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TRENCH OPERATIONS. For safety is not a gadget but a state of mind.  ~Eleanor Everet. Objectives . Governing Standards Anatomy of a Trench Soil Physics First arriving units actions/ Scene management Equipment Familiarization Type of Trench Collapses Techniques for Protection.

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trench operations


For safety is not a gadget but a state of mind.  ~Eleanor Everet

  • Governing Standards
  • Anatomy of a Trench
  • Soil Physics
  • First arriving units actions/ Scene management
  • Equipment Familiarization
  • Type of Trench Collapses
  • Techniques for Protection
osha cfr 1926 subpart p excavation
OSHA CFR 1926 Subpart P, Excavation:
  • Important to rescuers for several reasons
    • First the data and information will give you the information from which you can decide the protective systems.
    • Secondly, knowledge of the standard, its requirements, protective systems, and soil classifications will qualify the user as a “Competent Person”.
general requirements
General requirements

All trenches must be protected before entries except:

      • Those made entirely of stable rock.
      • Those less than five feet in depth, including the height of the spoil pile must be protected.
  • Protection:
    • Anything more than five feet in depth, including the height of the spoil pile must be protected.
  • Spoil Pile:
    • Must have two-foot set back for the lip.
  • Egress:
    • Trenches four feet or greater in depth must have a means of egress every twenty-five feet “Ladders”.
  • Atmospheric:
    • Trenches four feet or greater in depth must be tested before entry.
  • A “trench”, means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width measured at the bottom is not greater than 15 feet.



excavation includes a trench
”Excavation”, includes a trench

It means any man made cut, cavity, trench, or depression in an earth surface formed by the earths removal. Again, in practical terms, when a hole is more than 15 feet wide at its base, it is called specifically an excavation. Overall, an excavation is wider than it is deep.

competent person
Competent Person
  • One who can identify existing or predictable hazards in the surrounding that are unsanitary, hazardous, or dangerous to employees. Also has authorization by the nature of their position to prompt corrective measures to eliminate them. The person shall be knowledgeable in the requirement of this part.
how heavy is dirt
How Heavy is Dirt?
  • Physical forces associated with collapse:
    • Dirt has volume that has mass and weight
    • One cubic foot of dirt weights between 85 and 125 pounds per cubic foot.

Weight of one cubic yard of soil

Weight of a Volkswagen

2,785 Pounds

2,700 Pounds

soil physics
Soil Physics
  • Compounding the effects of gravity is hydrostatic pressure
  • Add the weight of water and rock, a cubic foot of dirt can be as much as 125 pounds per cu/ft
A six foot trench:
    • at the four foot level has approximately 400 pounds vertical pressure
    • Lateral forces could be expected to be 132 pounds
    • Distribution of lateral pressure occurs on about a 45 degree angle from the bottom
accidents without cave ins
Accidents without cave-ins
  • Most emergencies in trenches deal with something other than a collapse
  • Most of the work is done after the trench has been dug
  • In these cases don’t be lulled to sleep by a protected trench
  • Approach identically as an open trench
first arrival
First Arrival
  • Apparatus spotting
    • Spot at least 100 ft from location
  • Create Exclusion Zones (on next slide)
  • Size-up – accurate address of location, call for help
  • Secure RP, job foreman, or witness to accident
  • Safety 360 Review – approach trench from the end, Secondary size-up
  • Rescue or Recovery mode
  • Assess potential hazards to rescuers (Atmospheric, water,Trench etc)
  • Make The Trench Lip Safe – ground pads/ Ladder bridges
  • Shielding of patient – with material on site, plywood, backboard
  • Air monitoring – Bottom at patient, middle and top of trench
  • Apparatus Base Area with manager. location?
ground pads
Ground pads
  • For distribution of weight on trench edge
equipment familiarization
Equipment Familiarization
  • Strongbacks/Uprights = Shoring Panels
  • Yates Spec Pack
  • Waler
  • Palm nailer
  • Airshore
  • Speedshore
types of collapses
Types of Collapses

Spoil pile slide

  • Excavated earth too close to the lip
  • Heavy rain increasing wt of pile
slough in lip slide
Slough In / Lip slide

Slough failure

  • The loss of part of the trench wall
sheer wall
Sheer Wall

Shear wall collapse

  • section of soil that loses it’s ability to stand
toe failure
Toe Failure

Toe failure

  • Slough that occurs at the bottom
  • Found in location of fill dirt
bell pier condition
Bell Pier Condition

Bell pier condition

  • Long term toe failure on both sides
rotational failure
Rotational Failure

Rotational failure

  • Scoop shaped collapse that starts at the lip and transmits itself to the trench walls
wedge failure
Wedge Failure

Wedge failure

  • Occurs with intersecting trenches, T or L Trench
  • Angled section of earth falling from the corner of an intersecting trench
techniques for trench protection31
  • Ops operating within trench
  • Straight wall trench procedures:
    • Set middle set of panels as directly over the victim as possible
    • For Pneumatic Struts:
      • Set middle shore
      • Set top shore
      • Set bottom shore
outside waler
Outside Waler
    • Uses outside walers to span opening
  • Outside waler procedures:
    • Place pickets to tie walers
    • Place and tie off bottom of Waler
    • Place and tie off top of Waler
    • Set middle set of panels as directly over victim as possible
inside waler
Inside Waler
  • Inside walers are used to span a set of panels for the purpose of creating an open space
The intersecting “T” trench is a very unstable trench because not only is one wall exposed, but a section has been cut that intersects the other wall.