When  ascending  steep,  rocky  slopes,  do  not climb  directly  behind  another  crew  member.  If  the crew  member  were  to  accidentally  fall,  loosen  a rock,  or  drop  something,  it  could  mean  serious injury to anyone directly below the crew member. EXCAVATIONS WARNING When  your  work  involves  excavation, you should observe definite precautions to prevent accidents. To avoid slides or cave-ins, support the sides of the excavations 5 ft or more deep by substantial bracing,  shoring,  or  sheet  piling  if  the  sides  are steeper than the angle of repose. The ANGLE OF REPOSE is the maximum angle at which material will  repose  without  sliding.  Trenches  in  partly saturated  or  otherwise  highly  unstable  soil  should be stabilized with vertical sheet piling or suitable braces.   Foundations   of   structures   adjacent   to excavations  should  be  shored,  braced,  or  under- pinned as long as the excavation remains open. Excavated  or  other  material  should  not  be  allowed to  accumulate  closer  than  2  ft  from  the  edge  of an  excavation.  In  a  traffic  area  use  barricades, safety  signs,  danger  signals,  red  lights,  or  red flagging  on  at  least  two  sides. Do not enter a manhole until you are certain that it is free from dangerous gases. Do not guess. If  there  is  any  question  at  all  as  to  whether  a sewer  is  free  of  gas,  wait  for  clearance  from  a competent  authority.  If  necessary,  provide  first for  thorough  ventilation.  Do  not  smoke  in manholes; and if illumination is required, use only a  safety  flashlight  or  lantern. Avoid  contact  with  ALL  ELECTRIC  wiring. Never throw a metal tape across electric wires; if you must chain across wiring, do it by breaking chain.  Avoid  placing  yourself  so  that  you  might fall  across  wiring  in  the  event  of  an  accident. When walking, stay at least 2 feet away from the   edge   of   a   vertical   excavation.   Near thoroughfares  or  walkways,  excavations  should have temporary guardrails or barricades; and if permissible, depending on combat conditions, red lights  or  torches  should  be  kept  alongside  from sunset to sunrise. TREE  CLIMBING Before  climbing  a  tree,  be  sure  it  is  safe  to climb,  and  carefully  cheek  the  condition  of  the branches  on  which  you  are  likely  to  stand. Different kinds of wood vary greatly in strength. Oak,  hickory,  and  elm  trees  that  have  strong, flexible  wood  are  safer  for  climbing  than  trees such as poplar, catalpa, chestnut, or willow, which have  soft  or  brittle  wood.  Limbs  of  all  trees become  brittle  at  low  temperature—meaning  that they break more easily in cold weather than they do  in  warm.  Dead  branches  or  those  containing many knots or fungus growths are usually weak. When  standing  on  a  limb,  have  your  feet  as close to the parent trunk as possible. Climb with special  care  when  limbs  are  wet  or  icy.  Wear goggles when working in bushy trees; they may prevent an eye injury. WARNING Before climbing a tree, be sure there are no  overhead  wires  passing  through  its foliage.  If  you  MUST  take  a  position  in a tree within reach of live wire, place some sort of insulating safety equipment between yourself and the wire. DO NOT allow tree limbs   to   contact   live   wires   because moisture  in  a  limb  may  cause  a  short circuit. If   you   require   cutting   tools   to   clear   a working  space  in  a  tree,  haul  them  up  with  a handline,  and  lower  them  by  the  same  device. Tools  should  never  be  thrown  up  into  a  tree  or down  onto  the  ground. UNDERGROUND   AND OVERHEAD  LINES If  a  structure  has  an  access  opening  and  is below  the  street,  such  as  a  manhole  or  a transformer  vault,  it  should  be  protected  by  a barrier or other suitable guard when the cover to the  access  opening  is  removed. CROSSING ICE Do  not  cross  ice  unless,  and  until,  you  are certain  it  will  support  your  weight. 14-46