of  a  railroad  track  or  crane  truck,  or  in  any position where they would impede or prevent access  to  fire-fighting  equipment. When materials are being loaded or unloaded from   any   vehicle   by   crane,   the   vehicle operators  and  all  other  persons,  except  the rigging  crew,  should  stand  clear. When materials are placed in work or storage areas, dunnage or shoring must be provided, as necessary,  to  prevent  tipping  of  the  load  or shifting of the materials. All  crew  members  must  stand  clear  of  loads that tend to spread out when landed. When slings are being heaved out from under a load,  all  crew  members  must  stand  clear  to avoid a backlash, and also to avoid a toppling or a tip of the load, which might be caused by fouling of a sling. SHEAR LEGS The  shear  legs  are  formed  by  crossing  two timbers, poles, planks, pipes, or steel bars and lashing or  bolting  them  together  near  the  top.  A  sling  is suspended horn the lashed intersection and is used as a  means  of  supporting  the  load  tackle  system (figure 4-39). In addition to the name shear legs, this rig often is referred to simply as a “shears”. (It has also been called an A-frame.) The shear legs are used to lift heavy machinery and  other  bulky  objects.  They  may  also  be  used  as end  supports  of  a  cableway  and  highline.  The  fact that  the  shears  can  be  quickly  assembled  and  erected is a major reason why they are used in field work. A shears requires only two guy lines and can be used for working at a forward angle. The forward guy does  not  have  much  strain  imposed  on  it  during hoisting.  This  guy  is  used  primarily  as  an  aid  in adjusting the drift of the shears and in keeping the top of  the  rig  steady  in  hoisting  or  placing  a  load.  The after  guy  is  a  very  important  part  of  the  shears’ rigging,  as  it  is  under  considerable  strain  when hoisting. It should be designed for a strength equal to one-half the load to be lifted. The same principles for thrust on the spars or poles apply; that is, the thrust increases  drastically  as  the  shear  legs  go  off  the perpendicular. In rigging the shears, place your two spars on the ground parallel to each other and with their butt ends even. Next, put a large block of wood under the tops of the legs just below the point of lashing, and place a small  block  of  wood  between  the  tops  at  the  same point  to  facilitate  handling  of  the  lashing.  Now, separate  the  poles  a  distance  equal  to  about  one-third the  diameter  of  one  pole. As lashing material, use 18- or 21-thread small stuff. In applying the lashing, first make a clove hitch around one of the legs. Then, take about eight or nine turns  around  both  legs  above  the  hitch,  working towards the top of the legs. Remember to wrap the turns  tightly  so  that  the  finished  lashing  will  be smooth and free of kinks. To apply the frapping (tight lashings), make two or three turns around the lashing between the legs; then, with a clove hitch, secure the end of the line to the other leg just below the lashing (figure 4-39). Now, cross the legs of the shears at the top, and separate  the  butt  ends  of  the  two  legs  so  that  the spread between them is equal to one-half the height of the  shears.  Dig  shallow  holes,  about  1  foot  (30  cm) deep, at the butt end of each leg. The butts of the legs should be placed in these holes in erecting the shears. Placing  the  legs  in  the  holes  will  keep  them  from kicking out in operations where the shears are at an angle other than vertical. Figure 4-39.—Shear legs. 4-23