Patent Publication Number: US-11649648-B2

Title: Enhanced safety cage apparatus for work areas on top of rolling stock such as rail tank cars

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. application Ser. No. 15/966,853 filed on Apr. 30, 2018, which claims filing date priority benefit to U.S. application Ser. No. 62/501,436 filed on May 4, 2017, and to U.S. application Ser. No. 62/608,098 filed on Dec. 20, 2017, all of which is incorporated herein by reference for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE INVENTION 
     The subject matter disclosed herein generally involves fall protection equipment for accessing the tops of rolling stock, and particularly so-called worker safety cages that can be lowered down onto the tops of rolling stock. 
     BACKGROUND OF THE INVENTION 
     It is necessary to provide workers with access to various work areas at the tops of rolling stock such as tank cars, which are used to transport flowing materials that typically are in liquid form but occasionally in granular form. As these tank cars are cylindrical in shape, the tops of these tank cars are curved, making for curved surfaces on which workers must maintain their balance when accessing various work areas. Though some work areas are provided with level platforms, because flowing materials are involved, even work areas with such level platforms often include slippery surfaces on which the workers must tread when carrying out their assigned duties. Various weather conditions such as rain, sleet, snow and ice also can provide and/or exacerbate slippery surfaces that can cause workers to slip and fall when carrying out their assigned duties. Thus, these work areas typically are furnished with some sort of railing structure that runs the length and width of the work area at the top of the rolling stock. However, these railing structures typically are inadequate to prevent workers from falling to the ground after slipping through one of the openings in the railing structures or tumbling over the top of the railing structures. 
     Before workers are permitted to access the tops of rolling stock (tank trucks, tank railroad cars, etc.), a cage can be deployed surrounding the portion of the top of the rolling stock where the workers are to be engaged in their duties. Examples of these sorts of safety cages can be found in U.S. Pat. Nos. 7,216,741; 8,479,884; 8,403,109; 8,479,882; 6,405,831; 4,679,657; 9,409,755; which are hereby incorporated herein by this reference for all purposes. 
     Each cage typically assumes the shape of a rectangular box having contiguous pairs of the sides connected to each other in what is essentially a right angle. In some embodiments, the corners of each cage can be curved rather than a sharp right angle. Conventionally, the cage&#39;s side that is disposed closest to the structure from which the cage is deployed will be considered the inboard side of the cage. Similarly, the cage&#39;s side that is disposed farthest away from the structure from which the cage is deployed will be considered the outboard side. One of the opposite ends of the front of the cage is connected to the inboard side while the other opposite end of the front of the cage is connected to the outboard side of the cage. Similarly, one of the opposite ends of the back of the cage is connected to the inboard side while the other opposite end of the back of the cage is connected to the outboard side of the cage. 
     However, as depicted in U.S. Pat. Nos. 9,133,014 and 8,051,951, which are hereby incorporated herein by this reference for all purposes, because of the presence of the railing structure, such cages remain above the top handrails and fail to provide any fall protection deployed beneath the top handrails of the railing structure. As a result, the openings beneath the top handrail can range between 22 and 30 inches and thus remain big enough for a person to slip through, thereby failing to provide adequate worker fall protection. Moreover, these cages resting on the top handrails of the railing structure typically are small (on the order of a foot tall above the handrail). Some cage structures are more elaborate and require expensive subsystems that must be activated before it is deemed safe for workers to access the work areas on the tops of the rolling railing stock. However, improper activation of these subsystems renders them less effective, and thus these subsystems require the presence of workers who are trained to operate such subsystems. 
     Because the railing structures atop the tanks come in a variety of different configurations, it is difficult to match the cage configuration with the railing structure in a way that ensures fall protection for the workers engaged in their duties at the particular section of the top of the rolling stock where these worker duties are to be carried out. Having to stockpile different cages with different configurations in anticipation of satisfying the requirements of many different configurations for the railing structures is so problematical as to be economically not feasible. Moreover, the worker&#39;s duties involve tasks that sometimes must be performed when the rolling stock is parked in different sorts of environments that affect the best way for these cages to be deployed to address the particular location atop the loading stock where such worker tasks are to be performed. Even so, having personnel on hand who are sufficiently competent to manipulate the cages appropriately with respect to the environments where the loading stock is parked and with respect to the configuration of the various railing structures also poses problems. Less competent personnel take longer to deploy the cages, and securing personnel sufficiently competent to deploy the cages can delay the performance of the tasks and tie up loading sites while the requisite personnel are secured. Such delays add additional cost to the performance of these tasks. 
     Accordingly, a need exists for apparatus that addresses these issues raised above in a manner that is uncomplicated, reliable and minimizes the need for special worker training. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of embodiments of the invention. Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification. A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in this specification, including reference to the accompanying figures, in which: 
         FIG.  1    is an end view of an embodiment of the present invention with the fall protection cage disposed in an orientation lowered around the top of a tank of a railcar for which the Standard Plate C Envelope is schematically represented and being shown in relation to the edge of an adjustable positioning mechanism that ensures that the portable deployment apparatus is spaced from the railcar by a distance that ensures precisely lowering of the cage with respect to the fence at the top of the tank. 
         FIG.  2    is a schematic representation of a perspective view of an embodiment of a fence that typically might be encountered at the top of the tank of a railcar. 
         FIG.  3    is a perspective view of the embodiment of the present invention depicted in  FIG.  1    but with the adjustable positioning mechanism omitted for the sake of simplicity. 
         FIG.  4    is a view of the cage of the embodiment of the present invention depicted in  FIGS.  1  and  3    taken from above. 
         FIG.  5    is a perspective view of an alternative embodiment of a portable platform carrying an alternative embodiment of a cage in accordance with the present invention. 
         FIG.  6    is a perspective view of an alternative embodiment of a stationary platform carrying the alternative embodiment of the cage shown in  FIG.  5   . 
         FIG.  7    is an elevated perspective view of a cage illustrating aspects of an embodiment of the present invention. 
         FIG.  8    is an elevated perspective view of embodiments of components of an embodiment of a cage shown in  FIG.  7   . 
         FIG.  9    is an end elevation view of components shown in  FIG.  8   . 
         FIG.  10    is an elevated perspective view of a corner of an alternative embodiment of a cage similar to the embodiments shown in  FIGS.  1  and  3    and where the back frame of the cage meets the outboard side of the cage. 
         FIG.  11    is an end elevation view an embodiment of the present invention disposed in an orientation that is being lowered toward the top of a tank shown in partial outline wider than the tank depicted in  FIG.  1   . 
         FIG.  12    is a perspective view of components shown in  FIGS.  1 ,  3  and  4   . 
         FIG.  13    is a view of the inboard side the cage separated from the two end sections of the cage. 
         FIG.  14    is an end view an embodiment of the present invention disposed in an orientation that is being lowered toward the top of a tank shown in partial outline with the top hatch and guardrails. 
         FIG.  15    is an end view another embodiment of the present invention disposed in an orientation that is being lowered toward the top of a tank shown in partial outline narrower than the tank depicted in  FIG.  14   . 
     
    
    
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate at least one presently preferred embodiment of the invention as well as some alternative embodiments. These drawings, together with the written description, serve to explain the principles of the invention but by no means are intended to be exhaustive of all of the possible manifestations of the invention. 
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
     Reference will now be made in detail to present exemplary embodiments of the invention, wherein one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the embodiments of the invention. 
     Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     It is to be understood that the ranges and limits mentioned herein include all sub-ranges located within the prescribed limits, inclusive of the limits themselves unless otherwise stated. For instance, a range from 100 to 200 also includes all possible sub-ranges, examples of which are from 100 to 150, 170 to 190, 153 to 162, 145.3 to 149.6, and 187 to 200. Further, a limit of up to 7 also includes a limit of up to 5, up to 3, and up to 4.5, as well as all sub-ranges within the limit, such as from about 0 to 5, which includes 0 and includes 5 and from 5.2 to 7, which includes 5.2 and includes 7. Moreover, while specific spatial dimensions are provided for some of the exemplary embodiments described herein, the present invention is not limited to embodiments with those specific spatial dimensions. 
     The standard dimensional envelope occupied by a railway tank car, commonly referred to as the Standard Plate C Envelope, applies to the majority of the rolling rail stock throughout North America and is schematically represented in  FIG.  1    in an outline formed of two parallel vertical lines  31 ,  32 . The vertically extending line  31  in  FIG.  1    schematically represents the inboard side of the Standard Plate C Envelope in relation to the chassis of a portable loading apparatus  30 . The vertically extending chain-dashed line  32  in  FIG.  1    schematically represents the outboard side of the Standard Plate C Envelope in relation to the portable loading apparatus  30 . The vertically extending line  33  in  FIG.  1    schematically represents the vertical centerline of the Standard Plate C Envelope and often provides a convenient frame of reference for measuring the distance from the nearest edge of the portable loading apparatus  30 . 
       FIG.  1    also schematically presents the respective inboard side  31 , centerline  33  and outboard side  32  of the Standard Plate C Envelope in relation to a tank car  36  sitting stationary on a side track. However, for the sake of simplicity, only the upper portion of the tank car  36  is schematically represented in  FIG.  1   , the lower half being omitted. The main body of the tank car  36  is a tank  40  that typically has a cylindrical shape, and accordingly the top  41  of the tank  40  has a curved shape. Because workers easily lose balance when trying to find footing on such a curved shape and moreover because of the likelihood of encountering slippery surfaces thereon, provision must be made for protection of workers who might slip and fall from the top  41  of the tank  40 . Thus, often the top  41  of the tank  40  on railcars or trucks is outfitted with a fence around the work area of the top  41  of the tank  40 .  FIG.  2    schematically presents a perspective view of a simple version of this fence  43 , which typically includes posts  44  vertically extending above the top  41  of the tank  40 . The fence  43  typically is provided with a handrail  45  that is supported at the upper ends of the posts  44  and thus disposed above and surrounding the work area at the top  41  of the tank  40 . The handrail  45  of the fence  43  typically is composed of end rails  46  that are connected to the tops of the posts  44  and extend laterally across the width of the tank  40  shown in  FIG.  1   . Similarly, as schematically shown in  FIG.  2   , the fence  43  includes side rails  47  that extend lengthwise across the top  41  of the tank  40  shown in  FIG.  1   . Typically, a ladder is provided on the opposite sides of the tank  40 , and the ladder includes side rails  39  that conform at least partially to the curvature of the exterior sides of the tank  40  and extend outwardly from the top  41  of the tank  40  as schematically shown in  FIG.  1    for example. At the top of the ladder, as schematically shown in  FIG.  2   , there will be an entrance opening  42  through which workers can access the top  41  of the tank  40 . The entrance opening  42  in the fence  43  is defined by a pair of longitudinally spaced apart and vertically extending entrance posts  44   a , and the access opening  42  is defined in part by an interruption in the respective side rail  47 . However, depending upon the configuration of the tank  40  for example, the location of the ladder and the location of this entrance opening  42  can be varied. As schematically shown in dashed line in  FIG.  1   , the fence typically will surround a hatch  38  that controls access to the interior of the tank  40  and has a sidewall that extends vertically above the top  41  of the tank  40 . 
     As schematically shown in  FIG.  2   , a footing plate  48  desirably runs down the length of each side of the fence  43 , and the base of each post  44 ,  44   a  extends vertically above one of the respective footing plates  48 . As schematically shown in  FIG.  1   , each footing plate  48  rests against the top  41  of the tank  40 . As is apparent from the view shown in  FIG.  2   , the fence  43  leaves considerable open areas between the handrail  45  and the footing plate  48 . The same large open areas exist between the handrail  45  and the top  41  of the tank  40  schematically shown in  FIG.  1   . These open areas are problematical because a worker losing balance on the top  41  of the tank  40  can slide through these open areas and fall to the ground and accordingly sustain injury. 
     Thus, even when the top  41  of the tank  40  is provided with a fence  43 , additional railcar access fall protection is desired. Providing such additional railcar access fall protection can involve the deployment of a cage that must surround a particular region of the top  41  of the rolling stock. However, in deploying this additional cage, the pre-existing fence  43  must be accommodated in a way that does not compromise the desired fall protection for the workers engaged around the top  41  of the tank  40  in performing the tasks entailed by their duties. It is these sorts of cages and associated deployment apparatus that are the subject of the various embodiments of the present invention described more fully below. Examples of some embodiments of these cages and associated deployment apparatus that are intended for addressing environments remote from fixed loading stations are portable and are shown in various perspective views in  FIGS.  1 ,  3 ,  4  and  5   . While an example of other embodiments of these cages and associated deployment apparatus that are intended for fixed loading stations is shown in a perspective view in  FIG.  6    for example. 
     In the exemplary embodiments described herein, each cage defines a generally quadrilateral shape. For the sake of convenience, the embodiments of the cages of the present invention will be described with reference to the following conventions. The length of the work area with respect to which the cage is to be positioned during its intended use providing fall protection for workers performing duties on the top  41  of the rolling stock, whether the particular rolling stock should be a tank rail car or a tank truck, will define the longitudinal direction, which is typically parallel to the direction of transport of the railcar. The length of the work area is measured in the direction of the length of the rail car. The width of the work area defines the transverse direction, which is perpendicular to the longitudinal direction, and the width of the work area is measured in the direction of the width of the rail car and is the direction in which the Standard Plate C Envelope is shown in  FIG.  1   . The vertical direction is perpendicular to each of the longitudinal direction and the transverse direction and is the direction along which the gravitational force acts on the rolling stock and on the cage and associated deployment apparatus for the cage. The side of each cage through which the workers gain entrance into the cage when the cage is positioned to perform its intended function to provide fall protection for workers performing duties on top  41  of the rolling stock will be considered the inboard side of the cage and is one of the two sides of the cage that extends in the longitudinal direction, which is a direction that is parallel to the length of the rolling stock according to the convention adopted herein. The other side of the cage that extends in the longitudinal direction is termed the outboard side of the cage, which is disposed spaced apart in the transverse direction from the inboard side of the cage. Each of the respective opposite ends of the inboard side and outboard side of the cage is connected to each other by the span of a respective front section or back section of the cage. Thus, a first end of the outboard side of the cage is connected to a first end of the inboard side of the cage by a front section of the cage that extends in the transverse direction to span between these two opposing first ends of the respective inboard side and outboard side of the cage. Similarly, the opposite end of the outboard side of the cage is the second end that is connected to the second end of the inboard side of the cage by a back section of the cage that also extends in the transverse direction. The back section of the cage is disposed opposite the front section of the cage and spaced apart in the longitudinal direction from the front section of the cage by a distance according to the length of the respective inboard side of the cage and the length of the respective outboard side of the cage. Moreover, in a presently preferred embodiment, the configuration of each of the front and back sections of the cage typically is identical so as to simplify the inventory necessary to manufacture this presently preferred embodiment of the cage. However, each front section and back section can be differently configured to accommodate a customized railing configuration on the top of a railcar. The depth of the cage is measured in a direction that is perpendicular to each of the longitudinal and transverse directions and is the direction that is vertically disposed with respect to the work area when the cage is in operation and positioned around the work area. 
     In accordance with one aspect of the present invention, embodiments of a railcar access fall protection cage and associated deployment apparatus that are portable for addressing environments remote from fixed loading stations are shown in  FIGS.  1  and  3 - 5   . In the embodiment depicted in  FIGS.  1 ,  3  and  4   , the cage is generally designated by the numeral  60 . In the embodiment depicted in perspective view in  FIG.  5   , an alternative embodiment of the cage is generally designated by the numeral  160 . A stationary platform carrying the alternative embodiment of the cage  160  is shown in a perspective view in  FIG.  6   . 
     Examples of suitable portable deployment apparatus  30  associated with embodiments of the cage  60 ,  160  and including a platform, extension ladder, stationary ladder, base and chassis can be found for example in commonly owned U.S. Pat. No. 9,133,014, which is hereby incorporated herein by this reference for all purposes. Briefly, the cage  60  in  FIG.  1    is connected to and carried by a portable deployment apparatus  30  that desirably includes a chassis  50  that is rendered mobile by a plurality of rotatable wheels  51 ,  52  connected to the chassis  50 . A base  53  is connected to and carried by the chassis  50 . A stationary ladder  54  is suitably braced and supported above the base  53  and has a lower end anchored to the base  53 . An extension ladder  55  is selectively extensible and retractable from the stationary ladder  54 . A platform  56  is connected to the upper end of the extension ladder  55 . The direction in which the extension ladder  55  is extendable from the stationary ladder  54  has a component in the vertical direction as well as a component in the transverse direction relative to the base  53 . The platform  56  leads to an access opening  57  through which the worker can gain access from the extension ladder  55  to the top  41  of the tank  40 . 
     Turning now to the cages  60 ,  160  themselves, as schematically shown in  FIGS.  3 ,  4  and  5    for example, each embodiment desirably is formed by a lattice structure defining a generally quadrilateral shape. The lattice structure is defined by a top edge and a bottom edge, and the lattice structure has a depth that extends in a direction between the top and bottom edges. The lattice structure has a length measured in a longitudinal direction and a width measured in a transverse direction that is perpendicular to the longitudinal direction and perpendicular to the direction in which the depth extends. The lattice structure desirably is formed by a plurality of interconnected tubular members, which leaves a plurality of open areas between the tubular members but aims to constrain the size of each of the open areas to prevent passage of the body of a worker through the open area. In this way, the lattice structure functions as would a netting that prevents passage of bodies greater than a certain size and so compensates for the considerable open areas that exist between the handrail  45  and the footing plate  48  shown in  FIG.  2    for example. The interconnected tubular members of the lattice structure typically are hollow and have circular transverse cross-sectional shapes. However, tubular members with other transverse cross-sectional shapes, such as squares or rectangles, can be used. Moreover, each corner of the lattice structure desirably is anchored by a right-angle flange. In consideration of the trade-off between strength and weight, the lattice structure desirably is composed of structural aluminum. 
     As schematically shown in  FIG.  3    for example, the lattice structure of the fall protection cage  60  includes an outboard side that is designated generally by the numeral  61  and elongates along the length of the cage  60  between a front end  61   a  of the outboard side  61  and a back end  61   b  of the outboard side  61 . As schematically shown in  FIG.  5    for example, the lattice structure of the fall protection cage  160  includes an outboard side that is designated generally by the numeral  161  and elongates along the length of the cage  160  between a front end  161   a  of the outboard side  161  and a back end  161   b  of the outboard side  161 . 
     As schematically shown in  FIGS.  5  and  7    for example, the front end  161   a  of the outboard side  161  of the lattice structure forming the cage  160  defines a front fence notch  171  with a blind end  172  near the top edge of the cage  160  and an open end at the bottom edge of the cage  160 . Similarly, the back end  161   b  of the outboard side  161  defines a back fence notch  173  with a blind end  174  near the top edge of the cage  160  and an open end at the bottom edge of the cage  160 . The shape of each front fence notch  171  and back fence notch  173  is configured so that the outboard side  161  of the cage  160  can be fitted over the end rails  46  of the handrail  45  of the fence  43  shown in  FIG.  2    for example. 
     As shown in  FIG.  7    for example, each opposite end  161   a ,  161   b  of the outboard side  161  of the cage  160  is defined by a corner pillar  170  that desirably can be formed by a three-foot 10 inch length of angle iron formed of aluminum measuring 3″×3″×0.25″. Disposed centrally between the corner pillars  170  is a center grill (described more fully below) that is defined at each of its ends by a minor vertical support  175  that desirably is aligned parallel to the adjacent corner pillar  170  and disposed spaced apart from the adjacent corner pillar  170  in the longitudinal direction by a distance intended to accommodate most of the configurations of the fence  43  that are likely to be encountered on the top  41  of these tanks  40 . In the embodiments shown in  FIGS.  5 ,  6  and  7   , this distance is for example 8 inches forming a respective fence notch  171 ,  173  at each opposite end  161   a ,  161   b  of the outboard side  161  of the cage  160  in accordance with one aspect of the present invention. The minor vertical support  175  desirably is formed of 0.125 inch thickness aluminum tubing having a circular cross-section with a 1.5 inch outer diameter. 
     Thus, the fence notch  171 ,  173  formed at each opposite end  161   a ,  161   b  of the outboard side  161  of the cage  160  has a rectangular configuration in the embodiment shown in  FIGS.  5 ,  6  and  7    but notches of other shapes can be defined between the minor vertical support  175  and the adjacent corner pillar  170 . As shown in  FIGS.  14  and  15    for example, as the cage  160  is lowered, the fence notches  171 ,  173  between the minor vertical support  175  and the associated corner pillar  170  at each opposite end  161   a ,  161   b  of the outboard side  161  of the cage  160  will accommodate, by sliding over and receiving therein, the transversely extending railing portions  46  (See  FIG.  2   ) of the fence  43  on the top  41  of the tank  40 . The front fence notch  171  and the back fence notch  173  defined in the outboard side  161  of the cage  160  allows a certain amount of misalignment between the cage  160  and the end rails  46  of the fence  43  surrounding the work area at the top  41  of the tank  40 . 
     As shown in  FIG.  7    for example, the uppermost end of the minor vertical support  175  desirably is welded to the underside of a major horizontal support  176  of the outboard side  161  of the cage  160 . The major horizontal support  176  elongates in the longitudinal direction, which would be disposed parallel to the walking surface of the footing plate  48  of fence  43  when the cage  160  is deployed in operation around the top  41  of the tank  40 . Each opposite end of the major horizontal support  176  is rigidly attached to one of the legs of a respective one of the corner pillars  170 . The major horizontal support  176  desirably is formed of 0.125 inch thickness aluminum tubing having a rectangular cross-section measuring 2″ wide by 3″ tall. As shown in  FIG.  7    for example, a plurality, and desirably at least two, minor horizontal supports  176   a  are spaced apart from one another and are connected at their opposite ends to a respective one of the two minor vertical supports  175  of the outboard side  161  of the cage  160 . Each of these minor horizontal supports  176   a  similarly desirably is formed of 0.125 inch thickness aluminum tubing having a circular cross-section 1.5 inch outer diameter. Thus, the center grill is formed by the minor vertical supports  175 , the major horizontal support  176  and the minor horizontal supports  176   a , each rigidly connected as by welding as noted above. 
     The outboard side  61  of the cage  60  shown in  FIG.  3    for example does not include any notches for accommodating the fence  43 . This is because this embodiment of the outboard side  61  of the cage  60  is configured so that it can fit entirely within the fence  43  or the fence  43  can fit entirely within the cage  60 . Accordingly, the center grill extends completely across the entire length of the outboard side  61  of the cage without any interruption for any notches. When the cage  60  must be large enough to completely envelop the fence  43 , then the length of the outboard side  61  can demand a center crutch  177   a  disposed midway between the corner pillars  170 . In such an embodiment as shown in  FIG.  3   , each of the minor horizontal supports  176   a  will extend between the center crutch  177   a  and one of the corner pillars  170 . As shown in  FIG.  3    for example, the upper end of the center crutch  177   a  desirably is welded to a handrail  177  that elongates in the longitudinal direction, which would be disposed parallel to the walking surface of the footing plate  48  of fence  43  when the cage  60  is deployed in operation around the top  41  of the tank  40 . Each opposite end of the handrail  177  is rigidly attached to one of the legs of a respective one of the corner pillars  170 . 
     As shown in  FIG.  7    for example, spaced vertically above the major horizontal support  176  of the cage  160  is a handrail  177  that elongates in the longitudinal direction, which would be disposed parallel to the walking surface of the footing plate  48  of fence  43  when the cage  160  is deployed in operation around the top  41  of the tank  40 . So as to prevent central sagging of the handrail, a center crutch  177   a  can be disposed to extend in a vertical direction centrally between the handrail  177  and the major horizontal support  176  of the outboard side  161  of the cage  160 . Each of these center crutches  177   a  and handrails  177  similarly desirably is formed of 0.125 inch thickness aluminum tubing having a circular cross-section with a 1.5 inch outer diameter. Desirably, these elements of the outboard side  161  of the cage  160  are permanently connected to one another as by welding for example. 
     As schematically shown in  FIG.  3    for example, the lattice structure includes an inboard side  62  elongating along the length of the cage  60  between a front end  62   a  and a back end  62   b . The inboard side  62  of the cage  60  is disposed spaced apart from the outboard side  61  of the cage  60  along the width of the cage  62 . The inboard side  62  is configured for attachment to a deployment apparatus, such as the deployment apparatus  30  schematically shown in  FIG.  3    for example. Thus, the inboard side  62  of the cage  60  desirably includes a front section  63  that is spaced apart from a back section  64  so that an access opening  57  is defined between the two sections  63 ,  64  to either side of the platform  56  of the deployment apparatus  30 .  FIG.  13    is a view of an alternative embodiment of the inboard side  62  the cage  60  showing an alternative embodiment of the two sections  63 ,  64  separated from each other and defining the access opening  57  of the cage  60 . 
     The lattice structure of the cage  160  schematically shown in  FIGS.  5 ,  6  and  7    for example, similarly includes an inboard side  162  disposed spaced apart from the outboard side  161  of the cage  160  along the width of the cage  160 .  FIG.  7    shows a perspective view looking into the cage  160  from the outboard side  161  and back frame of the cage  160 . As schematically shown in  FIG.  7   , the inboard side  162  of the cage  160  elongates along the length of the cage  160  between a front end  162   a  and a back end  162   b . The inboard side  162  is configured for attachment to a deployment apparatus, such as the gangway apparatus  34  schematically shown in  FIG.  7    for example. Thus, the inboard side  162  of the cage  160  desirably includes a front section  163  that is spaced apart from a back section  164  so that an access opening  57  is defined between the two sections  163 ,  164  to either side of the platform  156  of the deployment apparatus  34 . 
     In accordance with one aspect of the present invention, each of the front section  163  and back section  164  includes a mechanism for slidable attachment to the deployment apparatus  34 . Because each of the front section  163  and back section  164  of the inboard side  162  of the cage  160  is provided with a comparable mechanism for slidable attachment to the deployment apparatus  34 , only the mechanism for the front section  163  will be described in detail for the sake of simplicity. As shown in  FIG.  8   , each of the two inboard sections  163 ,  164  is slidably connected to a fixed inboard rail section  35  that is rigidly connected to the outboard end of the gangway  34 . Each fixed inboard rail section  35  is disposed to one of the opposite sides of the access opening  57  through which worker passage between the gangway  34  and the interior of the cage  160  can take place. The vertically extending interior extrusions  35   a  of the fixed inboard rail section  35  define the boundaries of the access opening  57  and desirably are formed of aluminum angle irons and measuring 1-½ inch per side. As shown in  FIG.  8   , the front section  163  includes an outward extrusion  163   a  and an inward extrusion  163   b  spaced apart from outward extrusion  163   a . Each of the outward extrusion  163   a  and inward extrusion  163   b  extends vertically and parallel to the other. The outward extrusion  163   a  of the front section  163  desirably is formed of a hollow aluminum tube having a rectangular transverse shape and measuring 1 inch by 1-½ inch per side at the exterior. Each of a plurality of horizontally extending members  163   c  extending between and rigidly connecting the outward extrusion  163   a  and inward extrusion  163   b  of the front section  163  desirably is formed of a hollow aluminum tube, each having an exterior circular transverse shape and measuring 1 inch in diameter. However, as shown in  FIG.  8   , a horizontally extending member  163   c  formed of a hollow aluminum tube with a rectangular transverse shape can be employed, as can other transverse shapes. 
       FIG.  8    for example shows in a perspective view, the way that the front section  163  of the inboard side of cage  160  is slidably connected to a respective one of the fixed inboard rail sections  35 . Because the same arrangement applies to the back section  164  of the inboard side of cage  160 , for the sake of brevity the present description will only focus on the front section  163 .  FIG.  9    provides an end view of this arrangement. In the embodiment shown in  FIGS.  8  and  9   , the front section  163  is slidably connected to the fixed inboard section  35  by an upper tubular slide member  165   a  and a lower tubular slide member  165   b . The upper tubular slide member  165   a  is slidably received within a respective upper track  166   a  carried in a supportive horizontal disposition by the fixed inboard section  35 . Similarly, the lower tubular slide member  165   b  is slidably received within a respective lower track  166   b  carried in a supportive horizontal disposition by the fixed inboard section  35 . Each of the front section  163  and the fixed inboard section  35  is disposed to lie in a respective parallel plane and spaced apart from each other sufficiently to accommodate this mechanism for sliding guiding the front section  163  with respect to the fixed inboard section  35 . The upper slide member  165   a  desirably is welded to one end of each of a pair of flat flanges  167 . The opposite end of each of flat flange is  167  desirably is mechanically fastened to a respective one of the outward extrusion  163   a  or vertically extending inward extrusion  163   b  of the movable front section  163  of the inboard side  162  of the cage  160 . Similarly, the lower slide member  165   b  desirably is welded to one end of each of a pair of flat flanges  167 . The opposite end of each of flat flange is  167  desirably is mechanically fastened to a respective one of the outward extrusion  163   a  or inward extrusion  163   b  of the movable front section  163  of the inboard side  162  of the cage  160 . A plurality of threaded screws is suitable to effect both of these mechanical fastenings. 
     As shown in  FIGS.  8  and  9   , the upper track  166   a  desirably is welded to the interior surface of one leg of each of a pair of right angle flanges  168 . The exterior surface  131  of one end of the opposite leg of each of the right angle flanges is  168  desirably is mechanically fastened as by welding to a respective one of the vertically extending outward extrusions  35   a  of the fixed inboard rail section  35 , Similarly, the lower track  166   b  desirably is welded to the interior surface of one leg of the other one of the pair of right angle flanges  168 . The exterior surface  131  of one end of the opposite leg of the other one of the pair of right angle flanges is  168  desirably is mechanically fastened as by welding to the other one of the outward vertically extending extrusions  35   a  of the fixed inboard rail section  35 . 
     As schematically shown in  FIG.  7   , each pair consisting of a movable front section  163  and a fixed inboard rail section  35  is provided with a pneumatic cylinder  169  that can be operated via a pneumatic circuit (not shown) to move the cage  160  from side to side with respect to the access opening  57  at the distal end of the gangway  34 . One end of each pneumatic cylinder  169  is attached to the movable front section  163  of the pair, and the opposite end of the pneumatic cylinder  169  is attached to the pair&#39;s fixed inboard rail section  35 . By simultaneous operation of the pneumatic cylinders  169  attached respectively to the movable front section  163  and the movable back section  164  of the inboard side  162  of the cage  160 , the operator can position the fence notches  171 ,  173  defined at each opposite end of the outboard side  161  of the cage  160  so as to accommodate the transversely extending end rails  46  (See  FIG.  2   ) of the handrail  45  of the fence  43  on the top  41  of the tank  40 . In this way, the operator can adjust for any slight misalignment between the railing structure atop the tank  40  and the platform from which the gangway  34  is deployed. Moreover, the embodiment of the cage  60  shown in  FIG.  3    can be outfitted with a mechanism for slidable attachment to the deployment apparatus  30  substantially as described above. 
     As schematically shown in  FIGS.  3  and  7    for example, the lattice structure of each respective embodiment of the cage  60 ,  160  desirably includes a respective front frame  80 ,  180  elongating along the width of the respective cage  60 ,  160  between a respective inboard end  80   a ,  180   a  and a respective outboard end  80   b ,  180   b . The lattice structure includes a back frame  90 ,  190  that elongates along the width of the cage  60 ,  160  between an inboard end  90   a ,  190   a  of the back frame  90 ,  190  and an outboard end  90   b ,  190   b  of the back frame  90 ,  190 . The back frame  90 ,  190  is essentially a mirror image of the front frame  80 ,  180 , and accordingly the description of the front frames  80 ,  180  and the back frames  90 ,  190  are interchangeable. To take advantage of this coincidence for the sake of brevity, the perspective views shown in  FIGS.  3  and  7    will dictate whether the description that follows will reference the particular features of the front frames  80 ,  180  or the back frames  90 ,  190 . 
     As shown in  FIG.  7   , the inboard end  180   a  of the front frame  180  is connected to the inboard side  162  of the cage  160 , and the outboard end  180   b  of the front frame  180  is connected to the outboard side  161  of the cage  160 . As shown in  FIG.  7   , the inboard end  190   a  of the back frame  190  defines an inboard gap  191  with a blind end  191   a  near the top edge of the cage  160  and an open end at the bottom edge of the cage  160 . The back frame  190  further defines a central recess  192  disposed between the inboard end  190   a  of the back frame  190  and the inboard gap  191  at the inboard end  190   a  of the back frame  190 . The central recess  192  of the back frame  190  defines an open end at the bottom edge of the cage  160 . The central recess  192  of the back frame  190  defines a blind end  192   a  that is disposed generally intermediate the top edge of the cage  160  and the bottom edge of the cage  160 . 
     As shown in  FIG.  3    for example, the back frame  90  of the cage  60  includes a pair of central guard webs  120 , one of the central guard webs  120  being disposed closer to the respective inboard end  90   a  of the back frame  90 , the other one of the central guard webs  120  being disposed closer to the outboard end  90   b  of the back frame  90 . A corner of an alternative embodiment of a cage  260  similar in many ways to the embodiment depicted in  FIGS.  1 ,  3  and  4    is schematically shown in  FIG.  10   . The enlarged perspective view of  FIG.  10    schematically depicts the intersection of the outboard side  61  and the back frame  90  of cage  260  and will be described in more detail as follows. 
     As shown in  FIG.  10   , the uppermost ends of each of the central guard webs  120  desirably are welded to the underside of a major horizontal support  176  of the back frame of the cage  260 . The major horizontal support  176  elongates in the longitudinal direction and desirably is formed of 0.125 inch thickness aluminum tubing having a rectangular cross-section measuring 2″ wide by 3″ tall. As shown in  FIG.  10   , the central guard web  120  disposed toward the outboard end  90   b  of the back frame  90  includes a straight leg  12   a  that vertically depends from the major horizontal support  176 . The central guard web  120  disposed toward the outboard end  90   b  of the back frame  90  also includes an angled leg  12   b  that depends from the major horizontal support  176  and tilts at less than a right angle toward the straight leg  12   a  of this central web  120  disposed toward the outboard end  90   b  of the back frame  90 . Thus, the angled leg  12   b  is disposed between the straight leg  12   a  and the corner pillar  170  of the back frame  90 . These two legs  12   a ,  12   b  desirably are connected to one another by a bottom bridge  12   c  that connects the ends of these two legs  12   a ,  12   b  that are opposite the ends of the legs  12   a ,  12   b  that are connected to the major horizontal support  176 . Additionally, these two legs  12   a ,  12   b  are connected at the opposite ends of a middle bar  12   d  that is disposed about midway between the major horizontal support  176  and the bottom bridge  12   c  and elongates in the transverse direction and substantially parallel to the elongation direction of the major horizontal support  176 . The bottom bridge  12   c  desirably elongates at an angle to the elongation direction of the major horizontal support  176  and at an angle that is greater than a right angle by the degree of deviation with respect to the elongation direction of the major horizontal support  176 . 
     As shown in  FIG.  10   , the outboard end  90   b  of the back frame  90  defines an outboard gap  194  with a blind end  194   a  near the top edge of the cage  260  and an open end at the bottom edge of the cage  260 . The depth of the gap  194  is the distance between the open end of the gap  194  at the bottom edge of the cage  60 ,  260  and the blind end  194   a . For example, the outboard gap  194  is defined between the angled leg  12   b  of the central guard web  120  that is disposed toward the outboard end  90   b  of the back frame  90  and the corner pillar  170  of the outboard end  90   b  of the back frame  90  that is disposed closer to the outboard side  61  of the cage  260 . The outboard gap  194  of the back frame  90  is desirably configured so that the cage  260  is assured of being positioned clear of any longitudinally extending side rails  47  (See  FIG.  2    for example) of the fence  43  on the railcar that could potentially be located where the cage  260  drops down. The back frame  90  of the cage  260  defines a central recess  192  disposed between the outboard end  90   b  of the back frame  90  and the outboard gap  194  at the outboard end  90   b  of the back frame  90 . The central recess  192  defines an open end at the bottom edge of the cage  260  and a blind end that is disposed generally intermediate the top edge of the cage  260  and the bottom edge of the cage  260 . 
     In accordance with another aspect of the present invention, the outboard gap  194  in the back frame  90  is provided with its own self-adjusting straddle that is configured to encounter the side rails  47  ( FIG.  2   ) that extend longitudinally along the outboard side of the fence  43  atop the tank  40  where the cage  260  is to be deployed. The front frame similarly is provided with its own self-adjusting straddle in a mirror image of the self-adjusting straddle of the back frame  90 . This self-adjusting straddle feature of the outboard gaps in the front frame  80  and the back frame  90  of the cage  260  ensures that the side rails  47  ( FIG.  2   ) of the fence  43  at the top  41  of the tank  40  are received within the respective self-adjusting gap  194  that is formed at each respective front frame  80  and the back frame  90  at the outboard side  61  of the cage  260 . The self-adjusting gap  194  of this self-adjusting straddle feature is self-adjusting both as to the depth of the gap and as to the location within the gap where the cage  60 ,  260  will encounter the side rails  47  of the handrail  45  of the fence  43  at the top  41  of the tank  40 . The self-adjusting straddle aspect is perhaps best explained with reference to  FIG.  10   , which illustrates in a perspective view the corner of a cage  260  where the outboard side  61  meets the back frame  90 . 
     As shown in  FIG.  10   , the straddle desirably includes a dual track raceway  20 . The outboard end of the raceway  20  is connected to the opposite side of the corner pillar  170  of the outboard side  61  of the cage  260  to which the major horizontal support  176  of the outboard side  61  of the cage  260  is connected. The inboard end of the raceway  20  is connected to the  176  of the back frame  90  of the cage  260 . The dual track raceway  20  desirably includes three slats  20   a ,  20   b ,  20   c  extending parallel to each other and spaced apart from each other to define the dual tracks for the self-adjusting straddle. As shown in  FIG.  10   , a central slat  20   b  is disposed between a pair of side slats  20   a ,  20   c . The opposite ends of three slats  20   a ,  20   b ,  20   c  are connected to a respective one of the inboard end  20   d  of the raceway  20  and outboard end  20   e  of the raceway  20 . The central slat  20   b  is desirably spaced equidistantly between the two side slats  20   a ,  20   c  so as to define a pair of side-by-side tracks. As shown in  FIG.  10   , a proximal one of the two tracks so defined is disposed closer to the major horizontal support  176  than to the distal one of these two tracks. 
     As shown in  FIG.  10   , the self-adjusting straddle desirably includes a pair of pivot bars  201 ,  202 , which in the embodiment shown in  FIG.  10    are configured as straight bars along their entire lengths without any angled or curved sections. The lower end of a proximal pivot bar  201  is pivotally connected to the corner pillar  170  of the outboard side  61  of the cage  260 . One end of a proximal axle  29   b  is fixed in the vicinity of the distal end  170   a  of the corner pillar  170  and extends longitudinally therefrom, and the opposite end of the proximal axle  29   b  is carried in a bearing (not shown) that is rotatably carried by the lower end of the proximal pivot bar  201 . The upper end of the proximal pivot bar  201  extends through the proximal track and is constrained to pivot within the proximal track. The lower end of a distal pivot bar  202  is pivotally connected to the lower end of the angled leg  12   b  of the central guard web  120  that is disposed toward the outboard end of the back frame  90  of the cage  260 . One end of a distal axle  29   d  is fixed to the lower end of the angled leg  12   b  of the central guard web  120  that is disposed toward the outboard end  90   b  of the back frame  90  of the cage  260 , and the opposite end of the distal axle  29   d  is carried in a bearing that is rotatably carried by the lower end of the distal pivot bar  202 . The upper end of the distal pivot bar  202  extends through the distal track and is constrained to pivot within the distal track. Thus, the self-adjusting straddle desirably is configured so that each of the straddling pivot bars  201 ,  202  can undergo pivotal movement independent of the other. 
     As the cage  260  is lowered toward the top  41  of the tank  40 , each pair of pivot bars  201 ,  202  will encounter the longitudinally extending handrail  47  of the fence  43  atop the tank  40 . As the cage  260  continues to be lowered, the pivot bars  201 ,  202  will slide on the handrail  47  by virtue of the ability of the pivot bars  201 ,  202  to rotate within each respective track of the raceway  20 . In so doing, the pivoting pivot bars  201 ,  202  self-adjust to reduce size of the outboard gaps  194  permitted in the configurations of the front frame  80  and back frame  90  of the cage  260 . Where the two pivot bars  201 ,  202  intersect will define the blind end  194   a  of the outboard gap  194  in each respective front frame  80  and back frame  90  of the cage to  60 . Accordingly, the depth of the blind end  194   a  of the outboard gap  194  is self-adjusting so as to be automatically adaptable to the height configuration of the fence  43 . Similarly, where the two pivot bars  201 ,  202  intersect will determine whether the blind end  194   a  of the outboard gap  194  will be disposed closer to the outboard side  61  of the cage  260  or closer to the inboard side  62  of the cage  260 . Thus, the blind end  194   a  of the outboard gap is adaptable to the location of the handrail  47  of fences  43  having differing width dimensions. Moreover, each set of pivoting bars  201 ,  202  acts independently of the other set of pivoting bars  201 ,  202 , and thus the two sets in effect work together so as to compensate for any less than rectilinear lowering of the cage  260  with respect to the fence  43  configuration at the top  41  of the tank  40 . 
       FIGS.  1  and  11    are provided to explain a presently preferred embodiment of the pivot bars of the self-adjusting straddle feature of the present invention described above in connection with  FIG.  10   . As shown in  FIGS.  1  and  11   , the self-adjusting straddle desirably includes a pair of pivot bars  71 ,  72 . Each of the proximal pivot bar  71  and the distal pivot bar  72  is connected to the cage  60  in the same manner as already described above for the straight pivot bars  201 ,  202 . However, the configuration of the pivot bars  71 ,  72  shown in  FIGS.  1 ,  3 ,  11  and  12    differs from the configuration of the straight pivot bars  201 ,  202  shown in  FIG.  10   . The configuration of the proximal pivot bar  71  shown in a perspective view in  FIG.  12    for example is largely composed of an arcuate section  71   a  that has a radius of curvature that desirably falls within the range of 3 feet to 4 feet. One end of a straight section  71   b  of the proximal pivot bar  71  is connected to one end of the arcuate section  71   a , while the opposite end of the arcuate section  71   a  desirably is the end of the arcuate section  71   a  that is pivotally connected to the outboard side  61  of the cage  60  in the same manner as described above in connection with the embodiment depicted in  FIG.  10   . Thus, one end of a proximal axle  29   b  is fixed to the corner pillar  170  and extends longitudinally therefrom, and the opposite end of the proximal axle  29   b  is carried in a bearing (not shown) that is rotatably carried by the lower end of the arcuate section  71   a  of the proximal pivot bar  71 . 
     As shown in a perspective view in  FIG.  3    for example, the configuration of the distal pivot bar  72  is defined by two straight sections  72   a ,  72   b  connected to one another by a knee bend such that an obtuse angle is defined between the two straight sections  72   a ,  72   b . The obtuse angle desirably falls within the range of between 165 and 175°. The lengths of each of the two straight sections desirably are approximately equal to one another. Thus, the lower end of a distal pivot bar  72  (shown in  FIGS.  1 ,  3 ,  4  and  11   ) is pivotally connected to the lower end of the angled leg  12   b  of the central guard web  120  that is shown in  FIG.  10    and disposed toward the outboard end of the back frame  90  of the cage  60 . One end of a distal axle  29   d  is fixed to the lower end of the angled leg  12   b  of the central guard web  120  that is disposed toward the outboard end  90   b  of the back frame  90  of the cage  60 , and the opposite end of the distal axle  29   d  is carried in a bearing that is rotatably carried by the lower end of one straight section  72   b  of the distal pivot bar  72 . The upper end of the distal pivot bar  72  (shown in  FIGS.  1 ,  3 ,  4  and  11   ) extends through the distal track and is constrained to pivot within the distal track. Thus, the self-adjusting straddle desirably is configured so that each of the straddling pivot bars  71 ,  72  can undergo pivotal movement independent of the other. 
     As the cage  60  is lowered toward the top  41  of the tank  40 , the blind end  194   a  of the outboard gap  194  formed by the crossing intersection of each pair of pivot bars  71 ,  72  will encounter the longitudinally extending handrail  47  of the fence  43  atop the tank  40 . As the cage  60  continues to be lowered, the pivot bars  71 ,  72  will slide on the handrail  47  by virtue of the ability of the pivot bars  71 ,  72  to rotate within each respective track of the raceway  20 . In so doing, the pivoting pivot bars  71 ,  72  self-adjust to reduce the size of the outboard gaps that are permitted in the configurations of the front frame  80  and back frame  90  of the cage  60 . Moreover, each set of pivoting bars  71 ,  72  acts independently of the other set of pivoting bars  71 ,  72  and thus the two sets in effect work together so as to compensate for any less than rectilinear lowering of the cage  60  with respect to the fence configuration at the top  41  of the tank  40 . 
       FIGS.  1  and  11    illustrate the same cage  60  being lowered onto a tank car having the Standard Plate C Envelope but with different railing configurations. In  FIG.  1   , the upper ends of the side rails  39  of the ladder terminate at the foot of a railing system of six-foot width. While in  FIG.  11   , the width of the railing system is 8 feet. Comparing  FIG.  1    to  FIG.  11   , one can appreciate how the pivoting bars  71 ,  72  of the straddle at the outboard end of the cage  60  self-adjust to accommodate the different widths of the respective railing systems. As shown in  FIG.  1   , the inboard gap  191  straddles the vertical post  44  of the fence  43  with the vertical leg disposed closer to the vertical post  44  than is the case in the situation depicted in  FIG.  11    where the angled leg defining the inboard gap  191  is disposed closer to the vertical post  44 . In both cases, the pivot bars  71 ,  72  defining the outboard gap  194  engage the fence  43 , but at different locations due to the differing widths of the fence in  FIG.  1    versus the fence in  FIG.  11   . 
     As shown in  FIG.  12   , an arcuate grill  140  is carried between and by the arcuate sections  71   a  of the proximal pivot bars  71  at the opposite ends of the cage  60 . The exemplary embodiment of the grill  140  shown in perspective view in  FIG.  12    for example is defined by at least 3 straight rods  142  spaced apart from one another and extending parallel to one another. As shown in  FIG.  12   , each opposite end of each straight rod  142  is connected to one of the arcuate sections  71   a  of the proximal pivot bar  71  on either end of the cage  60 . As shown in  FIG.  12   , the arcuate grill  140  is further defined by a plurality of arcuately shaped ribs  144  that are disposed perpendicular to the straight rods  142  and connected to the straight rods  142 . The arcuately shaped ribs  144  desirably are disposed parallel to one another. The arcuate grill  140  carried by the arcuate sections  71   a  of the two proximal pivot bars  71  ensures blockage of any openings in the railing system at the top  41  of the tank  40  on the outboard side of the tank  40  and thus functions like a rigid net that prevents workers from slipping through gaps in the railing system at the top  41  of the tank  40 . 
     Though the embodiment of the straddling mechanism described above has been configured as part of the outboard side  61  of the cage  60 ,  260 , the same sort of straddling mechanism can be configured as part of the inboard side  62  of the cage  60 ,  260 . 
     In accordance with one aspect of the present invention schematically shown in  FIG.  1    for example, the portable deployment apparatus  30  desirably can include an adjustable positioning mechanism  150  that ensures that the portable deployment apparatus  30  is spaced from the railcar by a distance that ensures precisely lowering of the cage  60  with respect to a fence  43  at the top  41  of the tank  40 . Thus, the positioning mechanism  150  is provided to enable a reliably correct positioning of the cage  60 ,  160  so that when the cage  60 ,  160  is lowered onto the top  41  of the tank  40 , each of the notches in the cage  60 ,  160  avoids undesired interference with the fence  43  and any valve structure  38  on the top  41  of the tank  40 . As embodied herein and shown in  FIG.  1    for example, a positioning mechanism  150  is mounted to a stanchion  58  that has a lower end firmly attached to the forward end of the base  53  connected to the chassis  50  of the portable vehicle by which the cage  60 ,  160  can be moved into position adjacent the rolling stock located on a side track. The positioning mechanism  150  desirably includes a pair of hollow sleeves  151 ,  152 . One end of a top sleeve  151  is permanently attached as by welding to the uppermost end of the stanchion  58  so as to extend horizontally therefrom. Similarly, one end of a bottom sleeve  152  is permanently attached to the stanchion  58  as by welding at a location that is disposed beneath the top sleeve  151 . Desirably, the vertical spacing between the two sleeves  151 ,  152  is on the order of 3 feet. Each of the sleeves  151 ,  152  desirably is formed by an aluminum tube having a square transverse shape and measuring 2 inches per side, 0.125 inches thick and extending outwardly from the stanchion  58  by about 27 inches. 
     As shown in  FIG.  1    for example, the positioning mechanism  150  also includes a telescoping member  153  having a pair of opposed ends, each of which being configured to be slidably received within a respective open end of either the top sleeve  151  or the bottom sleeve  152 . The telescoping member  153  desirably takes the shape of three sides of a rectangle that includes a bottom leg,  154 , top leg  155  and a vertical leg  156  extending between and connecting the bottom leg  154  to the top leg  155 . The missing fourth side of the otherwise rectangular embodiment of the telescoping member  153  leaves the top leg  155  defining a free end that is configured to be received in the top sleeve  151  and similarly the bottom leg  154  defining a free and that is configured to be used received in the bottom sleeve  152 . Thus, the free ends of the respective top leg  155  and bottom leg  154  are slidably received in the respective top sleeve  151  and bottom sleeve  152  in a telescoping fashion. As shown in  FIG.  1    for example, each of the legs  154 ,  155  extends outwardly from the vertical leg  156 , which connects the legs  154 ,  155 , by a distance of about 3 feet. The telescoping member  153  desirably is formed of aluminum tubes 0.125 inches thick and having a square transverse shape measuring 1-½ inch per side. 
     Moreover, the positioning mechanism  150  desirably includes an adjustment feature by which the distance between the vertical leg  156  and the stanchion  58  can be varied selectively by the user. A series of holes (not shown) is provided along the length of the top sleeve  151  and aligned in a straight line therealong. These holes are spaced apart from each adjacent hole by about 1 inch. A matching series of holes (not shown) is provided in the free end of the top leg  155  of the telescoping member  153 . Alignment of one of the holes in the top leg  155  of the telescoping member with one of the holes in the top sleeve  151  affords the opportunity to insert a pin (not shown) through both aligned holes so as to fix the position of the top leg  155  with respect to the top sleeve  151 . A similar series of holes (not shown) desirably is provided in the bottom sleeve  152 , and a similar series of holes (not shown) desirably is provided in the free end of the bottom leg  154  of the telescoping member  153 . By operation of this adjustment feature, the position of the vehicle carrying the cage  60 ,  160  relative to the rolling stock onto which the cage  60 ,  160  is to be lowered is determined by when the vertical leg  156  reaches the inboard side  31  of the Standard Plate C Envelope as shown in  FIG.  1    for example. The user, having knowledge of the particular rolling stock involved, can adjust the distance of the vertical leg  156  from the stanchion  58  and in so doing determine the precise (to the degree of the spacing between the holes) positioning of the cage  60 ,  160  as the platform  56  is disposed at the appropriate height at the upper end of the extension ladder  55 . 
     While at least one presently preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.