GB2374922A

GB2374922A - A fume cupboard

Info

Publication number: GB2374922A
Application number: GB0204944A
Authority: GB
Inventors: Michael Stuart Horne; John Hennessey
Original assignee: PREMIER LAB SYSTEMS Ltd
Current assignee: PREMIER LAB SYSTEMS Ltd
Priority date: 2001-03-02
Filing date: 2002-03-04
Publication date: 2002-10-30
Anticipated expiration: 2022-03-04
Also published as: GB0105141D0; GB2374922B; GB0204944D0

Abstract

A fume cupboard 10 characterised by a working chamber consisting a base 30 and a profiled roof portion 18. The fume cupboard including a baffle assembly 16 with a plurality of vertically spaced apertures 32, an extract plenum chamber 14 in fluid communication with a rear boundary defined by the baffle assembly, a sash window 20 with an aerodynamically profiled sash pull 22 and an aerodynamically profiled bottom sill 24. Preferably the profiled roof portion has an arched profile with angled front, rear and side portions with the extract plenum chamber disposed there above. The sash window can be operated to give a variable access area, the window being counterbalanced and housed within runners 40. The sash pull is ideally situated on the windows lower edge and is constructed so that it has a radii used finger grip (48, fig.3) which curves upwardly and outwards. The sash pull also has a larger radii lower portion (50, fig.3) which curves downwardly and inwards. Preferably the bottom sill is of a curved, aerofoil profile. When the sash window is open, air can pass over the upper surface (58, fig.4) of the bottom sill and also through a slot (60, fig.4) defined by the underside of the bottom sill.

Description

FUME CUPBOARD This invention relates to improvements in fume cupboards and the like.

In present day industrial scientific practice and in teaching establishments, experiments involving the generation of potentially harmful fumes, vapours, dust or particles carried in air or the handling of toxic substances or pathologically harmful bacteria are required by Health and Safety regulations to be contained in a safe manner. Various means are available for containing such contaminants including fume cupboards, fume hoods, laminar flow booths, safety cabinets and Local Exhaust Ventilation (LEV) devices. For the purposes of this document, the term "fume cupboard"as stated hereinafter may also refer to the above various means for containing such contaminants. Protection is further achieved by applying an extract to remove the contaminated air from the work environment.

The majority of laboratories today use the fume cupboard (or fume hood as they are commonly known in America) or safety cabinet (used for pathological and general"Life Sciences"work) which as noted above are normally connected to an extract system, which in the case of a fume cupboard draws air into the fume cupboard chamber via an open sash window, past the user.

Early fume cupboards generally concentrated on the essential aspects of containment, namely to provide a boxlike structure to limit the spread of harmful fumes, vapours, dust or particles carried in air together with some means of inducing air removal from the working space so that the air would carry with it the harmful substances and discharge them into the atmosphere. Thus a basic air extract system would consist of a fume cupboard, extract ductwork and a fan unit.

It has always been assumed that in such basic extract systems an increase in air flow and hence velocity improved the containment efficiency and conversely a low velocity would be synonymous with low containment performance. The current British Standard, BS 7258: Part 1: 1994, relating to fume cupboards states that in practice, with the sash set to the maximum working opening, it is unlikely that face velocities below 0.3 ms-1 will give satisfactory containment.

Following from this the normal specification for airflow requirements in practice is to provide an average face velocity across the open sash area of 0.5 ms-1 (this is normally the minimum average face velocity specified and indeed can range up to 1.0 ms-1). Accordingly, where a number of fume cupboards are grouped together the total extract air volume may be very high.

In recent years attempts have been made to reduce the

flow rate of air required for safe operation of fume cupboards in order to reduce the high energy costs involved. This problem has not been addressed at the fume cupboard itself but on the extract\input systems, by varying the extract flow rate depending on the sash window position, known as the variable air volume system (VAVS).

For example, if the sash window is closed extract duty can be reduced by up to 20% of the total extract volume, however, if the sash window is open to the maximum working height, typically 500 mm, then the extract volume requires to be 100%.

Previous designs of fume cupboard share a number of common problems, some of which are mentioned below.

The protection of operators is only achieved if the contaminated air is entirely removed and does not spill back into the laboratory. Many fume cupboards do not achieve this under certain conditions or at all due to inappropriate design of the geometrical details and airflow characteristics.

Full operator protection is only achieved through the use of very high air volumes which results in discomfort to the operator and air turbulence within the workplace. The high extract volume also results in the evacuation of air from the laboratory which normally has to be replaced with conditioned air, increasing operational costs.

Large volumes of air moving at relatively high

velocities in ductwork often generates vibration and noise. If the air velocity is reduced, required duct sizes increase and add to the cost of mechanical installations as well as increasing building size through the space needed to accommodate the ducting.

The plant associated with the supply, treatment and removal of air is relatively bulky; in some modern laboratory buildings, plant space may add as much as 50% to the building volume.

It is among the objectives of the present invention to obviate or mitigate at least one of the aforementioned disadvantages.

According to a preferred aspect of the present invention there is provided a fume cupboard comprising: a working chamber having a base and a profiled roof portion to enhance vortical flow therein; a baffle assembly defining a rear boundary of the working chamber, said baffle assembly comprising a plurality of vertically spaced apertures positioned above the chamber base and allowing the passage of air therethrough; an extract plenum chamber in fluid communication with the baffle assembly apertures; a sash window defining a variable access area to the working chamber and being provided with an aerodynamically profiled sash pull along a bottom edge thereof; and

an aerodynamically profiled bottom sill positioned outwith the working chamber.

The features of this preferred aspect of the present invention combine to provide a fume cupboard which may be operated in a far more efficient manner than existing fume chambers, that is the cupboard of the present invention provides safe containment while only requiring a relatively low air velocity or flow rate.

Preferably during normal operation, the average face velocity of air across the open sash area is approximately 0.25 mus-', thus keeping the volume of air extracted from the surroundings to a minimum. This average face velocity is below the recommended safe minimum specified in BS 7258 mentioned above however extensive testing and computer simulations have shown that the containment levels offered by embodiments of the present invention at this low face velocity fall well within the requirements of the regulated standards.

In other aspects of the present invention the various features of the fume cupboard may also be provided singly, or in combination, as set out below.

According to another aspect of the present invention there is provided a fume cupboard comprising a working chamber having a profiled roof portion to induce vortical flow therein, and apertures in the boundary of the chamber allowing the passage of air therethrough.

The profiled roof portion enhances the airflow vortex within an upper portion of the working chamber, that is the presence of a substantially laminar swirling flow. The chamber configuration thus promotes total scouring of the chamber by the air passing through the chamber, and the elimination of turbulence and concentration of contaminants released in the course of performing experiments.

According to a further aspect of the present invention there is provided a fume cupboard comprising: a working chamber having a base; and a baffle assembly defining a rear boundary of the working chamber, said baffle assembly comprising a plurality of vertically spaced apertures positioned above the chamber base and allowing the passage of air therethrough.

The provision of a plurality of vertically spaced apertures, preferably in the form of horizontally extending slots, facilitates creation of a vortical flow in the chamber.

According to a still further aspect of the present invention there is provided a fume cupboard comprising: a working chamber; a baffle assembly comprising a plurality of spaced apertures allowing the passage of air therethrough; and an extract plenum chamber in fluid communication with the baffle assembly apertures.

The provision of the plenum chamber assists in equalising the rate of extraction between the apertures, and thus providing more uniform, and non-turbulent, extraction from the working chamber.

According to a yet further aspect of the present invention there is provided a fume cupboard comprising: a working chamber having a base and defining at least one extraction aperture; and a sash window defining a variable access area to the working chamber and being provided with an aerodynamically profiled lower edge.

In another aspect of the present invention there is provided a fume cupboard comprising: a working chamber having a base and defining at least one extraction aperture and an access opening; and an aerodynamically profiled bottom sill defining a lower portion of the access opening and positioned outwith the working chamber.

These two aspects of the invention each facilitate non-turbulent flow of air into the working chamber.

Drive means may be provided in combination with the fume cupboard to induce movement of air from the surrounding environment, such as a laboratory, into the working chamber, through the extract apertures or slots in the baffle assembly, into the extract plenum chamber and ultimately into the atmosphere through appropriate ducting.

The drive means may be, for example, a fan unit such as an axial flow or centrifugal flow fan unit.

The drive means may be variably controllable such that a range of extraction flow rates from the working chamber are available to the user. This facility enables the user to accommodate different conditions and levels of contamination within the working chamber, however in the preferred embodiment of the invention it is considered that this feature, and the corresponding increase in complexity, is not necessary to the efficient operation of the cupboard.

Preferably there is provided an optional baffle control to reduce velocity flow rates at the base of the working chamber when the sash window is closed, so that dispersal of fine powders and the like from the working chamber is prevented. For example, a flow control fluid damper may be positioned in a region at the rear of the baffle assembly in the entrance to the plenum chamber to control preferential extraction of air through the extract apertures in the baffle assembly, thus allowing control of the fluid velocity at the base of the working chamber.

Preferably the fume cupboard also comprises a worktop defining a lower boundary of the working chamber. The worktop provides a support surface for any apparatus which may be used in the fume cupboard.

Preferably the extract plenum chamber occupies a

position within an upper portion of the fume cupboard outwith the working chamber, and most preferably substantially directly above the working chamber.

Preferably also the extract plenum chamber is sealably attached to the baffle assembly such that air within the working chamber may only enter the extract plenum chamber by first passing through the apertures in the baffle assembly.

Conveniently the extract plenum chamber reduces the air velocity required to safely prevent contaminated air within the working chamber leaking into the surrounding air within say, a laboratory, through the open sash area. This reduced airflow leads to lower surrounding air disturbance and greater operator comfort due to less air movement.

Conveniently also the extract plenum chamber ensures that the extract air is flowed through the baffle assembly area in a controlled fashion, and the geometric configuration of the baffle assembly does not lead to preferential extraction from one area at the expense of other areas.

Preferably attached to a top outside portion of the extract plenum chamber is a short length of tubular ducting for salable engagement with extract ducting allowing air extracted from the working chamber to safely vent to the atmosphere. Preferably said short length of ducting-can be easily adapted or exchanged to enable the fume cupboard to

easily replace old or faulty fume cupboards for example, without any major reworking.

Preferably the baffle assembly has a lower extract aperture or slot, which may be defined by a lower edge of a baffle plate and a top surface of the worktop, and has at least one further upper extract aperture or slot on a vertically higher plane.

More preferably the baffle assembly has a plurality of upper extract slots which may be equally or variably spaced.

Most preferably the baffle assembly has four upper horizontal extract slots Preferably there is a division of the airflow extracted from the working chamber, air extracted through the lower extract slot being flowed to the extract plenum through a first channel and the air extracted through the upper extract slots being flowed to the extract plenum through a second channel.

The baffle assembly may be of any suitable material which is chemically and physically resistant to the substances handled in a fume cupboard and which can withstand the range of temperatures typically found or produced in a fume cupboard. Suitable materials may include metals, glass, ceramics, synthetics and the like.

Preferably the components of the baffle assembly are adapted to be assembled using a minimal number of fixings

such that the baffle assembly may be easily removed for cleaning and inspection purposes.

Preferably the baffle assembly has a thickness of around 6 mm. Preferably also the lower and upper extract slots have widths of approximately 40 mm and 25 mm, respectively.

Preferably the profiled roof portion of the working chamber has an arched or curved profile ensuring that there are no sharp corners which would result in re-circulation and\or stagnation of the air flowing within the working chamber. Preferably all corners have obtuse angles of approximately 1350. This internal profile of the working chamber enhances the airflow vortex therein so as to promote the total scouring of the working chamber by the air induced through the open sash area, thus eliminating turbulence and concentration of contaminants released in the course of performing experiments or the like.

Preferably the sash window hereinbefore mentioned is counterbalanced and runs within an appropriately dimensional frame comprising first and second runner sections to house corresponding first and second side edges of the sash window, said first and second runner sections being suitably fixed to the fume cupboard, for example, by screw fixings.

Preferably also the sash window can be held open by locking means, preferably at a range of working heights,

with a maximum sash working height of approximately 500 mm. In this instance the working height is defined by the distance between a lowermost portion of the sash window sash pull and an uppermost portion of the bottom sill.

Preferably the profiled sash pull has a longitudinal channel which is fitted over the full length of the bottom edge of the sash window and fixed thereto by appropriate means. Such fixing means may be adhesive, rivets, nuts and bolts and the like. Alternatively, or in addition, the channel may also be sprung to provide additional gripping force to the sash window.

Preferably the profiled sash pull has a radiused finger grip which curves upwards and outwardly from the bottom edge of the sash window, away from the working chamber. This provides suitable gripping means to assist opening and closing the sash window and also serves to facilitate non-turbulent flow.

Preferably also the profiled sash pull has a lower portion which curves downwards and inwardly from the bottom edge of the sash window towards the working chamber. The lower portion preferably has a relatively large'radius. This large radius curved portion provides an aerodynamically profiled surface which limits turbulence in the air being induced into the working chamber. Further, the large radiused profile along the length of, the sash pull lower portion ensures there is little or no spillage

of air from within the working chamber.

Preferably the aerodynamically profiled bottom sill is of a curved, aerofoil profile and, as mentioned, is positioned outwith the working chamber and extends the length of the fume cupboard. First and second ends. of the bottom sill may be fixed to respective first and second side wings of the fume cupboard by suitable fixing means such as screws and the like. Alternatively, the sill may be moveable in response to, for example, the position of the sash window. Air from the surroundings induced into the working chamber will flow over an upper surface of the bottom sill and also through a slot defined by an underside of the bottom sill and a front, upper edge portion of the worktop. The nature of the curved profile of the bottom sill limits turbulence in the induced air flow and assists in containment of the air within the working chamber.

Preferably there is provided a substantially planar top sill portion, attached to the bottom sill, against which the sash window closes.

Preferably when the sash window is in a closed position air can still pass through the slot between the bottom sill and the worktop.

Preferably the fume cupboard is mounted on a stand comprising height adjustable feet in order to obtain a level support. Alternatively the fume cupboard may be placed on top of existing benches and the like in the

desired location. Alternatively, the fume cupboard may extend from floor to ceiling height, that is in the configuration of a walk in style fume cupboard.

According to a further aspect of the present invention there is provided a working chamber profiled roof for use in a fume cupboard wherein said profiled roof is substantially arched and is partially defined by angled front, rear and side portions.

According to another aspect of the present invention there is provided a baffle assembly for use in a fume cupboard wherein said baffle assembly comprises a plurality of vertically spaced apertures allowing the passage of air therethrough.

According to a further aspect of the present invention there is provided an extract plenum chamber for use in a fume cupboard wherein said plenum chamber occupies an upper portion of the fume cupboard and reduces the air velocities required to safely prevent contaminated air within the fume cupboard from leaking into the surrounding air.

According to a yet further aspect of the present invention there is provided an aerodynamically profiled sash pull for use in a fume cupboard wherein said sash pull is for attaching to a sash window of the fume cupboard and for facilitating non-turbulent air flow into the fume cupboard.

According to a still further aspect of the present

invention there is provided an aerodynamically profiled bottom sill for use in a fume cupboard wherein said bottom sill limits turbulence in a flow of air flowing past it into the fume cupboard.

These and other aspects of the present invention will now be described, by way of example, with reference to the accompanying diagrams, in which: Figure 1 is a side view of the fume cupboard in accordance with one embodiment of the present invention; Figure 2 is a perspective view of the baffle assembly of the fume cupboard of Figure 1 ; Figure 3 is an end view of the sash pull of the fume cupboard of Figure 1; Figure 4 in an end view of the bottom sill of the fume cupboard of Figure 1; Figure 5 is an end view of the fume cupboard showing flow streamlines produced from results of a computational fluid dynamics (CFD) simulation; Figure 6 is as Figure 5 with the inclusion of obstacles and a heat source within the fume cupboard; and Figure 7 is as Figure 6 with the inclusion of an operator obstructing the sash window.

Reference is first made to Figure 1 which is a side view of the fume cupboard 10. The fume cupboard 10 comprises: a working chamber 12 having a profiled roof portion 18i an extract plenum chamber 14 above the chamber

12; a baffle assembly 16 defining a rear boundary of the chamber 12; a sash window 20 with an aerodynamically profiled sash pull 22; an aerodynamically profiled bottom sill 24; and a worktop 26.

The extract plenum chamber 14 is positioned within the upper portion of the fume cupboard 10 directly above the working chamber 12 and is in sealed fluid communication with the baffle assembly 16. Attached to the top outside portion of the extract plenum chamber 14 is a short length of tubular ducting 2, attached to the upper edge of which is a flange 4. Further lengths of ducting (not shown) are fixed to the flange 4 and through which the air extracted from the working chamber 12 is flowed to the atmosphere, with the air being driven by a fan unit (not shown) integrated into the ducting. Contained in the entrance to the plenum chamber 14 is a baffle flow control device 27 which controls the fluid velocities at the same level as the worktop 26.

The profiled roof portion 18 of the working chamber 12 has an arched profile, partially defined by angled front, rear and side plates, ensuring that there are no sharp corners which would result in areas of re-circulation and\or stagnation of the air flowing within the working chamber 12.

Referring now in particular to Figures 1 and 2, the geometry of the baffle assembly 16 will be described. The

baffle assembly 16 has a lower horizontal extract slot 28 defined by a lower edge 15 of a baffle plate 17 of the assembly 16 and the top surface 30 of the worktop 26. Also provided are four equally spaced upper horizontal extract slots 32.

The rear portion of the baffle assembly 16 defines a first channel 34 through which air extracted through the lower slot 28 is flowed to the extract plenum chamber 14, and a second channel 36 through which air extracted through the upper extract slots 32 is flowed to the extract plenum chamber 14. The relatively large cross-sectional area of the chamber 14 causes the air to decelerate and assists in equalising flow through the slots 28,32.

Referring in particular to Figure 1, the sash window 20 provides a variable access sash area 38 to the working chamber 12. The window 20 is counterbalanced and is housed within runners 40 (only one shown).

The profiled sash pull 22, shown in greater detail in Figure 3 (viewed from the opposite end as Figure 1), has a longitudinal channel 42 which is fitted over the full length of the bottom edge 44 of the sash window'20 and fixed thereto. The sash pull 22 has a radiused finger grip 48 which curves upwards and outwardly from the bottom edge 44 of the sash window 20. The sash pull 22 also has a large radiused lower portion 50 which curves downwards and inwardly from the bottom edge 44 of the sash window 20.

Reference is now made to Figure 4 which depicts a side view of the profiled bottom sill 24, which is positioned outwith the working chamber 12 (Figure 1). The bottom sill 24 extends the length of the sash opening area 38 and is of a curved, aerofoil profile. The ends 52 of the sill. 24 are fixed to respective side wings 54 (only one shown) of the fume cupboard. When the fume cupboard is in use and the sash window 20 is open, air from the surroundings 46 flows over the upper surface 58 of the bottom sill 24 and also through a slot 60 defined by the underside 62 of the bottom sill 24 and the front upper edge 64 of the worktop 26. Attached to the upper face of the sill is a substantially planar top sill portion 66 against which the sash window closes.

Referring again now to Figure 1, it may be seen that the fume cupboard 10 is supported by a stand 66 which has a number of adjustable feet 68 (only two shown) in order to obtain a level support.

Reference is now made to Figure 5 which is an end view of the fume cupboard 10 with streamlines produced by a Computational Fluid Dynamics (CFD) simulation showing the air flow patterns within the working chamber 12. As may be seen from the diagram, two main flow patterns exist within the working chamber 12 ; an airflow vortex 70 in an upper portion of the chamber 12 and substantially, laminar parallel flow 72 in a lower portion of the chamber 12.

This flow arrangement provides total scouring of the working chamber 12 and improved containment levels.

Referring now to both Figure 6 and Figure 7, the flow patterns are shown in a"real-life"situation, that is with obstacles 74,76 and heat sources in the working chamber, and with reference only to Figure 7, an operator 78 in front of the sash window. In these situations the flow appears to contain higher levels of turbulence than that seen in Figure 5 but in both cases there still exists an air flow vortex 80, 82 in an upper portion of the working chamber 12 and substantially parallel flow 84,86 in a lower portion of the chamber 12 around the obstacles 74, 76. Because this particular flow pattern is maintained in the presence of obstacles and heat sources within the working chamber 12, high containment levels are also maintained.

Various modifications may be made to the embodiment hereinbefore described without departing from the scope of the invention. For example, the baffle assembly may contain any suitable number of upper extract slots, which may be equally or variably spaced, depending on the'size of the fume cupboard and the extraction flow rate. The sash window may be motorised and the sash window sash pull finger grip may be a thin plate extending perpendicularly from the sash window. The extract plenum chamber may be positioned outwith the fume cupboard and integrated into

the ducting.

Embodiments of the present invention provide a number of benefits and advantages, some of which are mentioned below.

Whereas in conventional fume cupboards the level of containment is reduced or is not proven to be maintained when an operator stands or moves in front of the device, or where bulky equipment is placed inside the device, the fume cupboard as described above is substantially unaffected by such occurrences, which are frequently practised by scientists in the laboratory.

The reduced airflow required by the fume cupboard leads to lower air change levels and greater operator comfort and also to substantial energy savings, hence providing lower operating costs and improved environmental performance.

The lower extract and supply airflow volumes requires smaller ducts at lower costs and reduced space requirements within the building for ducting and plant equipment.

As the illustrated embodiment of the present invention is purely mechanical, the complications associated with complex control and control systems are avoided, hence initial costs and equipment failure are reduced and maintenance requirements simplified. In addition, the simple mechanical nature of the fume cupboard components allow for the components to be individually fitted into

existing fume cupboards, for example.

Whereas present fume cupboards operating at higher velocities make it difficult to handle dusts or carry out accurate weighing of substances, the lower velocity of the air present in the illustrated cupboard is better suited for these purposes.

Present day environmental standards are moving towards limits being placed on the quality of air ejected into the atmosphere. In order to purify the air, scrubbers can be built into the extract air stream. Scrubbing operations become more efficient when the velocity of air passing through is reduced, or alternatively, due to the lower velocity, a lesser quality of air needs to be scrubbed.

Claims

CLAIMS 1. A fume cupboard comprising: a working chamber having a base and a profiled roof portion to enhance vortical flow therein ; a baffle assembly defining a rear boundary of the working chamber, said baffle assembly comprising a plurality of vertically spaced apertures positioned above the chamber base and allowing the passage of air therethrough; an extract plenum chamber in fluid communication with the baffle assembly apertures; a sash window defining a variable access area to the working chamber and being provided with an aerodynamically profiled sash pull along a bottom edge thereof; and an aerodynamically profiled bottom sill positioned outwith the working chamber.
2. A fume cupboard comprising a working chamber having a profiled roof portion to induce vortical flow therein, and apertures in the boundary of the chamber allowing the passage of air therethrough.
3. A fume cupboard comprising:

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a working chamber having a base ; and a baffle assembly defining a rear boundary of the working chamber, said baffle assembly comprising a plurality of vertically spaced apertures positioned above the chamber base and allowing the passage of air therethrough.
4. A fume cupboard as claimed in claim 1 or 3, wherein the plurality of vertically spaced apertures in the baffle assembly are horizontally extending slots.
5. A fume cupboard comprising: a working chamber; a baffle assembly comprising a plurality of spaced apertures allowing the passage of air therethrough; and an extract plenum chamber in fluid communication with the baffle assembly apertures.
6. A fume cupboard comprising: a working chamber having a base and defining at least one extraction aperture; and a sash window defining a variable access area to the working chamber and being provided with an aerodynamically profiled lower edge.
7. A fume cupboard comprising:

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a working chamber having a base and defining at least one extraction aperture and an access opening; and an aerodynamically profiled bottom sill defining a lower portion of the access opening and positioned outwith the working chamber.
8. A fume cupboard as claimed in any preceding claim, further comprising drive means for inducing movement of air from the surrounding environment, through the working chamber and then into the atmosphere.
9. A fume cupboard as claimed in claim 8, wherein the drive means is a fan unit.
10. A fume cupboard as claimed in claim 9, wherein the fan unit is an axial flow fan unit.
11. A fume cupboard as claimed in claim 9, wherein the fan unit is a centrifugal flow fan unit.
12. A fume cupboard as claimed in any one of claims 8 to 11, wherein the drive means is variably controllable.
13. A fume cupboard as claimed in claim 1, wherein there is further provided a baffle control to reduce velocity flow rates at the base of the working chamber when the sash

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window is closed.
14. A fume cupboard as claimed in claim 13, wherein the baffle control is a flow control fluid damper positioned in a region at the rear of the baffle assembly in the entrance to the plenum chamber.
15. A fume cupboard as claimed in any preceding claim, wherein the fume cupboard further comprises a worktop defining a lower boundary of the working chamber.
16. A fume cupboard as claimed in claim 1 or 5, wherein the extract plenum chamber occupies a position within an upper portion of the fume cupboard outwith the working chamber.
17. A fume cupboard as claimed in claim 1,5 or 16, wherein the extract plenum chamber is located substantially directly above the working chamber.
18. A fume cupboard as claimed in claim 1,5, 16'or 17, wherein the extract plenum chamber is sealably attached to the baffle assembly such that air within the working chamber may only enter the extract plenum chamber by first passing through the apertures in the baffle assembly.

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19. A fume cupboard as claimed in any one of claims 1,5 and 16 to 18, wherein a length of tubular ducting for salable engagement with extract ducting is attached to a top outside portion of the extract plenum chamber to allow air extracted from the working chamber to safely vent to the atmosphere.
20. A fume cupboard as claimed in claim 1 or 5, wherein the baffle assembly has a lower extract aperture which is defined by a lower edge of a baffle plate and a top surface of the base of the working chamber, and has at least one further upper extract aperture on a vertically higher plane.
21. A fume cupboard as claimed in claim 20, wherein the baffle assembly has a plurality of upper extract apertures.
22. A fume cupboard as claimed in claim 21, wherein said plurality of upper extract apertures are equally spaced.
23. A fume cupboard as claimed in claim 21, wherein said plurality of upper extract apertures are variably spaced.
24. A fume cupboard as claimed in claim 21,22 or 23, wherein the baffle assembly has four upper horizontal extract apertures.

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25. A fume cupboard as claimed in any one of claims 20 to 24, wherein there is provided two channels through which air extracted from the working chamber flows to the extract plenum, the air extracted through the lower extract aperture in the baffle assembly being flowed to the extract plenum through a first channel and the air extracted through the upper extract apertures in the baffle assembly being flowed to the extract plenum through a second channel.
26. A fume cupboard as claimed in any one of claims 1,3, 5,14 and 16 to 25, wherein the baffle assembly has a thickness of around 6 mm.
27. A fume cupboard as claimed in any of claims 20 to 26, wherein the lower and upper extract apertures in the baffle assembly have widths of approximately 40 mm and 25 mm, respectively.
28. A fume cupboard as claimed in claim 1 or 2, wherein the profiled roof portion of the working chamber'has an arched or curved profile ensuring that there are no sharp corners which would result in re-circulation and\or stagnation of the air flowing within the working chamber.

1
29. A fume cupboard as claimed in claim 28, wherein all

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corners of the profiled roof portion have obtuse angles of approximately 1350.
30. A fume cupboard as claimed in claim 1 or 6, wherein the sash window is counterbalanced and runs within an appropriately dimensioned frame comprising first and second runner sections to house corresponding first and second side edges of the sash window, said first and second runner sections being fixed to the fume cupboard.
31. A fume cupboard as claimed in claim 1,6 or 30, wherein locking means are provided to hold the sash window open.
32. A fume cupboard as claimed in claim 31, wherein the locking means are adapted to hold the sash window open at a range of working heights.
33. A fume cupboard as claimed in any one of claims 1,6 and 30 to 32, wherein the sash window has a maximum working height of approximately 500 mm.
34. A fume cupboard as claimed in claim 1, wherein the profiled sash pull has a longitudinal channel which is fitted over the full length of the bottom edge of the sash window and fixed thereto.

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35. A fume cupboard as claimed in claim 34, wherein the profiled sash pull is fixed to the bottom edge of the sash window by any one, or a combination of adhesive, rivets and nuts and bolts.
36. A fume cupboard as claimed in claim 34 or 35, wherein the longitudinal channel of the profiled sash pull is sprung to provide additional gripping force to the sash window.
37. A fume cupboard as claimed in any one of claims 1 and 34 to 36, wherein the profiled sash pull has a radiused finger grip which curves upwards and outwardly from the bottom edge of the sash window, away from the working chamber.
38. A fume cupboard as claimed in any one of claims 1 and 34 to 37, wherein the profiled sash pull has a lower portion which curves downwards and inwardly from the bottom edge of the sash window, towards the working chamber.
39. A fume cupboard as claimed in claim 38, wherein the lower portion of the profiled sash pull has a relatively large radius.
40. A fume cupboard as claimed in claim 1 or 7, wherein

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the aerodynamically profiled bottom sill is of a curved, aerofoil profile.
41. A fume cupboard as claimed in claim 1,7 or 40, wherein the aerodynamically profiled bottom sill extends the length of the fume cupboard.
42. A fume cupboard as claimed in claim 1,7, 40 or 41, wherein first and second ends of the bottom sill are fixed to respective first and second side wings of the fume cupboard.
43. A fume cupboard as claimed in claim 42, wherein the bottom sill is fixed to fume cupboard using screws.
44. A fume cupboard as claimed in any one of claims 1,7 and 40 to 43, wherein the bottom sill is moveable in response to the position of the sash window.
45. A fume cupboard as claimed in claim 1, wherein there

I is provided a substantially planar top sill portion, attached to the bottom sill, against which top sill the sash window closes.
46. A fume cupboard as claimed in any preceding claim, wherein the fume cupboard is mounted on a stand comprising

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height adjustable feet in order to obtain a level support.
47. A fume cupboard as claimed in any one of claims 1 to 45, wherein the fume cupboard is adapted to be placed on top of an existing bench.
48. A fume cupboard as claimed in any one of claims 1 to 45, wherein the fume cupboard is sized to extend from floor to ceiling height.
49. A working chamber profiled roof for use in a fume cupboard wherein said profiled roof is substantially arched and is partially defined by angled front, rear and side portions.
50. A baffle assembly for use in a fume cupboard wherein said baffle assembly comprises a plurality of vertically spaced apertures allowing the passage of air therethrough.
51. An extract plenum chamber for use in a fume cupboard wherein said plenum chamber occupies an upper portion of the fume cupboard and reduces the air velocities required to safely prevent contaminated air within the fume cupboard from leaking into the surrounding air.
52. An aerodynamically profiled sash pull for use in a

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fume cupboard wherein said sash pull is for attaching to a sash window of the fume cupboard and for facilitating nonturbulent air flow into the fume cupboard.
53. An aerodynamically profiled bottom sill for use in a fume cupboard wherein said bottom sill limits turbulence in a flow of air flowing past it into the fume cupboard.
54. A fume cupboard as described herein and shown in the accompanying representations.