Abstract:
A laboratory fume hood apparatus and method for containing contaminated air within the confines of the fume hood which includes a generally rectangular housing having a vertically movable door for providing an opening to the interior of the fume hood. A contoured air foil on the bottom of the door, an adjacent sill, openings in the door, a bypass slot formed in the housing and an air directing wall portion within the housing combine to provide a flow of outside air downwardly along the interior surface of the door and then directly toward an exhaust plenum located at the rear wall of the interior cabinet.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to fume hoods used in laboratories and the like to permit technicians to work on materials within the confines of the interior cabinet of the fume hood without exposure to toxic or otherwise dangerous fumes that may be generated by such work, and more particularly to a fume hood of this type in which the fumes or contaminated air is maintained substantially within the confines of the interior cabinet, even when access to the interior is undertaken through a sash opening, by a unique pattern of air flow within the interior of the cabinet. 
     Fume hoods are constructed with a wide variety of air flow arrangements for directing the flow of outside air in a desired path within the confines of the interior chamber. For example, in Bayern U.S. Pat. No. 3,237,548 a flow path is created within the confines of the fume hood that includes a directed flow of air downwardly along the plane of the sash or door of the fume hood to prevent the escape of contaminated air when the door is open. 
     In Turko U.S. Pat. No. 3,747,505 a diffuser is provided to direct auxiliary air directly downward and somewhat outwardly when the fume door is open to combine with outside air and form an air flow path that sweeps along the plane of the open door and then along the bottom of the interior cabinet to contain contaminated air within the cabinet. A somewhat similar air flow path is disclosed in Chamberlin U.S. Pat. No. 3,752,056 where a plenum is located above and outside of the door of the fume hood. 
     In McNeil U.S. Pat. No. 2,819,666 a baffle plate is provided above the door to direct auxiliary air downwardly along the interior surface of the door of the fume hood when it is in its closed position, and this air flow is cut off when the door is opened and air from an upper plenum is used to created a screen of auxiliary air generally in front of the plane of the door when the door is open. Also, a flow of outside air is introduced into the bottom of the interior cabinet of the fume hood and is directed inwardly along the bottom wall of the interior cabinet to remove heavy contaminated air within the cabinet. 
     A somewhat similar flow pattern is disclosed in Grow U.S. Pat. No. 4,177,718 where a valve member is moved between one position when the fume hood door is closed to direct air downwardly along the interior surface of the door, and another position when the door is open to create a flow of auxiliary air downwardly along the outside plane of the open door. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an apparatus and method are provided for containing and properly directing contaminated air within the confines of a fume hood or the like. The apparatus includes a housing forming a generally rectangular interior cabinet that has side walls, a back wall, a top wall, and an open front face, and a door disposed for movement between a closed position closing the open front face and an open position creating an opening through which a technicians hands can extend to work within the interior cabinet. An exhaust plenum is located within the interior cabinet adjacent the back wall thereof, and it is adapted to be connected to an exhaust source for exhausting air from within the interior cabinet. A bypass slot is formed in the housing and disposed to direct outside air downwardly generally along the inside surface of the door, and openings are formed in the door and are disposed to admit outside air into the interior cabinet in a direction generally transverse to the flow of outside along the inside surface of the door to thereby cause the combined flow of the outside air to flow in a direction generally directly toward said exhaust plenum. 
     In the preferred embodiment of the apparatus of the present invention, the door moves in a vertical direction between the open and closed positions thereof, and a contoured air foil is attached to the bottom edge of the door to direct a flow of outside air inwardly toward the back wall when the door is in its open position. 
     Additionally, it is preferred that a wall portion be disposed adjacent the upper portion of the interior cabinet and be inclined inwardly and downwardly, and that the bypass slot be formed between the lower end portion of the wall portion and the upper end portion of the door. 
     It is also preferred that the housing include an air exhaust opening disposed in the top wall thereof generally adjacent the back wall thereof, and in communication with the exhaust plenum. 
     The method of the present invention includes the steps of creating a first flow path of outside air inwardly into the interior chamber through a by-pass slot formed in the fume hood housing in a direction generally downwardly along the inside surface of the door, creating a second flow path of outside air though the door which is generally inwardly toward the back wall of the interior cabinet, and creating an area of uncontaminated air adjacent the back wall of the interior cabinet. Preferably, the method includes the step additional of creating the aforesaid region of uncontaminated air through air flow through vertical clearance slots formed between the overlapping edges of glass panels included in the door. 
     In the preferred embodiment of the method of the present invention, such method includes the step of positioning a wall portion within the interior cabinet so that the lower edge thereof is spaced from the door to create the first flow path of air. The method may also include the step of disposing an airfoil along the bottom edge of the door and forming the airfoil with a contour for directing the second flow of outside air inwardly toward the back wall of the interior chamber when the door is opened. Finally the method may include the step of exhausting the outside air from the interior cabinet though an opening in the top wall of the interior cabinet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a fume hood according to the present invention; 
     FIG. 2 is a side elevational view of the fume hood illustrated in FIG. 1 taken in a vertical plane at the approximate center of the fume hood; 
     FIG. 3 is a detail view showing slots formed between the overlapping edges of glass panels that form part of the fume hood door; 
     FIG. 4 is a front view of the fume hood of the present invention with the front door raised; 
     FIG. 5 is a side elevational view of the fume hood illustrated in FIG. 4, and taken along the same plane as FIG. 2; 
     FIG. 6 is a detail view showing the air flow through the open door of FIG. 4; 
     FIG. 7 is a front view of the fume hood of the present invention with some of the glass panels in the door moved to form an opening in the front door; 
     FIG. 8 is a side elevational view, similar to FIG. 5, of the fume hood illustrated in FIG. 7; and 
     FIG. 9 is a detail view showing the air flow through the open glass panels in FIG.  7 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Looking now in greater detail at the accompanying drawings, FIGS. 1 and 2 illustrate a fume hood  10  that is used in laboratories and the like to permit technicians to work on materials within the confines of the fume hood without exposure to toxic or otherwise dangerous fumes that may be generated by such work. 
     The fume hood  10  includes a housing  12  that is formed with a generally rectangular interior cabinet  14  which includes side walls  14 , a back wall  16 , a top wall  18 , and a front face  20 . The front face  20  has door  22  mounted therein for vertical movement between a raised position at which the front face  20  is opened so that a technicians hands can extend there through to work within the interior cabinet  12 , and a lower or closed position at which the door  22  closes the opening in the front face  20 . The bottom of the fume hood is generally open allowing the fume hood to sit directly on a laboratory work surface  23  as best seen in FIG. 2, and the door  22  would normally rest on the work surface  23  when the door  22  is in its closed position, but the door  22  is shown in a slightly raised position in FIG. 2 to better illustrate the relationship between the door  22   20  and the work surface  23 . 
     As best seen in FIG. 2, the interior cabinet  12  includes an exhaust plenum  24  that extends vertically along the back wall  16 , and the upper end of the exhaust plenum  24  communicates with an exhaust opening  26  in the top wall  18 . The exhaust opening  26  is adapted to be connected to any convenient and conventional exhaust source, such as the intake of a blower (not shown), for exhausting air from the interior cabinet  12  in a manner well known in the art. The interior cabinet  12  also includes a conventional fluorescent light fixture  28  for illuminating the inside of the interior cabinet  12 , and an access panel  30  through which the side wall electrical and plumbing chase can be accessed through one of the interior side walls. The fume hood  10  may also include a conventional airflow alarm  32 , and a plurality of conventional plumbing service outlets  34 . 
     In accordance with one feature of the present invention, the interior cabinet  12  also includes a wall portion  36  that extends downwardly with an inwardly directed incline so that the lower end of the wall portion  36  is spaced from the upper end of the door  22  to thereby provide a bypass slot  38  which is disposed to direct outside air downwardly along the inside surface of the door  22  in a manner to be described in greater detail presently. 
     The door  22  is illustrated in FIG. 2 almost at its lowermost or closed position, and the bottom edge of the door  22  is provided with a contoured airfoil member  40 . The bottom surface of the airfoil  40  is curved slightly upwardly as best seen in FIG. 2 so that when the door  22  is raised to an open position, the contoured bottom surface of the airfoil  40  will direct air toward the back wall  16  and the exhaust plenum  24 , and slightly upwardly. In this same regard, the sill  42  of the work surface  23 , which is adjacent the airfoil  40  when the door  22  is in its closed position, has a slight upwardly inclined surface portion  44  which also tends to direct inwardly directed air flowing through the opening created by the raised door  22  generally toward the back wall  16  and the exhaust plenum  24 . 
     The door  22 , as best seen in FIGS. 2 and 3, includes a first sash  45  that that is formed as a solid rectangular panel, and a second sash  47  that includes a frame  46  in which are mounted a plurality of adjacent glass panels  48  as best seen in FIG.  3 . so that they are movable horizontally relative to one another, whereby the front face  20  of the fume hood  10  can be opened by either raising frame  46 , which raises the entire second sash  47 , or sliding one or more of glass panels  48  sideways to provide an opening in the second sash  47 . Additionally, the glass panels  48  are arranged so that the edges of each two adjacent glass panels  48  have a slight overlap, and the overlapping edges are spaced from one another to form relatively narrow vertical slots  50  that extend along the vertical height of the door  22  whereby outside air is permitted to flow through the slots  50 . As is well known in the art, the sashes  45  and  47  are connected to a conventional pulley and weight arrangement  49  which assist in raising the second panel  47  upwardly until an extension on the lower end thereof engages the upper sash  45 , after which both panels are moved upwardly together. While this arrangement of the sashes  45 ,  47  and the door  22  are preferred, it will be understood that other conventional, known or equivalent sash arrangements could be used in connection with the present invention so long as the door is formed with openings or slots that will result in the requisite amount of outside air flowing into the interior cabinet  12 , as described below. 
     The above-described structure of the fume hood  10  provides a unique airflow pattern that is particularly effective in creating a barrier flow of clean outside air between the technician located outside the fume hood  10  and the toxic fumes that may be present in the interior cabinet  12  of the present invention when the door  22  is opened. 
     More specifically, and as best illustrated in FIG. 2, when the exhaust opening  26  is connected to an exhaust source as described above, a negative air pressure is created in the exhaust plenum  24  along the back wall  16  of the fume hood  10 . This negative pressure within the interior cabinet  12 , even when the door  22  is closed as illustrated in FIG. 2, creates an airflow that is directed by the wall portion  36  downwardly through the bypass slot  38  and generally along the interior surface of the door  22  as indicated by the vertical component  52  of the airflow arrows  54 . It is also to be noted that the interior surface of the wall portion  36 , with its inwardly directed incline, deflects air circulating with the upper portion of the interior cabinet  12  away from the work area directly behind the door  22 . 
     At the same time, as best illustrated in FIG. 3, outside air is also drawn into the interior cabinet  12  through the vertical slots  50  in the door  22 , and this inwardly directed flow of outside air, which is directed toward the back wall  16 , influences the vertical airflow component  52  so that the confluence of the two airflows results in a generally rearward flow of the air toward the back wall  16  as indicated by the airflow component  56 . Thus, even with the door  22  closed, or substantially closed, there is a pattern of outside airflow which includes a vertically directed component that creates a barrier of outside air along the interior surface of the door  22 , and a general flow of air directly toward the exhaust plenum  24  at the back wall  16  of the interior cabinet  12 . 
     As discussed above, the door  22  can be opened by raising the second sash  47  in which case outside air flows directly into the fume hood beneath the bottom edge of the second sash  47  as illustrated in FIGS. 4-6, or the door  22  can be opened by sliding one or more of the glass panels  48  sideways, as illustrated in FIGS. 7-9. 
     Accordingly, when a technician begins raising the door  22  to work within the confines of the interior cabinet  12 , outside air will obviously be pulled into the interior cabinet  12  through the opening created by the open door  22 , and because of the above-described pre-existing airflow created within the interior cabinet when the door  22  is closed, the outside air flowing through the open door  22  will generally follow and to some extent augment the preexisting flow pattern toward the exhaust plenum  24 . By virtue of this arrangement, the airflow within the interior cabinet  12 , when the door  22  is open, does not form itself into a vortex that is generally conventional in the art and that can be difficult to control because of the angular momentum inherent in the vortex. Rather, the airflow pattern created by the present invention establishes a barrier of outside air at the door opening to prevent toxic fumes and the like within the interior cabinet  12  from flowing outwardly in a manner that would endanger the technician, and the pattern of the outside airflow moves in a generally straight line direction directly to the exhaust plenum  24  so that the toxic fumes are carried by the flow of outside air directly to the exhaust plenum  24  where they can be exhausted through the exhaust opening  26 , all as generally illustrated in FIGS. 5 and 8. Thus, the toxic fumes are removed from the interior cabinet  12  more quickly because of the direct flow to the exhaust plenum  26 , and in a more controlled airflow pattern as contrasted with a flow pattern in the form of a vortex. 
     Those skilled in the art will know that airflow patterns within the confines of a fume hood do not flow in straight, defined lines, and, therefore, it will be appreciated that the description of the airflow patterns created by the present invention is meant to describe the general direction of flow of the great majority of the air. Moreover, it will also be appreciated that the general nature of the airflow can be varied to some extent, if desired, depending on the size of the bypass slot  38  and the vertical slots  50  in the door  22 , and by selecting the blower that creates the negative pressure in the exhaust plenum  24 . Thus, these variables can be taken in consideration by those skilled in the art in carrying out the present invention in a manner that will best suit the particular application of the fume hood  10 . 
     It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.