GB2421064A

GB2421064A - Containment chamber with offset manhole in base

Info

Publication number: GB2421064A
Application number: GB0525253A
Authority: GB
Inventors: Lee B Markham; John A Boudry
Original assignee: Petrotechnik Ltd
Current assignee: Petrotechnik Ltd
Priority date: 2004-12-10
Filing date: 2005-12-12
Publication date: 2006-06-14
Anticipated expiration: 2025-12-12
Also published as: GB0427105D0; WO2006061653A1; GB2421064B8; GB0525253D0; GB2421064A8; GB2421064B

Abstract

A containment chamber or access chamber 20 for mounting over the manway 33 of a storage tank 32 has an aperture (22, figure 2) in the base which is offset relative to the longitudinal axis of the chamber 20. With this arrangement the manway 33 is further from one side of the chamber 20 than would be possible with a centrally located manhole in a chamber of the same size. This therefore provides more space in which to locate pipe couplings such as flange connections (24, 25), especially for large diameter pipes, without the coupling being made above the manway 33 so that it is easier to remove the manhole cover 21 when access to the tank 32 is required. The chamber may have a downwardly extending skirt 40 which can fit in a collar 41 surrounding the manway of a tank 32, and this may support the chamber 20 above the tank 32. The containment chamber 20 may further comprise a top or corbel 38 containing an access hatch 42, which may also be offset to match the aperture (22) in the base.

Description

I

IMPROVED CHAMBER

Field of the Invention

This invention relates to chambers and especially but not exclusively to fluid-tight underground containment chambers as found associated with subterranean fuel tanks or sumps, for example in petroleum forecourt installation.

Background of the Invention

In typical underground storage and distribution systems for hazardous fluids such as hydrocarbon fuels, the fuels are usually stored in a large storage tank buried in the ground and delivered through underground piping to delivery pumps or the like. In order to ensure that the fuels cannot leak into the ground surrounding the tanks and pipework, so-called secondary containment systems are used which essentially provide a second barrier of protection around the primary fluid supply storage and delivery systems.

Typically, secondary containment systems have included containment sumps or chambers, which are an offshoot from the so-called back fill retainer. There are a variety of chambers now on the market usually comprising a body defining an enlarged chamber, a riser connected to the body, where the riser is generally of smaller diameter than the body, and a cover fitting over the top end of the riser.

The containment or access chamber is installed below ground to provide a means of access to the manway, underground piping connections, submersible pumps, leak detection sensors, fire extinguisher and other plumbing components usually found connected to the top of underground storage tanks or under fuel dispensing units.

Access or containment chambers are multi-purpose in function: 1. They provide a means of surface access to equipment, plumbing and miscellaneous devices, installed underground.

2. They provide a means of ground isolation for contained components to prevent corrosion and decay.

3. They provide a means of secondary containment for those contained components which handle hazardous liquids.

4. They act as a collection sump for double wall piping entering the sump.

Underground storage tanks usually have an access hatch or manway on the top of the tank to permit access into the interior of the tank if necessary. The access chamber is installed over the manway to facilitate access to the interior of the tank once it is underground.

Protruding through and connected to the top of the manway are various pipes, elbows and connectors which are in turn connected to the underground pipework system, whose pipe ends usually enter through the side of the chamber wall. This enables the fuel stored within the tank to be distributed to the pumps.

Due to the limited space within the chamber and the necessary size of the manway to permit a person to enter the tank, the connections between the pipes entering through the side of the chamber wall and the pipes/fittings protruding through the top of the manway are usually made directly over the manway itself. Typically, flanges are used to connect together the underground pipework to the pipes/fittings associated with the manway lid.

On occasions it is necessary to remove the manway lid entirely. This can be problematic if not impossible when the flange connections are made over the top of the manway itself, as the presence of the pipes entering through the side of the access chamber prevent the removal of the manway. This is a particular problem when the pipes entering and leaving the chamber are of relatively large diameter.

This may mean that it is necessary to remove or partly dismantle some or all of the underground piping, to enable the manway lid to be removed which is both expensive and difficult. Alternatively the manhole lid must be man-handled at an angle out of the chamber with inherent health and safety problems.

In order to overcome this problem, it is possible to use a larger access chamber, thereby allowing the flange connection to be made away from the manway lid.

However, this is not without its own problems. As well as the additional expense in manufacturing a larger chamber, it is more difficult to handle, transport and install and requires a larger excavation which in turn requires more backfilling and other material.

Accordingly, it is an object of the present invention to mitigate or overcome some or all of the above-mentioned problems.

ummary of the Invention According to a first aspect of the invention, there is provided a containment chamber for installation over a manway on a storage tank, the containment chamber comprising: (i) abodyportion; (ii) a lower aperture configured to permit access, in use, to a manway from the containment chamber; and (iii) an upper aperture configured to permit, in use, a manway lid to pass through the upper aperture and out of the containment chamber; wherein at least a region of the body portion is offset with respect to the lower aperture, whereby the offset region can accommodate pipework coming into the containment chamber and its associated fittings, so that, in use, the vertical footprint of the manway remains substantially free from the incoming pipework and its associated fittings to allow the manway lid and its optionally associated pipework to be lifted out of the containment chamber, through the upper aperture, without obstruction by the incoming pipework and its associated fittings.

For the first time there is provided a region offset to one side of the manway, which provides the possibility of more space within the containment chamber to one side of the manway. This ensures that any connections between the incoming pipework through the side of the chamber and any pipework protruding through the manway can be made outside the vertical footprint of the manway lid. In other words, when the pipework is disconnected, the manway lid, together with its associated pipework and fittings, can be lifted in its entirety from the access chamber without any protruding pipes obstructing its path. The term removal of the manway can be equated to removal of the parts of the manway that need to be removed. Generally, this comprises the manway lid.

The region offset to one side of the manway, or offset region, is a specific region in the containment chamber that accommodates or contains the incoming pipework.

This offset region means that the available space within the containment chamber around the manway is not the same around its entire circumference. In other words, the available space is not concentric with the manway itself. Instead, a region is provided within the chamber, to one side of the manway, to enable the pipework to be accommodated without it protruding over the vertical footprint of the manway lid.

The vertical footprint of the manway lid can be considered can be thought of as the vertical space directly above the manway. Preferably, it can be considered the vertical space directly over the manway lid as this is the part that is to be removed.

Even more preferably it can be considered the vertical space directly over the manway lid and its associated fittings and/or pipework. This way, it is possible to lift the manway lid and its associated fittings and/or pipework directly out of the chamber. Thus, if a manway has a lid with associated pipework, the vertical space above the lid and its associated pipework is kept substantially clear, or preferably clear.

The incoming pipework generally consists of a pipe itself and its associated fittings.

The pipe is usually fixed to the wall of the chamber by means of a fitting to ensure a fluid tight seal. This fitting is encompassed by the term incoming pipework. The pipe terminates at a point and has a coupling attached to its end for connection to further pipework within the chamber, generally originating from the tank. This pipework is usually pipework extending from the manway itself.

The two sets of pipework described above are attached together with couplings on the ends of each respective piece of pipework. One method of attachment is by using flanges attached to the ends of the pipes. The flanges are aligned and bolted together. If it is necessary to uncouple the pipes (for example to remove the manway lid), the flanges are unbolted. According to the present invention, the incoming pipework and its associated fittings are outside of the vertical footprint of the manway lid. Therefore, if the connection is made with flanges, the flange attached to the incoming pipework is outside the vertical footprint of the manway.

That way the manway lid can be lifted out of the chamber without having to cut away any of the incoming pipework. Therefore, it can be seen that pipework associated with and attached to the manway itself can be within the vertical footprint provided that it does not interfere with removal of the manway lid. In general, it is lifted out with the manway lid if it is removed.

One way of thinking about the offset region is to liken the shape of the containment chamber where the pipework is to be accommodated to that of a cam, thus providing additional space to one side of the manway to place all of the connectors and other equipment which would otherwise block the path for removal of the manway.

Preferably the manway has further pipework for attachment to the incoming pipework, and wherein the connection between the incoming pipework and the manway pipework is made outside of the vertical footprint of the manway.

As described above, the part of the manway that is preferably removed is the manway lid. The lid often has associated pipework and/or fittings attached to it or in association with it. Ideally, these can all be removed with the lid. Particularly preferably is if the lid and the associated/aftached fittings and/or pipework can be removed as a single piece. Thus, once all of the pipework and/or fittings have been disconnected from the incoming pipework and/or any other connections within the chamber, the manway lid and its associated pipework and/or fittings can be removed out through the chamber to allow inspection in the tank or work on the lid.

Equally possible is for a specific section of the manway, its lid or associated pipework/fittings to be removed in isolation. The present arrangement allows for these section(s) to be removed without substantial obstruction because the vertical footprint is kept substantially free.

Advantageously, the manway lid can be lifted vertically out of the containment chamber without substantial manoeuvring around obstacles within the containment chamber and according to a particularly preferred embodiment, the vertical footprint of the manway is free from obstacles. This allows for easy removal of the manway lid.

This offset region can be achieved in a number of ways. One example is where the offset region is formed by an out-bulging (outwardly protruding) portion in the containment chamber. In this embodiment, the containment chamber can be thought of as concentric with the manway but a specific region is added to the containment chamber to accommodate the pipework outside of the vertical footprint of the manway. The out-bulging (outwardly protruding) region is preferably formed in the body of the containment chamber. The body of the containment chamber can be thought of as the middle section of the chamber. The bottom section is designed to mount the chamber onto the tank and the top section is generally a corbal to allow access into the chamber. The body of the chamber forms the main part of the chamber and comprises the main sidewalls.

Alternatively, the offset region is formed by the lower, and preferably the upper, aperture(s) being offset with respect to the longitudinal axis of the containment chamber, preferably the body portion of the containment chamber. The longitudinal axis of the containment chamber is defined as the line joining the mid-points of its bases or its longitudinal line of symmetry through the centre of the cylindrical part of the chamber body. Another way of describing the longitudional axis is the line through the middle of the chamber body. In essence, the shape formed between the base of the containment chamber and the aperture can be likened to that of a cam, thus providing additional space to one side of the manway to place all of the connectors and other equipment which would otherwise block the path for removal of the manway. For the first time there is provided an offset aperture which provides the possibility of more space within the containment chamber to one side of the aperture and thus the manway. This ensures that any connections between the incoming pipework through the side of the chamber and the pipework protruding through the manway can be made outside the footprint of the manway lid. In other words, when the pipework is disconnected, the manway can be lifted in its entirety from the access chamber without any protruding pipes obstructing its path.

Equally, the body portion of the containment chamber can be offset from the longitudinal axis of the manway.

Alternatively, the offset region is formed by the containment chamber being eccentric with respect to the manway. This can be achieved by attaching a cylindrical containment chamber onto the tank in an eccentric manner to the manway. Preferably, under these circumstances, the storage tank comprises a tank collar for supporting the containment chamber and the tank collar is eccentric with respect to the manway. This way, a standard containment chamber can be used but because the tank collar is eccentric, the same aim is achieved.

According to a particularly preferred embodiment the upper aperture is aligned (substantially concentric) with the manway. Especially preferred is when the upper aperture is aligned with the manway and/or the lower aperture. The lower aperture or hatch is often found in a corbel. It is particularly advantageous if the upper aperture is also offset to match the aperture in the base. Therefore, when lifting out the manway lid, there is a clear vertical path through the chamber to the manway lid.

Another way of describing this is that both apertures in the containment chamber are concentric. That is, if the lower aperture is offset, the upper aperture is equally offset to maintain the clear vertical path. Alternatively, the upper and lower apertures are centrally placed and the body of the chamber is offset. This results in the same idea but looked at in different ways.

Preferably, a downwardly depending skirt surrounds the circumference of the lower aperture. The skirt can fit into a tank collar surrounding the manway, thus supporting the containment chamber above the tank.

Preferably, the skirt has a substantially circular circumference to permit the containment chamber to be rotated relative to the tank. This means that if a multi-sided containment chamber is used, adjustments to the alignment of one of the faces with respect to incoming pipework can be made to ensure that a watertight seal can be formed between them.

The present invention covers any attachment method for attaching the chamber to the tank, either via an upstanding collar or directly attaching the chamber to the tank itself. A fluid tight seal between the chamber and the tank can be achieved by any method known to those skilled in the art and includes, but is not limited to, mechanical fastenings, adhesive glues and electrofusion couplings. In addition, an 0-ring seal can be incorporated to improve the seal if necessary.

Preferably, the containment chamber also comprises strengthening ribs between the skirt and the base of the chamber. This helps to ensure that the chamber is fully supported when placed on the tank collar.

Particularly preferably, the strengthening ribs are attached to the portion of the base whose outer diameter is furthest from the downwardly depending skirt. This portion of the chamber has the least support and requires the greatest strengthening.

The present invention provides a means of fitting a large bore pipe into a tank containment or access chamber with the disconnection flanges falling outside the footprint of the manway lid. This allows the manway lid to be disconnected and lifted straight out if required, It also keeps the size of the chamber to a minimum. In essence, the footprint of the manway lid can be thought of as the vertical space directly above the manway lid. Thus, the space above the manway is kept clear of protruding pipework or other equipment.

It will be appreciated that the present invention extends to a containment chamber incorporating the offset region, a containment chamber system, a method of removing a manway or manway lid from a containment chamber assembly once the assembly is fixed in position and to installations, including petroleum forecourt systems incorporating chambers according to the present invention.

The invention will now be described in detail with reference to the drawings.

Brief Description of the Drawings

The present invention will now be described by way of example only with reference to the accompanying drawings, wherein: Figure us a partially cut-away side view of part of a petroleum forecourt installation, which includes a tank having a containment chamber, and a pair of dispensing pumps having sump chambers, the chambers in accordance with the invention; figure 2 illustrates a schematic top view of a containment chamber according to one aspect of the present invention; and figure 3 illustrates a cut-away side view of a containment chamber assembly, together with a storage tank according to one aspect of the present invention; figure 4 illustrates a side view of an alternative containment chamber assembly together with a storage tank according one aspect of the present invention; figure 5 illustrates a cut-away view of the containment chamber of figure 4; figure 6 illustrates a perspective view of the containment chamber of figure 4.

Description of the Preferred Embodiments

The present embodiments represent currently the best ways known to the applicant of putting the invention into practice. But they are not the only ways in which this can be achieved. They are illustrated, and they will now be described, by way of example only. By way of terminology used in this document the following definitions apply:- Containment chamber any receptacle designed to keep a fluid in or out. This includes, but is not limited to, access manhole and sump chambers as described herein. It also includes tanks in general.

Containment chamber system - any part of the underground system, including the containment chamber, that is contained by, or attached to the containment chamber.

This includes the access chamber itself, corbel, frame neck or lid together with the underground tank, collar, manway and associated pipework.

Energy transfer means - a generic term describing any form of energy source.

Typically it takes the form of a resistance winding which heats up when an electrical current is passed through it. The term also encompasses other welding techniques including ultrasonic welding and induction welding.

Flange - any collar suitable for attaching the various sections of the containment chamber. In the examples given the surface of the flanges are substantially planar.

However, it will be understood that the flange must conform to the profile of the section to which it is to be joined. Thus the flange can adopt any suitable conformation to achieve the necessary contact with a flat or curved surface.

Fluid - whilst the examples provided relate mainly to liquids, the term fluid refers to liquids, vapours and gases. For example, should a leak occur in a secondarily contained pipe in a garage forecourt installation then petrol or petrol vapour will collect in the manhole chamber, It is essential that this petrol vapour cannot escape through the wall of the chamber and into the surrounding ground.

jpe - where pipes are referred to herein they are generally of circular cross- section. However, the term also covers other cross-sections such as box sections, corrugated and the like and secondarily contained pipes of the "pipe-within-a-pipe" type.

Glass reinforced plastic (GRP) - The term GRP has a very broad meaning in this context. It is intended to encompass any fibre-reinforced plastic wherein a fibre of any type is used to strengthen a thermosetting resin or other plastics material.

sible material - The term fusible material has a very broad meaning in this context, It is intended to encompass any polymeric material which when energy is applied to it can melt and fuse together with an adjacent material and is intended to cover thermoplastics, thermosets, elastomers and adhesives.

jastics Material - The term has a very broad meaning in this context and is intended to encompass any polymeric material including thermoplastics, thermosets, elastomeric or any other polymeric material.

The petroleum forecourt installation shown in Figure 1 comprises a pair of dispensing pumps 10 and 11 connected to a subterranean tank 12 through a pipeline 13. The pipeline 13 is formed from contiguously arranged sections of polyethylene pipe. The pipeline 13 extends from the pumps 10 and 11 through the sump chambers 14 and 15 having side walls 16 and bases 17 into a containment chamber 18 having a side wall 19 and a base 1 immediately above the tank 12.

Figure 1 shows two lines extending from the pipeline 13 into the tank 12. These lines relate to two alternative forms of fuel supply system and are both shown for the sake of completeness. In practice, only one of the lines would extend from the pipeline 13 into the manhole chamber 18. One of those lines is a suction line 2 which is used where the dispensing pumps 10 and 11 are fitted with suction pumps.

The alternative line, reference 3, is a pressure line connected to the pipeline 13 via a pump 4 which is operable to propel fuel from the tank 12 to the pumps 10 and 11.

It can be seen from Figure 1 that the walls 16 and 19 have to be apertured in order to allow the pipeline 13 to pass into the chambers. In order to prevent water leaking from the surrounding ground (here denoted by reference numeral 5) into the chambers 14, 15 and 18 through the aperture, the pipe is sealed to the waIls 16 and 19 by means of a fitting. In the event of a spillage or a leak in a supply pipe the seal also prevents fuel from escaping into the environment.

Figure 2 shows a schematic top view of a containment chamber system according to one embodiment of the present invention. It shows the containment or tank chamber 20 and a manway or manway lid 21 protruding through an aperture 22. It can be seen that the aperture 22 is offset from the longitudinal axis of the chamber.

That is, instead of two concentric circles, one within the other, sharing a common mid-point, the centre of the aperture is offset or displaced from the centre of the body of the containment chamber itself.

At the top of the manway is the manway lid 21 and it can be seen that there are a number of pipes 23, 24 protruding from and through the manway lid. This permits fuel to be removed from the storage tank (not shown). The pipe protrusions extend as far as flange connections 25, 26. It can be seen in this arrangement that these flange connections are outside of the vertical footprint of the manway. Entering through the sides of the containment chamber are pipes 27, 28. These are adapted to be connected to dispensing pumps, further containers or other storage tanks.

The pipes enter through the side of the containment chamber and are adapted to engage with the pipes protruding from the manway lid 23, 24 via flange connections on the outside of said pipes 29, 30. Thus, when the flanges are pressed together and a fluid-tight seal is formed between them, fuel can be withdrawn from the storage tank to the dispenser.

It is important to note that the flange connections are positioned away from the footprint of the manway. Therefore, if the manway lid needs to be replaced or removed, by undoing the flange connections, the lid can be lifted straight out of the containment chamber. Pipes 27 and 28 will not hinder this removal because they are not located over the removal path of the manway lid.

Whilst it is possible for the smaller pipes 24, 28 to be connected outside of the footprint area without the need for the increased interior volume as found in area 31, when a larger pipe is used, for example pipework 23, 27, this is not possible because of, among other things, the increase in size of all the associated equipment. This can be more clearly seen in Figure 3, which shows a cutaway view of an access or containment chamber 20 in position above a storage tank 32.

It can be seen that pipe 23 extends vertically out of the manway lid 21, on top of the manway 33. The pipe is then bent through substantially 90 in order to allow it to engage with the incoming pipe 27. When pipe 27 enters the chamber, through a hole in the chamber wall 34, this hole in the side of the chamber must be rendered fluid-tight. Therefore, there is usually some form of sealing element placed between the pipe 27 and the wall 34. This can be seen as sealing element 35. This can take up a substantial amount of room inside the containment chamber and therefore the flange connector 65 is pushed further into the chamber than is often desired, resulting in the connection being made over the manway lid itself. The larger the pipe, the larger the flange connector and also the wall sealing element. This pushes the connector even further over the manway. If the aperture was centrally placed in the base of the access chamber, the flange connections would inevitably be over the manway lid, thus hampering the lid's removal, and/or at least there would be very little room to form all the necessary fluid-tight seals between the pipes themselves and also the pipe in the chamber wall. The advantage of the present invention is that once the flange connection has been undone, pipe 27 does not protrude over the manway lid.

During construction, the access chamber is placed over the tank with the manway protruding through the aperture in the base of the access chamber before the external pipework 27 is placed in the chamber and rotated to the optimum position (see below). Therefore, whilst it is not a problem to install the manway lid and the access chamber because the pipe work is not in place, once the system is fully fitted, the pipework prevents easy access into the manway and it is often necessary to cut out the pipework in order to access the manway lid, which can cause severe disruption and add on cost.

The flange connection 65 is shown some distance from the vertical footprint of the manway lid. In practice, it is generally going to be closed to the footprint, but still outside of it. This way, the pipework 23 does not increase the clear footprint necessary to remove the lid and its pipework unnecessarily. This results in a smaller aperture 42 being necessary.

The access chamber comprises a base 36, side walls 37, defining the body of the chamber and a corbel 38. An aperture 39 is formed in the base of the containment chamber which is surrounded by a downwardly depending skirt 40. Strengthening ribs 41 are placed between the skirt 40 and the base of the chamber 36. It can be seen that these ribs are larger and more substantial on the side of the chamber which is least supported by the tank collar. The corbel comprises an aperture 42 which can contain an access hatch. Although not shown, the aperture 42 is advantageously offset in the same manner as the aperture 39 in the base. This ensures that the manway or manway lid can be directly lifted out of the containment chamber system and there is a clear line of sight from the top of the access chamber through to the bottom.

The body of the access chamber can be made from various cross-sectional shapes.

In one embodiment a circular cross section can be used, the chamber effectively being defined by a single wall which circles the circumference of the chamber.

Alternatively, a multi-sided chamber could be used. It is advantageous ifthe skirt 40 is of substantially circular cross-section. This allows the access chamber to be rotated on top of the collar 43 through 360 degrees.

The underground tank 32, is typically made of steel or glass reinforced plastic (GRP) having the collar section 43 fixed to the top of it. Within the collar section 43 is a manway 33, which permits access to the interior of the tank. At the top of the manway is a manway lid 21. The collar 43 is typically cylindrical and has a channel 44 extending radially outwards and upwards from the collar. The collar need not be strictly cylindrical, in that the cross-section need not be uniform along its length. The downwardly depending skirt or region 40 is shaped in a complementary manner such that it can be inserted, or pushed into the channel 44. Thus, if the channel has a circular cross-section, then the downwardly extending skirt will also have a circular cross- section. The channel can be filled with a sealant, preferably a polyurethane sealant before the chamber skirt is pushed into it. This then forms a fluid tight seal between the chamber and the collar.

If the collar and skirt are substantially cylindrical, the access chamber can be rotated in order for the internal region with the additional space 45 to be oriented at the point where the pipe enters the containment chamber. It is also useful to make minor adjustments to the orientation of the access chamber such that a perpendicular face is presented to the pipe as it enters the access chamber. This helps ensure that a fluid- tight seal is formed.

Figure 4 shows a side view of a containment chamber mounted on a tank. The chamber can be seen more clearly in figure 5 which shows a cut-away view of the tank in place on a storage tank. It can be seen that the incoming pipework and its associated fittings are outside the vertical footprint of the manway and that the lower aperture and the upper aperture are concentric. This can be seen by line 51. Detail B shows a detailed view of the channel that contains a polyurethane sealant 50.

The sealant is used to form a fluid tight seal between the chamber and the upstanding collar and holds the chamber in place.

Figure 6 shows a perspective view of a containment chamber and shows the upper aperture 52, access cover 53, access cover skirt 54, chamber corbel 55, chamber body 56 and chamber base 57. It also shows manway 58 and incoming pipework 59, together with tank 60.

The containment chamber of figures 4-6 is a decagonal (10 sided) shape, which means that it is extremely rigid and is compatible with all entry fitting design criteria.

The asymmetrical offset design means that the chamber has one large side for the 9Omm-llOmm secondary contained fill lines. Therefore, the 4-inch fill line flange fittings can be located outside the manway lid footprint allowing easy removal of the tank manway lid when required.

The direct sealing method shown in detail B of figure 5 means that the chamber base can fit into a groove on the tank collar filled with GRP (or some other) resin and the two surfaces bond to become one. The chamber base can be bonded onto the tank collar in the factory before delivery, dramatically reducing site installation time. The base can set to fix to 90 or 110mm mountings and can be adjusted for open or square collars. The tank is generally a minimum of 6mm thick GRP and has an anti static coating. It is height adjustable.

It should be noted that the term "access chamber" is analogous to the term "containment chamber" and both terms can be used interchangeably. The present invention provides a way of reducing the size of a containment chamber and also providing an easy way to remove the manway lid once all of the pipework is in place.

The containment chamber assembly can be manufactured from a variety of materials as selected by the materials specialist. Preferably the base section and the riser section are formed from the same material. By way of examples only suitable plastics materials may be selected from the group comprising:- polyethylene; polypropylene; polyvinyl chloride; polybutylene polyurethanes; polyamides, including polyamides 6,6.6,6.10,6.12, 11 and 12; polyethylene terphthalate; polybutylene terephthalate; polyphenylene sulphide; polyoxymethylene (acetal); ethylene/vinyl alcohol copolymers; polyvinylidene fluoride (PVDF) and copolymers; polyvinyl fluoride (PVF); tetrafluoroethyJeneethylene copolymer (ETFE); tetrafluoroethylenehexafluroethy(ene copolymers (FEP) ethylene tetrafluoroethylene hexafluropropylene terpolymers (EFEP) terpolymers of tetrafluoroethyfene hexafluoropropylene and vinylidene fluoride (THy); polyhexafluoropropylene; polytetrafluoroethylene (PTFE); polychlorotrifluoroethy; polychlorotrifluoroethylene (PCTFE); fluorinated polyethylene; fluorinated polypropylene; and blends and co-polymers thereof. Furthermore, it is known to use blends of two or more polymers and this invention extends to cover known and yet to be developed blends of plastics material.

Alternatively the chamber components may be formed from glass reinforced plastic (GRP) or fibre reinforced plastic (FRP).

Alternatively the chamber components may be formed from metal, for example steel or a coated metal.

This selection is not intended to be limiting but rather demonstrates the flexibility and breadth of the invention.

A major advantage of this invention is that it facilitates access to the manway lid and facilitates its easy removal. In addition, it gives the installer more room when forming the fluid-tight seals between the pipes and also the pipe and the chamber wall.

Methods for the construction of containment chamber systems are known. For example, GB0426600.3 relates to apparatus and methods for forming a fluid tight seal between components in a containment chamber system and GB0422066.1 relates to a method and apparatus for sealing the containment chamber to the collar. The text of GB0422066.1 and GB0426600.3 are incorporated herein by reference and are intended to form an integral part of this disclosure. This invention therefore encompasses containment chambers formed using those methods and incorporating those features described in GB0422066.1 and GB0426600.3.

Claims

Claims 1. A containment chamber for installation over a manway on a

storage tank, the containment chamber comprising: (i) a body portion; (ii) a lower aperture configured to permit access, in use, to a manway from the containment chamber; and (iii) an upper aperture configured to permit, in use, a manway lid to pass through the upper aperture and out of the containment chamber; wherein at least a region of the body portion is offset with respect to the lower aperture, whereby the offset region can accommodate pipework coming into the containment chamber and its associated fittings, so that, in use, the vertical footprint of the manway remains substantially free from the incoming pipework and its associated fittings to allow the manway lid and its optionally associated pipework to be lifted out of the containment chamber, through the upper aperture, without obstruction by the incoming pipework and its associated fittings.
2. A containment chamber according to Claim 1 wherein, in use, the manway has further pipework for attachment to the incoming pipework, and wherein the connection between the incoming pipework and the manway pipework is made outside of the vertical footprint of the manway.
3. A containment chamber according to any preceding claim wherein, in use, the manway lid can be lifted vertically out of the containment chamber without substantial manoeuvring around obstacles within the containment chamber.
4. A containment chamber according to any preceding claim wherein, in use, the vertical footprint of the manway is free from obstacles.
5. A containment chamber according to any preceding claim wherein the offset region is formed by an outwardly protruding portion in the containment chamber.
6. A containment chamber according to any of preceding claim wherein the offset region is formed by the lower aperture being offset with respect to the longitudinal axis of the body portion of the containment chamber.
7. A containment chamber according to any preceding claim wherein the offset region is formed by the longitudinal axis of the body portion of the containment chamber being offset, in use, from the longitudinal axis of the manway.
8. A containment chamber according to any preceding claim wherein the offset region is formed by the containment chamber being, in use, eccentrically positioned with respect to the manway.
9. A containment chamber according to Claim 8 wherein, in use, the storage tank comprises a tank collar for supporting the containment chamber and wherein the tank collar is eccentric with respect to the manway.
10. A containment chamber according to any preceding claim wherein, in use, the upper aperture is aligned with the manway.
11. A containment chamber according to any preceding claim wherein the upper aperture is aligned with the lower aperture.
12. A containment chamber according to any preceding claim wherein a downwardly depending skirt surrounds the circumference of the lower aperture.
13. A containment chamber according to Claim 12 wherein the skirt can fit into a tank collar surrounding the manway, supporting the containment chamber above the storage tank.
14. A containment chamber according to Claim 12 or Claim 13 wherein the skirt has a substantially circular circumference to permit the containment chamber to be rotated relative to the storage tank.
15. A containment chamber according to any of claims 12 to 14 wherein the containment chamber further comprises strengthening ribs between the skirt and the base of the chamber.
16. A containment chamber according to Claim 15 wherein the strengthening ribs are attached to the portion of the base whose outer diameter is furthest from the downwardly depending skirt.
17. A containment chamber according to any preceding claim wherein the containment chamber comprises a base portion which accommodates the lower aperture and the offset region, and a corbel, which accommodates the upper aperture.
18. A containment chamber system incorporating a containment chamber as claimed in any preceding claim.
19. A petroleum forecourt incorporating a containment chamber as claimed in any of claims 1 to 17.
20. A containment chamber substantially as hereinbefore described and with reference to the accompanying drawings.
21. A containment chamber system substantially as hereinbefore described and with reference to the accompanying drawings.