TRENCH OPERATIONS

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TRENCH OPERATIONS

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

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Objectives

• Governing Standards
• Anatomy of a Trench
• Soil Physics
• First arriving units actions/ Scene management
• Equipment Familiarization
• Type of Trench Collapses and Recognize hazards
• Assignments Responsibilities
• Techniques for Protection

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• Understand what is required to manage a Trench
  Rescue Incident
• Provide tools to enable the student in making
  safe and effective decisions during a trench
  rescue incident
• Implement the Incident Management /
  Accountability System

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NFPA 1670

• REQUIREMENTS FOR OPERATIONS AND TRAINING
• AWARENESS Level Functions
• Size-up of existing and potential conditions
• Development implementation of procedures for
  carrying out an emergency response system
• Site Control Scene Management
• Recognition of hazards and procedures to mitigate
  these hazards

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NFPA 1670 OPERATIONAL LEVEL FUNCTIONS

• Develop Implement procedures
• To make entry
• Shoring in non-intersecting trenches gt 8 feet
• To identify probable victim location
• For making the rescue area safe
• For initiating a one-call utility location
  service
• To ventilate the trench or excavation
• Placing ground pads protecting the lip
• To provide entry and egress paths
• For conducting a pre-entry briefing
• For record keeping
• For utilizing a RIT
• other responsibilities!

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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.

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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.

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Definitions

• 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.

WIDTH DEPTH
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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.

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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.

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Anatomy
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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.

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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

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• A six foot trench
• at the four foot level has approximately 400
  pounds vertical weight.
• Lateral forces could be expected to be 132
  pounds of horizontal pressure
• Distribution of lateral pressure occurs on about
  a 45 degree angle from the bottom

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Types of Worker Protective Systems

• Sloping
• Benching
• Shielding
• Shoring

• Determined by
• Soil class
• Work space required
• Economic factors

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Sloping and benching
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Trench Shield / Trench Box

• Shields are manufactured by a number of companies
  and are designed to protect workers working
  within the confines of the shield.
• Check tabulated data for the maximum allowable
  depth it can be used. The tabulated data must
  accompany the shield when it is being used.
• Additionally, the shield must be designed by a
  Registered Professional Engineer, be in good
  condition, and used properly.

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Shoring

• Shoring is one of the most common used methods of
  worker protection. It is light-weight, portable
  and easy to install.
• The manufacturer provides tabulated data with the
  shoring that provides the limitations,
  precautions, required spacing and proper use.

This photo shows an example of aluminum hydraulic
shoring.
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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 dont be lulled to sleep by a
  protected trench
• Approach identically as an open trench

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What makes trenches hazardous?
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Hazards Present?
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Most deaths occur in trenches 5 ft. to 10 ft. in
depth and 6 ft. wide.
90 of fatal accidents occurred in trenches less
than 20 deep
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First Arrival

• Apparatus spotting
• Spot at least 100 ft from location
• Create Exclusion Zones (on next slide)
• Size-up accurate address of location, length,
  width and depth of trench, number of victims,
  length of time from collapse, call for help
• Secure RP, job foreman, or witness to accident
• Safety 360 Review approach trench from the end,
  Secondary size-up
• Conduct Risk-to-benefit analysis
• 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?

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Trench Scene ManagementExclusion Zones

• Hot Zone 0 100 ft.
• Warm Zone 100 150 ft
• Cold Zone 150 300 ft.

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Ground pads

• For distribution of weight on trench edge

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Ladder Bridge
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Review of Monitoring Values
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Equipment Familiarization

• Strongbacks/Uprights Shoring Panels
• Timber
• Waler
• Palm nailer
• Airshore
• Speedshore

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Shoring Concept

• Works by creating double funnel effect
• Strong enough to prevent soil from starting to
  move set in four feet intervals vertically and
  horizontally as a general rule.

Strut pressurizes trench wall
in all directions
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Types of Collapses

• Spoil pile slide
• Excavated earth too close to the lip
• Heavy rain increasing wt of pile

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Slough In / Lip slide

• Slough failure
• The loss of part of the trench wall

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Sheer Wall

• Shear wall collapse
• section of soil that loses its ability to stand

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Rotational Failure

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

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Toe Failure

• Toe failure
• Slough that occurs at the bottom
• Found in location of fill dirt

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Bell Pier Condition

• Bell pier condition
• Long term toe failure on both sides

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Wedge Failure

• Wedge failure
• Occurs with intersecting trenches, T or L Trench
• Angled section of earth falling from the corner
  of an intersecting trench

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Assignments and Responsibilities

• Extrication/ Entry Team
• Developing plan for patient extrication
• Also personnel used for digging
• Assists Shoring Team to set shores
• Shoring Team
• Assembling, placing and removing shoring walers
• Panel Team
• Place ground pads
• Prepare and placement of panels

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TECHNIQUES FOR TRENCH PROTECTION

• 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

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TECHNIQUES FOR TRENCH PROTECTION
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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

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Inside Waler

• Inside walers are used to span a set of panels
  for the purpose of creating an open space

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• 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.

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• The L trench can be describe as two trenches
  that intersect at there ends

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• Deep trenches are those trenches over 10 feet
  but not more than 20 feet

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Pier-hole
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Trench Environments
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Tacoma incident w/ fatality

• Trench accidents have a 112 higher fatality rate
  that other construction accidents

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Take Home Points

• Create a Hot, warm and cold zone
• Hot zone 0 100 ft
• Warm zone 100 150 ft
• Cold zone 150 300 ft
• Call for help, location, Staging
• Control Traffic movement
• Shut down all heavy equipment operating within
  300 ft of the collapse
• Ladders for egress every 25 feet.
• Ground pads
• Air monitoring
• Spoil pile moved 2 feet from lip of trench