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: 
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. App. No. 62/143,529 filed Apr. 6, 2015, which is entitled “Safety Gate for Rail Car” and which is incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     BACKGROUND 
     Safety equipment and more particularly a safety gate for use with an open door in a mass transit vehicle to prevent a maintenance worker from accidentally falling out the open door are disclosed herein. 
     Mass transit vehicle doors, for example rail car doors, and particularly doors employed in electrified cars such as subway cars or other mass transit rail cars, are automatically actuated to open and close, as is known in the art. As with any automated or mechanical apparatus the doors require regular maintenance or repair. During maintenance and repair of the doors the vehicle is taken out of service. Often the vehicle is transported to a yard for service. In many cases a vehicle door is opened and maintenance or repair personnel are positioned in the open doorway when working on the door, which exposes the worker to the possibility of falling out the open door, resulting in injury. It would be advantageous, therefore, to have a safety gate that can be installed in the door opening to prevent such falls. It also would be advantageous if the gate were light weight, transportable, easy to install and to remove and if it were easily adaptable to different size openings. 
     Moreover, the vehicle being serviced or repaired may be parked on rails having an electrified third rail, either on the track or in the yard. It would be advantageous if the safety gate is not electrically conductive, comprised of dielectric material so that inadvertent contact with an electrified rail does not pose a risk of electrocution or system shutdown. 
     BRIEF SUMMARY 
     An expandable safety gate for a vehicle door opening comprising a first substantially rectangular frame and a second substantially rectangular frame slidingly engaged in the first frame such that the two frames are positioned in the same vertical plane, the second frame being extendable from the first frame to be fitted to different sized rail car door openings. There are locking mechanisms to secure the second frame relative to the first frame in its useful extended position within the opening. 
     The safety gate is comprised of dielectric material, such as fiberglass or other non-conductive material, is lightweight, portable and easily installed and removed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a front plan view of an aspect of the safety gate mounted in an open doorway; 
         FIG. 2  is another front plan view of the gate; 
         FIG. 3  is a front perspective view thereof; 
         FIG. 4  is an end plan view; and 
         FIG. 5  is a top plan view thereof. 
     
    
    
     Corresponding reference numerals will be used throughout the several figures of the drawings. 
     DETAILED DESCRIPTION 
     The following detailed description illustrates the safety gate by way of example and not by way of limitation. This description will clearly enable one skilled in the art to make and use the claimed invention, and describes several embodiments, adaptations, variations, alternatives and uses of the claimed invention, including what I presently believe is the best mode of carrying out the claimed invention. Additionally, it is to be understood that the safety gate is not limited in its application to the details of construction and the arrangements of components or the dimensions set forth in the following description or illustrated in the drawings. The safety gate is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
     Referring to the drawings, and particularly  FIG. 1 , one aspect of a safety gate is referred to generally by number  10 . As shown, the gate  10  is installed in the opening O of a vehicle door. The vehicle can be any vehicle, such as a mass transit vehicle or rail car, for example, a rail car in a rapid transit or subway line. It will be understood, however, that gate  10  may be used in any environment to block an opening and prevent accidental or unintended egress through the opening, such as a fall out of the opening. 
     The gate  10  includes a first substantially rectangular frame  12  and a second substantially rectangular frame  14  at one end of the first frame. The first frame  12  includes a first vertical end post  16  and an opposed second vertical end post  18 . In the illustrated aspect, there are four horizontal frame members,  20 ,  22 ,  24  and  26  extending between the end posts  16 ,  18 . At least the upper and lower most horizontal frame members  20  and  26  define inner channels and have a larger cross-sectional area than the middle frame members  22  and  24 . 
     There is an upper mounting bracket  28  at the top of first end post  16  and a lower mounting bracket  30  at the bottom of end post  16 . Each mounting bracket includes a transverse slot  32  and can be attached to the vehicle wall W adjacent the opening O. A fastener  34  extends through the slot  32  and engages the post  16  to secure the post to the brackets. In one aspect, the fastener  34  can be a knob having a threaded extension that engages a threaded hole in the post. However, any fastener that conveniently and easily attached the post to the brackets may be employed. 
     The second rectangular frame  14  includes a vertical end post  36 , an upper horizontal frame member  38 , a center horizontal frame member  40  and a lower horizontal frame member  42 . As shown, the upper frame member  38  and the lower frame member  42  are aligned with and dimensioned to slidingly engage inside the horizontal frame members  20  and  26 , respectively, of the first rectangular frame. In one aspect, the center frame member  40  can define an externally threaded rod which extends through an opening (not seen) in the second end post  18  and through a locking device  46  located on the second end post  18 . In the illustrated aspect, the locking mechanism  46  can be a handle with a threaded bore that engages the external threads on member  40 . For example, the locking device  46  can be rotatably mounted to the second end post, such that as the locking device is rotated, the engagement of the threaded rod with the threads of the locking device cause the second frame to move axially relative to the first frame. Alternatively, locking mechanism  46  can employ a swaged arrangement that does not require threads on center frame member  40 . Any locking mechanism will suffice. 
     There is an upper mounting bracket  48  at the top of first end post  36  and a lower mounting bracket  50  at the bottom of end posts  36 . Each mounting bracket includes a transverse slot  52  and can be attached to the vehicle wall W adjacent opening O. A fastener  54  extends through slot  52  and engages post  36  to secure the post to the brackets. 
     In use, the width of the gate  10  can be adjusted to accommodate different widths of openings O. Brackets  28 ,  30 ,  48  and  50  can be removably secured to the wall W. Fasteners  34  and  54  are loosened and vertical end posts  16  and  36  are positioned adjacent the vertical walls of opening O. Because the upper frame member  38  and the lower frame member  42  of the second rectangular frame are slidingly engaged inside horizontal frame members  20  and  26 , respectively, of the first rectangular frame  12 , the second rectangular frame  14  can be extended or retracted laterally relative to the first rectangular frame to fit within the opening O. The gate  10  is optimally positioned in opening O, fasteners  34  and  54  are tightened and the locking mechanism  46  is secured around horizontal member  40  to secure the gate in place. 
     To remove the gate, brackets  28 ,  30 ,  48  and  50  can be removed from wall W. Alternatively, the fasteners  34  and  54  can be removed from the gate to release gate  10  from the vehicle, leaving the brackets  32  and  54  in place for future use. 
     The general dimensions of the various elements are relative and they are configured and dimensioned to fit in any desired opening. In one aspect, the various elements comprise a non-conductive material such as fiberglass or other resin. If the gate is to be installed where there is no exposure to electric current, the various elements may comprise another lightweight and durable material such as light gauge steel, aluminum or alloys. 
     In view of the above, it will be seen that the several objects and advantages of the present invention have been achieved and other advantageous results have been obtained. 
     As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Summary:
An expandable safety gate for a vehicle door opening comprising a first substantially rectangular frame and a second substantially rectangular frame slidingly engaged in the first frame such that the two frames are positioned in the same vertical plane, the second frame being extendable from the first frame to fit within the door opening; and locking mechanisms to secure the second frame in its extended position within the vehicle door opening, wherein safety gate is comprised of non-conductive material.