GB2069687A

GB2069687A - Fume cupboards

Info

Publication number: GB2069687A
Application number: GB8103653A
Authority: GB
Original assignee: University of Liverpool
Current assignee: University of Liverpool
Priority date: 1980-02-06
Filing date: 1981-02-06
Publication date: 1981-08-26
Also published as: GB2069687B

Abstract

This invention relates to a fume cupboard, one face of which comprises a flexible material 13 and has a plurality of spaced apertures 15. The face comprising the flexible material and spaced apertures may also comprise a baffle along its lower edge. One edge of the flexible material 13 is attached to the bottom edge 13 of the fume cupboard door 3 and the opposite edge to a spring loaded roller 11. The slots 15 in the flexible material Bell generator access while containing noxious fumes. The flexible material may comprise glass-fibre, plastics or canvas, and may be transparent or translucent or have a central transparent panel. The material may be arranged as parallel spaced strips, as a bead curtain, or as a venetian blind. <IMAGE>

Description

SPECIFICATION Improvements in or relating to enclosures The present invention relates to enclosures, for example fume cupboards and the like ventilated enclosures.

The main function of fume cupboards, e.g. in research, analytical, industrial or school laboratories, is to ensure that noxious fumes and air-borne bacteria are carried away from the person using the fume cupboard. This is generally achieved by drawing a stream of air, e.g. by means of a pump or fan, from the laboratory past the person using the fume cupboard, through the cupboard and then through ducts until it is discharged safely into the atmosphere outside the building housing the laboratory, or decontaminated, e.g. by scrubbing. The velocity of the air stream being drawn through the cupboard is therefore very important as it will affect the efficiency with which the noxious fumes and air-borne bacteria are carried away from the person using the cupboard.

Although the efficient withdrawal of noxious fumes and air-borne bacteria from the vicinity of the person using the fume cupboard is important, many of the existing fume cupboards do not satisfactorily achieve this under operating conditions.

For example, the efficiency of the ventilating system of many existing fume cupboards is only satisfactory when the front glass panel (sash) of the fume cupboard is lowered to leave only a narrow space between the bottom edge thereof and the floor of the fume cupboard. This situation is general ly unsatisfactory since it is very difficult, if not impossible, to reach materials or equipment in the fume cupboard when the front glass panel is in its lowered position.

One means for overcoming the above disadvantage is to increase the velocity of the air stream being drawn through the fume cupboard, for example by increasing the power of the pump or fan or by providing additional forced air currents. It is, however, expensive to install new and more powerful fans or pumps in existing fume cupboards and provide larger or additional ducting. Such changes frequently require upgrading in the space heating and general ventilation systems to cope with the increased movement of air through the laboratory in which the cupboard is situated. Such changes may also produce an unwelcome increase in the noise level. Further, although the increased air flow velocity would allow the fume cupboard to be used with the sash in the raised position, it may create unacceptably high local flow rates within the cupboard when the sash is in its lowered position.Such high local flow rates are a disadvantage since solid objects such as glass vessels may be easily blown over and broken. Large air flows and velocities greatly increase the difficulties of scrubbing exit gases effectively.

An alternative means for increasing the efficiency with which air is drawn through the fume cupboard, and away from the person using the cupboard, is to modify the internal shape of the cupboard to achieve a more aerodynamically satisfactory design. However, this means of improving the efficiency of existing fume cupboards is also expensive. Moreover, the very presence of any apparatus within the cupboard induces some turbulence, and (depending upon the size, shape and positioning of the apparatus) can render the aerodynamic design ineffective.

A further disadvantage of existing fume cupboards is that they only give anyone using the cupboard protection against spillage of and splashing by hazardous liquids when the sash is in its lowered position. As mentioned above, it is very difficult, if not impossible, to satisfactorily handle materials or equipment housed in the fume cupboard when the sash is lowered.

According to the present invention there is provided an enclosure, for example a fume cupboard or the like ventilated enclosure, one face of which comprises a flexible material and has a plurality of spaced apertures therein.

By practice of the present invention there is provided an enclosure which gives anyone using it protection against fumes, gases, smokes, fogs, vapours, air-borne bacteria and any air-borne spray, splash, dust or powder or any similar dispersed solid phase and also some protection against spillages of hazardous liquids.

The flexible material is preferably in the form of a single sheet having the spaced apertures therein.

However, it is to be understood that other suitable arrangements may be used if desired. For example, the flexible material may be in the form of a plurality of strips of flexible material so positioned that a plurality of spaced apertures are formed therebetween. In such an arrangement, the strips are preferably substantially parallel to each other. Again, the flexible material may, for example, take the form of a bead curtain or a venetian blind. The venetian blind arrangement allows the width of the spaced apertures to be varied as desired.

When the enclosure is a ventilated enclosure, it is important that provision be made to retain the flexible material, for example in the form of a sheet or a plurality of strips, so that it is not sucked into the enclosure. This is achieved by suitably fixing the flexible material, for example at its ends. If objects are to be passed through the spaced apertures, then such fixing is made to allow the necessary flexibility, e.g. fixing by means of spring loading or, if vertical strips of flexible material or a sheet of flexible material having vertical slots are used, by simple weighting. Spring loading or simple weighting may also be used if a bead curtain is used as the flexible material.

The spaced apertures may be of any suitable size and spacing. For example, when the enclosure is to be used as a fume cupboard, the spaced apertures are preferably of a size and have a spacing such that a person using the fume cupboard may be able to place his or her arms through the apertures comfortably and satisfactorily see and handle materials or apparatus in the fume cupboard. It is also advantageous, if the enclosure is to be used as a fume cupboard, for the apertures to be of a size such that the materials or apparatus can be readily passed therethrough and into the cupboard.

The spaced apertures may have any suitable shape, although they are preferably in the form of elongated slots. If the apertures are in the form of elongated slots, such slots are preferably substantially parallel to one another. Further, the slots will usually be vertical but may be positioned at any other desired angle.

Any suitable material may be used as the flexible material. If preferred, the flexible material may be transparent or translucent. Further, if corrosive chemicals are to be used in the enclosure, as is often the case when the enclosure is a fume cupboard, the flexible material must be resistant to attack by the corrosive chemicals. The flexible material is also preferably readily cleanable.

When flammable materials are to be used in the enclosure, it is important that the flexible material be fire-resistant.

An example of a flexible material that may be used in accordance with the present invention is glass fibre. However, when the flexible material is not going to come into contact with corrosive chemicals or organic solvents, or where there is no fire danger, plastics materials or materials such as canvas may be used as an alternative to glass fibre.

The centre section of the flexible material may, for example, be transparent to allow a clear view into the enclosure with the spaced apertures being located to either side of this central transparent section. In this case, the spaced apertures on either side of the central transparent section should be more closely spaced than if they were evenly spaced across the width of the flexible material/spaced aperture combination.

In one embodiment of the present invention, the flexible material is detachable from the face of the enclosure such that it can readily be removed when desired or when the enclosure is not in use.

In a further embodiment of the present invention, the flexible material is adapted such that it can be folded or rolled away when not in use, for example by means of a spring-loaded roller system. This embodiment is particularly advantageous when the flexible material is in the form of a single sheet in which slots have been provided.

When a roller system, for example a spring-loaded roller system, is utilized, the roller is preferably attached to one edge of a sheet of flexible material and the roller itself attached to the enclosure. The roller may be attached to the enclosure in any suitable position. For example, if the flexible material is to cover the front, back or a side of the enclosure, the roller may be mounted above, below or on a side edge of the front, back or side of the enclosure.

If a spring-loaded roller system is used in conjunction with a fume cupboard having a glass front which can be raised to open the cupboard or lowered to close the cupboard, then the roller may be mounted below the front of the fume cupboard and the edge of the flexible material, opposite to the edge attached to the roller, may be attached to the lower edge of the glass front. In such an embodiment, as the glass front is raised, the flexible material is unrolled from the roller and covers the front of the fume cupboard thereby enabling a person to handle materials or equipment, situated within the cupboard, readily and yet still have the protection from any air-borne bacteria, hazardous gases or dusts, etc., and some protection from spillages of or splashing by harmful materials.

When the enclosure is in the form of a ventilated enclosure having a positive ventilation system, for example in the form of a fume cupboard, the flexible material/spaced aperture combination has the important advantage that the air flow velocity through the apertures is greater than the airflow velocity through the front of the same enclosure without such a flexible material/spaced aperture combination. For example, the air flow velocity through the front of a fume cupboard may be increased from about 80 feet/min, when the glass front is raised and there is no flexible material/spaced aperture combination present, to 200 feet/min or more, when the glass front is raised and a flexible material/spaced aperture combination is used in accordance with the present invention.The flexible material/spaced aperture combination also has the advantage that it reduces the effect of the turbulence or vortex created by someone walking past the enclosure. Such turbulence is well known to be capable of drawing air out of the enclosure against the general line of flow.

Many fume cupboards, especially those which extract at the top only and do not have baffles or any other form of air flow control, operate such that major eddies are set up within the cupboard. This is significant because it results in an air flow being set up, near the bottom of the fume cupboard, which is against the main stream of air entering and passing through the fume cupboard. There is, therefore, at the bottom near the front of the fume cupboard, in which the direction and speed of the air flow changes greatly in a short distance. A disturbance, for example, an incidental draught, such as a draught caused by a person passing bythefume cupboard, or even a person standing in front of the fume cupboard so as to impede the incoming air flow, can easily upset such an air flow within the fume cupboard and this can result in fumes, etc.

escaping from inside the cupboard into the laboratory without people in the laboratory being aware of the fact. Whilst the use of an enclosure according to the present invention having a face comprising a flexible material and a plurality of spaced apertures - as a fume cupboard reduces the risk of fumes, etc.

escaping from inside the fume cupboard into the laboratory, it has been found that the efficiency of the fume cupboard may be further increased by providing a baffle along the lower edge of the face comprising the flexible material and the plurality of spaced apertures.

Accordingly, in one embodiment of the present invention there is provided an enclosure, one face of which comprises a flexible material, a plurality of spaced apertures and a baffle located along the lower edge of said face.

The baffle may, for example, be separated from the lower edge of the face comprising the flexible material and the plurality of spaced apertures.

The baffle may, for example, be separated from the lower edge of the face comprising the flexible material and the spaced apertures such that air can pass between the baffle and the lower edge of the face into the enclosure. Further, the baffle may, for example, have an upper section which extends into the lower region of the enclosure.

The baffle may, for example, be made of any suitable material, e.g. aluminium alloy.

Whilst it has been found that the efficiency of a ventilated enclosure having a positive ventilation and a face comprising a flexible material and a plurality of spaced apertures may be increased by providing a baffle along the lower edge of the face, it has also been found that a ventilated enclosure having a positive ventilation system in which the baffle is provided along the lower edge of an opening in one face of the enclosure but the face does not comprise the flexible material and the plurality of spaced apertures is more efficient than a simple ventilated enclosure having an opening but no baffle, flexible material or plurality of spaced apertures.

The present invention will now be further described with reference to the accompanying drawing, in which: Figure 1 is a schematic front view of one embodiment of the present invention wherein the enclosure is a fume cupboard; Figure 2 illustrates the path taken by air passing through the apertures in the flexible sheet present in the embodiment depicted in Figure 1; Figure 3 illustrates the air flow velocity through the open front of a known relatively inefficient fume cupboard; Figure 4 illustrates the air flow velocity through the same fume cupboard as that represented in Figure 3 but wherein the cupboard has been modified according to the present invention to include a flexible material/spaced aperture combination over the open front face thereof; Figure 5 illustrates the airflow velocity through the open front of a known moderately efficient fume cupboard;; Figure 6 illustrates the air flow velocity through the same fume cupboard as that represented in Figure 5 but wherein the cupboard has been modified according to the present invention to include a flexible material/spaced aperture combination over the open front face thereof; Figure 7 is a schematic, cross-sectional side view of a fume cupboard according to the present invention having a baffle located along the lower edge of the front opening and illustrates the flow of air through the cupboard; Figure 8 is a schematic, cross-sectional side view of a fume cupboard similar to that of Figure 7 but without the baffle and illustrates the flow of air through the cupboard;; Figure 9 is a schematic, cross-sectional side view of a fume cupboard according to the present invention having a flexible material sheet comprising a plurality of slots on the front face and a baffle located along the lower edge of the front face and illustrates the air flow velocity through the cupboard at selected points; and Figure 10 is a schematic, cross-sectional side view of a fume cupboard similar to that of Figure 9 but without the baffle and illustrates the air flow velocity through the cupboard at selected points.

Referring to Figure 1, there is illustrated a fume cupboard 1 having a front cover 3. The front cover 3 comprises an outer frame 5 and a central glass panel 7 and is slidable vertically between runners 9. This enables the front of the fume cupboard to be opened or closed as desired.

Attached to the fume cupboard, below the front face thereof, is a spring-loaded roller 11 on which is mounted a sheet 13 of flexible material, for example a sheet of glass fibre.

The sheet 13 of flexible material has a plurality of substantially parallel elongated slots 15 therein.

One edge of the sheet 13 is attached to the spring-loaded roller 11 and the opposite edge of the sheet 13 is attached to the lower edge of the frame 5 of the cover 3, for example by means of a spring wire or a rod.

When it is desired to use the fume cupboard, the front cover 3 is raised. This unrolls the sheet 13 of flexible material such that it covers the front face of the fume cupboard. Anyone using the fume cupboard can then place his or her arms through the apertures 15 and readily handle materials or apparatus present in the cupboard. It is also possible to introduce apparatus into the fume cupboard through the apertures. For example, a 2 litre round-bottomed flask can readily be passed through the apertures.

When in use, air is drawn through the fume cupboard by a pump or fan (not shown) and the presence of flexible sheet 13 having apertures 15 therein increases the velocity of the air being drawn through the front face of the cupboard. The presence of sheet 13, however, does not result in a high linear velocity of air through the body of the fume cupboard since the linear velocity drops sharply immediately after passing through the apertures 15 (See Figure 2). Whereas the air flow velocity is increased as it passes through apertures 15, it rapidly falls again after passing through the apertures. The avoidance of high velocity air flow within the body of the fume cupboard is an important advantage since such high velocities can easily result in the blowing over of apparatus situated within the fume cupboard.Since there is little change in the total volume of air flowing through the fume cupboard, no changes are needed in fans or ducts or in space heating and general ventilation in the laboratory housing the fume cupboard. Scrubbers are not affected. There is no noise nuisance.

Figures 3 to 6 illustrate the effect that placing a flexible material/spaced aperture combination over the front face of two known fume cupboards has on the velocity of the air (at the face) being drawn through the fume cupboards. The flow velocities referred to in each of Figures 3 to 6 are measured in feet/minute.

Figure 3 illustrates the front face air velocity of a relatively inefficient fume cupboard without the use of a flexible material/spaced aperture combination and Figure 4 illustrates the front face air velocities for the same fume cupboard but with a flexible material/ spaced aperture combination being present over the open front face of the cupboard. The flexible material/spaced aperture combination in this instance comprises vertical 10 cm wide strips of flexible material having 5 cm gaps between adjacent strips, there being 8 gaps altogether. The large numbers quoted in Figures 3 and 4 represent the average linear air flow velocity at the positions indicated.

Approximate upper and lower limits found during the observation period are indicated by the superand sub-script numbers.

Figure 5 illustrates the front face air velocity of a moderately efficient fume cupboard without the use of a flexible material/spaced aperture combination and Figure 6 illustrates the front face air velocities for the same fume cupboard but with a flexible material/ spaced aperture combination, the same as that used in Figure 4, present over the open front face of the cupboard.

From Figures 3 to 6, it can clearly be seen that the air flow velocity through the front face of a fume cupboard is considerably increased by the presence of a flexible materialtspaced aperture combination, and that the flow of air is much more evenly distributed over the working face.

Figure 7 illustrates the passage of air through a fume cupboard 19 having a slotted front screen 21 and a baffle 23 in accordance with the present invention. Air is drawn into the fume cupboard 19 through the slotted screen 21 and passes out of the cupboard 19 through an opening 25. The means by which air is drawn through the fume cupboard 19 is not shown but may, for example, be a fan.

In addition to the main airflow into the fume cupboard 19 through slotted screen 21, air is also drawn into the fume cupboard 19 through the space between baffle 23 and the base 27 of the cupboard.

The presence of baffle 23, therefore, results in air being drawn from relatively dead space directly into the bottom of the fume cupboard 19.

Figure 8 illustrates a fume cupboard 29 similar to the fume cupboard 19 of Figure 7 except that it does not have the baffle 23 of the cupboard 19 of Figure 7.

The fume cupboard 29 has a slotted front screen 31 similar to screen 21 of the fume cupboard 19 of Figure 7 and has an opening 33 similar to the opening 25 of the fume cupboard 19 of Figure 7.

It can be seen from Figure 8 that, when a baffle is not provided along the lower edge of the front of the fume cupboard, eddies are set up in the lower region of the fume cupboard, these eddies causing air to flow against the main stream of air through the fume cupboard 29. Consequently a region is set up in which the direction and speed of airflow changes greatly in a short distance. A disturbance (e.g. an incidental draught, such as of a person passing by the fume cupboard, or even a person standing in front of the fume cupboard to impede the incoming air flow) can, therefore, easily upset the balance and can allow fumes from inside the fume cupboard to escape into the laboratary without workers being aware of the fact.

It can be seen by comparing the air flow through the fume cupboard 29 of Figure 8 with the air flow through the fume cupboard 19 of Figure 7 that the presence of baffle 23 in the fume cupboard 19 of Figure 7 lessens the risk of fumes passing out of the fume cupboard into the laboratory due to a disturb- ance outside the cupboard because the baffle results in air being drawn from relatively dead space directly into the bottom of the fume cupboard.

Figure 9 illustrates the air flow velocity at selected points in a fume cupboard 35 having a slotted front screen 37, a baffle 39 and an opening 41. Air is drawn through the front screen 37 and between the baffle 39 and the floor 42 of the fume cupboard 35 and this air passes out of the fume cupboard through opening 41. The various points at which the air flow velocity was measured are indicated by asterisks.

These points are 5 cms. from the front screen 37 and are 2.5,33 and 60 cms above the floor 44 of the cupboard 35. The values given for the airflow velocities are measured in feet/minute.

Figure 10 illustrates the air flow velocity at selected points in a fume cupboard 43 which is similar to the fume cupboard 35 of Figure 9 except that it does not have a baffle. Fume cupboard 43 has a slotted front screen 45 through which air is drawn into the fume cupboard, an opening 47 through which air passes out of the fume cupboard, and a floor 48. The various points at which the air flow velocity was measured are indicated by asterisks.

These points are 5 cms from the front screen 37 and are 2.5,33 and 60 cms above the floor 48 of the cupboard 43. The values given for the air flow velocities are measured in feet/minute.

In both the fume cupboards 35 (Figure 9) and 43 (Figure 10) the air can be drawn through the cupboards by any suitable means (not shown). For example, the air can be drawn through the fume cupboards by means of a fan located outside the cupboard but connected to the outlet (i.e. outlet 41 of Figure 9 or outlet 47 of Figure 10).

By comparing the airflow velocities in Figures 9 and 10, it can be seen that the fume cupboards 35 of Figure 9 is more efficient since, in the lower region of the cupboard air is passing away from the front of the cupboard and towards the back of the cupboard.

In the fume cupboard 43 of Figure 10, however, air ib passing, in the lower region of the cupboard, away from the back of the cupboard and towards the front of the cupboard i.e. the flow is reversed to that in the lower region of cupboard 35 of Figure 9. Consequently, the fume cupboard 35 of Figure 9 is less likely to be adversely affected (i.e. fumes being drawn out of the cupboard into the laboratory) by disturbances outside the front of the cupboard than is the fume cupboard 43 of Figure 10.

Claims

1. An enclosure, one face of which comprises a flexible material and has a plurality of spaced apertures therein.

2. An enclosure as claimed in claim 1, in which the flexible material is glass fibre.

3. An enclosure as claimed in claim 1, in which the flexible material is a plastics material.

4. An enclosure as claimed in any of claims 1 to 3, in which the flexible material is transparent or translucent.

5. An enclosure as claimed in claim 1, in which the flexible material is canvas.

6. An enclosure as claimed in any of claims 1 to 5, in which the flexible material is in the form of a single sheet having the plurality of spaced apertures therein.

7. An enclosure as claimed in any of claims 1 to 5 in which the flexible material is in the form of a plurality of strips of flexible material arranged such that the plurality of spaced apertures are formed therebetween.

8. An enclosure as claimed in claim 7, in which the strips of flexible material are substantially para llel to each other.

9. An enclosure as claimed in any of claims 1 to 3, in which the flexible material has a central transparent section and the plurality of spaced apertures are located to either side of the central transparent region.

10. An enclosure as claimed in any of claims 1 to 9, in which the spaced apertures are in the form of elongated slots.

11. An enclosure as claimed in claim 10, in which the elongated slots are substantially parallel to one another.

12. An enclosure as claimed in claim 10 or claim 11, in which the elongated slots are vertical.

13. An enclosure as claimed in any of claims 1 to 4, in which the flexible material is in the form of a bead curtain.

14. An enclosure as claimed in any of claims 1 to 5, in which the flexible material is in the form of a venetian blind.

15. An enclosure as claimed in any of claims 1 to 14, which is in the form of a ventilated enclosure.

16. An enclosure as claimed in claim 15, in which the flexible material is retained such that it is not sucked into the enclosure by the ventilation.

17. An enclosure as claimed in claim 16, in which the flexible material is retained by weighting.

18. An enclosure as claimed in claim 16, in which the flexible material is retained by spring loading.

19. An enclosure as claimed in any of claims 1 to 18, in which the flexible material is detachable from the face of the enclosure.

20. An enclosure as claimed in any of claims 1 to 19, in which the flexible material is adapted such that it can be folded or rolled away when not in use.

21. An enclosure as claimed in claim 20, in which the flexible material is attached to a spring-loaded roller system such that it can be rolled away when not in use.

22. An enclosure as claimed in any of claims 1 to 21, in which the face comprising the flexible material and the plurality of spaced apertures also comprises a baffle along its lower edge.

23. An enclosure as claimed in claim 22, in which the baffle is separated from the lower edge of the face comprising the flexible material and spaced apertures such that air can pass between the baffle and the lower edge and into the enclosure.

24. An enclosure substantially as hereinbefore described and with reference to any of Figures 1,2,4,6,7 and 9 of the accompanying drawings.

24. An enclosure as claimed in claim 21 or claim 22, in which the baffle has an upper section which extends into the lower region of the enclosure.

25. An enclosure, which comprises a face having an opening therein and a baffle located along the lower edge of the opening.

26. An enclosure as claimed in claim 25, in which the baffle is separated from the lower edge of the opening such that air can pass between the baffle and the lower edge of the opening and into the enclosure.

27. An enclosure as claimed in claim 25 or claim 26, in which the baffle has an upper section which extends into the lower region of the enclosure.

28. An enclosure substantially as hereinbefore described and with reference to any of Figures 1,2,4,6,7 and 9 of the accompanying drawings.

New claims or amendments to claims filed on 20th May1981 Superseded claims 1 to 28 New or amended claims

1. A ventilated enclosure, one face of which comprises a flexible material and has a plurality of spaced apertures therein which, in use, serve to allow air to be drawn into the enclosure and also serve to allow the insertion of articles into, the withdrawal of articles from or the manipulation of articles within the enclosure by an operator who remains outside the enclosure.

7. An enclosure as claimed in any of claims 1 to 5, in which the flexible material is in the form of a plurality of strips of flexible material arranged such that the plurality of spaced apertures are formed therebetween.

8. An enclosure as claimed in claim 7, in which the strips of flexible material are substantially parallel to each other.

14. An enclosure as claimed in any of claims 1 to 5, in which the flexible material is in the form of a ventetian blind.

15. An enclosure as claimed in any of claims 1 to 14, in which the flexible material is retained such that it is not sucked into the enclosure by the ventilation.

16 An enclosure as claimed in claim 15, in which the flexible material is retained by weighting.

17. An enclosure as claimed in claim 15, in which the flexible material is retained by spring loading.

18. An enclosure as claimed in any of claims 1 to 17, in which the flexible material is detachable from the face of the enclosure.

19. An enclosure as claimed in any of claims 1 to 18, in which the flexible material is adapted such that it can be folded or rolled away when not in use.

20. An enclosure as claimed in claim 19, in which the flexible material is attached to a spring-loaded roller system such that it can be rolled away when not in use.

21. An enclosure as claimed in any of claims 1 to 20, in which the face comprising the flexible material and the plurality of spaced apertures also comprises a baffle along its lower edge.

22. An enclosure as claimed in claim 21, in which the baffle is separated from the lower edge of the face comprising the flexible material and spaced apertures such that air can pass between the baffle and the lower edge and into the enclosure.

23. An enclosure as claimed in claim 20 or claim 21, in which the baffle has an upper section which extends into the lower region of the enclosure.