke intensity seeming to move along the route and indicating the direction to follow. When the laser beam is located in a duct the airstream can readily be located in the duct. The airstream should therefore be outwardly along the escape route. This could be from the beginning of the escape route, but there supply of clean cool air might be a problem. Alternatively supply of air could be from the exit to the escape route. Generating the airstream from the exit has advantages. Smoky air can be drawn out through any ducting surrounding the laser beam and vented to atmosphere. The ducting may include an air supply duct and air could be pumped in from the exit down to the beginning of the exit route and there supplied to the beam shroud. Air could be drawn out of the exit end of the beam shroud to encourage the air flow around the beam. An arrangement in which air is drawn through the shroud to the exit has the advantage that this air flow can be generated by the fan or fans that may be utilized to cool the laser. This arrangement can be used in conjunction with smoke sensors so that the system can be constantly sampled and can switch itself on when it detects a smoke density above a normal use level or containing components characteristic of a fire. This same smoke sensor could be used to initiate a sprinkler system - effective at least to cool the laser beam shroud and thus maintain its integrity. Localised smoke detectors might be more appropriate for initiating sprinkler systems aimed at quenching the fire itself. Access of smoky air to the shroud is typically via holes in the shroud. The size of these holes could be graded so that the amount of air drawn into the shroud was greatest at the location most remote from the fan and lowest at the location closest to the fan so as to ensure that air was drawn in all along the escape route. Thus according to the broadest and first aspect of the present invention a method of providing an indication of an escape route from a system having one or more enclosed locations and one or more routes to one or more exits comprises providing a least one beam of laser light along a route between at least one of the locations and at least one of the exits when a smoke condition exists in the said system, the laser beam providing an indication of the escape route, the said beam being located in a shroud within which the beam is visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, and causing the air and gases within the shroud to at least simulate movement towards an exit. According to a second broad aspect of the present invention a method of providing an indication of an escape route from a system having one or more enclosed locations and one or more routes to one or more exits from the system which method comprises providing at least two beams of laser light along a route between at least one of the locations and at least one of the exits when a smoke condition exists in the said system, the laser beams providing an indication of the escape route, the said beams being located in shrouds within which the beams are visible at least intermittently, the said shrouds having smoke ingress means affording ingress of the said smoke into the said shrouds, there being at least two shrouds of which the ingress means afford differing degrees of ingress of smoke into the said shrouds. The beams or at least one of the beams is preferably substantially continuous. The beam itself or the beams themselves indicate the escape route by being visible to persons in the system and being made visible by scattering of light in the beams by the smoke. The air movement in the shroud gives the appearance of the smoke moving towards the exit. This second aspect of the present invention thus utilizes two or more shrouded laser beams the shrouding of one beam, which will be referred to as the early warning beam, being such as to allow considerable access of smoke to the interior of the early warning beam shroud, whilst the shrouding of the other beam or beams, which will be referred to as the indicator-beam or beams, is such as to allow much less access of smoke to the interior of the indicator-beam shroud. A succession of indicator-beam shrouds with progressively less access of smoke being afforded could be used but an arrangement having a single-indicator-beam is probably the best compromise of efficacy and cost. In addition in order to provide signal continuity for conditions where very high temperature fires (burning with little or less smoke) occur a completely unshrouded continuity-beam could be provided so that even if both shrouds were distorted, so that, under extreme conditions, they blocked their beams, there would still be a signal passing along that affected link. Our earlier case recommended shrouding to ensure against damage to eyes by the laser beam but did not contemplate the use of combinations of beams and shrouds with differential provision of access by smoke so that they provide visibility of the beams in different smoke conditions whilst diminishing the attenuation of at least one beam (which will be the indicator-beam) in severe smoke conditions. The system of the present invention has the advantage that it adjusts to different smoke conditions purely by its mechanical configuration, though electronic enhancement of the beams with varying smoke intensity is not precluded. The teaching of our earlier case concerning safety is still applicable in this invention. Thus if the laser beam is to be positioned where direct intra-beam viewing would be possible accidentally or wilfully i.e. at head height or lower or where it is at a height contrary to local Health and Safety Regulations then the beam should be shrouded e.g. directed along a duct whilst access to the beam by the smoke is maintained, the shrouding being such as to prevent intra-beam viewing whilst maximizing the amount of the beam which can be seen. Such a duct could be a channel e.g. U-shaped and whilst open, to enable the beam to be seen, narrow enough to prevent direct intra-beam viewing, or could be an apertured tube. In the U.K., Health and Safety Regulations stipulate that class 2 lasers, which are low powered lasers emitting visible radiation (400-700 nanometres) are not inherently safe but eye protection is normally afforded by aversion responses including the blink reflex. British Standard Specification No. 4803 identifies class 2 lasers as having an average power of 1 milliwatt. Class 3A lasers have an output power of up to 5 milliwatts (as collected by an 80 mm diameter measuring optic) for continuous wave lasers and 5 milliwatt peak power for repetitive pulsed and scanning lasers that operate in visible wavelengths. The irradiance (beam power density) at any point in the beam does not exceed 2.5 milliwatts per sq.cm. i.e. equivalent to 1 milliwatt over a 7 mm diameter pupil size. Protection for the unaided eye is again afforded by aversion 1. responses, including the blink reflex.

2 Class 3B lasers emit visible radiation at either

3 an output power not exceeding 0.5 watts in the case of continuous wave lasers or in the case of pulsed lasers a radiant exposure of less than 10⁵ Jm~². Direct intra-beam viewing of these class 3B lasers and specular reflections are hazardous. Class 4 lasers are devices with output powers exceeding those of class 3B lasers. In addition to the hazard from intra-beam or specular reflections they are capable of producing hazardous diffuse reflections. They may also present a fire hazard. The risk of such specular or diffuse reflections from the mirrors involved in the system of the present invention can be minimized or avoided because the mirrors are intended to be fixed (and the shrouding aspects afford secure fixings which could be made difficult to tamper with) and any which move can be protected by an interlock on the component itself e.g. if a mirror is moved outside preset limits the laser is switched off, thus providing a fail-safe device. Class 4 lasers if used should be positioned and shrouded in such a way that the risk of diffuse and specular reflections is contained to acceptable levels e.g. by having the laser beam viewed through controlled openings (such that the laser source cannot be seen) , which could be either shrouded or masked or be protected by tinting, bearing in mind the risk this use of the laser is avoiding and such as to minimize the risk of the laser beam itself being a cause of fire. All laser beams used will be provided with beam stops or absorbers which are non-flammable and absorb the wavelength of the laser beam in question. Emissions outside the 400-700 nanometre range are preferably kept to a minimum. Class 2 and class 3A lasers may be used above eye level preferably at high elevations e.g. at least 3 metres above the highest surface on which a person can stand below them, or at lower levels but then desirably are shrouded to prevent direct intra-beam viewing. Class 3B lasers should be mounted and shrouded to prevent intra-beam viewing and also to ensure that the minimum 'distance to which the eye can be brought to observe the beam is at least 5 cms and preferably at least 10 cms. Our earlier case suggested that combinations of different power lasers could be used with smoke density sensors switching into operation the higher power lasers only when smoke density levels reach such values as to attenuate the beam sufficiently to reduce the specular and diffuse reflections to non-hazardous levels. However this is an expensive and complex arrangement; the present invention is far simpler and cheaper and enables exit indications still be provided under a wide variety of smoke conditions. As distinct from discrete light sources a laser beam affords a continuous strip of light which when revealed by smoke can be followed continuously by the escaper. A laser beam can be bent e.g. refracted e.g. by a prism or reflected by a mirror and can thus pass through a curved tunnel or pass round a corner substantially without break. A laser beam can also be split e.g. by a part transmitting/part reflecting mirror or prism. Mirrors with the split between reflection and transmission falling in a wide range of individual values can readily be obtained e.g. a 50/50 split, an 80% reflection/20% transmission or higher reflection level, or to an 80% transmission/20% reflection or higher transmission level as well as intermediate values can all be obtained. Mirrors of this type are obtainable typically from Messrs. Specal Ltd. Laser beams having power ratings 3 milliwatts and 6 milliwatts produced by Gas helium-neon lasers of white colour have been satisfactorily split, 50% transmission/50% reflection, and 80% transmission/20% reflection using special mirrors. These lasers were Scientifia-Cook Ltd lasers models EL-H/3 (3 mWatt (milliwatt)) and EL-H/6 (6 mWatt (milliwatt)) . Another possibility is that the shrouding of the beam may be complete over parts of the route to escape by being conveyed through a wave guide e.g. a fibre optic cable, though such a waveguide should permit light to radiate from it so that its position is apparant and it can also be followed. This could be useful where particularly sharp corners or complex changes in direction are needed and the use of mirrors or prisms and duct type shrouding would intrude objectionably into the passage way. Desirably these waveguide aspects would be used downstream from the primary location being evacuated e.g. an underground station platform since the interaction of the smoke with the beam is a forceful visual warning of the hazard condition. This change in appearance would not occur when the beam is totally enclosed in a waveguide or optical fibre. A disadvantage of waveguides is that they are liable to damage if not encased. Reference to a substantially continuous beam means a beam which extends substantially from the remote location to an exit; it may be made up of a number of sequential lasers but the beginning of the second beam is next to the end of the first beam and so on so that a person following the first beam will immediately be able to locate the second beam and so on to the exit; a continuous beam may have bends or corners in it and may have its intensity reduced along its length by diversion of part of the beam and part of the beam may be located within an optical fibre. The actual length of the escape path can vary widely e.g. from the length of a railway wagon e.g. a channel tunnel wagon up to considerably greater lengths such as in tunnels and underground railway systems as well as subterranean building locations, hotels, conference halls, oil rigs and such environments. Alternatively part of one or more of the laser beam (or beams) may be diverted to illuminate one or more direction signs or indications or mixtures thereof: these can indicate the escape route. Splitter mirrors or prisms may be used to divert just sufficient of the beam to achieve the necessary illumination. Our earlier case contemplated that the system of the earlier case would permit the beam to be shrouded from the eye and only be open to the wall of the space in which the system is located and thus might permit higher power lasers to be used. The earlier case also contemplated that combinations of lower power visible beams and higher power shrouded beams illuminating the wall could be used, and could be operated together or in sequence either the higher or the lower power devices being used when there was less smoke. However our earlier case did not contemplate the bleeding of smoke into an indicator beam duct or shroud in controlled and small amounts so as to achieve visibility of the beam whilst avoiding its extinction or excessive attenuation. In addition our earlier case did not contemplate the first aspect of the present invention. Seidenko failed to appreciate the risk of extinction of the beam and indeed only contemplated the beam being used to create an exit sign within the room from which escape was needed. Moreover Seidenko clearly did not contemplate any problem of extinction of the laser beam. Direction signs and instruction panels which are to be so illuminated are preferably made of highly reflective material or material which luminesces or fluoresces in the particular laser light being used. Clearly a combination of a visible beam and diversion of some of the beam to illuminate signs can also be used. The signs may be such that they are normally invisible and an advantage of this is that it reduces the risk of them being defaced and also concentrates attention on them when there is a hazard situation. Referring again to the first aspect of the present invention, the movement of air in the shroud to the exit may be caused by pumping air from the interior end of the shroud to the exit or preferably sucking air out 1. of the exit to the shroud so as to draw air and smoke

2 if present out through the system. A fresh air supply

3 duct from the exit to the innermost location and for

4 intermediate locations of the shroud could also be

5 provided to enhance such air flow.

6 Preferably the laser beam is provided or

7 established by being switched on in response to

8 detection of fire or smoke anywhere in the system. The

9 switching on of the laser beam may be carried out by 0 automatic means responsive to the detection of fire or 1 smoke in the system or may be switched on by a human or computer controller after an assessment of the severity 3 of the condition detected and its location in the system. The system may be provided with a mimic diagram on which are represented the location of the smoke or fire detectors and the structure of the system e.g. the rooms, passages, corridors, tunnels, hallways, platforms, lifts, escalators etc. and the laser beams. The mimic diagram can be interrogated by a human operator or computer to determine the source and severity of the detected condition and the safest routes to one or more exists from each part of the system and the appropriate laser beams can then be actuated. Such actuation could be under automatic control of computing means running under software control. As mentioned above the laser beam(s) or other laser beams may also be used to illuminate normally invisible direction signs or escape instructions or both. Part of the laser beam or either or both of the laser beams may be diverted e.g. by mirror splitters to illuminate direction signs or instructions. Such signs are preferably holographic or other images which are invisible in incandescent or fluorescent light but visible in laser light and may be such as to luminesce or fluoresce. An advantage of only establishing the laser beam(s) in response to detection of a smoke or fire condition is that the presence of the beam(s) revealed by the smoke (or dust in the air in an underground railway system) acts as an automatic visual alarm signal. • Since it then affords a method for escape it may be anticipated to have a calming effect on the persons using it to escape from the system. The directions and instructions may be positioned adjacent the beam(s) or on a more remote location where more people could see it simultaneously (as might be advantageous in the early stages of an emergency before the smoke had become too thick) . Posters visible in ordinary light advising users of the system about the laser escape route indicator and thus making them aware of it would be also advisable. Pulsed wave lasers could be used to provide directional instructions intrinsically in the beam, the escaper following the direction of the pulse; clearly the pulse speed would have to be slow enough for the direction of the pulse to be visible. Directional instructions to different escape routes could also be given by arranging beam diversion means so that different indications of the direction to be followed could be illuminated at will. Such beam diversion means could be splitter mirrors movable between positions where in one position one direction indicator is illuminated and in another position a different indication of direction is illuminated. The mirrors could be motorized or solenoid driven under appropriate control e.g. from a central controller. A directional "arrow" could also be achieved by setting "beam splitters" in the path of the main beam, first to split the beam(s) in two into opposite directions, which would then be reflected by angled mirrors sending the beam back to its original position where it would then be straightened by two further mirrors or a converging lens so as to reconstitute the laser beam which would then continue undiminished. The invention also extends to the utilisation in the arrangement of a system for imparting directional information to a laser beam which comprises placing beam splitter means in the beam so as to direct a proportion of the beam or the whole of the beam away from the axis thereof, collector means adapted to collect the said diverted laser light and return it back to the axis of the said beam at a location spaced along the beam from the beam splitter and converging means for converging the said returned laser light and directing it along the axis of the laser beam. The beam splitter could be a first mirror transmitting a proportion of the beam (e.g. 50%) and reflecting the remainder to one side of the axis of the original beam where a fully reflecting mirror reflects the beam back to a converging lens positioned at the axis of the beam, and a second mirror reflecting the remainder of the beam to the other side of the axis of the original beam where another fully reflecting mirror reflects the beam back to the converging lens, the 1. converging lens being such as to converge the reflected

2 laser light into a beam parallel to the original laser

3 beam. The direction to be followed could also be indicated by having pairs of lasers set up in opposing positions, so that the end point or beam stopper can be perceived as the direction to be followed; one or other of the pairs of beams would be switched on thus indicating the direction to be followed. This would be particularly useful with a pulsed laser. The laser or one or both of the lasers in a pair could have a continuous beam or a pulsed beam or one could be with a continuous beam and the other with a pulsed beam. We now turn to specific consideration of the use of the system in an underground railway system. Each platform would have a double laser beam array, each beam being shrouded, one shroud housing an early-warning-beam and one shroud housing an indicator-beam, depending from the roof of the platform about midway across its width and extending substantially its full length. The beams would be split and part diverted down each exit e.g. by use of beam splitting and fully reflecting mirrors. If there were a number of exits, more than one pair of lasers could be used so as to provide a more intense beam for diversion down the exit tunnel. Ideally one pair of laser beams would be provided for each tunnel so that each beam could be diverted unattenuated down the tunnel to which it was assigned. Portions of the beams e.g. minor portions e.g. 10 to 30% such as 20% could be diverted to illuminate normally invisible direction 1. signs and instruction panels. Splitter mirrors as

2 described above could be used for this purpose.

3 Direction signs would best be located on the wall of

4 the platform. However as discussed above at least some

5 of the instruction panels might best be located remote

6 from the beam e.g. on the far wall or roof of the tunnel beyond or over the tracks. A feature of the smoke pattern in fires in underground railway systems appears to be that the smoke is more dense at the floor than at the ceiling. Thus having the directional beam and direction indicators and instructions at a high rather than a low level in the tunnel may be advantageous. This is the reverse of what appears to happen in domestic fires. This is thought to be due to the tubular shape of a subway system. The pattern of smoke build up characteristic of the particular system should therefore be born in mind when installing a system in accordance with the present invention. When the system is being installed during the building of an environment or system it may be convenient to sink the shrouds into channels in the walls at about head height or lower. When the system is to be installed in an already existing environment the shrouds can be wall or surface mounted. The use of ducts has the advantage of providing a ready location and mounting for beam deflectors to bend the beam and for beam reflectors and beam splitters. Our earlier case contemplated that the shrouding or ducting would be best apertured to ensure adequate access of the smoke to render the beam visible but that it might also be desirable for one or both upstanding 1. walls of a duct to be transparent or translucent. When

2 higher power lasers such as class 4 or even class 3 are being used transparent duct walls disposed between the beam and the escapers head height may well fulfill a useful safety role for the eyes. Again however our earlier case did not contemplate the use of two shrouds with differential access of smoke to the interior of the shrouds. In certain systems an escape route may have branches connecting it to a number of platforms. The earlier case contemplated that in order to indicate which is a feeder tunnel and which is the escape route, different coloured lasers could be used for the different ranking of tunnels e.g. red for a feeder and green for a main route or having the main route a double or triple beam possibly obtained by splitting the beam or providing a separate extra laser beam running parallel to the original beam. However our earlier case did not contemplate the use of a red laser beam for the early-warning-beam and a green laser for the indicator beam. The present case contemplates that a single laser could be used, be split and have one part of the beam stepped down in wavelength e.g. from 600 nm to 500 n , i.e. from red to green. Any tunnel which is connected to an active exit (i.e. one where air is being drawn out through the ducts) will tend to have an indication of the direction to be followed, imparted to it by smoke being drawn through the duct to the exit. The invention thus extends not only to a method as set out above but also to a system such as an underground railway station provided with means for carrying out the method. The first aspect of the invention also extends to apparatus for indicating an escape route through an environment when the said environment contains smoke, comprising means for generating at least one laser beam and at least one shroud leading to an exit from the said environment, the said shroud being adapted for passage there through of the said beam and within which the beam is visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, and means for causing air and gases within the shroud to more towards the exit. Such means may be an extractor fan located at or adjacent the said exit. Alternatively or in addition one or more fans may be located in the shrouds or adjacent the shrouds along the length thereof from the interior location to the exit. Such fans may be axial flow fans located in the duct e.g. with spaced blades (which can advantageously produce chopping or pulsing of the beam) or may be cross flow fans which are disposed to one side of the beam and do not interfere with it. The motive force for the fans could be mains electricity or local battery supply and the fans could be switched on by the laser beam being switched on. As mentioned above a clean air supply duct can be provided to lead air from the exit to the interior of the shroud. Such a duct could be made as an integral moulding or extrusion with the shroud or could be secured e.g. glued or fastened or mechanically clipped to the shroud. Since it does not have to have any transparent portions it could be made of metal and could provide reinforcement for the shroud. Indeed it could constitute a means by which the shroud could readily be secured to the wall or roof of the location. The metal duct could also carry control and power and other cables and serve as a mounting for such items as beam splitters, benders etc., and fan motors and fans. The invention in its second aspect extends to apparatus for indicating an escape route through an environment when the said environment contains smoke, comprising means for generating at least two laser beams and shrouds leading to an exit from the said environment, the said shrouds being adapted for passage there through of the said beams and within which the beams are visible at least intermittently, the said shrouds having smoke ingress means affording ingress of the said smoke into the said shrouds, there being at least two shrouds of which the ingress means afford differing degrees of ingress of smoke into the said shrouds. The invention also extends to apparatus for indicating an escape route from a location via one or more passages to one or more exits, the apparatus comprising laser means mounted in the said location so as to provide at least two, preferably substantially continuous, shrouded laser beams extending between a location and an exit via one or more passageways, beam stopping means for the end of each laser beam one shroud enclosing an early-warning-beam and being provided with apertures to give ready access of smoke to the interior of the said shroud, and another shroud 1. enclosing an indicator-beam and being provided with

2 apertures to give only restricted access of smoke to

3 the interior of the said shroud and means for directing

4 the laser beams between the location and an exit

5 therefrom and thence along a passageway or passageways

6 connecting the exit from the location to the exit from

7 the system, and means for directing the laser beams

8 along the said passageway or passageways between the

9 exit to the location and an exit from the system. 0 Seidenko refers solely to a laser being energised 1 "so as to emit a laser beam in the direction in which evacuees must escape in case emergency evacuation". Our earlier case was not so limited but only described systems as in Seidenko where the laser was located in the interior of the system from which people would wish to escape. The inventor has now perceived that this increases the risk that the fire could interfere with operation of the laser or its activation. He has now realised that outward indication of the escape route can readily be given even if the laser beam is directed inwardly from the exit to the system or its vicinity. Such outward indication can be given by the laser beam illuminating signs pointing in the correct outwardly disposed direction, or by the shroud having signs imparting an outward directional sense, or by the induction of outward flow of air gases and smoke in the shroud, or by a combination of any two or more of these expedients. Thus according to a third aspect of the present invention a method of providing an indication of an escape route from a system having one or more enclosed 1. locations and one or more routes to one or more exits

2 from the system which method comprises providing a beam

3 of laser light along a route between at least one of the locations and at least one of the exits when a smoke condition exists in the said system, the laser beam providing an indication of the escape route, the said beam being located in a shroud within which the beam is visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, the laser beam or beams being directed inwardly from one or more of the exits to the system or the vicinity thereof, or from a location intermediate the ends of the route. This third aspect of the invention also extends to apparatus for indicating an escape route through an environment when the said environment contains smoke, comprising means for generating at least one laser beam and at least one shroud extending between an exit from the said environment and an interior location of the said environment, the said shroud being adapted for passage there through of the said beam and within which the beam is visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, and laser means located at or in the vicinity of an exit from the said environment or at a location intermediate an exit and the said interior location and disposed to direct their beams inwardly into the said environment. In one form of the second aspect of the invention the shroud affording the greater degree of ingress of smoke, which will be referred to as the early-warning-beam shroud, has an outlet for smoke to the shroud affording the lesser degree of ingress of smoke, which will be referred to as the indicator-beam shroud. The outlet from the early-warning-beam shroud preferably affords the sole or substantially the sole ingress of smoke to the indicator-beam shroud. The early-warning-beam shroud and the indicator- beam shroud may conveniently share a common wall. The outlet from the early-warning-beam shroud, which will be called the restriction hole is preferably located in the said common wall. The early-warning-beam shroud preferably has a multiplicity of access holes distributed along its length or has a slot affording said access extending along its length or along substantial portions thereof. The shrouding may be made up of modules having regions of substantially constant cross-section. Preferably in the regions of substantially constant cross-section, the access ratio (as defined herein) is greater than the restriction ratio (as defined herein) . The ratio of the access ratio to the restriction ratio is preferably in the range 10:1 to 200:1. The access ratio is desirably in the range 1:1 to 1:300. The restriction ratio is desirably in the range 1:100 to 1:1000. The indicator-beam shroud is preferably located above the early-warning-beam shroud. The indicator-beam shroud may contain two beams. It will be appreciated that the beam could be directed either outwardly from the location to the exit or inwardly from the exit to the location and different directions of the beams could be used for different parts of the route; all that is necessary is that substantially continuous beams be established extending between the location and the exit. Whilst the invention has been described with reference to evacuation from a location it will be appreciated that any one located in one of the passageways will be able to pick up the escape route. Detection of the correct direction to follow along the beam is also provided for as described above. All parts of the system are desirably provided with route indicating means in accordance with the present invention and may be led to a single escape route via feeder beams as described above or could be led to a different escape route. When more than one escape route is provided in a system these are preferably differentiated so that if one escape route becomes blocked or dangerous escapers can be directed to the or one of the other routes. In addition to the system and apparatus aspects of the present invention it also extends to novel shrouding means preferably provided with means for mounting the various elements of the system and to the metal air duct means affording a support for the shroud or shrouds to an assembly of the shrouding with the elements mounted thereon and the duct with the shrouding and elements mounted thereon and to a kit of parts of the shrouding and individual elements, and the ducting, the shrouding and the individual elements. The apparatus preferably includes one or more means for directing laser light onto one or more direction indicators, pictograms or instructions for escape which preferably are invisible in incandescent or fluorescent light. The means for directing laser light onto the indicators, pictograms or instructions preferably comprise means for diverting a proportion of the said substantially continuous laser beam onto the said indicators or instructions whilst permitting the rest of the beam to continue. The apparatus desirably includes smoke or fire or temperature detector means and means responsive to detection of an alarm condition in the system for establishing the said laser beams. The shrouding means conveniently may carry mounting means for the beam diverting means or the beam bending or reflecting or absorbing means or for the laser means or for the smoke, fire or temperature detection means, or means for mounting the shrouding in the system or for connecting such mounting means to the shrouding or any combination thereof. Conveniently the shrouding means has mounted on it the laser or lasers and beam stops for each beam, beam diverting means, and beam bending means, e.g. which may diffract or reflect the beam. Apart from the safety and differentiating aspects of the shrouding it also provides a very convenient and rapid way of aligning the components of the system and a very adaptable way of mounting the whole assembly in the system e.g. in an underground railway station, (which is enhanced when the metal ducting is also

used) . When elements of the system such as beam diverters are to be movable under remote control the shrouding or ducting can also provide a mounting for the drive means e.g. a motor or solenoid and furthermore for the power supply and control wires therefor. Indeed the shrouding or ducting also provides a ready route and mounting means for the power and control cables or the lasers involved in the system and for smoke, fire or temperature detectors associated with the system even if they^'are not actually mounted on the shrouding or ducting. The shrouding or ducting could also carry cabling for loudspeakers whereby audio instructions could be given as well as for microphones or telephones which could assist in the detection of survivors or the reporting of an alarm condition to a central control location (which could itself be remote from the system actually being protected) . The shrouding or ducting could also carry such loudspeakers or microphones. It could carry telephones at locations where the shrouding or ducting was at head height or there abouts or lower. The invention may be put into practice in various ways and a number of specific embodiments as applied to an underground railway station and to a channel tunnel wagon will be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-section of a platform in an underground railway system; Figure 2 is a diagrammatic longitudinal section on the line II-II of Figure 1 of part of the platform shown in Figure 1 showing an end exit tunnel and a side exit tunnel; Figure 3 is a diagrammatic perspective view of an underground railway station showing one of several platforms, and various exit tunnels; Figure 4A is a side elevation of a first dual shroud embodiment of the present invention; Figure 4B is a cross-section on the line IVA-IVA of Figure 4A; Figure 4C is a plan view on the line IVC-IVC of Figure 4A; Figure 5A is a side elevation of a second dual shroud embodiment of the present invention; Figure 5B is a cross-section on the line VB-VB of Figure 5; Figure 6A is a side elevation of a third dual shroud embodiment of the present invention; Figure 6B is a cross-section on the line VIB-VIB of Figure 6A; Figure 7A is a side elevation of a fourth dual shroud embod iment o f the pre s ent i nvent i on incorporating an enlarged viewing window or panel ; Figure 7B is a cross-section on the line VIIB-VIIB of Figure 7A; Figure 8A is a side elevation of a fifth dual shroud embodiment of the present invention; Figure 8 B is a cross-section on the l ine VIIIB-VIIIB of Figure 8A; Figure 9A is a side elevation of a sixth dual shroud embodiment of the present invention; Figure 9B is a side elevation on the line IXB-IXB of Figure 9A; Figure 9C is a plan view on the line IXC-IXC of Figure 9A; 1. Figure 9D is a plan view on the line IXD-IXD of

2 Figure 9B;

3 Figure 10A is a side elevation of a modified window format for use in the embodiment of Figure 9A; Figure 10B is a cross-section of the arrangement shown in Figure 10A; Figure IOC is a cross-section of a modified version of Figure 9B; Figure 11 is a plan view on the line XI-XI of an alternative arrangement to that shown in Figure 9D; Figure 12 is a similar view to that of Figure 11 of a modified beam corrector for use in the embodiment of Figure 9A; Figure 13 is a diagrammatic side elevation of a split beam power source with a wavelength alternator for supplying the early warning beam and the indicator beam to any one of the dual shroud arrangements shown in Figures 4 to 9; Figure 14 is a view similar to Figure 13 of a modified power source providing a split beam; Figure 15A is a side elevation of the laser cradle shown in Figures 13 and 14, this figure shows both a single laser cradle and a dual laser cradle; Figure 15B is a plan view of the laser cradle shown in Figure 15A; Figure 15C is a typical section of the dual laser cradle shown in Figure 15A showing the juxtaposition of the cradle to the shrouding with which it will be used; Figure 16A shows a beam collector array 1600 in part cross-section for collecting a laser beam from a shroud and conveying it to a fibre optic cable; Figure 16B shows a beam emitter array 1650 in part cross-section for emitting a laser beam from the end of a fibre optic cable e.g. supplied from the array shown in Figure 16A; Figure 17 shows in cross-section an elbow design for reflecting the laser beams around a bend; Figure 18A shows in cross-section how the dual shrouded array of the present invention could be mounted in a railway carriage; Figure 18B shows in cross-section how the invention could be mounted in a double height long vehicle -or wagon e.g. a channel tunnel vehicle carrying wagon; Figure 18C shows in side elevation how the invention could be disposed along a vehicle wall to avoid doors and windows; Figure 19A shows a modified form of shrouding which could be disposed over each of the shrouds or over both shrouds; and Figure 19B shows a modified form of such shroud built into the lining of the vehicle with the duct configuration and smoke access not shown. Figure 20 is a diagrammatic side elevation of an arrangement embodying both the first, second and third aspects of the invention, namely air is drawn through the shrouding, two shrouds are provided with restricted access from the first, the early warning beam shrouding, to the second, the indicator beam shrouding, and the laser beam is directed into the system from the exit thereto or the vicinity thereof. Figures 1 to 3 are general diagrammatic views showing how the present invention (which is described in detail for various embodiments in Figures 4A to 19B) may be located in a hypothetical large and complex underground, subway or metro train station. Figure 1 shows one end of a platform PI, with a train tunnel TT and a platform exit PE1 leading to a tunnel Tl. Mounted on the end wall of the platform is a laser LI positioned to direct its beam 20 (see Figure 2) along the platform generally parallel to the wall. It will be appreciated that whilst this embodiment utilises a laser directing its beam outwardly through the system an arrangement in which the laser was located -a one exit, or there was a laser at each exit (i.e. EXITS 1, 2 and 3) directing its beam inwardly to the platform PI or each platform is equally practicable and has operational, maintenance and safety advantages. The platform here is shown as being straight; when the platform is curved, the beam will be made up of a number of arcs created by bending the beam an appropriate extent by suitable beam bending means (e.g. a prism or mirror) in a series of straight interconnecting lines following the curve. High and low level smoke detectors 21 and 22 are secured to the wall of the platform. These are set to detect a predetermined smoke density and to send a signal to a central controller (not shown) . Alternatively they may directly activate the laser LI. The laser LI may be provided with power from a central location or have a local standby e.g. battery driven power supply and may be under central or local control as by the smoke detectors. The laser beam 20 is split just after emerging from the laser LI by a beam splitting mirror 30 which allows a major part of the beam to be transmitted while reflecting the remainder downwards to a 100% reflecting mirror 31 which reflects the beam along the roof of the exit tunnel PEL The diminished beam 23 now continues to a motorized beam splitting mirror 40 which allows a high percentage e.g. 90% to pass and directs the remainder e.g. 10% down onto the wall onto one or other of two direction signs e.g. arrows 41 and 42. These are invisible in incandescent or fluorescent light but become strongly visible in laser light. They may be holographic or be such as to luminesce or fluoresce. With the mirror in one position the arrow 41 will be illuminated directing escapers to the tunnel PE1, with the mirror in the other direction escapers will be directed in the other direction. The beam is, in the second aspect of the present invention, made up of two beams, an early-warning-beam and an indicator beam. The early-warning-beam is preferably afforded by a red laser. It is housed in an early warning beam shroud provided with smoke access means e.g. apertures which provide ready access of smoke to the interior of the early-warning-beam shroud. The indicator-beam is housed in an indicator-beam shroud located on the early-warning-beam shroud and provided with smoke access means from the interior of the early-warning-beam shroud which give only restricted access of smoke to its interior. Preferred arrangements are described in detail below. The further diminished beams 24 now continue to a stationary beam splitting mirror 50 which allows a high percentage e.g. 90% to pass and directs the remainder e.g. 10% across the tunnel to the far wall beyond the tracks onto a panel 43 (see Figure 1) giving instructions about the escape route and the direction indicating system. This panel or the letters are again invisible in incandescent or fluorescent light, or, if visible so as to instruct users prior to an alarm condition, are rendered of increased visibility in laser light. They may be holographic or be such as to luminesce or fluoresce. The diminished beams 25 now continue to a beam splitting mirror 60 which allows part of the beams to be transmitted while reflecting the remainder downwards to a 100% reflecting mirror 61 which reflects the beam along the roof of the side exit tunnel PE2. The further diminished beams 26 now continue along the platform and are used to illuminate direction signs and instructions as well as such other exit tunnels as may emerge from the platform. (Figure 3 shows four such tunnels but for simplicity we will discuss the arrangement of Figure 2 as if only the two exit tunnels shown are provided.) Assuming that it is desirable that the intensity of the beams used to indicate the entrance to a tunnel is the same for each tunnel it will be necessary to divert a higher % of the beam at the mirror 60 than was necessary at the mirror 30. The appropriate % transmission and % reflection at each mirror will depend on the dimensions of the platform and the number of exits and the number of directions and instructions it is wished to illuminate. The laser LI on the platform being positioned high up can be of high power; lower power lasers (if unshrouded) can be used in the tunnels to carry the substantially continuous laser light beams on through the tunnels to the exit and illuminate direction indications from time to time. Such additional beams may be in parallel with the original beams or those beams may be stopped with beam stops and the additional beams carry on in replacement of the original beams. It will be appreciated that a combination of inwardly directed laser beams and outwardly directed laser beams can be used. Thus the laser LI could be used on the platform and inwardly directed beams could be used to provide the directional indication from the exits PE1, 2, 3 and 4 from the platform to the exits 1, 2 and 3 from the system. Returning to Figure 2 the beams 26 can be used to illuminate further direction indicators but since we have made the assumption that PE1 and PE2 are the only exits from the platform PI such further arrows would be in the sense of arrow 41 directing escapers on the platform back to the exit PE2 or PEL Turning now to Figure 3 the platform PI is provided with exits PE1 and PE4 at the ends of the platform and PE2 and PE3 as side exits. PE4 links directly to an exit 3 via a tunnel T4 and is the only platform in the station provided with such a direct emergency exit. PE1 links directly via a tunnel Tl to a main concourse tunnel T7 from which the normal entrance and exit is via an exit TE7, a tunnel T8 and a tunnel exit TE8 to an escalator hall EH from which access to the main exit 1 is via an escalator El. The concourse tunnel T7 is provided with an exit TE9 to a tunnel T9 which leads directly to an emergency exit 2. The concourse tunnel T7 also has exits TE5 and TE6 which lead via tunnels T5 and T6 to other parts of the station e.g. other platforms. The concourse tunnel T7 is also fed by exit TE2 to a tunnel T2 and TE3 to a tunnel T3. However tunnels T2 and T3 each branch. T2 branches into one branch T2A leading to platform PI by the exit PE2 and the other branch T2B leads to another part of the station e.g. a platform parallel to PL T3 branches similarly into T3A and T3B; T3A connects via exit PE3 to PI and T3B connects to the same platform as T2B. Each of the tunnels Tl to T9, each of the platforms and EH and El are provided with the means to establish substantially continuous laser beams therein and these beams link up to form a substantially continuous network leading to the exits. Preferably the laser beams in tunnels T8, . T9 and T4 can be separately switched on and off independently of each other and the remainder of the system whilst the beams on each platform and its exit tunnels are separately controllable. As a fail safe whilst the beams on the platforms have the function of indicating the location of the exits and the beams in the tunnels Tl, T2, T3, T5 and T6 are also separately controllable, it may be desirable for the platform beams to be taken at least as far as T7 even if added to by additional beams in these tunnels. When the invention is being used in its third aspect with the laser beam being directed inwardly, laser beams originating in T7 and directed inwardly to each platform may conveniently be utilised. Systems in which a single beam is used along the 1. whole length of the escape route clearly have maximum

2 simplicity and integrity, though reinforcement of such

3 a single beam with contingrous or co-axial additional

4 beams can also be beneficial.

5 These various beams may be under a central

6 controller so that particular beams can be switched off

7 to prevent escapers being lead to the seat of the fire.

8 However the escapers may themselves be able to

9 sense approach to, particularly if a fan assisted 0 shroud (see below) is used, the seat of the fire and it 1 may be better to maintain the route indications on at all times. This is a matter for experimentation on the 3 use of the invention in a particular environment. Possible use of the system will now be described in various scenarios. 6 Scenario 1: Assume a fire in El. The beams in T8 could be switched off or motorized beam splitters used to indicate arrows pointing towards T7. TE7 could be provided with a motorized beam splitter to illuminate a "danger no entry sign" (as could all exits TE1-TE9 and PE1-PE4) . Escape could then be via TE9 to EXIT 2. Scenario 2: The fire in El has burnt along T8 and is emerging from TE7. Escapers in T2, T5 and T6 could go back to PI and escape via PE4 and T4 or less advisedly via PE3, T3A, T3, TE3, TE9 and T9 to Exit 2. Scenario 3: Assume a fire between TE7 and TE9. Escapers from Tl, T2 and T6 could escape via TE7 and T8 and EH to exit 1. Escapers from T3B or T2B or T3 could escape via PI and T4 or less advisedly via T2 or Tl and TE7 etc. In scenarios 2 and 3 appropriate "no entry" signs at the relevant tunnel exit or platform exits would be illuminated and the direction arrows in the tunnels would be reversed to direct escapers away from the seat of the fire. We have mentioned the desirability of differentiating a main escape route from feeder tunnels. In Figure 3 T2, T3 and T7 are main escape tunnels whilst T2A, T2B, T3 , T3B, T5 and T6 are feeder tunnels. Tl and T4 and T9 are also main escape tunnels. The main escape tunnels should preferably have double pairs of beams whilst the feeder tunnels have a single pair of beams. It will be understood that these scenarios are merely illustrative and the logic to be used in any given environment will need individual development. We will now describe the specific structures of shrouded dual or double beam arrangements mentioned above which are illustrated in Figures 4A to 19B of the accompanying drawings. Figures 4 to 12 describe six dual shroud embodiments and two modifications to the sixth embodiment. It should be emphasised that the relative frequency and relative sizes of the windows in the shrouds can vary and the two shrouds do not have to have the same number of windows nor do the windows have to be the same size. Figures 4A, B and C illustrate the first embodiment. Referring to Figure 4A, the side elevation, this has an upper row of windows 401 and a lower row of windows 402 which are housed in super-imposed housings 411 and 412 shown more clearly 1. in Figure 4B in cross-section. Periodically along the

2 run of the upper housing 411 there will be provided

3 sealed units 450 provided to facilitate directional

4 indications. As shown in Figure 4B this unit can be

5 hinged out around a hinge 451 located at the front

6 bottom edge of the upper housing 411. This unit has

7 cleanable end windows 452 and two beam splitting

8 mirrors 454 and 455 mounted one above the other and at

9 90° to each other and at 45° to the longitudinal axis 0 of the shroud or housing. 1 The front window 460 of this sealed unit may be in the form of a hologram window and may have a single or 3 dual layered structure. The hologram in the window can be backlit, or side lit, by bleeding light from the main beam by means of the splitting mirrors 454 and 455 or be lit by general spillage. One mirror will illuminate an upper directional arrow 461 and the lower mirror will illuminate a lower directional arrow 462 which is orientated in the opposite direction. As can be seen in Figure 4B the upper housing 411 contains a pair of green lasers 465 and 466 positioned along the axis of the housing and spaced one above the other so as to impinge on the mirrors 454 and 455 respectively. The lower housing 412 contains a red laser, the early warning laser 467. The laser 467 is again positioned along the axis of the lower shroud 412 and opposite the windows 402. The axes of the lasers 465., 466 and 467 in Figure 4A are shown by the discontinuous lines 465, 466 and 467. The width of the housing is determined by the number and frequency of the correcting lenses which are needed to be placed in line along the beams and this depends upon the length of the run which is to be provided by each individual laser. Access of smoke to the shrouding in this arrangement is provided initially via a series of spaced apart holes 470 which are provided one per window along the run, thus each window 402 is associated with a hole 470. The area of the hole 470 is about 1.8 sq. units and it supplies smoke to a volume of about 19 cubic units per individual hole. Figure 4A has a small scrap section at the bottom below one of the windows 402 showing the location of the hole 470 and illustrating diagrammatically the region associated with that particular window which can be thought of as the volume being supplied by the individual hole 470. This hypothetical volume is defined by the lines 471 and 472. It can be seen that the hole 470 is of a diameter of about 1.5 units and the volume 469 which it is supplying, is of a height of about 2.4 units, a depth of about 2.3 units and a length of about 3.4 units, i.e. a volume of about 19 cubic units. The area of the hole 470 is about 1.8 square units. This ratio of inlet area to volume supplied will be called the access ratio and here it is seen as being 1.8:19 or 1:10.5. The ready access of smoke to the shroud 412 provides early warning of a smoke condition. As the smoke condition intensifies the red laser in the shroud 412 may become extinguished or severely attenuated. This is when the indicator beams in the shroud 411 come into play. The shroud 411 is provided with only restricted access for smoke so that only in severe smoke conditions would it become particularly apparent but nonetheless even under severe smoke conditions it will not become significantly attenuated. This restricted smoke access is provided by a hole 480 located in a wall common to the housings 411 and 412 which will be called the partition wall. The hole 480 may be referred to as the throttle or restriction hole. The function of the restriction hole 480 is to meter or bleed smoke from the space 469 inside the early warning shroud to the space 483 inside the indicator shroud when the external smoke conditions are increasing or becoming severe such that the early warning beam is extinguished or liable to become so. The objective is that the indicator beam should become visible before the early warning beam is extinguished. Smoke can diffuse through a hole into an otherwise enclosed space whether the space is above, below or to one side of the hole. As described below with reference to Figure 20 it could also be induced or assisted when fans are used. However if more rapid access is desired one may provide finer bleed or egress aperture 482 (not shown) from the space 483. This egress hole might be in the top of the shroud or near the top of the side walls or could be another hole in the partition wall 481, thus providing for convection circulation of smoke through the indicator beam housing and back into the lower early-warning-beam housing. The throttle hole 480 is smaller, preferably much smaller than the access hole 470. Each of the embodiments of Figures 4 to 12 described below can be provided with egress holes 482, 582, 682, 782, 882 or 982 respectively if desired. The area of the restriction hole 480 as shown in Figure 4B is 0.07 square units, its diameter being 0.3 units. It feeds a volume 3.8 units high, 2.4 units deep and 3.4 units wide i.e. 28 cubic units in volume. The throttle or restriction ratio, the ratio of the area of the restriction hole 480 to the volume of the space 483 being provided with smoke by each restriction hole 480, is thus 0.07:28 i.e. 1:400. The particular access ratios and restriction ratios required for a particular location will depend largely upon the anticipated smoke conditions and upon the power of the lasers which will be used. Simple experimentation will enable appropriate ratios to be chosen for particular environments and equipment. However the first aspect of the present invention is beneficial in that it can ensure that even bleeding of smoke from the early warning beam along into the indicator beam housing occurs. Thus the movement of air through the shrouds is preferably only through the indicator beam shroud. Thus this has little access of air along its route and lower power will be needed to move air through it than would be the case if air was drawn through the early warning beam shroud. Drawing air through the indicator beam shroud may also remove the need for the egress holes 482, 582, 682, 782, 882 and 982. In another alternative these holes could be used as a source of fresh air from a supply manifold. They could also be used as a means of flushing air through the system to clean it after a fire. Turning now to Figures 5A and B similar reference numerals will be used for similar parts, the only difference being that the first digit will change from a four to a five. The main difference from the Figure 4 embodiment in this second embodiment is that the early warning beam is placed above the indicator beams and that instead of individual holes 470 being provided for each window 402, a continuous slot affords the ingress aperture for the early warning beam, this slot being referenced 520. The slot is throttled within the structure so that the functional part of the slot 521 indicated by the arrows in Figure 5B is of lesser width than the slot 520. It will be seen that this slot 521 is about 0.4 units wide. The spacing between the windows is again defined by the hypothetical lines 571, 572 and in this arrangement they are about 3.5 units apart. The area of the slot per volume is accordingly 0.4 x 3.5 or 1.4 square units. The volume of the space 569 being supplied with smoke via the slot 521 can be considered as being made up of three separate volumes taken from the window side to the rear in turn as being 0.5 X 2.0 X 3.5 = 3.5 cubic units, 0.5 X 3 X 3.5 = 5.25 cubic units and 1.3 x 3.3 x 3.5 = 15 cubic units, i.e. 23.75 cubic units in all. Accordingly the access ratio is 1.4 to 23.75 or 1:17. The slot 520 may be screened by an optional grill 522. Access to the indicator beam shroud 511 is via a restriction hole 580 located in a partition wall 581. The front portion of this partition wall 581 namely 584, is inclined downwardly slightly to accommodate the upwardly inclined access slot 520. The total volume of the space 583 ignoring the triangular region removed by the inclined partition wall 584 is 34.6 cubic units. The restriction hole 580 has an area of 0.07 square units and the ratio between this area and the volume of 34.6 is 1:490. If the volume is taken as 30 cubic units the ratio falls to 1:425. Again it may be desirable to provide an egress hole 582 in the compartment 511. Also it might be preferred to invert the structure and provide the access slot along the bottom edge of the compartment 512. Figures 6A and 6B again are similar in arrangement to the arrangement shown in Figure 4 and again like reference numerals will be used except that the first digit will be a six instead of a four. The differences from Figures 4 and 5 are that spaces 669 and 683 are largely circular in cross-section and a single directional green laser 665 is used. However dual green lasers could be used as in the Figure 4 and Figure 5 arrangements. Figures 7A and 7B have like reference numerals for their components to those shown in Figure 4. The shape of the shrouds is slightly different both having rounded ends or tops and bottoms respectively for the indicator shroud 711 and the early warning shroud 712. The volumes of the spaces 769 for the early warning beam and the space 783 for the indicator beam are the same. The relative dimensions of the access aperture 770 and the restriction hole 780 are the same in the Figure 7 arrangement as in the Figure 4 arrangement. The diameter of the hole 770 is 1.5 units and the diameter of the hole 780 is 0.3 units. The volumes of the spaces 769 and 783 are 27 cubic units. The access ratio accordingly is 1.75:27 or 1:15. The restriction 1. ratio (the area of the hole 780 to the volume of the

2 space 783) is 0.07:27 or 1:385.

3 This ratio overall will in fact be considerably

4 higher due to the extra volume provided by the

5 modification to the indicator beam shroud which occurs

6 periodically at the region 791 when it is wished to

7 provide an enlarged indicator window 790 which can

8 provide substantially more information and could

9 provide a message. The lines 771 and 772 are intended 0 in fact to refer to regions of the system away from the 1 protrusion 791. Figures 8A and 8B again are similar in arrangement 3 to the arrangement shown in Figure 4 and again like reference numerals will be used except that the first digit will be an eight instead of a four. The differences from Figures 4 and 5 are that spaces 869 and 883 are part circular in cross-section and a single directional green laser 865 is used. However dual green lasers could be used as in the Figure 4 and Figure 5 arrangements. The dual shroud arrangement is shown nested into a channel 830 e.g. in a wall. One of the row of windows 801 is modified as 863 to afford or be a directional sign. The access hole 470 of Figure 4 is replaced by a slot 870 similar to the slot 520 in Figure 5 and is provided with an optional screen 822 again as in Figure 5. The slot 820 extends inwardly into the shroud 812 and its functional slot is defined by the line 821 in Figure 8B. The volume of the early warning shroud is thus that inwardly of the line 821. This access slot 1_. is 2.3 units deep by 3.5 units long i.e. it has an area

2 of 8 sq. units. The volume of the area 869 is 2.7 high

3 x 3.2 deep x 3.5 wide i.e. 30 cubic units. The access

4 ratio is accordingly 8:30 or 1:3.75. The volume of the space 883 can be thought of as being made up in three parts a rectangular lower part 1.7 high x 3.2 deep x 3.5 long = 19 cubic units a square front upper part 1.5 high x 1.6 deep x 3.5 long = 8.4 cubic units and a rear upper 4 cylinder part of 1.5 cubic units i.e. a volume of 28.9 cubic units. The area of the hole 880 is 0.07 sq. units i.e. the restriction ratio is 0.07:28.9 or 1:410. Figures 9A, B, C and 'D have like reference numerals for their components to those shown in Figure 4. The shape of the shrouds is the same as that for Figure 7A and B both having rounded ends or tops and bottoms respectively for the indicator shroud 911 and the early warning shroud 912. The volumes of the space 969 for the early warning beam and the space 983 for the indicator beam are the same. The access aperture 970 is however different in shape, being a round cornered rectangular shape as shown in Figure 9C. In addition there are two such access apertures 970 per window 901. The area of each aperture is 1.0 x 2.5 or 2.5 sq. units (disregarding the areas of rounding) . The volume of the space 969 is the same as 769 and is 27 cubic units; thus the access ratio is 5:27 or 1:5.4. The restriction ratio i.e. area of hole 980 to the volume 983 is the same as in Figure 7 namely 1:385. The apertures 970 can be provided with a mesh screen 922. Figure 9D has a sealed unit 950 similar to the unit 450 with end windows 952 and inclined mirrors 954, 955 though for clarity of presentation only one is shown. In this arrangement the arrows 961 and 962 are superimposed rather than being vertically spaced. The unit has a front window 960 provided in the same way as the window 460. In addition the unit 950 can be provided with beam steering prisms 941 and 942 as required. Similarly in each arrangement of Figures 4, 5, 6, 7 and 8 the sealed unit can be of the form shown with reference to 450 or 950. Figure 10A shows a modified form of sealed unit or node 990 having a double width for bifurcation of the beam. The sealed units can be hinged at 951 as shown in Figure 10B or can be snap-out units. Figure 10C shows a modified version of Figure 9B in which the windows 901 have inner and outer layers or coatings 903 and 904, which may be photoluminescent. Figure 11 shows a modified version of Figure 9D with a different form of sealed unit 995. However it still has end windows 952 and a pair of mirrors 954 and 955. Figure 12 shows an optical or mirror beam corrector. In all these various embodiments, the shroud construction can conveniently be metal e.g. extruded aluminium with windows provided in it which can be filled by a window material e.g. polycarbonate, or can be an extruded fire retardant polycarbonate having opaque masked areas alternating with clear windows. When an aluminium extrusion is used an external layer of polycarbonate could be provided to afford the windows or it could be an internal lining. In each of the arrangements the interior faces of the shrouds could be provided with an electro or photo luminescent lining as indicated at 792 and 793 in Figure 7. The access ratios (AR) , and restriction ratios (RR) in Figures 4-9 above are given in Table 1 below.

Table 1 Figure AR RR AR:RR 4 1:10.5 or 0.095 1:400 or 0.0025 38:1 5 1:17 or 0.059 1:425 0.0023 26:1 or 1:490 0.0020 30:1 6 7 1:15 or 0.067 1:385 or 0.0026 26:1 8 1:3.75 or 0.27 1:410 or 0.0024 113:1 9 1:5.4 or 0.19 1:385 or 0.0026 73:1

i.e. the AR values are in the range 1:3.75 to 1:17 and the RR values are in the range 1:385 to 1:490. More broadly the AR is preferably 1:1 to 1:300 more preferably 1:2 to 1:100 especially 1:3 to 1:50. The RR is preferably 1:100 to 1:1000 more preferably 1:200 to 1:800 especially 1:300 to 1:600. The access ratio will be observed to be larger than the restriction ratio; i.e. 1:10.5 being larger than 1:400. The ratio between AR and RR is preferably in the range 25:1 to 115:1, or more broadly 10:1 to 1. 200:1.

2 Referring now to Figure 13 the laser housing has

3 an outer housing 1300 conforming in cross-section to

4 the shrouding with which it will be used. It is

5 provided with a securable connecting lip 1301 to which

6 the shroud e.g. 711/712 can be connected by screws

7 1302. The housing has end windows 1305, 1306 through

8 which the laser beams pass into the shroud spaces 769

9 and 783. The housing has internal bosses 1310 to which 0 a standby battery 1315 can be connected by screws 1311. 1 The housing also has bosses 1317 by which a laser cradle 1500 can be connected by screws 1318. The laser 1550 is mounted in the cradle 1500 and adjustment of its position can be carried out by a roll micrometer 1501 mounted between the laser and the cradle. The housing is surrounded by an appropriate heat shield 1320. The housing and heat shield have an aperture 1321 by which connections can be made from the devices inside the housing e.g. the laser, standby battery etc. to the exterior e.g. to sensing and control devices e.g. computer, mimic diagram and control panel. The output beam 1330 from the laser is split by an appropriate mirror 1335 into an upper and lower beam 1336 and 1337. The beam passes 1336 passes through an optical device 1340 effective to alter the wavelength and thus into the space 783. The beam 1337 impinges on a beam steering mechanism 1345 and passes into the space 769. If a red laser (wavelength 600 nm) is used the device 1340 can reduce its wavelength to 500 nm producing a green beam. The arrangement in Figure 14 is the same as Figure 13 except that the device 1340 is omitted. Thus both beams are of the same wavelength or colour, preferably green. Like parts have the same reference numerals but start fourteen rather than thirteen. Referring now to Figures 15A, B and C these show the cradle 1500 for the laser; Figure 15A showing a single cradle array (the top structure) and dual cradle array (both structures) . Each cradle has end frames 1505 and 1506 spaced apart by longitudinally extending bars 1507, 1508 and 1509, the lower bar 1507 being fixed. The bars 1507, 1508 and 1509 have mounted on them between the end frames, circular clamps 1515 and 1516, provided with adjusting screws (not shown) . Each clamp 1515 may be provided with a roll micrometer 1501 whose output head 1502 bears on the output end 1551 of the laser 1550 so that fine adjustments of the alignment of the laser in the cradle can be made. Figure 15B is a plan view on the line XVB-XVB of Figure 18C. The laser 1550 is shown in chain lines. Figure 15C shows a round cross-section laser mounted in the top cradle and a square cross-section laser in the bottom cradle. Mention has been made above that in certain parts of a system in accordance with the invention the beam may need to be conveyed by fibre optic cable past obstacles or reflected round bends. Figures 16A and B give details of suitable fibre optic arrays and Figure 17 gives details of an elbow design suitable for reflecting the laser beams through sharp angles e.g. of 90°. Referring now to Figure 16A the beam collector array 1600 has a housing made up of three parts 1601, 1602 and 1603 connected together by screw threads, mating "clip-on" configurations or screws passing through the walls into bosses. At the lower end of the array, the input end, beam steering prisms (not shown) may be provided to gather the beams together. The beams are then fed into a laser fibre illuminator collector head 1605. This device is of conventional construction and has an attenuator knob 1606. The device also has a focus adjustment 1607. The head 1605 is mounted in an adjustable mounting post 1610 located inside the housing part 1601. The head feeds the beam into a flexible fibre optic cable 1615 which is preferably an armour clad cabled fibre. The cable then passes out through a slot or hole (not shown) in the end wall 1616 of the housing part 1603. The cable can then pass by the obstacle to the beam emitter array 1650 shown in Figure 16B. This again has a housing in three parts 1653, 1652 and 1651. The cable 1615 enters the end wall 1666 of the housing part 1653 via a hole 1667. The cable then passes into an output piece 1670 from the end 1671 of which the output beam emerges. The output piece 1670 is mounted in an adjustable mounting post 1660 located inside the housing part 1651. The part 1651 also has an access port 1661. The housing part 1653 has a portion 1654 which is coaxial with the rest of the housing and an angled end piece 1655 which extends away therefrom at an angle. Figure 17 shows an elbow piece 1700 having two arms 1701 and 1702 disposed at right angles. The arm 1702 is provided with conforming structures enabling it to mate with and be reliably secured to the end of a run of shrouding 1705. The arm 1701 and the shrouding 1705 have windows 1710 formed in their front faces. The juncture of the arms 1701 and 1702 at the rear has an inclined mounting surface disposed at 45° to the axes of the arms. This affords a base for an adjustable precision gimbal mirror mount or a beam steering mount (neither of which are shown) . Adjusting screw locations 1715, 1716 are also provided for fine adjustment of this base or the devices mounted thereon. Mention has also been made above of the use of the invention in relatively restricted spaces such as channel tunnel wagons or railway cars. Figures 18A, B and C show appropriate locations for the dual beam dual shroud arrangement of the present invention in railway vehicles (Figures 18A and 18C) and a channel tunnel wagon or other double decked vehicles e.g. vehicle ferries (Figure 18B) . In Figure 18A the locations are in the ceiling 1801 or at waist or chest height 1802. Figure 18C shows how a waist height alignment could be deflected over a door using beam benders at 1803 and 1804 (e.g. as shown in Figure 17) . Figure 19A shows an indicia containing form of outer shroud 1900 which could be located over a transparent dual shroud dual beam arrangement of the present invention either one such outer shroud 1900 for each enclosed beam space e.g. 469 and 483 or one large outer shroud 1900 with the apertures 1901, 1902 of such dimensions as to overlap both spaces 469 and 483 simultaneously. The apertures 1901 have a directional content. Figure 19B shows a similar type of outer shroud 1910, with similar apertures 1911 and 1912, built into the lining of a vehicle body. It again may constitute an outer cover for the dual shroud dual beam array of the present invention and obviously must not prevent access of smoke to the space 469. Figure 20 is a diagrammatic side elevation of an arrangement embodying both the first, second and third aspects of the invention, namely air is drawn through the shrouding, two shrouds are provided with restricted access from the first, the early warning beams shrouding, to the second, the indicator beam shrouding, and the laser beam is directed into the system from the exit thereto or the vicinity thereof. Reference numerals are as for figure 4 but begins '20^» rather than •_.•. Figure 20 shows a double shroud arrangement having a lower early warning shroud 2012 and a superposed upper indicator shroud 2011 extending between a source of fire 2010 and smoke 2013, and an exit 2014. A fan 2015 is connected to the exit end of the shroud 2011 and vents exhaust air to a vent 2017. A green laser 2050 is disposed opposite the end of the shroud 2011 at the exit and its beam 2065 travels down the space 2083. The beam from the laser 2015 passes a beam splitter 2016 and part is diverted down to a mirror 2017 (or prism) which reduces its wavelength to produce a red beam 2067 which travels down the space 2069. If the reducer is not used the beam will be green. Air and smoke is drawn through the shroud 2011 by the fan 2014 and contains smoke 2013 from the fire 2010 which enters the space 2069 inside the shroud 2012 through the access holes 2070 and is then drawn via the restriction holes 2080 into the space 2083 in the shroud 2011. The beams are visible, due to the smoke particles, over the distance 2051 from the exit to the vicinity of the fire and the risk of extinction of the beams only occurs near the fire. The drawing of smoke through the shroud 2011 gives an early warning of approach to the fire because the smoke will show up in the shroud at some distance from the fire. One can thus turn back and retrace one's steps before entering regions of dangerous smoke levels. Rescue workers can don breathing apparatus as soon as they see smoke in the shrouds. Clearly experimentation will be needed to balance the air flow of the fan to the shroud capacity and the sizes of the restriction holes. Use of a clean air supply duct of controllable supply capacity may also facilitate maintenance of a visible laser beam in the shroud over a wide range of smoke conditions. Optical sensors could be installed in the shrouds to give feedback signals to modify air flow so as to maintain visibility of the beam.

Claims

L A method of providing an indication of an escape route from a system having one or more enclosed locations and one or more routes to one or more exits from the system which method comprises providing at least one beam of laser light along a route between at least one of the locations and at least one of the exits when a smoke condition exists in the said system, the laser beam providing an indication of the escape route, the said beam being located in a shroud within which the beam is visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, and causing the air and gases within the shroud to move towards an exit.

2. A method of providing an indication of an escape route from a system having one or more enclosed locations and one or more routes to one or more exits from the system which method comprises providing at least one beam of laser light along a route between at least one of the locations and at least one of the exits when a smoke condition exists in the said system, the laser beam providing an indication of the escape route, the said beam being located in a shroud within which the beams are visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, the laser beam or beams being directed inwardly from one or more of the exits to the system or the vicinity thereof or from a location intermediate the ends of the route.

3. A method of providing an indication of an escape route from a system having one or more enclosed locations and one or more routes to one or more exits from the system which method comprises providing at least two beams of laser light along a route between at least one of the locations and at least one of the exits when a smoke condition exists in the said system, the laser beams providing an indication of the escape route, the said beams being located in shrouds within which the beams are visible at least intermittently, the said shrouds having smoke ingress means a fording ingress of the said smoke into the said shrouds, there being at least two shrouds of which the ingress means afford differing degrees of ingress of smoke into the said shrouds.

4. A method as claimed in any one of Claims 1 to 3 in which the colour of the beam in the shroud which affords a greater degree of ingress of smoke is such as to signify a warning or alarm e.g. red, orange or yellow and the colour of the other beam or beams is different, e.g. green or blue.

5. Apparatus for indicating an escape route through an environment when the said environment contains smoke, comprising means for generating at least one laser beam and at least one shroud leading to an exit from the said environment, the said shroud being adapted for passage there through of the said beam and within which the beam is visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, and means for causing air or gases within the shroud to move towards the exit.

6. Apparatus for indicating an escape route through an environment when the said environment contains smoke, comprising means for generating at least two laser beams and shrouds leading to an exit from the said environment, the said shrouds being adapted for passage there through of the said beams and within which the beams are visible at least intermittently, the said shrouds having smoke ingress means affording ingress of the said smoke into the said shrouds, there being at least two shrouds of which the ingress means afford differing degrees of ingress of smoke into the said shrouds.

7. Apparatus for indicating an escape route through an environment when the said environment contains smoke, comprising means for generating at least one laser beam and at least one shroud extending between an exit from the said environment and an interior location of the said environment, the said shroud being adapted for passage there through of the said beam and within which the beam is visible at least intermittently, the said shroud having smoke ingress means affording ingress of the said smoke into the said shroud, and laser means located at or in the vicinity of an exit from the said environment or at a location intermediate an exit and the said interior location and disposed to direct their beams inwardly into the said environment.

8. Apparatus for indicating an escape route from ^~ a location via one or more passages to one or more exits which comprises, means for providing at least two laser beams mounted in the said location so as to provide two or more substantially continuous laser beams extending between a location and an exit via one or more passageways, beam stopping means for the end of each pair of laser beams and means for directing a pair of laser beams from within the location to an exit therefrom and thence to a passageway or passageways connecting the exit from the location to the exit from the system, and means for directing the pair of laser beams or a further pair of laser beams between the said location along the said passageway or passageways and an exit from the system, shrouds being provided along which the said beams pass and within which the beams are visible at least intermittently, the said shrouds having smoke ingress means affording ingress of the said smoke into the said shrouds, there being at least two shrouds of which the ingress means afford differing degrees of ingress of smoke into the said shrouds.

9. Apparatus as claimed in any one of Claims 5 to 8 in which the shrouding is made up of modules having regions of substantially constant cross-section.

10. Apparatus as claimed in Claim 9 in which in the regions of substantially constant cross-section, the access ratio (as defined herein) is greater than the restriction ratio (as defined herein) .

11. Apparatus as claimed in Claim 10 in which the ratio of the access ratio to the restriction ratio is in the range 10:1 to 200:1.

12. Apparatus as claimed in Claim 9, 10 or 11 in which the access ratio is in the range 1:1 to 1:300.

13. Apparatus as claimed in Claim 9, 10, 11 or 12 in which the restriction ratio is in the range 1:100 to 1:1000.

14. Shroud means as claimed in any one of Claims 5 to 13.

15. A kit of parts consisting of shroud means as claimed in Claim 14 and one or more of laser means, laser stop means, beam diverting means, beam bending means, and direction signs or instruction sets which are rendered visible by laser light.