GB2336667A

GB2336667A - Fume cupboards

Info

Publication number: GB2336667A
Application number: GB9909223A
Authority: GB
Inventors: William Edward Evans
Original assignee: PSE ENGINEERING Ltd
Current assignee: PSE ENGINEERING Ltd
Priority date: 1998-04-23
Filing date: 1999-04-23
Publication date: 1999-10-27
Also published as: GB9808575D0; GB9909223D0

Abstract

A fume cupboard or containment chamber comprises a cabinet (11) enclosing a space (10) and having a working window (14) in one wall of the cabinet. The window (14) is arranged to be closed by a sash (15) and also has a bottom sill (25) and side edge members (27, 28). The lower edge of the sash (15) and each of the side edge members, and the bottom sill (25) are each provided with a respective strip (22, 23, 24 and 21) respectively defining a respective duct between the strip and the respective edge of the window (14). The ducts create a laminar air flow about each respective edge to channel air into the window (14) when open without creating turbulence which might otherwise entrain contaminated air to escape from the space (10) via the window (14).

Description

2336667 IMPROVEMENTS IN FUME CUPBOARDS This invention relates to

improvements in fume cupboards and containment chambers.

Fume cupboards are enclosures which are intended to isolate a zone in which experimental or working procedures which are likely to generate toxic, noxious or unpleasant fumes or other emissions such as airborne particles or droplets, may be carried out with relative safety. Fume cupboards aim to achieve this isolation by arranging for a flow of air into the enclosure, away from the user, to be vented or fed to purification apparatus depending upon the nature and scale of the fumes or other emissions. This flow may be forced by use of an extractor fan.

It is found in practice however that turbulent flow around the edges of the operator's window, which serves to give the operator access to the working zone and as an inlet for air flow into the enclosure, allows some leakage of possibly contaminated air back into the space occupied by the operator.

An embodiment of a typical fume cupboard according to the prior art is illustrated in Figs. 1 and 2 of the accompanying drawings, Fig. 1 being a diagrammatic vertical cross-section of the fume cupboard, and Fig. 2 a horizontal cross-section on line 11-11 of Fig. 1.

The prior art fume cupboard comprises an enclosed space 10, within a cabinet 11, and providing a working surface 12 at a convenient height on -2a pedestal 13, which may contain storage space, or service conducts for gas, electric and water supplies to the space 10.

The cabinet 11 provides a window 14 which can be closed and opened by a sash 15 which is adapted to be slidably raised and lowered. A back baffle 16 defines a rear duct 17 which channels air from the back of the working surface 12 to an extractor duct 18 at the top of the cabinet.

The airflow pattern of the fume cupboard is illustrated by arrows in the drawing. The main flow of air into the space 10 through the window 14 is shown by arrows 19. However around the edges of the window 14, that is along the bottom edge of the sash, the front edge of the working surface or lower sill of the window, and the sides of the cabinet, turbulence arises due to the drawing in to the window of outside air from around the cabinet as well as in the main direct flow, due to the forced circulation caused by an extractor fan, in the extractor duct 18. This drawn in air flow forms eddies about the edges, and entrains some air from the interior of the space 10, which may be contaminated by fumes, to flow from the cabinet as suggested by the arrows in Figs. 1 and 2. Air from the upper region of space 10 is particularly likely to be contaminated due to circulation of air within space 10, and to be entrained to flow out of t.he window below the edge of sash 15.

The escape of air from the space 10, particularly when working with procedures which generate particularly toxic or noxious gasses, such as H2S; HM, or HCI, is potentially sufficiently injurious to the immediate safety or medium-term health of operators to require a remedy, and it is an object the invention to provide an improvement which can be built into new fume cupboards or containment chambers, and can be fitted to existing fume cupboards and containment chambers to alleviate the problem of leakage of potentially contaminated air from the interior of the cabinet.

According to the invention, a fume cupboard or containment chamber is characterised in that along at least one edge of a working access window, a strip member is provided, said strip member providing an airflow channelling duct between the strip member and said edge to induce laminate flow of air into the window.

There may be a strip member mounted along each edge of the window, that is each vertical side, the base, and the lower edge of the sash.

The strip members each may be shaped to channel air flow in contact with the respective edge, inwardly into an inner volume of the enclosure.

An embodiment of an example of fume cupboard according to the invention is illustrated in Figs. 3 and 4 of the accompanying drawings, which are similar to Figs. 1 and 2 already described, that is, Fig. 3 is a diagrammatic vertical cross-section of the fume cupboard, and Fig. 4 is a horizontal cross section on line IV-IV of Fig. 3.

The fume cupboard of Figs. 3 and 4 is closely similar to that of Figs.

1 and 2, that is it comprises an enclosed space 10 within a cabinet 10 and providing a working surface 12 at a convenient height on a pedestal 13, which may contain storage space or service conducts for gas, electric and water supplies to the space 10.

Cabinet 11 has a window 14 which can be opened and closed by a sash 15 which is adapted to be slidably raised and lowered. A back baffle 16 defines a rear duct 17 which channels air from the back of the working surface 12 to an extractor duct 18, with an extractor fan (not shown) at the top of the cabinet.

The fume cupboard according to the invention differs from the prior art cupboard in that shaped strips, 21, 22, 23, and 24 are mounted in relation to the base edge 25, the bottom edge 26 of the sash 15, and the right and left side edges 27, 28 respectively of the window 14. The strips 21, 22, 23 and 24 define respective ducts 29, 30, 31 and 32 between the strips and the respective edges. The ducts 29-32 are configured to channel air drawn into the volume 10 by the under pressure created by the extractor fan along the surfaces of the cabinet, around the respective edges and into volume 10, without the creation of the turbulent flow vortices encountered in the prior art construction, and create laminar flow into the window 14, as shown by the arrows in Figs. 3 and 4.

This ensures that there is no turbulence to draw contaminated air from the volume 10 out through the window, thus ensuring that there is no -5leakage from the cabinet of unwanted fumes.

A further feature is the provision of bypass vents 33 at the upper front edge of the cabinet. These enable air to be drawn into the upper volume of space 10 between the sash 15 and the cabinet.

The shapes of the strips 21-24 are selected for the particular location of the strip. Strip 21 provides a relatively wide entry to duct air in an almost straight path, whilst strip 22 describes a curve through a right angle, to divert downward laminar flow down the sash 15 into the window 14, whilst strips 23, 24 each provide a substantially semi circular crosssection to turn laminar flow from behind the cabinet in contact with the side walls through substantially 180', to flow into the window.

The strips 21-24 and the bypass vents 33 may be retro filled to existing fume cupboards and isolation cabinets, or may be provided as features of new cupboards and cabinets on installation.

2.

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Claims

1 A fume cupboard or containment chamber characterised in that, along at least one edge of a working access window of the fume cupboard, a strip member is provided, said strip member providing an airflow channelling duct between the strip member and said edge to induce laminar flow of air into the window. A fume cupboard or containment chamber according to claim 1 wherein a strip member is mounted along each edge of the window, that is each vertical side, the base and the lower edge of a sash closure of the window.

3. A fume cupboard or containment chamber according to claim 2 wherein the strip members are each shaped to channel air flow in contact with the respective edge of the window into an inner volume of the enclosure. A fume cupboard or containment chamber according to any preceding claim wherein the access window has an edge member at each vertical side, and each edge member has a strip member disposed to form a duct between the strip member and the edge members. A fume cupboard or containment chamber according to claim 4 wherein the strip member has a substantially U-shaped cross section. A fume cupboard or containment chamber according to any one of 7.

8.

claims 1 to 3, wherein the access window has a sash with a lower edge, and a strip member mounted to define a channel about said lower edge of the sash, to direct air flowing down the sash into the interior of the cupboard or cabinet.

A fume cupboard or containment chamber according to any one of claims 1 to 3 wherein the access window has a lower edge or sill, wherein a strip member is mounted to define a channel between said lower edge or sill and the strip member to direct air flow from below into the interior of the cupboard or cabinet.

A fume cupboard or containment chamber according to any preceding claim wherein bypass vents are provided in the upper front part of the cabinet, above the window.

A fume cupboard or containment chamber substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.