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]    The invention relates to building construction and, in particular, to suspended ceilings. 
       PRIOR ART 
       [0002]    Building areas such as corridors or hallways and small rooms typically have short spans between opposing walls. Frequently, the space above such areas is utilized for air ducts and other utilities. It can be desirable or mandatory that a suspended ceiling be provided with removable panels to allow ready access to the space or plenum above a ceiling. The existence of primary air ductwork and other objects in the overhead space often makes hanging conventional suspension wires difficult or prohibitive. Any solution for constructing a suspended ceiling should avoid the need for extensive and/or specialized labor and, ideally, will actually reduce the labor and skill requirements. 
       SUMMARY OF THE INVENTION 
       [0003]    The invention resides in a short span suspended ceiling system with a unique grid runner and wall angle attachment. The attachment is made by permanent magnets carried on the ends of the grid runners that extend perpendicularly to the wall angles. The magnets are arranged to be strongly attached to the horizontal leg of a steel wall angle. The wall angles are of sufficient strength to support the grid runners and the ceiling tiles carried on the grid runners. The invention can be embodied with the type of grid runner that has a box section with an open slot on its bottom face. In this case, a magnet is inserted in the box section at each end of the grid runner. The grid runners are cut to a length such that their ends and the associated magnets overlie the horizontal legs of oppositely facing wall angles. 
         [0004]    The invention is useful with the more common style of grid runner or tee with flat flanges at their lower sides. In such a case, the ends of the tees can be modified by displacing material from a web above the flange for reception of a magnet. 
         [0005]    With the invention there is no need to index the spacing of a runner along the length of the wall angles. The position of the runners, for example, can be determined by the width of the ceiling tiles or panels as they are being installed or by lengths of short cross runners if the latter are used. The grid runners of the invention can be used in trapped modules where the grid runner ends are supported on elements that, like the wall angles, cannot be deflected or rotated laterally to receive or release a connector designed to extend through such an element, for example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a fragmentary isometric view of a short span suspended ceiling system constructed in accordance with the invention; 
           [0007]      FIG. 2  is a fragmentary isometric view of a grid runner constructed in accordance with the invention shown in relation to supporting wall angles; and 
           [0008]      FIG. 3  is a fragmentary isometric view, similar to  FIG. 2 , showing an alternative grid runner profile. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0009]    A short span suspended ceiling is represented at  10 . The ceiling  10  and walls  11  can represent, for example, a corridor or hallway that typically is of a length substantially greater than its width. However, the invention can be used for the ceiling of a small room. The ceiling  10  comprises a plurality of spaced parallel grid runners  12 , extending transversely to the length of the corridor, and rectangular ceiling panels or tiles  13  carried by the grid runners  12 . 
         [0010]    On the walls  11 , at ceiling height is a pair of opposed, elongated wall angles  14 . The wall angles  14  are made of sheet steel which may be hot dipped galvanized and painted. Each wall angle  14  has a horizontal leg  16  and a vertical leg  17 . 
         [0011]    The illustrated style of grid runner in  FIGS. 1 and 2  is of a known style, disclosed for example in U.S. Pat. No. 4,535,580. This style of grid runner has a hollow box-like structure  21  at its lower side. The profile of the grid runner  12  includes an upper hollow reinforcing bulb  22 , a vertical web  23 , and two inwardly facing C-shaped flanges  24  that mutually form the box section or structure  21 . The flanges  24  are at the lowermost part of the runner  12  and are spaced from one another to leave a gap or slot  26 . Typically, the grid runner  12  is roll-formed of sheet steel that can be hot dipped galvanized and painted. 
         [0012]    The invention is particularly useful in arrangements where the grid spans a distance of between about 5′ to about 9′. At the longer spans within this range, the grid runner can be made of relatively heavy gauge stock and/or can be reinforced by adding layers of sheet steel to the reinforcing bulb  22  and/or can be increased in height to make it stronger. The length of a grid runner  12  is cut to provide moderate clearance with the inside surfaces of the vertical legs  17  of the opposed wall angles  14 . 
         [0013]    A permanent magnet  27  is assembled at each end of a grid runner  12  into the flange formed box  21 . The magnet  27  will tend to hold itself in position in the flange box  21  at which it is placed. An adhesive, indicated at  28 , can be used to secure a magnet in position, if desired. 
         [0014]    The ceiling tiles  13  can be standard commercially available units typically with nominal rectangular face dimensions of 2′×2′, 2′×4′, or 2-½′×5′, or metric equivalents thereof. The ceiling  10  can be constructed by initially installing the wall angles  14  on opposite walls  11  at the desired height. Wall angles, not shown, can be similarly installed at the end or ends of the corridor. Alternatively, a grid runner or runners  12  can be used for starting and ending at the beginning or end of a hallway. Starting at one end of a corridor or hallway, the walls  11  or wall angles  14  can be marked to indicate the desired centers for the grid runners  12 . Normally, the runners will be arranged perpendicularly to the walls. Typically, the grid runners  12  will be positioned on 2′ centers. The magnets  27 , being disposed directly over the horizontal legs  16  of the wall angles  14 , will releasably hold the grid runners  12  in the positions at which they are manually set. The tiles  13  can be laid on the grid runners  12  in a conventional manner by manipulating them through the plane of the grid runners  12 . If desired, the steps of laying out the centers of the grid runners along the respective walls angles  14  can be omitted and the grid runners  12  can be roughly positioned on the wall angles. Thereafter, successive grid runners  12  can be more precisely positioned using a row of installed tiles  13  as a gauge. From the foregoing, it will be understood that the position of a grid runner  12  along a wall angle  14  is not dictated by locating features on the wall angle. The magnets  27  will hold their respective grid runner ends firmly, but releasably, in place on the wall angles  14 . The grid runners are installed in a so-called “trapped module” where there is no horizontal freedom available for the wall angles  14 . 
         [0015]    The broken lines  31  in  FIG. 1  represent abutting edges of panels  13  or locations of cross runners aligned with the walls  11 . As is conventional, the panels or tiles  13  can be cut to fit the width of the corridor. If desired, the grid runners  12  can be provided with regularly spaced slots along their lengths. Such slots, in a conventional manner, can receive connectors on the ends of the cross runners as is known in the art and shown, for example, in aforementioned U.S. Pat. No. 4,535,580. 
         [0016]    It will be understood that the ceiling components comprising the wall angles  14 , grid runners  12 , and tiles  13 , can be installed in locations where there is little or essentially no overhead clearance available in the space above the ceiling  10 . Moreover, a high level of access is afforded to the space above the ceiling  10  since an installed grid runner  12  can be moved out of position by simply lifting the tiles  13  it supports and shifting it along the wall angles  14 . A grid runner  12  can be completely removed from the ceiling  10  with intuitive motion, not requiring special technique and not requiring any movement of the supporting wall angles  14 . Temporary removal of one or more grid runners  12 , as well as associated ceiling tiles  13  afforded by the invention, gives full unobstructed access to the plenum above the ceiling. The risk of damaging these displaced ceiling parts is reduced where work is being conducted through the plane of the ceiling. 
         [0017]      FIG. 3  illustrates the invention applied to a common form of grid runner that has the general shape of an inverted tee. The grid runner or tee  36 , as is typical, is roll formed of sheet steel and includes a hollow upper reinforcing bulb  37 , a vertical web  38 , and a lower flat flange  39 , extending on opposite sides of the web. The web  38  is notched at each end of the grid runner  36  to receive a respective permanent magnet  27 . To supplement the attractive force on the grid runner  36 , the magnet can be adhesively secured to the runner and/or the notch, designated  41 , can be configured to mechanically hold the magnet in position. The grid runner or tee  36  can be used in the manner described above in connection with the grid runner  12 . 
         [0018]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.

Summary:
An elongated metal grid runner for a suspended ceiling, the grid runner having a cross-section with an upper hollow reinforcing bulb, a vertical web extending below the bulb, and lower flange elements extending laterally from opposite sides of the web, the length of the grid runner being less than about 9′, a permanent magnet disposed on each end of the grid runner at its flange elements, the magnet being adapted to overlie and be attracted to a horizontal leg of a steel wall angle to thereby releasably retain the grid runner in position on the wall angle.