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Title:
IMPROVEMENTS RELATING TO THE PROTECTION OF BUILDINGS
Document Type and Number:
WIPO Patent Application WO/2002/066749
Kind Code:
A1
Abstract:
A system for use in protecting buildings from the ingress of subterranean gases by preventing a flow of gas from a gas-containing region to an adjacent region comprises a gas impermeable barrier (10) installed so as to separate the gas-containing region and the adjacent region and provide at least one void between them; a pump (23) communicates with the void for pumping gas into it to create a pressure differential between the void and the gas-containing region, and special valves (29) are provided in flow communication with the void for opening the void to the surrounding atmosphere if the void pressure generated by the pump (23) falls below a minimum value, the valves (29) being installed in such way that air currents in the atmosphere which create a pressure differential between respective open ends thereof ventilate the void when open to the atmosphere.

Inventors:
NICHOLS PAUL IAN (GB)
Application Number:
PCT/GB2002/000635
Publication Date:
August 29, 2002
Filing Date:
February 13, 2002
Export Citation:
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Assignee:
PRESTIGE AIR TECHNOLOGY LTD (GB)
NICHOLS PAUL IAN (GB)
International Classes:
A01M1/24; E02D31/00; (IPC1-7): E02D31/00; E04B1/72
Foreign References:
US5489462A1996-02-06
GB2261002A1993-05-05
US4938124A1990-07-03
AU7403274A1976-04-08
US5197862A1993-03-30
US5003750A1991-04-02
US6065901A2000-05-23
EP0784723A11997-07-23
Attorney, Agent or Firm:
Bryer, Kenneth Robert (7 Gay Street Bath BA1 2PH, GB)
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Claims:
CLAIMS
1. A system for use in protecting buildings from the ingress of subterranean gases by preventing a flow of gas from a gascontaining region to an adjacent region; the said system comprising: a gas impermeable barrier installed so as to separate the said gas containing region and the said adjacent region and provide at least one void between the said two regions ; pumping means communicating with the said at least one void for pumping gas into the said at least one void to create a pressure differential between the said at least one void and the said gascontaining region; characterised in that; first and second valve means are provided in flow communication with the said at least one void for opening the said at least one void to the surrounding atmosphere in response to the void pressure generated by the said pumping means being below a minimum value, the said first and second valve means being installed with respect to each other such that air currents in the atmosphere (that create a pressure differential between respective open ends thereof) ventilate the said at least one void when open to the atmosphere.
2. A system as claimed in Claim 1 wherein the said first valve means comprises a first inlet section connected to the said pumping means, a second inlet section connected to the said respective open end of the said first valve means and an exit section connected for communicating the said respective air or gas flow from the respective first or second inlet section to the said at least one void.
3. A system as claimed in Claim 2 wherein the said first valve means comprises a bifurcated duct in which the said first inlet section is provided by a first duct sector and the said second inlet and exit sections are provide by a second duct sector, the said first duct sector converging with the said second duct in the downstream direction of the said pumping means, the said first duct section having a smaller effective flow diameter than the said second duct section such that the discharge flow from the said pumping means is diffused as it enters the said second duct section, thereby to minimise leakage of the pumping means discharge flow to the said second inlet section and to vent the said at least one void to the atmosphere via the said second inlet section when the discharge flow is removed.
4. A system as claimed in Claim 1 wherein said second valve means comprises an inflatable seal member for closing the said valve means in response to pressurisation of the said seal member.
5. A system as claimed in Claim 4 wherein said inflatable seal member is pressurised by the said pumping means and deflates on removal of the pressurised flow from the said pumping means.
6. A system as claimed in Claim 1 wherein the first and second valve means are installed such that their respective open ends face in substantially different directions.
7. A system as claimed in Claim 6 wherein the respective open ends of the said two valve means face in substantially opposite directions.
8. A system as claimed in Claim 1 wherein the first and second valve means are installed such that their respective open ends are installed in a vent trench or riser pipe.
9. A system according to any preceding claim wherein the said gas impermeable barrier comprises a sheet like material having a plurality of upstanding projections spaced apart with respect to each other such that the region between the projections defines the said at least one void.
10. A system as claimed in Claim 9 wherein the said projections are formed as hollow embossments on one side of the said barrier.
11. A system as claimed in any preceding Claim wherein the said gas impermeable barrier is laid horizontally under a building, and gas distribution means are provided for delivering gas discharge pressure from the said pumping means to create localised pressure differential regions at a plurality of points in the said at least one void over at least a major part of the area of the said barrier.
12. A system as claimed in any preceding Claim wherein the said gas impermeable barrier is laid horizontally under a building, and the said second valve means is connected in flow communication with a manifold means extending along at least part of at least one side of the said area for venting the said at least one void.
13. A system as claimed in Claim 11 or Claim 12 wherein the said barrier further comprises a layer of concrete in the said sheet like material.
14. A method of preventing the flow of gas from a gascontaining region to an adjacent region; the said method comprising the steps: installing a gas impermeable barrier between the said gas containing region and the said adjacent region to separate the two regions and provide at least one void between the two regions; pumping gas into the said at least one void to create a pressure differential between the said at least one void and the said gascontaining region; characterised in that; connecting first and second valve means in flow communication with the said at least one void for opening the said at least one void to the surrounding atmosphere in response to the void pressure being below a minimum value, the said first and second valve means being installed with respect to each other such that air currents in the atmosphere that create a pressure differential between respective open ends thereof ventilate the said at least one void when open to the atmosphere.
15. A system for use in protecting buildings from the ingress of subterranean gases by preventing the flow of gas from a gascontaining region to an adjacent region; the said system comprising: a barrier installed between the said gas containing region and the said adjacent region, so as to separate the two regions ; a layer of cast material cast on the side of the said barrier facing the said adjacent region, the cast material forming a gas impermeable composite layer with the said barrier; characterised in that a plurality of upstanding hollow projections are provided on the said barrier, the said projections defining a respective plurality of cavities on the side of the barrier facing the said adjacent region and at least one void in the region between the said projections on the opposite side thereof, the said layer being formed such that the said cavities contain cast material integral with the said layer and thereby support the said cast layer with respect to the said gascontaining region.
16. A system as claimed in Claim 15 wherein the said gas impermeable layer is laid horizontally under a building.
17. A system as claimed in Claim 15 or 16 wherein the said barrier is laid directly on the ground below the building.
18. A system as claimed in any one of Claims 15 to 17 wherein the said projections are arranged in a generally regular pattern on the said barrier.
19. A system as claimed in any one of Claims 15 to 18 wherein the said projections taper towards the base of the said cavities.
20. A system as claimed in any one of Claims 15 to 19 wherein the said cast material is concrete.
21. A system as claimed in any one of Claims 15 to 20 wherein means are provided for venting the said at least one void to the atmosphere.
22. A system as claimed in Claim 22 wherein the said means for venting comprise a natural ventilation or forced ventilation means.
23. A method for protecting buildings from the ingress of subterranean gases by preventing the flow of gas from a gascontaining region to an adjacent region; the said method comprising the steps: installing a gas impermeable barrier to separate the said gas containing region and the said adjacent region, casting a layer of material on the side of the said barrier facing the said adjacent region, characterised in that, the barrier comprises a plurality of upstanding hollow projections defining a plurality of cavities on the side of the barrier facing the said adjacent region and at least one void in the region between the said projections on the opposite side thereof, and the said layer being cast such that the said cavities contain cast material integral with the said layer and thereby support the said layer with respect to the said gascontaining region.
24. A method of protecting buildings from the ingress of subterranean gases by preventing the flow of gas from a gascontaining region to an adjacent region; the said method comprising the steps of : installing a gas impermeable barrier between the said gascontaining region and the said adjacent region to separate the two regions and provide at least one void between the two regions; and creating a pressure differential between the said at least one void and the said gascontaining region ; characterised in that the pressure differential is created by a passive ventilation system of ducts communicating with the atmosphere in such a way that air movements in the atmosphere create a pressure differential between the said at least one void and the gascontaining region; monitoring the said at least one void for the presence of the said subterranean gases in the said void, and providing a forced flow of air to the said at least one void if the concentration of the said subterranean gases therein exceeds a predetermined threshold value.
25. A method as claimed in Claim 24, characterised in that the step of providing a forced flow of air includes installing one or more motor driven fans subsequent to the installation of the gas impermeable barrier if the monitoring step reveals that the concentration of the said subterranean gases exceeds the said threshold value.
26. A system for protecting buildings from attack by agencies such as termites or fungi, in which a void is formed between the building and the said adjacent region, a ventilation system of ducts communicating between the said void and the atmosphere, the duct outlets to the atmosphere being formed such that air movements in the atmosphere create a pressure differential between the void and the atmosphere, nature means for closing the communication between the ducts and the atmosphere, and means for introducing a treatment material into the void.
27. A system according to Claim 26, characterised in that a gasimpermeable barrier forms one wall of the sand void.
28. A system according to Claim 26 or Claim 27 characterised in that the said means for introducing a treatment material comprises a pump for delivering a treatment gas.
29. A method of protecting buildings from attack by agencies such as termites or fungi comprising the steps of creating a void space between the building and an adjacent region from which the attack is expected, installing a duct system for communication between the void space and the atmosphere, the inlets and/or outlets to and/or from the duct systems being formed such that air movements in the atmosphere create a pressure differential between the void space and the atmosphere, the duct system having valve means operable to close communication between the void space and the atmosphere, the method comprising periodically closing the said valve means and introducing a treatment material into the void space, allowing the treatment material to permeate the said void space, and after a suitable delay to allow the treatment material to take effect, opening the said valve means to allow the void space to be ventilated.
30. A method according to Claim 29, characterised in that the treatment material is a gas or an airborne powder or vapour, and the step of introducing the treatment material is effected by pumping it into the void space as or after the said valve means are closed.
Description:
IMPROVEMENTS RELATING TO THE PROTECTION OF BUILDINGS

The present invention relates to the protection of buildings, particularly by dispersal of gases permeating large volumes of material, and in particular (but not exclusively) the protection of buildings from harmful or inflammable gases permeating the ground in general. The present invention also relates to the protection of buildings against attack by degrading agents such as termites or fungi.

As technology improves and more advanced testing is carried out, there is an increasing awareness that the ground around us may be permeated by gases such as radon or hydrocarbons which are injurious to health or may cause an explosion if allowed to concentrate in enclosed volumes, such as buildings. Such gases may be naturally occurring or produced for example by reactions in landfill sites.

Particularly in the latter case, there is a need to ensure, before the sites are commissioned, that measures are taken to prevent the gases from escaping into the surrounding terrain.

One measure which is currently used to prevent the spread and accumulation of underground gases is to dig a trench along a selected boundary of the contaminated ground, to line the side of the trench opposite the contaminated ground with gas- impermeable sheeting and to fill the trench with loose aggregate to provide a vent.

The intention is that any gases reaching the trench will permeate up through the aggregate and will be dispersed into the atmosphere along its entire length, avoiding any build up in a particular area and preventing the further spread of the gases.

A problem which is found with this arrangement is that trenches tend to silt up over long periods of time to the extent that the aggregate loses its permeability in certain areas and the gases tend to be channelled along defined routes to exit from the trench at discrete locations rather than along its entire surface. Thus, in time, the trench promotes a concentration of gas in the atmosphere at certain locations, exactly the effect that it is intended to stop.

One known system for protecting buildings from the ingress of subterranean gases is described in EP-A-0,784,723 in the name of Prestige Air Technology Ltd. This system comprises a composite barrier which is installed between the gas containing region and an adjacent region which may be on the underside of a building. The barrier comprises a gas-impermeable layer and a gas permeable membrane separated by a plurality of upstanding projections which extend from the impermeable layer and are secured to the permeable membrane to create an interspace region or void between the permeable layer and permeable membrane. The composite barrier is installed with the permeable layer facing the gas containing region and a pumping means in the form of a fan is connected to an aperture in the barrier for pumping gas into the interspace to create a pressure differential across the permeable membrane to cause gas to flow through the membrane and thereby prevent the ingress of harmful subterranean gases in the building.

A problem which is found with the arrangement of EP-A-0,784,723 is that the system will allow harmful gases permeating the ground to enter the building if there is fan failure or a power cut. Although fan failures are a very rare occurrence, power cuts are a real possibility.

A further problem with the system of EP-A-0,784,723 is that the cost of providing an entirely gas-impermeable membrane or layer is prohibitive for most low risk applications.

Natural ventilation systems provide a low cost alternative in situations where a pressurised system such as that disclosed in EP-A-0,784,723 is cost prohibitive.

Natural ventilation systems rely upon the wind to generate air currents to disperse and prevent the build up of gases in cavities formed in the ground below buildings. The problem with natural ventilation systems is that they are entirely dependant upon the strength and to some extent the direction of the wind. Natural ventilation systems are therefore almost always provided with a secondary protection system in the form of a gas-impermeable membrane positioned so as to prevent gases in the cavity entering the building on top of the cavity on days where there is little or no wind.

There is a requirement therefore for a system for use in protecting buildings from the ingress of subterranean gases in the event of a fan failure or temporary power cut.

There is a further requirement to provide a low cost system in which a gas resistant

barrier can be provided for preventing subterranean gas entering enclosed volumes such as buildings without requiring the relatively costly gas-impermeable membrane which was an essential requirement of prior art systems.

According to one aspect of the present invention there is provided a system for use in protecting buildings from the ingress of subterranean gases by preventing a flow of gas from a gas-containing region to an adjacent region; the said system comprising: a gas impermeable barrier installed so as to separate the said gas containing region and the said adjacent region and provide at least one void between the said two regions; pumping means communicating with the said at least one void for pumping gas into the said at least one void to create a pressure differential between the said at least one void and the said gas-containing region; characterised in that; first and second valve means are provided in flow communication with the said at least one void for opening the said at least one void to the surrounding atmosphere in response to the void pressure generated by the said pumping means being below a minimum value, the said first and second valve means being installed with respect to each other such that air currents in the atmosphere that create a pressure differential between respective open ends thereof ventilate the said at least one void when open to the atmosphere.

The above system provides both a closed cell type pressurised system in which pressure is maintained in the void by the pumping means, and also a passively redundant natural ventilation system which responds to the pressure in the void being

less than a predetermined minimum so that in a event of a power cut or failure of the fan the void is ventilated naturally by air currents that enter and exit the void through the respective first and second valve means. In this way the system provides a low cost redundant system as a back up to the primary void pressurisation system. The combination of the pressurisation and natural ventilation systems provides a highly reliable system for protecting buildings from the ingress of subterranean gases. The provision of the first and second valve means readily permits existing void pressurisation systems to be modified to include a secondary natural ventilation system. Since the first and second valve means respond to the void pressure they operate immediately in the event of a fan failure or power cut.

Preferably, the said first valve means comprises a first inlet section connected to the said pumping means, a second inlet section connected to the said respective open end of the said first valve means and an exit section connected for communicating the said respective air or gas flow from the respective first or second inlet section to the said at least one void. This provides a compact valve which readily provides a vent for natural ventilation of the void in event of fan failure or a power cut.

In preferred embodiments the said first valve means comprises a bifurcated duct in which the said first inlet section is provided by a first duct section and the said second inlet and exit sections are provide by a second duct, the said first duct converging with the said second duct in the discharge flow direction of the said pumping means, the said first duct section having a smaller effective flow diameter than the said second duct section such that the discharge flow from the said pumping means is diffused as

it enters the said second duct section, thereby to minimise leakage of the pumping means discharge flow to the said second inlet section and to vent the said at least one void to the atmosphere via the said second inlet section when the discharge flow is removed. In this arrangement the first valve means defines a venturi-valve which prevents a back pressure forming up stream of the bifurcation in the second inlet section and thereby prevents escape of the pressurised gas from the pumping means at the open end of the valve which provides a vent to the atmosphere. This provides a very efficient system in which the pressure generated by the pumping means is fully utilised to pressurise the void. In the event of fan failure or a power cut the valve functions as a vent for the void to the atmosphere along the first duct section. The venturi-valve therefore has two modes of operation in which the operating mode is entirely dependent on the pressure generated by the pumping means such that the valve switches to a second mode of operation to provide a vent to the void immediately the pressure in the first duct section falls below a predetermined minimum value. This value will depend upon the exact geometry of the first and second ducts.

Preferably, said second valve means comprises an inflatable seal member for closing the said valve means in response to pressurisation thereof. This provides a reliable seal at the second valve means.

In preferred embodiments, said inflatable seal member is pressurised by the said pumping means and deflates on removal of the pressurised flow from the pumping means. In this way it is possible to cause the second valve means to open immediately

the discharge pressure of the pumping means is reduced below the predetermined minimum value. In this way the first and second valve means operate to change the operation of the system from that of a void pressurisation system to a natural ventilation system immediately the pressure falls below the predetermined minimum value. Since the system is controlled by the discharge pressure from the pumping means there is not requirement for an active control to switch the valves. This provides a simple and reliable system in which the valves may be switched to provide vents to the void even after prolonged periods of pressurised operation. The system is entirely pneumatic and operation of the valves is directly controlled by the discharge pressure of the pumping means.

In preferred embodiments, the first and second valve means are installed such that their respective open ends face in substantially different directions. In this way the respective open ends of the first and second valve means can be exposed to different air current dynamic pressures when placed in close proximity to one another and exposed to the wind.

Preferably, the respective open ends of the said two valve means face in substantially opposite directions. This can optimise the dynamic pressure differential at the open ends of the first and second valve means so that the air flow through the void is a maximum for the prevailing weather conditions.

In preferred embodiments, the first and second valve means are installed such that their respective open ends are installed in a vent trench or riser pipe. This can

overcome the problem of providing vent ducts having an opening many metres above the ground level of the building.

Preferably, the said gas impermeable barrier comprises a plurality of upstanding projections spaced apart with respect to each other such that the region between the projections defines the said at least one void. This provides for ready installation of the barrier and the void on installation of the system. In this way a continuous void can be provided over many hundreds of square metres if necessary by joining appropriate lengths of adjacent sheets along their edges.

Preferably, the said projections are formed as hollow embossments on one side of the said barrier. This readily allows adjacent sheets to be joined in an overlapping relationship along their edges by nesting of the projections along the edges of the adjacent sheets.

In preferred embodiments, the said gas impermeable barrier is laid horizontally under a building, and gas distribution means are provided for delivering gas discharge pressure from the said pumping means to create localised pressure differential regions at a plurality of points in the said at least one void over at least a major part of the area of the said barrier. This provides for an even distribution of gas pressure from the pumping means over the area of the barrier so that a positive pressure differential is maintained at all points on the area of the barrier under the building.

In preferred embodiments, the said gas impermeable barrier is laid horizontally under

a building, and the said second valve means is connected in flow communication with a manifold means extending along at least part of at least one side of the said area for venting the said at least one void. The manifold readily enables the air flowing through the void during periods of natural ventilation operation to enter or exit the void via the second valve means at a plurality of points along one or more sides of the void so that harmful gases are not able to build up in any region of the void.

Preferably, the said barrier is over laid with concrete. This improves the gas resistant properties of the barrier and readily enables the barrier to be sealed with respect to building foundation piles and other foundation structures and the periphery of the void so formed.

According to another aspect of the invention there is provided a method of preventing the flow of gas from a gas-containing region to an adjacent region; the said method comprising the steps: installing a gas impermeable barrier between the said gas containing region and the said adjacent region to separate the two regions and provide at least one void between the two regions; pumping gas into the said at least one void to create a pressure differential between the said at least one void and the said gas- containing region; characterised in that; connecting first and second valve means in flow communication with the said at least one void for opening the said at least one void to the surrounding atmosphere in response to the void pressure being below a minimum value, the said first and second valve means being installed with respect to each other such that air currents in the atmosphere that create a pressure differential between respective open ends thereof ventilate the said at least one void when open

to the atmosphere.

According to a further aspect to the invention there is provided a system for use in protecting buildings from the ingress of subterranean gases by preventing the flow of gas from a gas-containing region to an adjacent region ; the said system comprising : a gas impermeable barrier installed so as to separate the said gas containing region and the said adjacent region, a layer of cast material laid on the side of the said barrier facing the said adjacent region, characterised in that a plurality of upstanding hollow projections are provided on the said barrier, the said projections defining a plurality of cavities on the side of the barrier facing the said adjacent region and at least one void in the region between the said projections on the opposite side thereof, the said layer being formed such that the said cavities contain cast material integral with the said layer and thereby support the said layer with respect to the said gas-containing region.

The system readily enables a void to be formed on one side of a gas impermeable layer between the impermeable layer and the gas containing region. This can avoid the problem of providing an entirely gas impermeable membrane on the side of the void adjacent to the region to be protected from the ingress of subterranean gases.

The layer of cast material can be cast in-situ on the side of the barrier to seal the barrier with respect to the void on the other side thereof. By casting the layer of cast material on the side of the barrier facing the adjacent region the cavities are filled with the cast material to provide a reinforced gas impermeable composite layer with

intimate connections between the barrier and cast material at the cavities. The cavities also support the cast material with respect to the gas containing region and provide a load bearing support in the region of the void between the cast layer and the gas containing region. The composite layer can be readily formed and at significantly lower cost than conventional systems using a gas impermeable membrane.

Preferably, the said gas impermeable barrier is laid horizontally under a building. In this way the gas impermeable layer can be installed as part of or with the foundations of a building during construction with the load bearing cavities supporting at least a portion of the foundations of the building.

In preferred embodiments, the said barrier is laid directly on the ground below the building. In this way very little preparation of the ground is required. The ground may be compacted by conventional compacting apparatus before the barrier is laid on the ground to prevent sinking of the cast layer when formed.

Preferably, the said projections are arranged in a generally regular pattern on the said barrier. This allows adjacent sheets to be readily joined along their edges in an overlapping relationship by engagement of the projections on one sheet of the barrier with respective cavities on an adjacent sheet and on their respective edges.

In preferred embodiments, the said projections taper towards the base of the said cavities. This can improve the joint between adjacent sheets and also enables sheets of barrier material to be stacked in a nested configuration for ease of storage and

transportation before installation. In addition the tapered projections enable the barrier material to be moulded more readily.

Preferably, the cast material is concrete. This readily enables the impermeable composite layer to support the weight of a building or similar structure by providing a load bearing platform in contact with the ground at the ends of the projections.

In preferred embodiments, means are provided for venting the said at least one void to the atmosphere. In this way any subterranean gases emanating from the gas containing region and entering the void can be readily vented to the atmosphere to prevent the build up of harmful and dangerous gases.

In preferred embodiments, the means of venting comprise a natural ventilation and/or a forced ventilation means. In this way the ventilation system may have a dual mode of operation so that the void may be vented naturally in the event of malfunction of the forced ventilation means.

In preferred embodiments means are provided for pressurising the said at least one void to create a pressure differential between the said void and the gas-containing region. In this way it is possible to prevent harmful and/or dangerous gases entering the void.

According to a further aspect to the invention there is provided a method for protecting buildings from the ingress of subterranean gases by preventing the flow of

gas from a gas-containing region to an adjacent region; the said method comprising the steps: installing a gas impermeable barrier to separate the said gas containing region and the said adjacent region, and casting a layer of material on the side of the said barrier facing the said adjacent region, characterised in that, the barrier comprises a plurality of upstanding hollow projections defining a plurality of cavities on the side of the barrier facing the said adjacent region and at least one void in the region between the said projections on the opposite side thereof, and the said layer being cast such that the said cavities contain cast material integral with the said layer and thereby support the said layer with respect to the said gas-containing region.

The present invention also comprehends a method of protecting buildings from the ingress of subterranean gases by preventing the flow of gas from a gas-containing region to an adjacent region; the said method comprising the steps of installing a gas impermeable barrier between the said gas-containing region and the said adjacent region to separate the two regions and provide at least one void between the two regions; and creating a pressure differential between the said at least one void and the said gas-containing region; characterised in that the pressure differential is created by a passive ventilation system of ducts communicating with the atmosphere in such a way that air movements in the atmosphere create a pressure differential between the said at least one void and the gas-containing region ; monitoring the said at least one void for the presence of the said subterranean gases in the said void; and providing a forced flow of air to the said at least one void if the concentration of the said subterranean gases therein exceeds a predetermined threshold value.

In the performance of this method the step of providing a forced flow of air may include installing one or more motor driven fans subsequent to the installation of the gas impermeable barrier if the monitoring step reveals that the concentration of the said subterranean gases exceeds the said threshold value.

The present invention also provides means and a method for protecting buildings against attack by other agencies such as termites or fungi.

Various embodiments of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic cut away perspective view of a barrier for use in a system of an arrangement of the invention, Figure 2 is a schematic perspective view of an embodiment of a system according to the invention, installed to prevent seepage of gas from the ground into a building; Figure 3 is a schematic sectional view of a valve for use in a system shown in Figure 2; Figure 4 is a sectional view of a further valve for use in the system shown in Figure 2; Figure 5 is a schematic cut away perspective view of an alternative form of barrier; Figure 6 is a sectional view of part of a floor of a building and the ground on which it is built incorporating a modified barrier in accordance with another embodiment of the invention;

Figure 7 is a schematic sectional view of another embodiment of the invention; and Figure 8 is an enlarged view of a detail of Figure 7.

With reference to Figure 1, a barrier for use in a system according to the invention is shown generally indicated 10. The barrier 10 is constituted by two layers, a gas-and water-impermeable sheet 11 and a gas-permeable non-woven textile membrane 12.

The sheet 11 is made from a flat sheet of polyethylene which is press-moulded such as to have a regular array of spaced projections 13 upstanding from one face 14 thereof. The projections 13 are generally cylindrical but with a slight taper for ease of moulding and with substantially flat, coplanar tops 15 parallel to the face 14. The projections 13 are spaced apart by distances slightly greater than their diameters.

They are shown arranged in a rectangular lattice array, that is, in mutually perpendicular lines and rows, but could be in any array, whether regular or irregular, provided that there are substantial, interconnecting air spaces between them, which together constitute an interspace 16.

The membrane 12 comprises a mat of nylon fibres which is adhered to the flat tops 15 of the projections 13 so as to define the interspace 16 between the membrane 12, the face 14 of the sheet 11 and the projections 13.

The barrier 10 is formed as a panel which may be manufactured individually or cut

from a larger sheet. Before use, it may be sealed around its entire periphery or along parts thereof. Apertures may be left or formed at the periphery and/or centrally of the panel for connection to appropriate pumping equipment for pumping air into or out from the interspace 16.

With reference to Figure 2 of the drawings, this shows a building 20 located over a region of ground 21 contaminated by harmful gas such as methane or radon. A barrier such as the barrier 10 of Figure 1 has been laid over the entire ground area covered by the building 20 beneath the floor slab 22 of the building. The barrier 10 is laid with the permeable membrane 12 being on its underside. A plurality of diffusers 22 are connected to apertures (not shown) in the impermeable sheet 11 at spaced locations and connected to pumping equipment 23 by a network of ducts 24. In use, the pumping equipment 23 which may comprise a fan of suitable pressure ratio, delivers air under pressure to each inlet aperture through the diffusers 22 from where it spreads readily through the void region 16 and permeates out through the membrane 12 into the contaminated ground 21. This active flow of gas together with the presence of the impermeable sheet 11, prevents the contaminated gas from rising up into the building 30. In this way the gas flow is deflected along the underside of the permeable membrane to the ground 25 outside the building. The extent to which the air spreads from each inlet diffuser 22 through the void to achieve a delivery through the membrane 12 in to the ground 21 is indicated by the circles of dash lines 26 around each diffuser 22.

In addition to the air pressure delivery ducts 24 two further ducts 27 and 28 are

provided which extend substantially along opposite sides of the base of the building.

The ducts 27 and 28 are connected to a series of apertures (not shown) in the impermeable sheet 11 at spaced locations along the length of the ducts. The ducts 27 and 28 are L shape and emerge in the ground at the side of the building 25 where they terminate at a respective valve 29 connected to a respective venting duct 30. The venting ducts 30 can be located in respective venting trenches in the ground at the side of the building 25 for dispersal of gases collected from the region underneath the building as will be described. In an alternative arrangement the venting ducts are provided by riser pipes which extend above the roof level of the building to disperse the vented gases in the atmosphere. In both arrangements the venting ducts vent the collected gases to the atmosphere.

The ducts 24 are connected to the pumping equipment 23 by means of a main manifold duct 31 which has an open end 32 in the region outside the building. The end 32 of the manifold may be located in a venting trench in the region 25 at the side of the building or may be provided at the end of a riser duct also at the side of the building.

The pumping equipment 23 is connected to the manifold 31 by means of a branch duct 33 as can best be seen in Figure 3. The branch duct has a smaller diameter than the main manifold 31 and typically has a diameter of 50mm and the manifold has a diameter of 100mm. The branch duct joins the manifold 31 at a relatively shallow angle indicated 34 so that high pressure discharge flow from the pumping equipment 23 enters the manifold 31 in the direction indicated by arrows 35. A guide vane 36 is

provided in the region of the junction of the branch 33 with the manifold to assist the turning of the fan discharge flow into the manifold 31. In use, the effect of the fan discharge flow entering the larger diameter manifold at the junction of the branch duct causes a venturi effect which prevents a back pressure being developed in the manifold duct 31 downstream from the junction as indicated at 36. This prevents leakage of the fan discharge flow in the direction indicated by arrow 37 to the atmospheric vent at the end of the manifold at 32. Entrapment of air in the region 36 of the manifold pipe will occur due to the venturi effect but if necessary this can be minimised by optimising the delivery pressure of the flow.

With reference to Figure 4, in the region outside the outside the building 25 the valves 29 are located between the ducts 27 and 28 and the respective vent ducts 30. The valves 29 comprise a cavity 40 within a valve housing 41 and contained within the cavity 40 there is an inflatable seal 42 which is made of a gas impermeable material.

The seal 42 is provided with an aperture 43 for inflation of the seal by means of high pressure air entering the seal from a duct 44 which is connected at one end to the aperture 43 and the other to either the pumping means 23 or a point on the manifold 31 or duct network 24 for maintaining a supply of high pressure air from the pumping means 23. When inflated the seal 42 closes the valve 29 so that no gas can flow between the vent duct 30 and the manifold ducts 27,28. An inspection cover 45 is provided at the top of the casing 41 so that the condition of the valve 49 can be inspected periodically by removal of the cover 45.

In use, pressure from the pumping equipment 23 maintains the seal at the valves 29

and therefore seals the void region from the atmosphere. In the event that the pumping equipment fails or fails to deliver pressure above a predetermined minimum pressure the seals 42 deflate so that the void under the building is vented naturally by the ventilation ducts 30 on each side of the building. In this situation the venturi effect at the junction of the main manifold 31 and the branch duct 30 no longer occurs and the main manifold also provides a vent for the void to the atmosphere. Depending on the wind direction at the time of such a failure air will enter one of the venting ducts 30, pass through the void region on the underside of the building and exit the void via the venting duct 30 on the other side of the building. The vent 32 at the end of the main manifold will act either as an entry point or exit point for air currents generated by the wind depending on the wind direction. By positioning the vents on opposite sides of the building only moderate wind speeds will be required to generate a pressure differential sufficient to cause an air flow through the void and remove any harmful gases that have accumulated due to the loss of pressurisation. The same effect may of course be provided by positioning the ends of the respective vents 30 and 32 with respect to one another so that they face in different directions so that the dynamic pressure due to the wind acting on at least one of the vents will be greater than the dynamic pressure due to the wind acting on at least one other of the vents.

With reference to Figure 5 in an alternative embodiment of the invention the barrier 10 of Figure 1 has been modified by removal of the membrane 12 so that the sheet 11 constitutes the barrier.

As best seen in Figure 6 the barrier sheet 11 is laid generally horizontally over the

contaminated ground 21 which has been compacted to prevent sinkage of the building on that ground. The barrier sheet 11 is overlaid with a layer of concrete 50 which may comprise the slab foundation of the building located over the region of ground 21. The concrete is cast in situ on top of the barrier sheet 11 so that the hollow protrusions 13 are filled with concrete to form an integral load bearing structure in which the barrier 11 is joined to the concrete layer 50 over its upper surface (to the top of the drawing of Figure 6). The void 16 is formed on the underside of the barrier sheet 11 in the same way as in the arrangement of Figure 1 but in this case the sheet 11 is in direct contact with the ground 21 along the co-planar surfaces 15 of the projections. The composite layer formed above the void by the sheet 11 and cast concrete layer 50 provides both a gas impermeable layer for preventing ingress of subterranean gases into the building above the impermeable layer since any gaps or pores in the barrier 11 will be filled by the concrete matrix material when laid over the barrier sheet 11.

Although the invention has been described with reference to the embodiments shown in the accompanying drawings it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications may be affected without exercise further inventive skill. For example, in the embodiment of Figures 5 and 6 the barrier sheet 11 may be laid directly on the ground 21 or on a geo-textile sheet if desired. In addition in the embodiment shown in Figure 3 it is to be understood that only two vents to the atmosphere are required in order to create a pressure differential across the void under the building but it may be desirable to provide more than this if desired. For example, three vents are shown in the

embodiment of Figure 3 although a single vent in addition to the vent provided by the main manifold 31 would be sufficient to generate a pressure differential to create a flow of air in the void region.

The present invention may also be put into practice another way. That is, rather than providing for natural ventilation to back up a forced flow of air it is possible to provide a system initially designed to operate with a natural flow of air by locating suitable ventilation outlets and inlets around the protected building, but also to include underground pipework to which fans can be connected to provide a forced flow positive pressurisation if the meteorological conditions change so that it becomes impractical or insufficient to rely on natural air movements, or if the emission of ground-emanating gases should increase to the point where the natural ventilation is insufficient. It is then a simple matter to connect fans to the preliminarily installed pipework for this purpose for the forced-ventilation arrangements to be brought quickly and easily into effect.

Figures 7 and 8 illustrate a further embodiment of the invention similar to that illustrated in the previous figures. A building 46 is underlain by a barrier 14, which may be of the form illustrated in Figure 1 or Figures 5 and 6, defining beneath it a void space 47 to which are connected ducts 48,49 having openings to the atmosphere, which may be considered either as inlets or outlets, 50, 51 respectively. Each of the ducts 48,49 has a respective valve 52,53 which may be of any suitable form, for example of the type described in relation to Figure 4. Communicating with the duct 48 is a treatment material delivery system 54 which, as illustrated in Figure 8,

comprises primarily a container or housing 55 for the treatment material and a pump 56. The pump 56 delivers air to a pipe 57 having a venturi section 58 communicating via an orifice 59 with a lower part of the container 55. The venturi section 58 connects to a pipe 60 which leads into the duct 48 at a point between the valve 52 and the void cavity 47.

Although shown as a single void space 47 with individual ducts 48,49 the arrangement may be like that of Figure 2 in which the ducts lead to individual outlets within the void 47 to create individual regions of influence throughout the area covered by the barrier 14.

Likewise, although the void 47 is illustrated in this embodiment as being between the building and the ground, it is possible to envisage situations where the void may be between one building and an adjacent building in order to have a corresponding effect as will be described in more detail hereinbelow.

The embodiment illustrated in Figures 7 and 8 is particularly adapted for use in protecting buildings not just from ground-emanating gases (although it is usable for this purpose in the same way as the earlier embodiments) but also for protecting buildings against attack by other aggressive phenoma, in particular insects such as termites, or fungi. In some areas of the world attack by insects such as termites on the lower part of buildings is a serious problem, detrimentally affecting their integrity and, consequently, their stability. The system of the present invention allows the void space 47 to be ventilated naturally, when the valves 52,53 are both open, by any air

movements flowing past the openings 50,51 causing a pressure differential between the void 47 and the external atmosphere resulting in an inward or outward flow of air.

This air flow will be in different directions at different times depending on the instantaneous air flow around the building, although it may on average have a preponderant wind direction and therefore a tendency towards positive or negative pressurisation of the void 47 with respect to the environment. By closing one or other of the valves 52,53, or by closing both of them, the open ventilation system of the void 47 is closed, so that subsequent operation of the pump 56 can serve to deliver treatment material such as a powder, vapour or gas from the container 55 into the duct 60, and from there into the void 47. Such application of treatment material may take place for, say, an hour or more until the entirety of the void space 47 is invested with the treatment material, whether it is a gas, a vapour or an air-borne dust or powder.

Because the valves 52,53 are closed the treatment material permeates the entirety of the void space creeping in to all nooks and crannies therein. The treatment material may, for example, be an insecticide, a fungicide, a herbicide or other treatment dependent on the attack from which it is intended to defend the building. The valves 52,53 can remain closed for a sufficiently long time for the treatment material to take effect, and this may vary from a matter of a few hours to 24 hours or more. Again, the precise length of time for which the treatment material is held within the void 47 will depend on the nature of the material and the agency it is intended to treat.

After this the valves 52,53 are opened and the natural ventilation of the void space 47 through the openings 50,51 may continue. If desired the valve 52 may be closed and the valve 53 opened with the pump 56 operating so that a forced flow of

pressurised air is delivered to the chamber 47, the treatment material in the container 55 either being exhausted or isolated from the duct 60 by a valve (not shown) which prevents it from being drawn through the opening 59 into the venturi tube 58. The building 46 can be periodically treated at intervals dependent on the nature of the attack. This may be monthly or more frequently, or annually or less frequently and may be automatically timed to take place regularly in order to protect the building without conscious management, or maybe implemented only at the command of the building's occupants.