Patent Publication Number: US-6907957-B1

Title: Trench shield ladder

Description:
This application is a continuation-in-part of application Ser. No. 10/179,781 filed Jun. 25, 2002, now abandoned. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a ladder for use with a trench shield to allow the user to climb down the ladder into a trench located within the walls of the trench shield. More specifically, the present invention is a ladder that is movable with the trench shield when the trench shield is pulled through a trench and can be lengthened with an extension so that the ladder is of the desired length when trench shields are stacked on top of each other for use in deep trenches. The present ladder meets applicable safety standards, and usage of this ladder can prevent injuries that often occur when using other types of ladders in this type of service. 
   2. Description of the Related Art 
   When workmen need to work in a trench in the ground, such has for example when laying cable or pipe or when doing repair work on underground lines, a trench shield is employed to prevent the sides of the trench from caving in and burying the workmen. Trench shields are made of two parallel walls that are held approximately 3 feet or more apart so that the workmen can work between the walls. The walls are approximately 8 feet tall and are strong enough to shield the workmen from a possible collapse of the trench walls. The walls are also several feet in length. The most common lengths are 8, 12, 16, 20 and 24 feet. 
   Currently, in order for workmen to climb down the walls of the trench shield to enter the trench, they must climb down a traditional straight ladder that has been placed into the trench between the walls of the trench shield. Use of a traditional straight ladder presents several safety problems. First, if the trench is deep, often a pair of trench shields will be employed so that one trench shield is stacked on top of the other one. Often a straight ladder is not long enough to safely use in these deep trenches. 
   Second, in order to use a straight ladder, safety regulations require that the ladder be tied off so that it does not tip when the workmen are on the ladder and does not fall in on top of them when they are in the trench. 
   As work is completed in one section of the trench, it is normally necessary to move the trench shield to another section of the trench by dragging it through the trench. When a traditional straight ladder is employed with a trench shield, the lower end of the ladder rests on the bottom of the trench. In order to safely move the trench shield along the trench, the ladder must first be untied from the trench shield and then pulled out of the trench shield. Then it is safe to pull the trench shield through the trench to its new location. After the trench shield has been moved, the straight ladder is then reinserted between the trench shield walls and is again tied off. This is a time consuming procedure and workmen will often become lazy and not take the time to perform this procedure in a safe manner. For example, they may instead push the straight ladder out the back end of the trench shield so that the trench shield can be moved without removing the ladder from the trench. If they are in the trench when they push the ladder outside of the trench shield, they often place themselves at risk because once they are beyond the walls of the trench shield, they are no longer protected from falling debris and a possible cave in of the sides of the trench. Also, once the ladder is placed outside the walls of the trench shield, workmen will often use the ladder in that unprotected location rather than take the time to reposition the ladder within the trench shield and properly tying the ladder to the trench shield. Workmen have been injured and killed by falling rocks and trench cave ins while they were in a trench but outside the protective walls of the trench shield. 
   The present invention addresses these problems by providing a ladder that can be extended to the desired length to permit safe access to any depth of trench shield and trench. The present invention also rests on the upper lip of the trench shield instead of the bottom of the trench and therefore can be moved with the trench shield. The present ladder fits securely over the upper lip of the trench shield and is held in place by gravity so that it is not necessary to tie the ladder to the trench shield to insure that the ladder is stable and does not fall sideways or drop off of the upper lip of the trench shield. Further, the present invention is provided with a safety platform at the top of the ladder and rails that extend over the top of the ladder to make it safe and easy for the workmen to climb into and out of the trench. Still further, the present invention is provided with stand off arms so that the workmen can fully engage the main and extension rungs of the ladder with their feet along the entire length of the ladder. The present invention is designed to fit on trench shields of varying thicknesses, easily fitting on the common trench thicknesses of approximately 4 inches and approximately 8 inches. 
   SUMMARY OF THE INVENTION 
   The present invention is a trench shield ladder that attaches to the top lip of a trench shield and hangs on the wall of the trench shield to provide workmen safe access to the trench. Because the ladder hangs on the wall of the trench shield, it is moved with the trench shield as the trench shield is pulled through the trench. Also, because the ladder fits securely over the upper lip of the trench shield and is held in place by gravity, it is not necessary to tie the ladder to the trench shield to insure that the ladder is stable and does not fall sideways or drop off of the upper lip of the trench shield. 
   Still further, the present invention is provided with stand off arms so that the workmen can fully engage the main and extension rungs of the ladder with their feet along the entire length of the ladder. The present invention is designed to fit on trench shields of varying thicknesses, easily fitting on the common trench thicknesses of approximately 4 inches and approximately 8 inches. 
   Further, the present invention is provided with a safety platform at the top of the ladder and hand rails that extend approximately 36 inches over the platform of the ladder to make it safe and easy for the workmen to climb into and out of the trench. 
   The ladder can be extended to the desired length to permit safe access to various depths of trench and various heights of trench shield and by use of an extension portion of the ladder. The extension portion is provided with hooks on the upper end of the legs of the extension portion so that the hooks can be looped over any of one the main rungs of the ladder to thereby allow the ladder to be extended to any length desired. The extension portion is not as wide as the main portion of the ladder so that the legs of the extension rest between the legs of the main portion of the ladder when the extension portion is in use. The extension portion hangs from the main portion of the ladder via gravity and is provided with stand off arms similar to the stand off arms provided on the main portion of the ladder. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a trench shield ladder constructed in accordance with a preferred embodiment of the present invention with the location of an extension portion shown in outline and with a portion of the top platform cut away to reveal the supporting framework. 
       FIG. 2  is a perspective view of the extension portion of  FIG. 1 , shown with the main portion of the trench shield ladder shown partially cut away in outline. 
       FIG. 3  is a front elevation of the trench shield ladder of  FIG. 1  shown attached to a wall of a trench shield. 
       FIG. 4  is a side view of the trench shield ladder of  FIG. 3 . 
       FIG. 5  is a top plan view of the trench shield ladder of  FIGS. 3 and 4 . 
       FIG. 6  is a front elevation of the lower end of the trench shield ladder showing the extension portion in use. 
       FIG. 7  is a side view of the lower end of the trench shield ladder and extension portion of  FIG. 6 . 
       FIG. 8  is a top view of the lower end of the trench shield ladder and extension portion taken along line  8 — 8  of  FIG. 6 . 
       FIG. 9  is a perspective view of the trench shield ladder in combination with a trench shield. 
       FIG. 10  is a side view of the trench shield ladder in combination with the trench shield of  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT THE INVENTION 
   Referring now to the drawings and initially to  FIG. 1  and  FIGS. 3–5 , there is illustrated a main portion  10  of a trench shield ladder  12  that is constructed in accordance with a preferred embodiment of the present invention. This trench shield ladder  12  can be extended in length by employing an extension portion  14 , as shown in outline in  FIG. 1 .  FIG. 2  illustrates the extension portion  14  and shows the main portion  10  of the trench shield ladder  12  in outline. Both the main portion  10  of the ladder  12  and the attached extension portion  14  are illustrated in  FIGS. 6–8 . 
   As illustrated in FIGS.  1  and  3 – 5 , the main portion  10  of the ladder  12  is provided with two front legs  15 A and  15 B that extend vertically downward approximately parallel to each other on a front side  16  of the ladder  12 . Spaced apart ladder main rungs  18  are provided extending approximately horizontally between the two legs  15 A and  15 B on the front side  16  of the ladder  12 . The two legs  15 A and  15 B continue at the top end  20  of the ladder  12  as a pair of inverted u-shaped hand rails  22 A and  22 B that extend over a top platform  24  of the ladder  12  and terminate on a back side  26  of the ladder  12  as two rear legs  28 A and  28 B that extend vertically downward approximately parallel to each other and approximately parallel with the two front legs  15 A and  15 B. 
   Stand off arms  30  for removably engaging an inwardly facing surface  31  of a wall  32  of a trench shield  34  are provided on the two front legs  15 A and  15 B so that the stand off arms  30  extend rearward from the front legs  15 A and  15 B and are approximately perpendicular to the front legs  15 A and  15 B. A foot  36  is provided on a distal end  38  of each stand off arm  30  for engaging the inwardly facing surface  31  of the wall  32  of the trench shield  34  when the ladder  12  is in use. The stand off arms  30  hold the front legs  15 A and  15 B of the ladder  12  away from the wall  32  of the trench shield  34  so that the workmen can fully engage the main rungs  18  of the ladder  12  with their feet along the entire length of the ladder  12  as they ascend and descend the ladder  12 . 
   When in use, the rear legs  28 A and  28 B of the ladder  12  extend on the outside of the trench shield  34  and engage an outwardly facing surface  38  of the trench shield wall  32 , and the front legs  15 A and  15 B extend into a trench  40  adjacent the inwardly facing surface  31  of the wall  32  of the trench shield  34  so that the feet  36  of the stand off arms  30  contact the inwardly facing surface  31  of the wall  32  at least at a lower end  42  of the main portion  10  of the ladder  12 . The stand off arms  30  and the rear legs  28 A and  28 B are separated a sufficient distance so that the ladder  12  can be employed with trench shields  34  having walls  32  of various thicknesses, with thicknesses of 4 inches and 8 inches being the most common thicknesses currently employed. 
   Although the drawings illustrate that the ladder  12  hangs on the wall  32  of the trench shield  34  so that all of the feet  36  of the stand off arms  30  engage the inwardly facing surface  31  of the wall  32  of the trench shield  34 , i.e. both at the top and lower ends  20  and  42  of the main portion  10  of the ladder  12 , this is only possible when the wall  32  of trench shield  34  is at the higher end of the range of thicknesses accommodated by the ladder  12 . For trench shield walls  32  of lesser thicknesses, the feet  36  on the top end  20  of the ladder  12  will not engage the inwardly facing surface  31  of the wall  32  of the trench shield  34 , but the feet  36  on the lower end  42  will engage the inwardly facing surface  31  of the wall  32  and the rear arms  28 A and  28 B will engage the outwardly facing surface  38  of the wall  32  on the other side of the same wall  32  to hold the ladder  12  stable as the ladder  12  hangs on the wall  32 . 
   Because the ladder  12  hangs over the wall  32  of the trench shield  34 , it is moved with the trench shield  34  as the trench shield  34  is pulled longitudinally through the trench  40 . Also, because the ladder  12  fits securely over the wall  32  of the trench shield  34  and is held in place by gravity, it is not necessary to tie the ladder  12  to the trench shield  34  in order to insure that the ladder  12  remains stable and does not fall sideways or drop off of the wall  32  of the trench shield  34 . 
   The top platform  24  is supported by a frame  44  that extends between the two front legs  15 A and  15 B, between the two rear legs  28 A and  28 B and between the front and rear legs, i.e. between legs  15 A and  28 A and between legs  15 B and  28 B. The platform  24  has a cover  46  that can safely hold the weight of a workman as the workman steps onto the platform  24  while entering and leaving the trench  40  via the ladder  12 . Each of the inverted unshaped hand rails  22 A and  22 B is preferably approximately 36 inches in height so that they provide a safe handhold for workmen as the workmen descend and ascend the ladder  12 . 
   The ladder  12  may be used with only the main portion  10  attached to the wall  32 , or alternately, with the main portion  10  attached to the wall  32  and the extension portion  14  attached to the main portion  10 , depending on the depth  48  of the trench  40 . The depth  48  of the trench  40  is illustrated in  FIGS. 3 and 4 . Obviously, the depth  48  of the trench  40  will also dictate the total height of the trench shield  34 , or alternately, the total height of a pair of stacked trench shields  34  with which the ladder  12  is employed. 
   Referring now to  FIGS. 2 , and  6 – 7 , the extension portion  14  of the ladder  12  will be described. The ladder  12  can be extended to the desired length to permit safe access to various depths  48  of trenches and various heights of trench shields by use of the extension portion  14  of the ladder  12 . The extension portion  14  is provided with two approximately vertical and approximately parallel extension legs  50 A and  50 B and with spaced apart extension rungs  52  extending approximately horizontally between the two extension legs  50 A and  50 B. 
   Each of the extension legs  50 A and  50 B is provided with an inverted u-shaped hook  54  on the upper end  56  of the extension legs  50 A and  50 B so that the hooks  54  can be looped over any one of the main rungs  18  of the main portion  10  of the ladder  12  to thereby hang the extension portion  14  onto the ladder  12  onto the main portion  10 , and thereby allowing the ladder  12  to be extended to any total length desired. The extension portion  14  is not as wide as the main portion  10  of the ladder  12  so that the extension legs  50 A and  50 B hang between the front legs  15 A and  15 B of the main portion  10  of the ladder  12  when the extension portion  14  is in use. The extension portion  14  hangs from the main portion  10  of the ladder  12  via gravity and is provided with stand off arms  58  and associated feet  60  that are similar in structure and function to the stand off arms  30  and feet  36  provided on the main portion  10  of the ladder  12 . 
   Combination Ladder and Trench Shield 
   Referring to  FIGS. 9 and 10 , there is shown the trench shield ladder  12  in combination with the trench shield  34  with which it is employed. The trench shield  34  is provided with two spaced apart planar panels or walls  32  and  33  that are approximately parallel with each other. The trench shield  32  is provided with a plurality of support rods  62  extending between and secured to the two walls  32  and  33 . The support rods  62  serve to hold the walls  32  and  33  apart so that a working space  64  is provided between the planar walls  32  and  33 . The purpose of the trench shield  34  is to provide a safe environment for workmen who must work in a trench in the ground. By placing the trench shield  34  into the trench, the walls  32  and  33  serve to prevent the sides of the trench from caving in on the workmen as they are working in the bottom of the trench. 
   While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for the purposes of exemplification, but is to be limited only by the scope of the attached claim or claims, including the full range of equivalency to which each element thereof is entitled.