US2567622A - Fume hood - Google Patents

Description

Sept. 11, 1951 M. D. TAYLOR 2,567,622

FUME HOOD Filed Sept. 19, 1947 Patented Sept. 11, 1951 Marion D. Taylor, Berkeley, Calif., assigner to Shell Development Company, San Francisco,

Calif., a corporation of Delaware Application September 19, 1947, S'iial No'. 774,930

1 'hi-s invention relates to fume hoods of the cabinet type and isy more particularly, concerned with ran improved hood suitable for use in laboratories Where light and/or heavy iumesof noxious or disagreeable properties are generatecl. and must be withdrawn through an exhaust duct.

Cabinet type A'fume hoods provided with vents for discharging light 'and heavy fumes from the top and bottom of thecabinet are already known. (See, for example, U. S. Patent No. 1,934,808) Such fume h'oods'are installed in laboratories and industrial establishments to permit chemical and physical processes involving the generation or discharge vof fumes to be carried out. The main purpose Vof using 'such hoods is to prevent the -escape of such fumes into the space surrounding the hood, e. g., into the laboratory room. I-le're` tofore `hoods vhai/e been designed particularly to facilitate 'the 'withdrawal'of the fumes from `vari*- ous parts of the space within the hood, and the purpose has been to cause the fumes to move backward, i. e., away from the front; 'for this purpose the intakes or at least some of the intakes to the suction duct have been located near the back of the hood. While such hoods are effective to draw off fumes from within the hood, they have not been fully effective in preventing the fumes from drifting out from the front of the hood unless the front closure is shut.

According to the present invention it was found that fumes can be more effectively prevented from escaping out from the front of the cabinet Hwhen 'theolosure is open by drawing the fumes off at the front instead of at the sides or rear, it being the distinguishing feature of this invention that a strong suction eiect is provided at the front. In the preferred embodiment of the invention'the 'heavy fumes are caused to flow toward the 'front of the cabinet and then downwardly around the forward edge of the work bench, and the bench is tted closely against the sides and rear of the cabinet to provide no other drawoff point. It is also possible to employ auxiliary drawof apertures in the bench or in the sides or rear of the cabinet; however, it was found that, with a given capacity of the duct system to which the hood'is connected, the use o-f-'su'ch auxiliary drawoii apertures or vents dissipates the available vacuum and that better results are obtained by applying substantially all of the available suction at the front of the cabinet. While heavy fumes may to a certain ex'- tent collect at the rearof the cabinet with such an arrangement, they are not objectionable at that location, yand the main object of using a fume hood, viz., thek escape of fumes into vthe-space surrounding the hood, is "achieved more eec'- tive1y.

The instant invention has, for an object, Vthe improvement 'of the vheavy vapor -drawof system whereby heavy *vaporsv` or fumes are more veffectively prevented from flowing out of the iront of the fume hood when the front closure is'open. A further object is to provide an improved fume hood of the cabinet type which is suitable for full-length use, without acounter, as well as for use with a counter, 'as desired, which is arranged for the drawoff of light and/or Vheavy fumes, as desired.

The improved fume hood according to this invention cor'nprises' adam at the `front of the cabi-- net rising a suitable distance, e. g., 2 to 5 inches or more, 'above the level of the work bench, 'and installed so as" to be in position regardless vof whether' the `front "closiire of the cabinet above the 'dam is closed or lis-"ope'n V'to permit access vto the equipment within the cabinet. A vent for causing a down draft is provided 'at or 'near the .dam to draw oihea-vy fumes and prevent them from accumulating on the work 'bench to a height sulicient to overow the dam.

In one embodiment of the invention, the fume hood comprises a cabinet Vforming a working chamber and provided with suction vents at `the top and at the bottom, the ventsbeing connected wither to sepa-rate suction ductsv or to a commonouct; the cabinetis provided with 'a 'removable or adjustable counter, positioned between said vents and the bottom of the cabinet may, optionally, form 'a bottom or lower work bench. The front closure is constructed vto provide a dam or baffle extending 'above the bottom of the working chamber', regardless of whether this bottom be the adjustable counter or, when the counter is removed, the Vlower bench at the bot tom of the cabinet.v A heavy vapor draw-off space or slot only between the forward or outer edge of the working counter and the dam lor baille whereby va more effective removal of the heavy Yfumesis effected.

According to another embodiment of `the `invention the suction'vent Yat'the bottom of the cabinet is arranged along the dam at the front of the hood.

The invention will be better understood from the following detailed description, taken Y-together Awith the drawings forming a part ofthe specication and Villustr'ating `one preferred ema bodiment oflthelinvention, wherein:

Fig. 1 is a front elevation view of the improved fume hood;

Fig. 2 is a vertical sectional View taken on the line 2 2 of Fig. l;

Figs. 3 and 4 are horizontal sectional views taken on lines 3 3 and 4, respectively, of Fig. 2;

Fig. is a vertical, sectional View, similar to Fig. 2, showing a modified construction, and

Fig. 6 is a horizontal sectional View taken on line 6 6 of Fig. 5.

Referring to Figs. 1-4 of the drawings, the fume hood comprises a supporting base I having a lower bench 2, side walls 3, and a rear wall 4 and a roof 5, forming a working chamber. A drain trough 6 is recessed in the lower bench and may be connected to a liquid discharge line, such as a sewer, not shown. A false back wall or partition 'I extends substantially the full height of the cabinet and has its upper portion inclined forwardly. A draw-off duct 8 at the top of the cabinet, provided With an adjustable damper 9, may be connected by means of a connecting duct, not shown, to some means of suction, such as a fan. The space between the walls 4 and 'I forms a heavy vapor drawoff duct, such vapors entering this duct at the bottom through the opening or vent between the drain trough and the bottom of the wall l. This opening may be adjusted by means of an adjustable damper I0. An adjustable damper I I at the top of the wall 'I permitsthe vent between the top of the cabinet and the vent to be adjusted.

A removable shelf or counter I2, forming an upper work bench, is mounted at an intermediate level by means of support I3 secured to the f wide walls. The supports I3 are disposed at different levels to permit the counter to be adjusted to different heights, the counter being shown in its upper position. When the counter is installed, it divides the cabinet into a working space above the counter and into a heavy fume collecting chamber beneath the counter. The counter I2 is in engagement with the side walls 3 and the false wall 1 but its forward edge is set back of the lower bench 2, as explained hereinafter. A fixed baille I4 extends along the front of the cabinet 2 forming a transverse dam. 'IheV top of the baiile I4 is preferably above the level of the counter I2 when the latter is in its lower position. A similar baille I5 extends downward from the roof. The space between the bailies I4 and I5 is closed by three panels which may be window sashes mounting shatterproof glass panes. The upper (outer) sash I6 may be removable or xed to the cabinet; the intermediate (inner) sash I1 and the lower sash I8 are vertically slidable in sash frames on the side walls 3. The sashes I6 and II may be mounted in the forward-most and rear-most sash frames, respectively, as shown, to provide a slot between them through which air may enter the cabinet at a point intermediate to the top and bottom of the working chamber. The lower sash I8 is of such a height as to extend above the level of the removable counter I2 when in its lower position, thereby forming a dam or baiile to prevent heavy vapors from drifting out of the cabinet even when the intermediate (inner) sash I'I is raised. It extends upwardly only through a minor portion of the height of the working chamber, e. g., 2 to 5 inches, whereby access to the chamber is not obstructed. Sash I 8 is positioned so as to leave a space or vent I9 between the front edge of the counter and the sash. The bottom of the sash I8 fits inside of the baille I4.

f and are drawn off past the damper The intermediate (inner) sash I'I closes the space between the upper and lower sashes except for the slot between it and the sash I6. Sashes I'I and I8 are disposed as shown in Fig. 2 so that both may be raised to positions behind the upper (outer) sash I6, thereby aiording access to the cabinet. A conduit 20 is mounted on the side walls 3 and discharges into the trough 6. It is provided with inlets 20a, providing a tableheight drain.

When the fume hood is in use a suction is applied to the duct 8 and fumes are drawn into it from the top and bottom of the hood in accordance with the setting of the dampers I0 and II.

The space at the top of the cabinet behind the upper (outer) sash I6 and baiiie I5 forms a light fume collecting space from which the fumes are drawn olf.

When the fume hood is used for operations at table-height, the counter 'I2 is installed as shown and the lower sash I8 is in its lower position. The space beneath the counter I2 now forms a fume collecting chamber for heavy vapors, which enter downwardly through the space or vent I9 III and through the heavy vapor drawoff duct behind the wall l. This ow will occur regardless of the position of the intermediate (inner) sash Il. When, however, this sash is in its raised position, the arrangement described above is particularly advantageous because ity was found that heavy fumes are best prevented from leaving the hood by applying a strong suction near the front of the counter, and by providing a dam, such as is formed by the upwardly extending portion of the sash I8. By providing the Vent I9 substantially only at the front a more eiiective suction can be attained at this point with a given vacuum at the duct 8 than when providing vents also at the sides and rear of the counter.

When the hood is used as a full height hood the counter I2 is lowered to its lower position, or removed entirely. In this use the lower sash I8 may be in its lower or raised position, and with the counter in its lower position heavy fumes enter the heavy vapor drawoff duct as before. When the sash I8 is raised the baffle I4 prevents such fumes from drifting out toward the front of the cabinet. When the counter I2 is removed from the cabinet heavy fumes are not drawn forward, but enter the lower vent at the rear directly.

The dampers I0 and II may be adjusted in accordance with the nature of the fumes to be drawn off. Thus, When only light fumes are to be drawn oif, the damper II is open and the damper I may be partially or entirely closed; conversely, when only heavy fumes are to be drawn off, the damper I0 is open and the damper II may be partially or entirely closed. In other situations the dampers may be adjusted to provide simultaneous draw-off of light and heavy fumes. It was found that the damper I0 may in certain cases be omitted because when the damper II is fully open a negligible amount of vapor is drawn in from the bottom with a moderate vacuum on the vent 8.

Referring to Figs. 5 and 6, like reference characters indicate parts previously described for Figs. 1 to 4. In this embodiment the lower vent is arranged in the form of a sheet iron duct 2I secured to the inner face of the lower baille I4 having a narrow longitudinal aperture 22 facing downwardly to prevent the entrance of liquid. The ductl 2I sconnected by connecting ducts 23 at Ythe Sides of the cabinet to the duct 8; If desired, damper-s 24 may be provided.

The' embodiment according to Fig. 5 may be used with the counter l2 in the manner previously described; When the counter I2 is removed entirely for using the fume hood as a fullheight cabinet, this form provides suction at the front of the cabinet at the dam or baffle I4, for preventing the overflow of heavy fumes from thefront of the cabinet when the sashes |11 and/or I8 are in their raised positions.

I claini as myinvention:`

l, A; fume hood comprising a cabinet having side walls, a rear wall and a roof, a lower bench at the bottom of said cabinet near the floor level, a drain trough for liquidat the bottom of the cabinet, a removable working Vbench at an intermediate level of the cabinet near table height forming a working chamber thereabove and a heavy fume collecting chamber therebeneath, a drain having its intake within said working chamber and discharging into said drain trough, duct means for withdrawing fumes from the bottom ofy said collecting chamber and from said working chamber, an adjustable damper above said drain trough for regulating the passage of heavy fumes from said collecting chamber into said vent, and a vent between said working chamber and said collecting chamber.

2. A fume hood comprising a cabinet having side walls, a roof and double rear walls forming a duct therebetween, a lower bench at the bottom of said cabinet, a vertically adjustable imperforate working bench at an intermediate level of the cabinet, fitting closely against the sides and rear of the cabinet and dividing the cabinet into a working chamber thereabove and a heavy fume collecting chamber therebeneath, communicating vents between the bottom of said collecting chamber and said duct and between the top of the working chamber and said duct, damper means for regulating the passage of fumes through said vents, a transverse baffle at the bottom of the cabinet extending across the front of the collecting chamber and forming a first dam extending upwardly from the lower bench for a portion only of the height of said chamber, a second transverse bafe at the top of the cabinet extending across the upper portion of the working chamber, and a front closure for the cabinet comprising a pair of vertically slidable panels, one for the working chamber and the other for the collecting chamber, the latter panel being spaced from the removable bench to provide a vent for the downward flow of heavy fumes from the Working chamber into the fume collecting chamber and being of such height as to extend, when in its lower position, to above the level of the removable working bench through a minor portion of the height of the working chamber to provide a second dam.

3. A fume hood comprising a cabinet having side walls, a rear wall, and a roof and containing a working bench at an intermediate level, said bench defining above itself a working chamber within the cabinet, the front of the working chamber being adapted to be at least partially open to aicrd access thereto; a drawoff duct in communication with said working chamber above the bench for drawing ofi' light fumes from said working chamber; and means for drawing heavy fumes generated within said working chamber forwardly along said bench to the front of the cabinet and thence downwardly without escape through said open front compris- 6 ing a bal eXte'hdihg across the front of the cabinet to form a fume dam rising upwardly through only a ini-nor portion of the height of the Working chamber but through a substantial height suiiicient to prevent the escape of heavy fumes at the front of the cabinet, a vent opening along the front of the bench and in rear of the baiiie for the downward passage of fumes, and an elongated, confined duct extending transversely across the cabinet beneath the front of the bench and-immediately in rear of the dam, said duct bei-ng apertured along the length thereof to receive heavy fumes from said vent opening and to apply a suction to the working chamber through said vent. 1 Y

e. A fume hood comprising acabinet having sidewalls,- a rear wall and a roof; a lower bench at the bottomof said cabinet near the floor; a removable working bench at an intermediate level ofthe cabinet *nearv table height dening a working chamber above itself* and a fume collecting* chamber beneathitself and the lower bench, the front ci" the working chamber being adapted to be at least partially open to aiford access thereto; a light fume drawoff duct in communication with said working chamber above the working bench for drawing on light fumes from said werking chamber; a heavy fume drawo'i duct communicating with said collecting chamber beneath the working bench for drawing oi heavy fumes therefrom; a baffle extending across the front of the lower bench and forming a first fume dam extending upwardly from the lower bench for a portion only of the height of the collecting chamber but through a substantial height tc retain heavy fumes therein against escape from the front; and a first movable c10- sure for said collecting chamber extending across the front thereof and disposed to close the front i of said chamber above said rst baflle and extending upwardly in front of and above the level of the working bench through a minor portion of the height of the working chamber but through substantial height sufcient to prevent the escape of heavy fumes from the working chamber at the said open front thereof to form a second heavy fume dam; a second movable closure extending across the front of the working chamber and rising upwardly from the top of the second fume dam for closing the front of the working chamber; and a vent opening along the front of the working bench in rear of the second dam, said collecting chamber being isolated from said working chamber by said working bench except for said vent opening whereby heavy fumes generated within said working chamber will be drawn forwardly along said bench to the front of the cabinet and thence downwardly through said vent opening into the collecting chamber for evacuation through the heavy fume drawoi duct.

5. A fume hood comprising a cabinet having side walls, a rear wall and a roof; a lower bench at the bottom of said cabinet near the iioor; a removable working bench at an intermediate level of the cabinet near table height dening a working chamber above itself and a fume collecting chamber beneath itself and the lower bench, the front of the working chamber being adapted to be at least partially open to afford access thereto; a light fume drawoff duct in communication with said working chamber above the working bench for drawing off light fumes from said working chamber; a heavy fume drawoff duct communicating with said collecting chamber beneath the working bench for drawing off heavy fumes therefrom; a batile extending across the front of the lower bench and forming a first fume dam extending upwardly from the lower bench for a portion only of the height of the collecting chamber but through a substantial height to retain heavy fumes therein against escape from the front; and a vertically slidable closure for said collecting chamber which when in its lowered position rises from said rst baille to a height well above the level of said working bench at the intermediate level to form a second heavy fume dam preventing the escape of heavy fumes from the working chamber at the said open front thereof, but through only a minor portion of the height of the working chamber to provide access thereto, said closure extending fully across the front of the cabinet; and a vent opening along the front of the working bench in rear of the second dam, said collecting chamber being isolated from said Working chamber by said working bench except for said vent opening whereby heavy fumes generated within said working chamber will be drawn forwardly along said bench tothe front of the cabinet and thence downwardly through said vent opening into the collecting chamber for evacuation through the heavy fume drawoi duct.

6. The fume hood according to claim wherein the heavy fume drawoif duct comprises an elond gated, conned duct within the collecting chamber extending transversely with respect to the cabinet in rear of the baffle at the front of the cabinet and near the lower bench, said duct being apertured along the length thereof to receive heavy fumes from said vent opening and from said lower bench.

7. The fume hood according to claim 5 wherein the said slidable closure is spaced forwardly from the front edge of the Working bench to provide a slit-like space between itself and the bench, the said space constituting the said vent opening.

MARION D. TAYLOR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,117,551 Coleman Nov. 17, 1914 1,218,718 Throop Mar. 13, 1917 1,608,082 Curren Nov. 23, 1926 1,934,808 Liptay Nov. 14, 1933 1,968,532 Liptay July 31, 1934 1,972,917 Buckel Sept. 11, 1934 2,332,174 Shreve Oct. 1'7, 1943

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