You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to providing an unobstructed passageway through a sliding door and additionally to providing a barrier to prevent water infiltration through the door opening.  
         [0003]     2. Summary of the Background Art  
         [0004]     In many areas prone to high velocity winds and rain, a watertight barrier is provided to prevent water intrusion into a building. For example, the threshold frame member forming the lower portion of the frame structure extending around a sliding door is provided inside the door with a leg extending upward from the floor to a height required to accommodate a particular water level or design pressure. The problem with this approach is that the barrier presents a tripping hazard to people walking through the open doorway, and a serious obstacle to anyone trying to roll a wheelchair or wheeled cart through the door opening. There are numerous instances of conflict between building codes requiring such barriers to prevent damages from water penetration and federal regulations covering ADA (Americans with Disabilities Act) Standards for Accessible design.  
         [0005]     In some locations, these problems can be alleviated by building ramps extending downward from the top of the obstruction to the surfaces inside and outside the building. However, when such ramps are built at the degree of slope mandated for wheelchair usage, they are often too long to be used with narrow walkways, balconies or patios outside or with small rooms inside. Therefore, what is needed is a mechanism for sealing against water intrusion that moves out of the way, as a sliding door is opened.  
         [0006]     Sliding doors of vehicles, such as vans, and of many railroad freight cars, are provided with airtight sealing mechanisms that are additionally watertight at least under rain conditions, with the door being mounted on cranks that allow it to move inward into the mating opening and outward therefrom. The sealing process occurs as the door is moved inward, and the seals are broken as the door is moved outward. While the door is held outward by the cranks, it is slid along the outside of the wall of the vehicle or railroad car. What is needed is a way for providing a watertight opening at a sliding door within a building where weather conditions include high winds and rain, without requiring a different type of door movement and without significantly changing the appearance of the building when the door is open.  
         [0007]     U.S. Pat. No. 5,870,859 describes a watertight sliding door structure including a movable door, a stationary door, which is made watertight without increasing the height of a portion of the sill. The movable door and the stationary door are each provided with a stile extending vertically along the central edge of the door. As the movable door is closed, these stiles meet one another, with the gap between them being sealed by elastomeric strips. Horizontally extending sealing strips are also provided along the upper and lower frame members of the doors. A pressure-equalized clearance area is formed between the sill of the window frame of the movable door and the stationary door and attachments provided on the sill. Additionally, an airtight member is provided to divide the pressure-equalized clearance area into and an inside clearance area of the single movable door. By forming the pressure-equalized clearance area between the inside clearance area and the outside clearance area of the single movable door in the sill partition, a difference in the pressure between the sill portion and the outside is not produced, so that rain water is exhausted by a dead load. What is needed is a method for sealing a sliding door assembly without requiring that a movable door to be slid open and shut with elongated sealing members in sliding contact with opposing surfaces.  
         [0008]     Japanese Patent Application 11182154A describes a water barrier plate hat moves vertically with the movement of a flexible door extending around the walls of a stall within a bathroom. The door is opened by moving the flexible door so that a space between its opposite ends is aligned with an opening in the walls, with pins at these opposite ends moving the water barrier plate downward into a slot within the threshold as the door is fully opened. The door is closed by moving the flexible door so that the space between these opposite ends is aligned within the walls, with these pins moving the water barrier plate upward within the slot. What is needed is a water barrier that can be moved out of the way without causing the barrier to retract into a slot extending downward within the floor, so that there is no need to weaken the floor structure with such a slot, and so that the apparatus can be readily installed in an existing building. Additionally, what is needed is an apparatus operable with a conventional sliding door, in which the entire door moves to one side of a passageway as it is opened.  
         [0009]     U.S. Pat. Nos. 4,692,961 and 5,560,164 describe water-shielding structures for removable placement in openings of buildings. What is needed is a structure that can be left attached within a doorway without impeding traffic through the passageway.  
         [0010]     A number of patents, such as U.S. Pat. No. 4,237,664, describe door sill structures including surfaces of different elevations to prevent water intrusion without addressing the difficulties in access by foot or wheelchair that may be caused by such changes in elevation.  
       SUMMARY OF THE INVENTION  
       [0011]     According to a first aspect of the invention, apparatus is provided for sealing a notch within a barrier plate extending across a lower portion of an opening covered by a sliding door movable between open and closed positions. The apparatus includes a compression panel, a carrier bracket, a compressible gasket, and an actuator. The carrier bracket is attached to the sliding door. The compression panel is mounted within the carrier bracket to be movable toward the barrier plate and away from the barrier plate. The compressible gasket is disposed between the compression panel and the barrier plate to extend adjacent the notch with the sliding door in the closed position. The actuator is disposed adjacent the compression panel with the sliding door in the closed position. The actuator is mounted to move along a stationary surface between a disengaged and an engaged position. Movement of the actuator into the engaged position with the sliding door in the closed position causes the compression panel to be moved in contact with the actuator toward the barrier plate, compressing the compressible gasket between the compression panel and the barrier plate. Movement of the actuator into the disengaged position with the sliding door in the closed position allows movement of the compression panel in contact with the actuator away from the barrier plate, releasing compression of the compressible gasket between the compression panel and the barrier plate.  
         [0012]     According to another aspect of the invention, this apparatus additionally includes a sliding door and a frame mounting the sliding door to move between open and closed positions, with the frame including a barrier plate having a notch forming a part of a passageway covered by the sliding door in its closed position.  
         [0013]     For example, the actuator includes an elongated member extending adjacent the component panel with the sliding door in the closed position, with the apparatus additionally including stationary ramps disposed adjacent opposite ends of the stationary member. The actuator then moves along the stationary ramps between the disengaged position and the engaged position, with the stationary ramps being inclined to move the actuator toward the barrier plate in contact with the compression panel with the sliding door in the closed position as the actuator is moved into the engaged position.  
         [0014]     According to yet another aspect of the invention, a method is provided for retrofitting a passageway enclosed by a door sliding within a frame having a barrier plate extending upward to form a lower edge of the passageway. The method includes: 
        making a notch within the barrier plate along the lower edge of the passageway;     attaching a carrier bracket to the sliding door,     mounting a compression panel on the carrier bracket to be movable toward the barrier plate and away from the barrier plate;     mounting a compressible gasket to be disposed between the compression panel and the barrier plate to extend adjacent the notch with the sliding door in the closed position; and     mounting the actuator adjacent the compression panel with the sliding door in the closed position.        
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is front elevation of a door assembly built in accordance with the invention, shown with a sliding door therein partly open;  
         [0021]      FIG. 2  is a fragmentary cross-sectional elevation of the door assembly of  FIG. 1 , taken as indicated by section line  2 - 2  therein to show a compression panel subassembly and an actuator subassembly;  
         [0022]      FIG. 3  is a fragmentary cross-sectional plan view of the door assembly of  FIG. 1 , taken as indicated by section line  3 - 3  in  FIG. 2 ;  
         [0023]      FIG. 4  is a fragmentary cross-sectional elevation of the door assembly of  FIG. 1 , taken as indicated by section-line  4 - 4  therein, showing a sliding door therein in a closed position;  
         [0024]      FIG. 5  is a fragmentary cross-sectional elevation of the door assembly of  FIG. 1 , taken as indicated by section-line  5 - 5  therein, showing a passageway formed by opening the sliding door therein;  
         [0025]      FIG. 6  is a fragmentary cross-sectional elevation of the door assembly of  FIG. 1 , taken as indicated by section line  6 - 6  therein to show a latch lever;  
         [0026]      FIG. 7  is a fragmentary cross-sectional plan view of the door assembly of  FIG. 1 , taken as indicated by section line  7 - 7  therein;  
         [0027]      FIG. 8  is a fragmentary elevation of a barrier plate having an alternative compressible gasket for use in the door assembly of  FIG. 1 ;  
         [0028]      FIG. 9  is a cross sectional view of the barrier plate of  FIG. 8 , taken as indicated by section line  9 - 9  therein;  
         [0029]      FIG. 10  is a fragmentary plan view of a first alternative actuator for use in the door assembly of  FIG. 1 ; and  
         [0030]      FIG. 11  is a cross-sectional plan view showing an alternative latch lever for use with the first alternative actuator of  FIG. 10 ;  
         [0031]      FIG. 12  is a fragmentary plan view of a second alternative actuator for use in the door assembly of  FIG. 1 ; and  
         [0032]      FIG. 13  is a fragmentary cross-sectional elevation of a door assembly including the second alternative actuator of  FIG. 12 , taken as indicated by section line  13 - 13  therein. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]      FIG. 1  is a front elevation of a door assembly  10  built in accordance with the invention, as viewed from inside a structure. The sliding door assembly  10  includes a sliding door  12 , shown as partly closed, a stationary door  14 , outwardly disposed from the sliding door  12 , and a doorframe  16 . To provide the various features of the invention, the door assembly  10  additionally includes a barrier plate  18  extending upward from a level of a floor  20  to prevent water penetration. To avoid presenting a tripping hazard to individuals walking through the passageway  22  within the doorframe  16  with the sliding door  12  moved in the direction of arrow  24  into its open position, and further to avoid presenting a barrier to wheelchair access through this passageway  22 , the barrier plate  18  includes a notch  26  extending downward to enlarge this passageway  22 .  
         [0034]     In order to maintain the water sealing function of the barrier plate  18 , the notch  26  is sealed by means of a compression panel subassembly  28 , attached to the sliding door  12  by bolts  30 , to move out of the passageway  22  when the sliding door  12  is opened. The door assembly  10  additionally includes an actuator subassembly  32  extending along the floor  10  adjacent the compression panel subassembly  28 . When the sliding door  12  is in its closed position, the actuator subassembly  32  operates in response to movement of a latch lever  34  connected to the actuator subassembly  32  by means of a flexible member  36  to seal the notch  26  to prevent water damage and to release seal on the notch  26  to allow movement of the sliding door  12 . While the flexible member is shown as a steel cable, it is understood that the flexible member may alternately be, for example, a flexible plastic strap.  
         [0035]      FIG. 2  is a fragmentary cross-sectional elevation of the door assembly  10 , taken as indicated by section line  2 - 2  in  FIG. 1 . The barrier plate  18  is shown to be an upstanding portion of a threshold frame member  40 , which forms a lower portion of the doorframe  16 . The sliding door  12  is movably mounted on an inner rail  42  of the threshold frame member  40  by means of a number of rollers  44 , while the stationary door  14  rests on an outer rail  46  of the threshold frame member  40 .  
         [0036]     The compression panel subassembly  28  includes a panel mounting bracket  50  attached to the sliding door  12  by the screws  30 , a decorative cover  52  fastened to the panel mounting bracket  50  by means of a number of screws  54 , and a compression panel  56  slidably mounted on the panel mounting bracket  50  by means of a number of shoulder screws  58 . Each of the shoulder screws  58 , which is attached to the compression panel  56  by threads  60 , includes a shoulder  62  sliding within a hole  64  in the panel mounting bracket  50 . In this way, the compression panel  56  is mounted to move in and opposite the engagement direction of arrow  66 , with a number of compression springs  68  pushing the compression panel  56  in the direction opposite arrow  66  through the shoulder screws  58 . The upper surface of the compression panel  56  is as high as the upper surface of the barrier plate  18 .  
         [0037]      FIG. 3  is a fragmentary cross-sectional plan view of the door assembly  10 , taken as indicated by section line  3 - 3  in  FIG. 2 . While  FIGS. 1 and 2  show the sliding door  12  partly open,  FIG. 3  shows the sliding door  12  fully closed. Referring to  FIGS. 2 and 3 , a compressible gasket  70  is attached to an outer surface  72  of the compression panel  56 . The compressible gasket  70  extends adjacent the notch  26  in the barrier plate  18 , so that, when the compression panel  56  is driven in the engagement direction of arrow  66 , the compressible gasket  70  is compressed between the outer surface  72  of the compression panel  56  and the inner surface  74  of the barrier plate  18  within an area extending adjacent the notch  26 . Both  FIGS. 2 and 3  are cross-sectional views taken through a vertically extending portion of the gasket  70  adjacent an end  76  of the notch  26 .  
         [0038]     The actuator subassembly  32  includes an actuator  80  rolling along a pair of inclined surfaces  82  by means of rollers  84 . The actuator  80  is pulled to the right, in the direction of arrow  86 , by means of the flexible member  36  attached to the actuator  80  by a pin  88 , which is in turn pulled by the latch lever  34  (shown in  FIG. 1 ). As the latch lever  34  is moved to allow movement of the actuator  80  opposite the direction of arrow  86 , the actuator is returned to the left by a force applied by an actuator spring  90 . The actuator  80  is an elongated member to which the rollers  84  and  94  are rotatably attached. The rollers  94  roll against an adjacent surface  96  of the compression panel  56 . The inclined surfaces  82  extend along stationary ramps  98  attached to ramp brackets  100 . The ramp brackets  100  are in turn fastened to the underlying floor by means of self-threading concrete fasteners  102 . A shim  104  is used to align the actuator subassembly  32  with the compression panel  56  in the vertical direction of arrow  106 . Each of the ramp brackets  100  additionally includes a plastic bearing plate  110 , fastened to the bracket  100  by means of screws  111 , to provide a surface along which the actuator  80  slides.  
         [0039]      FIGS. 4 and 5  are fragmentary cross-sectional elevations of the door assembly  10 , taken as indicated by section line  44  in  FIG. 1 , with  FIG. 4  showing the sliding door  12  in its closed position, and with  FIG. 5  showing the passageway  22  provided by opening the sliding door  12 .  
         [0040]     Referring to  FIGS. 2-4 , the actuator subassembly  32  additionally includes a threshold cover  112 , supported on the surface of the shim  104  by its edge  114  and by downward extending ribs  116 ,  118 , with rib  118  being divided into sections with intervening spaces  120 . As additionally shown in  FIG. 1 , the threshold cover  112  extends adjacent the stationary door  14  as well as the sliding door  13 .  
         [0041]     Comparing  FIG. 5  with  FIG. 4 , when the sliding door  12  is opened, the compression panel subassembly  28  moves with it, leaving a passageway  22  that is easy to walk through and to roll a wheelchair through, with the highest elements being the threshold cover  112  and the surface  122  forming the bottom of notch  26  in the barrier plate  18 . The actuator  80  is protected by the threshold cover  112  from being damaged by traffic moving through the passageway  22 .  
         [0042]     The latch lever  34  will now be discussed, with particular reference being made to  FIGS. 6 and 7 .  FIG. 6  is a fragmentary cross-sectional elevation of the door assembly  10 , taken as indicated by section line  6 - 6  in  FIG. 1  to shown the latch lever  34  and associated structures, while  FIG. 7  is a fragmentary plan view of the door assembly  10 , taken as indicated by section line  7 - 7  in  FIG. 1 . While  FIG. 1  shows the sliding door  12  as partly open,  FIGS. 6 and 7  show the door  12  as fully closed.  
         [0043]     The latch lever  34  is pivotally mounted by a pin  124  on a pair of brackets  125 , which are in turn fastened to a mounting bracket  126  by means of screws  127 . The mounting bracket  126  is in turn mounted to a wall  128  by a number of screws  130 . In  FIGS. 6 and 7 , the latch lever  34  is shown as pivoted into its raised position, pulling the actuator in the direction of arrow  86  (shown in  FIG. 3 ) by means of the flexible member  36 , so that the gasket  70  is compressed between the pressure panel  56  and the barrier plate  18 . Preferably, the latch lever  34  additionally includes a locking pawl  134  that prevents the opening of the sliding door  12  from its closed position when the latch lever  34  is in its raised position. In the example of these figures, a locking plate  136  has been attached to the sliding door  12  to provide a surface  138  to be stopped by the locking pawl  134  if an attempt is made to open the sliding door with the latch lever  34  in its raised position. The locking plate  136  is fastened to the sliding door  112  by a pair of bolts  140 .  
         [0044]     Referring to  FIGS. 3, 6 , and  7 , the flexible member  36  is fastened to a U-shaped attachment frame  142 , which is in turn fastened to the latch lever  36  by means of a pivoting pin  144 . The attachment frame  142  extends through a pair of holes within the pin  144 , being held in place by a pair of nuts  146  engaging threads along the ends of the frame  142 . The flexible member  36  extends downward from the attachment frame  142  and partly around a pair of pulleys  150 ,  152 , to be attached to the actuator  80  by means of the pin  88 . The pulleys  150 ,  152  may be individually fastened to the floor  20 , below the shim  104 , and to the wall  128 , as shown, or they may be fastened to a common bracket (not shown) that is in turn fastened to the floor  20  or to the wall  128 .  
         [0045]     Starting with the sliding door  12  in its closed position, and with the latch lever  34  in its raised position, the latch lever  34  is lowered into the position indicated in  FIG. 6  by dashed lines  154  before the sliding door  12  can be opened. During this process, the locking pawl  134  moves out of the path of surface  138  of the locking plate  136 , so that the door  128  can be opened. Also, as the lever  34  is lowered, the pivoting pin  136  moves along an arcuate path  156 , so that the upper end of the flexible member  36  moves downward, allowing the actuator spring  30  to move the actuator  80  to the left, opposite the direction of arrow  86 . Preferably, the bracket  126  includes a lower motion limiting tab  160  limiting the pivoting motion of the latch lever  34 . The resulting movement of the actuator  80  along the inclined surfaces  82  allows the springs  58  (shown in  FIG. 2 ) to move the compression panel  56  opposite the direction of arrow  66 , so that the compressible gasket  70  is moved away from the barrier plate  18 . Then, the sliding door  21  is opened by sliding to the left.  
         [0046]     Preferably, the arcuate path  156  extends on both sides of the pivot pin  124 , so that the latch lever  34  acts as a toggle, being held in both raised and lowered portions by a force applied by the actuator spring  90  through the flexible member  36 .  
         [0047]     While the sliding door  12  remains open, the latch lever  34  is left in its lowered position, as indicated by dashed lines  154 . Then, after the sliding door  12  is fully closed, the latch lever  34  is rotated into its raised position, with the flexible member  36  pulling the actuator  80  in the direction of arrow  86 . As the rollers  86  are pulled up along the inclined surfaces  82 , the actuator  80  is also moved in the direction of arrow  55 , so that the gasket  70  is compressed against the barrier plate  18 . This movement of the latch lever  34  into its raised position additionally moves the locking pawl  134  into place to prevent the re-opening of the sliding door  12   
         [0048]     The preceding discussion has described the compressible gasket  70  as being attached to the an outer surface  72  of the compression panel  56 , providing an advantage of moving the gasket  70  out of harm&#39;s way with the sliding glass door  12 , so that subsequent movement of individuals through the passageway  22  with the sliding door  12  open will not damage the gasket  70 . Nevertheless, it is understood that a compressible gasket may alternatively be attached to the barrier plate, as shown in  FIGS. 8 and 9 .  FIG. 8  is a fragmentary elevation of the barrier plate  18 , having an elastomeric strip  166  attached thereto, while  FIG. 9  is a cross-sectional elevation of this plate  18  and elastomeric strip  166 , taken as indicate by section line  9 - 9  in  FIG. 8 . The elastomeric strip, which is composed, for example, of a material such as a closed cell neoprene foam, is adhesively attached to the barrier plate  18 .  
         [0049]      FIG. 10  is a plan view of an alternative actuator  170 , which is composed of a parallelogram linkage  172  driven by a crank  174  through a crank link  176 . The parallelogram linkage includes a pair of arms  178  and a connecting link  180 . Each of the arms, which is pivotally attached to the floor  20  by means of a shoulder screw  182 , includes a rotatably mounted roller  184 . As the crank  174  is rotated between the position in which it is shown and the position indicated by dashed lines  186 , the linkage  178  moves from the position in which it is shown into the position indicated by dashed lines  188 , with the rollers  184  rolling against the adjacent surface  96  of the compression panel  56 , so that this portion of the panel  56  is moved in the direction of arrow  66  into the position indicated by dashed lines  190 . When the crank  174  is rotated from the position indicated by dashed lines  186  into the position in which it is shown to this process is reversed, with the springs  63 , shown in  FIG. 2 , returning the compression panel  56  from the position indicated by dashed lines  188 .  
         [0050]      FIG. 11  is a partly sectional plan view showing a cross-section of the sliding door  12 , together with a plan view of a latch lever  192  turning the crank  174  by means of a shaft extending downward between the lever  192  and the crank  174 , being pivotally mounted in a bearing block  196  attached to the wall  128  and in a bearing plate  198  attached to the floor  20 . Preferably, the bearing plate  198  also includes a pair of tabs  200  limiting the rotational movement of the crank  174 . As the latch lever  192  moves from the position in which it is shown into the position indicated by dashed lines  202 , the crank  174  is moved from the position in which it is shown into the position indicated by dashed lines  186 , so that the compressible gasket  70  or  168  is clamped by the clamping plate  56 . As the latch lever  192  is then returned to the position in which it is shown, the compressible gasket  70  or  168  is released. Preferably, the latch lever  192  also includes a locking pawl  204 , which slops movement of the sliding door  12  from its closed position by contacting a stop plate  206  attached to the door  12  when the latch lever is in the position indicated by dashed lines  202 .  
         [0051]     The use of a second alternative actuator will now be discussed with particular reference to  FIGS. 12 and 13 .  FIG. 12  is a fragmentary plan view of the second alternative actuator  210 , along with associated elements of a door assembly, while  FIG. 13  is a fragmentary cross-sectional view thereof, taken as indicated by section lines  13 - 13  in  FIG. 12 . For use with this actuator  210 , a compression panel  212 , which is otherwise similar to the compression panel  56  described above in reference to  FIGS. 1-4 , is provided with a pair of rollers  214 , which are rotatably mounted on pins  216  attached within attachment blocks  218  clamped in place on the compression panel  214 . Similarly, a pair of rollers  220  is rotatably mounted to stationary brackets  222  by means of pins  224  extending within attachment blocks  226 . The attachment blocks  218 ,  226  may be metal or plastic. The stationary brackets  222  are attached to the floor by means of bolts  230 , which may extend into bolt anchors  232 , or which may be fastened directly into the floor by means of self-tapping threads. The stationary brackets  222  are disposed so that the rollers  220  are aligned with the rollers  214  in the direction of arrow  234 .  
         [0052]     The second alternative actuator  210  includes an elongated bar  236  and a pair of ramp structures  238 , which are disposed along the actuator  210  to move between the opposing rollers  214  and  220  at the actuator  201  is moved in the engagement direction of arrow  240 . The rollers  214  are held in contact with the actuator  210  by means of a number of springs (not shown), which act in the manner of springs  68 , described above in reference to  FIG. 3 . Thus, when the actuator  210  is pulled in the engagement direction of arrow  240  the compression panel  212  moves in the direction of arrow  234 . For example, the flexible member  36  is directed around a floor-mounted pulley  242  to be attached to the actuator  210  by means of a screw  244 , so that the actuator is moved in the direction of arrow  240  in response to upward movement of the latch lever  34 , as described above in reference to  FIGS. 6 and 7 , This movement in the direction of arrow  234  compresses a compressible gasket  70  in the manner described above in reference to  FIGS. 1-4 . An actuator spring  246  is provided to maintain tension within the flexible member  38  and to return the actuator  210  in the direction opposite that of arrow  24 . As the sliding door  12  (shown in  FIG. 3 ) is opened, the compression panel  212  moves to that its rightmost attachment block moves along the outer surface  252  of the bar  236  into the position indicated by dashed lines  254 .  
         [0053]     While the ramp structures  238  are shown as extending outward from both sides of the elongated beam  238 , it is understood that these structures  238  may alternately extend outward only from one of these sides, in the direction of arrow  234  or opposite thereto.  
         [0054]     It is additionally understood that the alternative actuator  170  may otherwise be moved by the flexible member  36  and by the actuator spring  90 , generally as described in reference to  FIG. 3 , and that the actuator  80  may alternately be moved by a linkage in the manner generally described in reference to  FIGS. 10 and 11 .  
         [0055]     The invention may be applied at a doorway of a building during the construction of the building. Alternately, the invention may be applied at an existing doorway after the construction of the building by cutting the notch  26  in the existing barrier plate and by fastening the various components of the invention in place as described on the floor, wall, and the sliding door.  
         [0056]     While the invention has been described in its preferred versions with some degree of particularity, it is understood that this description has been given only by way of example, and that numerous changes in the configuration and combination of parts may be made without departing from the spirit and scope of the invention, as defined in the appended claims.

Summary:
A sliding door assembly includes a barrier plate extending across the lower portion of the doorway to prevent the intrusion of water during severe weather conditions. A notch within the barrier plate, enlarging the passageway opened by the sliding door to form an obstruction-free passageway, is sealed by compressing a gasket between the barrier plate and a compression plate mounted to move with the sliding door. An actuator, mounted along the floor adjacent the compression plate with the sliding door closed, moves the compression plate toward the barrier plate, compressing the gasket, in response to operation of a latch lever.