Patent Publication Number: US-10329812-B1

Title: Tank cover access hatch with safety barrier

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns liftable hatch covers for decks or tank cover structures, especially for covers over tanks in sewage treatment plants. In particular the invention encompasses a safety barrier or grate that cooperates with the hatch cover and prevents service personnel from falling through an open hatch of such a tank cover. 
     Tank covers, particularly for sewage treatment tanks, are shown in U.S. Pat. Nos. 6,151,835, 6,012,259 and 5,941,027 of Hallsten Corporation. The tank covers, as well as liftable hatches for incorporation in the tank covers, are typically formed of interconnected extruded aluminum components, as shown in each of the above-listed patents. 
     The prior Hallsten patents, especially U.S. Pat. No. 5,941,027, show tank access hatches that hinge back a full 180° when fully opened, and this can be achieved via a special hinge, essentially a “gear hinge”. 
     Such tank access covers, especially for sewage treatment tanks, are opened for several reasons: to enable a worker actually to enter the tank for servicing, or to extend a servicing implement into the tank; or simply to admit a flow of air into the tank for aeration, the air being drawn by a fan located elsewhere in or on the tank. The open hatches present a problem of a worker accidentally falling through the opening. 
     This problem of open hatches, whether over a hatch opening in a public sidewalk, a floor access hatch, or a roof access opening or skylight, has been addressed previously. For example, see the “Hatch Safety Net”, marketed by Safe Approach of Poland, Me., comprising a polyester net that attaches to hook anchors on an aluminum frame that supports a hinged, solid hatch cover. The safety net can be removed from the hook anchors for access into the space below. The hatch with safety net is described as capable of being retrofitted in floor access hatches, roof scuttles, automatic fire vents or skylights. Also, USF Fabrication of Hialeah, Fla. produces a sidewalk hatch with hatch panels hinged on a frame, and one or more safety grate sections separately hinged along an edge of the frame which is perpendicular to the hinged edges of the hatch covers. The apparatus is described as “Double Safety Grate” or “Hinged Hatch Safety Grate”. The hatch/grate apparatus is typically used for public sidewalk access openings. 
     Another safety grate product, called “RETROGRATE SERIES X”, is produced by Halliday Products Inc. of Orlando, Fla. An aluminum double-door hatch cover is combined with a grate just below the doors, the grate being swingable upwardly for full access into the space below. Like the previously described product, the grate is pivoted on an axis perpendicular to the pivot axes of the hatch covers themselves. 
     The above safety grate devices are not directed to tank covers in sewage treatment applications, nor do they exhibit the efficient construction, operation and safety features of the invention described below. 
     SUMMARY OF THE INVENTION 
     The invention encompasses several different forms of combined hatch cover and safety grate or barrier, as applied to a tank cover particularly of a sewage treatment plant. The tank cover is formed of assembled plank, edge connector and beam components, primarily aluminum extrusions, as described in the previous Hallsten patents noted above. The access cover for the hatch can advantageously be produced from the same aluminum extrusions, especially the planks and edge connectors (interlocking deck channels). 
     In a first embodiment the hatch cover/grate configuration of the invention forms a “A” shape when raised to the open position with the barrier deployed. 
     A hatch cover, preferably with a gear hinge on one edge that allows the hatch to fold completely back onto the deck (through) 180°, has a safety grate attached to its bottom side by a grate hinge. The grate hinge pivots at the forward, free end of the hatch cover, bottom side. Thus, when the hatch cover is opened, the grate structure will hang freely down from the hatch cover, unless latched back to the cover. For access of a person down into the tank, the grate can be held or latched back against the bottom of the hatch cover, to swing the two components back against the deck, stacked together. For using the opening as an air intake vent, the grate can be spread outwardly from the hatch cover, swung about the gear hinge, to the point that the bottom edge of the grate can be engaged against the deck at the edge of the opening, at the opposite side of the opening from the hatch cover hinge. Braces or struts are included as a limiting device, similar to those employed in a step ladder, on both sides, so that an “A” shape is formed. This sets the angle of the grate and cover and allows the hatch opening to serve as a ventilation opening, for admitting air into the tank, and there can be a series of these openings set up for ventilation (one or more fans exhaust the air at points on the tank distant from the hatch openings). 
     With the struts extended, holding the grate at its fixed position to form an “A”, the struts, the grate and the hatch cover form safety barriers around the opening at all four sides. 
     Thus, this form of hatch cover/grate serves the dual purpose of (a) allowing full access into the tank when needed; and (b) serving as a ventilation opening when needed, with safety barriers surrounding the hole. 
     In a second form of the invention the hatch cover can be essentially the same as in the first form, and the grate can also be similar. The grate has a pair of hinge legs extending upwardly (perpendicular to the grate) at its back end. When lying horizontally in the normal position of the grate, the grate will be pivotally connected to a beam or other fixed structure via the vertical legs, lying, for example, a few inches below the deck of the tank cover. The pivot point for the legs preferably is just below and inward of the opening, relative to the hatch cover hinge. Once the hatch cover is opened fully, through 180°, and folded back onto the deck, the grate will provide a protective barrier, lying horizontally across the opening, to prevent fall-through accidents. If access is needed for a person to enter the tank, the grate is simply pulled up and hinged about the pivot points of the legs, to swing the grate back, upside down and stacked against the opened hatch cover. The length of the hinge legs is such as to allow the opened safety grate to lie essentially flatly against the opened hatch cover. 
     A third form of safety grate arrangement is similar to the second form described above, except that the grate, again with hinge legs at one edge, is hinged at the opposite side of the opening from the hatch cover hinge. The hinge legs allow the grate to sit a selected distance below the closed hatch cover. When the hatch cover is opened, both the hatch and the grate can be fully opened to 180° so that each lies flatly on the deck, on opposed ends of the opening. Alternatively, the hatch can be opened, e.g. to a vertical position, and the grate can be opened at the opposite side of the access hole, also to a vertical position, for ventilation or to allow access into the tank. The system includes some form of hold open device for each of the hatch cover and the grate, such as foldable struts or a telescoping locking strut device, which will stow beneath the deck when the grate and the hatch cover are both closed. 
     This forms a pair of safety barriers, one at each side of the opening. Flexible lines, such as chains or cords, can be connected from the hatch cover to the grate, spanning across the side spaces that would otherwise be vulnerable to personnel falling into the tank. This provides a four-sided safety barrier around the access hole. If access through the hole is needed, the safety chains or cords at one side can be removed. 
     A variation of the above embodiment is to have the same hatch cover and grate opened into an “A” configuration, as in the first form described above. The free end of the grate can simply engage into a space at the bottom of the hatch cover, near its free end, and a latch can be provided to retain the two together at this point. A flexible line or chain can be put in place at each open side of the “A” configuration, so that the hatch opening will be protected by a barrier at all four sides. 
     The grate when in place on the opening can be supported on all four sides, if a typical extruded component as in Hallsten Corporation tank covers or decking is welded to or otherwise fixed to a beam tube at the lateral sides of the hatch opening. These are the sides of the opening that extend at right angles from the hatch hinge. Supporting the grate at all four sides allows the grate to be of lighter materials, for less total weight. The grate in this case could be a lifted-out grate, without hinges, or it could be hinged at one edge. 
     Essentially the same configuration could be used for another purpose, with a solid inner layer rather than a grate. This is essentially another piece of decking beneath the hatch cover. Such an inner layer can be repeated under all deck or tank cover sections, not only at hatch covers, for providing an insulation layer in the case of a high-temperature sewage treatment process. The system called ATAD (auto thermophilic aerobic digestion) is operated at 180° F., and must be well insulated, up to R-20 insulative value. The deck panels of the invention are essentially all lift-out panels, and the lower panels can also be liftable, so that each panel can provide access. 
     The hatch cover/safety grate system of the invention is of simple and lightweight construction, is highly compatible with a tank cover of extruded aluminum components, is easily operated, and is effective to prevent fall-through accidents. These and other objects, advantages and features of the invention will be apparent from the following description of a preferred embodiment, considered along with the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A, 1B and 1C  are perspective views showing a tank cover with a hatch cover of the invention, shown closed and opened. 
         FIG. 2  is a sectional elevation view showing the hatch cover closed and showing an attached barrier or grate. 
         FIG. 3  is a sectional elevation view similar to  FIG. 2 , with the hatch cover partly opened. 
         FIG. 4  is a further sectional view showing the grate being deployed. 
         FIG. 5  is a similar sectional view showing the grate fully deployed, with the hatch cover and grate in a “A” configuration protecting the hatch opening. 
         FIG. 6  is an elevational view, partially in section, showing the opened hatch and grate. 
         FIG. 7  is a plan view showing a closed hatch in a tank cover, in another embodiment. 
         FIG. 8  is a sectional elevation view as seen along the line  8 - 8  in  FIG. 7 . 
         FIG. 9  is a sectional elevation view as seen along the line  9 - 9  in  FIG. 7 . 
         FIG. 10  is a plan view showing the hatch opened. 
         FIG. 11  is a sectional elevation view showing the hatch cover partially opened, with a barrier below. 
         FIG. 12  is a similar elevation view showing the hatch cover fully opened and folded back onto the deck or tank cover. 
         FIG. 13  is a plan view showing the barrier or grate fully opened and folded back onto the opened hatch cover. 
         FIG. 14  is a sectional elevation view indicating opening of the grate. 
         FIG. 15  is a similar sectional elevation view showing the grate fully opened and folded back, as in  FIG. 13 . 
         FIG. 16  is a plan view showing a further embodiment of the invention, showing the hatch cover and grate in closed position. 
         FIG. 17  is a sectional elevation view seen along the plane  17 - 17  in  FIG. 16 . 
         FIG. 18  is a plan view of the system shown in  FIGS. 16 and 17 , with the hatch cover opened and folded back onto the deck, and showing the barrier/grate in place over the opening. 
         FIG. 19  is a sectional elevation view showing the hatch cover being opened. 
         FIG. 20  is a similar sectional view showing the hatch cover partially opened and the barrier being moved to the open position. 
         FIG. 21  is a similar sectional view showing the hatch cover and barrier, hinged at opposite sides of the opening, fully erected into an “A” configuration. 
         FIG. 22  is a similar sectional view but showing the hatch barrier both opened to and retained in vertical orientations. 
         FIG. 23  is a plan view showing a portion of a tank cover and liftable panel in another embodiment of the invention. 
         FIG. 24  is a sectional elevation view of the embodiment shown in  FIG. 23 . 
         FIG. 25  is a cross-section elevation view, showing a variation. 
         FIG. 26  is a sectional view showing components of  FIG. 25  in another configuration. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1A-1C  show a deck or tank cover  10 , formed almost entirely of interconnected aluminum extrusions, essentially as in the patents of Hallsten Corporation referenced above, as well as other Hallsten patents. The deck or tank cover includes an access opening with a hatch  12 , openable via a hinge  14  which, as noted above, can be as described as in Hallsten U.S. Pat. No. 5,941,027. The hatch  12  includes a handle  16  which is incorporated in one of the extruded aluminum planks  18 ,  18   a  that form the hatch cover (“hatch”). As explained above, the hatch/safety barrier of the invention is advantageously used in sewage treatment tank covers. 
       FIG. 2  shows the hatch opening closed, with the hatch cover  12  supported by the hinge  14  at the left of the drawing, and with a free end  20  formed as a lip that resides on a flange  22  which can be part of an extrusion  24  at the edge of the hatch opening, i.e. fixed structure. A barrier or grate  26  is shown suspended below the closed hatch  12 . In this embodiment the grate  26  is secured by a grate hinge  28  to the outer extrusion  18   a  of the hatch cover.  FIG. 2  shows the grate substantially fully engaged against the bottom of the hatch cover, and this configuration can be retained by an appropriate form of latch if desired, such as a simple hook and eye or a slide bolt (not shown). 
     As shown in  FIG. 3 , for access the hatch  12  is swung upwardly about the hinge  14 , with the grate  26  retained against the bottom of the hatch cover. In  FIG. 4  the cover  12  has been raised sufficiently to deploy the grate  26  as a safety barrier, spreading it outwardly via the grate hinge  28  to a fully extended position, shown in  FIG. 5 . As shown in these views, the pivoted brace  30  opens in the manner of a stepladder brace, fully extended in the erected position of  FIG. 5 . The opened brace  30  may be permitted to travel slightly over-center to form the locked position. In this configuration the assembly makes an “A” shape, the brace  30  being repeated at both sides. The grate (barrier)  26  when deployed engages its foot end against the edge of the access opening, at the extrusion  24 . This is preferably via an elastomeric end piece, such as a D-seal  32  as shown. 
     In the example shown, the access opening has a width (as viewed in  FIG. 5 ) of about two feet eight inches to two feet ten inches, with the hatch  12  angled upwardly at about 35° (or 25° to 45°). The length of the grate  26 , i.e. the dimension shown in  FIG. 5 , can be about 14 inches, or about 13 inches to 18 inches. The dimensions and angles can be selected as desired, and suited to the size of the access opening. 
     With the braces  30 , the structure shown in  FIG. 5  provides a barrier on all sides of the access opening. 
       FIG. 6  is a further illustration of the erected hatch/barrier system shown in  FIG. 5 . This elevation view is from the right relative to  FIG. 5 . This view, partially in section, indicates extruded aluminum interlocking beam tubes  34  that may frame the access opening, these beam tubes  34  normally being secured to structural aluminum or steel beam tubes  36  below. The beam tubes  34  have upwardly hooked flanges at each side as shown. A deck plank  38  is seen at the far side of the opening in  FIG. 6 , retained at edges (as with other deck planks) by an extruded aluminum interlocking deck channel or  10  framing channel  40 , which has a downwardly hooked flange to be received on the flange. The deck channel  40  also rests at its bottom side on the beam tube  34  as shown (on a lateral protrusion  34   a  of the beam tube). This is consistent with typical liftable panels of Hallsten Corporation as seen in previous Hallsten patents. 
     In the example shown, the spacing from beam to beam ( 36 ) can be about three feet, although the dimension can vary as desired. The grate  26  can have a width of about 24-26 inches, although this, too, can vary. In  FIG. 6  the grate is seen as a preferably aluminum frame  27  supporting crossing internal pieces. 
     The erected configuration shown in  FIG. 5  is useful when the hatch opening is to used as an aeration vent, as discussed above. When access through the opening into the tank is desired, the hatch hinge  14  ( FIG. 3 ) allows the hatch  12  to be completely folded back onto the deck, through 180°. The grate  26 , preferably latched in place, can remain against the bottom of the hatch, to be stacked on the top of the hatch when the hatch is fully opened. 
       FIGS. 7 to 15  show another form of the invention. In the plan view of  FIG. 7  the hatch is closed, the hatch cover being seen at  12 . Interlocking beam tubes are seen at  34 , at opposed non-hinge edges of the access opening. In dashed lines the grate  26   a  is indicated, just below the hatch cover  12 . The sectional view of  FIG. 8 , a lateral view taken along the line  8 - 8  in  FIG. 7 , shows the positions of the hatch  12  and the grate  26   a , as well as the surrounding interlocking beam tubes  34  and structural beam tubes  36 . The hatch  12  rests via its side edges on structure of the interlocking deck channels  34 , or structure attached thereto, in the manner shown for another panel in  FIG. 6 . The hatch is liftable upwardly at a hinge  14  which is not seen in  FIG. 8  but is illustrated in  FIG. 9 . In this embodiment the grate  26   a  is supported in a different way.  FIG. 9  shows that the grate has, at its back end adjacent to the hatch hinge  14 , hinge legs  42  that serve to space the grate downwardly an appropriate distance. The pivot for the grate is at  44 , below the hatch hinge  14  and slightly inward of the opening relative to the hinge  14 . The pivot  44  is a hinge that occurs at both sides of the grate, or it could be continuous, and it is supported on fixed structure (i.e. the planks  18  of a panel to the left as seen in the drawing) by a mounting bracket  46 .  FIG. 9  shows the point  20  at which the free end of the hatch  12  rests on the surrounding deck structure when closed. 
       FIG. 10  shows the hatch assembly of this embodiment with the hatch cover  12  fully opened, folded back against the deck. The grate  26   a  protects against fall-through accidents at the opening. The brackets  46  that support the grate for pivoting are seen in dashed lines in  FIG. 7 . 
     The side elevation views of  FIGS. 11 and 12  indicate the opening of the hatch  12  and its fully opened position. The free end of the grate, at  48 , rests on fixed structure of the adjacent panel or other structure (not shown), or it can simply be supported fully along the length of the sides, as shown schematically in  FIG. 8 . 
       FIGS. 13 to 15  show opening of the grate for access of a service person into the tank.  FIG. 8  shows that, as here, both the hatch and the grate preferably are fully supported along the length of both sides, via engagement of extrusions. The beam tube  36 , below  34 , supports fixed structure to receive the grate  26   a  (a ledge  49  is indicated schematically for support at both sides of the grate). In  FIG. 14  two different positions of the grate are shown, as it is swung upwardly.  FIGS. 14 and 15  show the reason for the hinge legs  42 , the length of which is just enough to allow the grate  26   a  to lie flatly against the opened hatch cover  12 . 
       FIGS. 16 to 22  show another form of the hatch/grate system of the invention.  FIG. 16  is a plan view, with the hatch closed and the grate  26   a  in place below. A sectional elevation view looking left would be similar to  FIG. 8 , in regard to position and supporting of the hatch  12  and the grate  26   b  below. Note that the apex of the triangle indicator in these plan views denotes the hinge side of the hatch. 
       FIG. 17  is a section view looking in the plane  17 - 17  in  FIG. 6 , i.e. a side view. The hatch is at  12 , with the hinge of the hatch shown at  14 . The principal difference in this embodiment is that the grate  26   b  is supported at the opposite end as compared to the embodiment of  FIGS. 7 to 15 . The grate  26   b  has hinge legs  42 , similar to those shown in  FIGS. 9-15 , establishing a spacing of the grate  26   b  below the deck appropriate to allow the grate to be folded back through 180°. In this case the grate will be opened in the opposite direction from that of the hatch, so that when fully opened, the two will lie at opposite ends of the access opening. 
       FIG. 18  shows the hatch both fully opened, lying on the deck at the left side of the access opening as seen in this plan view. The barrier or grate  26   b  is in place, for protection against fall-through accidents. The pivot or hinge support of the grate is indicated at  46 , and is similar to that shown in  FIGS. 11-15 , although at the opposite end of the opening. Side support for the grate, at both lateral sides, is not shown but preferred. 
     The position shown in  FIG. 18  is appropriate for using the opening as an air intake, as discussed above. The components can assume different positions, as well, for use as an air intake.  FIG. 19  illustrates the swinging up of the hatch cover  12 , and  FIG. 20  shows the upward deployment of the grate, as the hatch  12  is held in position. Once the components reach the position shown in  FIG. 20 , they can be secured together as in  FIG. 21 , in the “A” configuration. For this purpose a bracket  50  is included on the bottom side of the hatch, near its outer end. This can have pins that couple with structure or openings in the grate, to retain the erected configuration shown in  FIG. 21 . Also, chains or flexible lines can be included, one at each side of the erected hatch/grate assembly, to provide a form of safety barrier at all four sides, in conformity with safety requirements. 
     As noted above, if access through the opening is needed, the hatch  12  and the grate  26   b  can each be fully swung to 180°, to rest against the deck. The hinge legs  42  at the hinged end of the grate have length selected for this purpose. 
       FIG. 22  shows an alternate erected configuration for the hatch  12  and grate  26   b  of  FIGS. 16-21 . In this case each is set to a vertical configuration, with pivot braces  30  provided at each side of each of the hatch and grate, as schematically shown in the drawing. The lower ends of these foldable braces can be secured to the interlocking beam tube  34  or structural beam tube  36 , or to structure supported by those members. 
     In  FIG. 22  pairs of chains or cables  52  are shown at upper and lower locations, extending between the hatch cover  12  and the grate  26   b , to provide a four-sided safety closure around the opening. The height of the upper cable  52  is such as to meet safety handrail requirements. 
     As explained above, the assembly shown in  FIGS. 16 to 22  can be modified for a special purpose, such as for ATAD, a sewage treatment system operated at high temperature, e.g. about 180° F. Lower support plates can be placed in a position of the horizontal grate  26   b , potentially capable of lifting out, but preferably not pivoted. These can provide a means for insulating the space between the deck panels and the barrier plate, and this can occur at every panel of a deck or tank cover. 
       FIGS. 23 and 24  illustrate one implementation of such a system for insulation. In  FIG. 23  a liftable panel  60  is shown, broken away at ends (left and right in the drawing) and of any desired length. No hinges are shown in the drawing; the panel  60  could be hinged at one end, or simply configured as a lift-out panel. As in the other embodiments, interlocking beam tubes  34  support panels typically at both sides of the beam tube, with the beam tubes  34  in turn supported by structural (preferably aluminum) beam tubes  36 . The panel is not affixed to the interlocking beam tubes  34 , but rests on extruded flanges as explained above and as typical of tank covers of Hallsten Corporation. Note that this detail can be typical for all panels in a tank cover. 
     Beneath the lift-out panel  60  is a lower support plate or solid inner layer  62  which is analogous in some respects to the safety grate discussed above. The support plate  62  can also be formed of aluminum planks and interlocking deck channels at edges of the series of planks, and it can rest on brackets  64  secured to the structural beam tubes  36 , as illustrated. It is thus supported at sides in the same manner as shown in  FIG. 8  for the illustrated grate discussed above. A section of rigid insulation is shown at  65 , supported on the removable support plate  62 . To allow for the insulation section to be installed and removed as needed, it has edges that terminate at a gap  66 , thus being of less width than the opening formed when the lift-out panel or hatch  60  is removed. Small end pieces  65   a  can be located to fully extend the insulation to the beams  36 , resting on the structure  64  at both sides. 
     As explained earlier, such insulation can be installed to provide an insulative value up to R-20, for a high-temperature sewage treatment process. In this way, the illustrated assembly allows for full access into the tank by removal of the lift-out panel or hatch  60 , then the insulation section  65 , and finally the support plate or solid inner layer  62 . When all are in place and installed, the solid inner layer  62  provides an air space below the liftable cover panel  60  which provides a small degree of thermal barrier. The insulation  65  and  65   a  fills essentially all this space, to result in an effective insulative barrier for the high-temperature process. 
       FIG. 25  shows the system of  FIGS. 23-24  but with both the deck panel  60  and the lower plate  62  being hinged, as in some of the hatch arrangements discussed above. In the elevational section views of  FIGS. 25-26 , seen in the direction perpendicular to that of  FIG. 24 , the system functions as a hatch opening with cover, but in this case the lower hinged element  62  is not a safety grate but an essentially impermeable lower plate or panel. A two-arm brace  30  can be included, as explained above, to hold the lower plate  62  in an opened position, and a hinge leg  42  is included so that the plate  62  could be folded all the way back, at 180°, if desired. In this case the insulation panel  65  is secured to the liftable deck panel  60 , and remains with the deck panel when it is swung open about its hinge  14  to the folded-back position as shown in  FIG. 25 . This provides access through the opening. 
       FIG. 26  shows a deck or tank cover opening with the same components as in  FIG. 25 , but with both the hinged deck panel  65  and the solid barrier  62  opened to vertical position, again to allow access into the tank. This is essentially the same as in  FIG. 22  described above, with foldable braces  30  for each of the components  65  and  62 , but with the insulation panel  65  attached to the underside of the deck panel  60 . As in  FIG. 22 , safety lines or chains  52  are shown secured between the deck panel and the lower plate  62 , for safety requirements. These can be released at one side for access. 
     The assemblies described above are simple in construction and efficiently operated to provide, in main embodiments, safety barriers at tank cover access openings. The barrier or grate is in place for any situation wherein the access opening is to be left open for a period of time, and this can include use of the openings for admission of air for aeration or ventilation of the treatment process in the tank. The system of simple and interconnectable components is more efficient than the previously described safety barriers. 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to these preferred embodiments will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.