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Trenching and Shoring

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					Trenching and Shoring
          the
    Safety Lesson
     isn't boring!




    P bar Y Safety Consultants Alberta Canada
         A Trenching Tragedy
• Had a false sense of security
• Knew they were out of compliance
• Thought the soil was stable
• Conditions
  changed
  overnight
• A worker died


               P bar Y Safety Consultants Alberta Canada
           Trenching Statistics
• About 400 U.S. workers die in trench-related
  accidents each year
• About 6,400 are seriously injured




                P bar Y Safety Consultants Alberta Canada
       Did you do your homework
•   Did you look around
•   Did you do your hazard assessment
•   Did YOU!
•   If that's the case why are emergency services
    on site, lets review




                  P bar Y Safety Consultants Alberta Canada
     Inspections and risk mapping
• We can make walk through inspections, or
  area, task or hazard specific inspections
• As we go we need to make notes and
  drawings to help us make a report
• As we do this we need to ask workers about
  their opinions regarding hazards, health
  problems or accidents and ideas for
  improvements
• We can organise the investigation and
  information about risks as follows…..
              P bar Y Safety Consultants Alberta Canada
             Physical Hazards

• Falls from heights,scaffolds, roofs, ladders,
  trips and slips
• Excavation hazards and confined spaces
• Machinery, entrapment, cuts
• Transport (forklifts, hoists, cranes)
• Electricity
• Manual handling and lifting, repetitive work
• Noise and vibration

                P bar Y Safety Consultants Alberta Canada
         Chemical Hazards
• Solvents (paints, laquers, varnishes,
  strippers, glues)
• Pesticides (e.g. timber treatments)
• Dust (wood, cement, MMF, silica, gypsum)
• Lead and other metal fumes (welding)
• Diesel and carbon monoxide
• Cement
• Asbestos

              P bar Y Safety Consultants Alberta Canada
              Biological Hazards
•   Contaminated water supply
•   Malaria
•   Dengue
•   Weil’s disease (rats)
•   HIV AIDS
•   Infectious diseases, such as hepatitis or
    tuberculosis


                   P bar Y Safety Consultants Alberta Canada
  Main OSH observations on site
• Housekeeping: order and tidiness
• Safety organisation: safety officer, safety
  rep, safety committee, information and
  training
• Working habits and PPE
• Falls protection: scaffolding, roof work,
  interior shafts: edge protection, guard rails,
  boarding

                 P bar Y Safety Consultants Alberta Canada
    Trenching and Shoring Goals
• Hazards, soil, protective systems
• Safe work practices and hazard awareness




               P bar Y Safety Consultants Alberta Canada
           What Is a Trench?
• A narrow excavation
  that is deeper than
  it is wide
• No more than 15 feet
  wide at bottom
• Walls will eventually
  fail


                P bar Y Safety Consultants Alberta Canada
            What Is a Cave-in?
• Soil or rock that suddenly falls or slides
  into an excavation
• Sufficient quantity to entrap, bury, injure,
  or immobilize
• Soil gravitates downward, pressure pushes
  soil inward toward the trench
• Bottom third of wall typically fails first
• Soil above the collapsed lower wall follows
                 P bar Y Safety Consultants Alberta Canada
              Cave-in Injuries
• Soil weighs 125 lbs.
  per cubic foot
• A worker can be
  crushed by soil,
  rock, or an object
• Suffocation—even if
  worker’s head is not
  buried, soil prevents chest expansion
• Worker becomes immobilized by soil’s
  suction effect
                 P bar Y Safety Consultants Alberta Canada
             Soil Classification
•   Grain size
•   Saturation
•   Cohesiveness
•   Unconfined
    compressive
    strength



                   P bar Y Safety Consultants Alberta Canada
                 Soil Types
• Type A (most stable)—dense and heavy clay
• Type B—silt, sandy loam, medium clay
• Type C (least stable)—gravel, loamy sand,
  soft clay




               P bar Y Safety Consultants Alberta Canada
          Sloping and Benching
• Sloping: angling of walls at an incline
• Benching: series of steps to angle walls
• Soil type determines angle of slope/bench
  —Type A: 3 feet horizontal to 4 feet vertical (3/4:1)
  —Type B: 4 feet horizontal to 4 feet vertical (1:1)
  —Type C: 6 feet horizontal to 4 feet vertical (1-1/2:1)
  —Benching not permitted for Type C soil



                  P bar Y Safety Consultants Alberta Canada
                      Shoring
• Support walls designed to prevent cave-in
• Usually built in place and designed by
  an engineer
• Components include
  uprights (sheeting),
  wales, and cross
  braces


                P bar Y Safety Consultants Alberta Canada
                   Shielding
• Withstands forces of a cave-in
  and protects employees within
• Permanent or portable
• Trench boxes




                P bar Y Safety Consultants Alberta Canada
               Trench Boxes
• Often designed to stack
• Never use sheeting to extend the height
• Can be used in conjunction with sloping
  and benching
• No one permitted
  inside when
  being raised or
  lowered

                P bar Y Safety Consultants Alberta Canada
    Trenching and Shoring Goals
• Hazards, soil, protective systems
• Safe work practices and hazard awareness
• Quiz




               P bar Y Safety Consultants Alberta Canada
         Excavation Inspections
• Inspections conducted before work starts,
  throughout shift, after rainstorm
• Excavations inspected for:
  —Evidence of possible cave-ins
  —Indications of failure of protective systems
  —Potential hazardous atmosphere
• If hazardous condition found, workers
  are removed

                  P bar Y Safety Consultants Alberta Canada
          Signs of Soil Distress
• Fissures or cracks on excavation face
• Slumping of material from excavation face
• Bulging or heaving of material at the bottom
  of excavation wall
• Sinking of excavation’s edge
• Ravelling, or small amounts of material
  (e.g., pebbles) trickling into excavation


                P bar Y Safety Consultants Alberta Canada
  Conditions Causing Soil Distress
• Nearby vibrating
  machinery
• Nearby heavy,
  moving loads
• Seeping water or rain
• Hot, dry weather



                P bar Y Safety Consultants Alberta Canada
       Hazardous Atmospheres
• Excavations near sewers, landfills, hazardous
  substances storage area
• Test atmosphere when deeper than 4 feet
• Ventilation or appropriate PPE
• Rescue and emergency equipment




                P bar Y Safety Consultants Alberta Canada
       Falling Soil or Equipment
• Protect workers from loose rock/soil that may
  fall from an excavation face
    —Use scaling to remove loose soil
    —Use protective barricades, such as shoring
     or shields
• Protect workers from material or equipment
  that could fall into the excavation
    —Keep material/equipment 2 feet from edge
    —Use retaining devices

                 P bar Y Safety Consultants Alberta Canada
          Adjacent Structures
• Excavations might endanger stability of
  buildings, walls, other structures
• Sidewalks, pavement not undermined unless
  supported to prevent collapse on excavation
  workers
• Shoring, bracing, or underpinning used to
  ensure stability for employee protection


               P bar Y Safety Consultants Alberta Canada
          Water Accumulation
• Never work in an excavation where water is
  accumulating without proper precautions:
    —Special shoring or shield system
    —Water removal system
    —Use of safety harness and lifeline




                 P bar Y Safety Consultants Alberta Canada
          Other Trenching Issues
•   Mark underground utilities
•   Stand away from lifting/digging equipment
•   Use warning systems or barricades
•   Use hard hats




                 P bar Y Safety Consultants Alberta Canada
      Other Trenching Issues (cont.)
• Trenches 4 feet deep or more must have exit means within
  25 feet of every worker
• Use fall protection
• Do not work on sides of sloped or benched excavation
  above other workers
• For parallel construction have a worker on top to watch
  excavation walls to warn trench workers of potential
  hazards




                    P bar Y Safety Consultants Alberta Canada
    Trenching and Shoring Goals
• Hazards, soil, protective systems
• Safe work practices and hazard awareness




               P bar Y Safety Consultants Alberta Canada
                    Summary
• Cave-ins occur suddenly and can entrap,
  bury, or injure
• Soils have varying stability that determines
  the appropriate protection
• Always use protection systems
• Be aware of signs of soil distress
• Be aware of all the hazards associated
  with working around excavations
                 P bar Y Safety Consultants Alberta Canada

				
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posted:11/12/2010
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Description: safety