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Trench and Excavation Search and

Rescue

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Objectives (1 of 3)

• Identify the need for trench emergency search and rescue operations.

• Describe various types of trench emergencies.

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Objectives (2 of 3)

• List general hazards associated with a trench emergency incident.

• Describe the resources needed to conduct a trench collapse search and rescue operation.

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Objectives (3 of 3)

• Describe response planning and incident management requirements related to a trench emergency search and rescue incident.

• Describe site control operations at a trench collapse incident.

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Terms

• Excavation:– Any human-made cut, cavity, trench,

depression made in earth that is wider than it is deep

• Trench: – Excavation that is narrow in relation to its

width– Depth greater than width; width not greater

than 15 feet (4.6 m)

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Trench Anatomy

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Major Occupational Hazards

• Cave-ins

• Underground utility exposure

• Atmospheric hazards

• Material or equipment falling into trench

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Types of Trench Emergencies

• Cave-ins

• Spoil-pile slide

• Falling rocks

• Shoring collapse

• Other causes

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Cave-in (1 of 2)

• Separation of a mass of soil or rock material from side of excavation or trench

• Loss of soil from under trench shield or support system

• May entrap, bury, or otherwise injure and immobilize person

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Cave-in (2 of 2)

• More fatal than other types of construction related accidents

• Often related to lack of or inadequate support systems

• Primary hazard of trench work

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Trench Collapse Patterns

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Spoil Pile

• Contains excavated soil and materials

• Placed in mound beside open trench:– Must be placed minimum of 2 feet (0.6 m)

away from open edge per OSHA

• May slide into trench and cause collapse

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Falling Rocks

• May break loose from trench wall and strike workers

• May or may not cause collapse

• May render victim unconscious; trench must be stabilized before victim may be accessed

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Shoring

• Designed to support sides of excavation

• May collapse if left in place for long time (destabilize)

• Requires daily inspection by “competent person” on construction sites per OSHA 1926.32

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Other Causes of Trench Emergencies

• Overturned construction equipment falling into trench

• Broken utility lines (electric, water, sewage, or natural gas)

• Unanticipated atmospheric hazards (build-up of methane gas)

• Medical emergencies unrelated to trench

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Protection Against Trench Emergencies

• OSHA requires trenches be protected from collapse by:– Shoring system– Shielding (trench box)– Sloping trench walls– Benching system

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Shielding System

Courtesy of Robert Rhea

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Sloping System

• Uses inclined excavating to form sides that incline away from excavation to prevent cave-in

• Bases angle of incline on various factors:– Soil type– Environmental conditions of exposure– Application of surcharge loads

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Benching System

• Involves excavating side of trench to form one or more horizontal levels or steps, usually with vertical or near-vertical surfaces between levels

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Trench Soil Properties (1 of 3)

• Trench walls are columns of soil weighing 100 pounds (45.4 kg) per cubic foot for each foot of depth – 10 foot (3 m) trench = 1-foot-square (0.1 m2),

10-feet-tall (3 m) column – Weighs 1000 pounds (453.6 kg) – Exerts vertical force of 1000 pounds (453.6

kg) per square foot

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Trench Soil Properties (2 of 3)

• Soil column also exerts horizontal force in all outward directions equal to ½ vertical force.– Column in 10-foot (3 m) trench exerts outward

force at base of 500 pounds (226.8 kg) per square foot (0.09 m2)

• Outward force increases with trench depth.

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Trench Soil Properties (3 of 3)

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Three Phases of Trench Collapse (1 of 2)

1: Trench wall moves into trench at its lowest level near bottom, creating overhang of soil at top of

2: Most of overhanging soil falls into trench, causing smaller, unsupported cantilever of soil near trench lip.

3: Trench lip fails.

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Three Phases of Trench Collapse (2 of 2)

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Responder Tips

• Time may elapse between collapse phases, placing responders and victims at risk of exposure to a secondary collapse.

• Partially buried victim may become totally buried before shoring is in place.

• Responders should never enter a unprotected trench, regardless of circumstances.

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Trench Collapse Contributing Factors (1 of 4)

• Narrow roadways:– Traffic causes superimposed loads on trench

walls.

• Vibration:– Road traffic, heavy construction equipment,

rail traffic, and other vibration sources increase collapse risk.

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Trench Collapse Contributing Factors (2 of 4)

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Trench Collapse Contributing Factors (3 of 4)

• Weather:– Heavy rain can flood trench.– Subsurface water seepage can undercut

trench walls.– Saturated soil can cause wall instability.– Drought can dry out trench and make it

unstable.– Freezing, thawing cycles can undermine

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Trench Collapse Contributing Factors (4 of 4)

• Soil:– Previously disturbed soil is unstable.– Intersection of two or more trenches creates

unstable soil situations, particularly at the corners.

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OSHA Soil Classifications (1 of 2)

• Stable rock: natural mineral matter with vertical sides that remain stable when exposed to lack of support

• Type A: cohesive soils and cemented soils: – Clay, silty clay, sandy clay, hardpan

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OSHA Soil Classifications (2 of 2)

• Type B: cohesive soil with less compressive strength than Type A:– Angular gravel, silt, silt loam

• Type C: sandy soils, sandy loam, gravel soils, submerged soils, or soils where water is freely flowing from trench walls

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“Competent Person” Categorizes Soil on Scene

• Visual tests:– Looking at trench walls– Observing spoil material as removed

• Manual tests:– Thumb penetration– Plasticity tests to determine soil’s unconfined

compressive strength

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Soil Layering (1 of 2)

• Dangerous collapse hazard when soil types inclined downward toward trench floor

• Areas where layers make contact lubricate nonhomogenous soil types, causing a slide.

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Soil Layering (2 of 2)

Courtesy of Cecil “Buddy” Martinette.

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Applicable Standards (1 of 2)

• NFPA 1006, Standard for Technical Rescuer Professional Qualifications for technician-level

• NFPA 1670, Standard on Operations and Training for Technical Search and Rescue Incidents:– All responders must meet awareness-level

requirements for confined-space search, rescue, and general requirements in Chapter 4 of NFPA 1670.

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Applicable Standards (2 of 2)

• OSHA Standard 1926.650, 651, and 652: – Identifies safety requirements for workers who

perform excavation and trench work– Provides resource for responders because it

identifies hazards, training requirements, hazard control requirements, trench stabilization options, other safety requirements

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Search and Rescue

• Identify injured victims who escaped.

• Extricate partially buried victims seen from safe area outside trench.

• Locate totally buried victims.

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Equipment Resources (1 of 2)

• Soil removal hand tools: – Entrenching shovels, small buckets, trowels,

posthole diggers

• Chipping and cutting tools:– Pneumatic chisels, electric rotary hammers,

demolition hammers, hand/power saws, knives

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Equipment Resources (2 of 2)

• Lifting tools: – Air bags, slings, timbers, rigging, bolting

devices

• Specialized tools: – Mechanical vacuum devices, heavy digging

equipment

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Lifting Resources

Courtesy of Cecil “Buddy” Martinette.

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Specialized Resources

Courtesy of Robert Rhea

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Personnel Resources

• EMS at both BLS and ALS level

• Hazardous materials teams

• Utility company workers

• Law enforcement

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Incident Management Objectives

• Evaluate the scene and identify potential victims and location.

• Initiate operations to minimize hazards to operating personnel and trapped victims.

• Effectively search for total burial victims.• Effectively rescue and remove trapped

victims.• Minimize further injury to victims during

search, rescue, and removal operations.

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ICS Management Personnel

• Incident commander

• Rescue group supervisor

• Planning section chief

• Logistics section chief

• Safety officer

• Public information officer

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IAP Includes

• Multiple rescue options

• Two or more functional work areas

• Plan for coordination with EMS

• Awareness that tactical-level officers trained in manage trench and excavation emergencies may be necessary

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Rescue Officer Responsibilities

• Anticipating tool usage and allowing sufficient space to perform tool operations and patient packaging

• Reassessing shoring system competency throughout rescue

• Ensuring existing shoring system not disrupted during rescue activities

• Recommending additional staffing, specialized equipment to IC

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Needs Assessment

• Determines jurisdiction’s vulnerability to trench and excavation emergency events

• Includes written procedures to request mutual aid or private sector resources

• Includes organizations’ personnel capabilities, such as level of training

• Dispatch procedures

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Initial Hazard Assessment (1 of 3)

• Position response vehicles 100 feet (30.5 m) from collapse area.

• Cordon off the rescue site with barrier tape. • Remove unnecessary individuals. • Locate the work-site foreman. • Try to determine type of collapse, number of

victims, and if victims are partially or totally buried.

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Initial Hazard Assessment (2 of 3)

• Mark all known and approximate victim locations.

• Determine time period of when the collapse occurred.

• Determine the presence of underground utilities.• Assess medical requirements of trapped or

injured victims.• Avoid approaching the trench or spoil pile.

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Initial Hazard Assessment (3 of 3)

Courtesy of Captain David Jackson, Saginaw Township Fire Department

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Awareness-Level Responders(1 of 3)

• Initiate the ICS.• Set up control zones with barrier tape. • Deny entry into hazard zone.• Identify locations of trapped victims.• Mark potential locations of total-burial

victims.• Gather incident information from

bystanders or coworkers.

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Awareness-Level Responders(2 of 3)

• Lower helmet to a visible, mobile victim. • Lower oxygen mask attached to oxygen

tubing to victim and instruct how to use.• Request response from appropriate utility

companies, if necessary.• Lower ladder to victims who are mobile

and not trapped, if safe.

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Awareness-Level Responders(3 of 3)

• Assist operations- or technician-level responders by serving as tool/equipment runners or helping to remove spoil pile.

• Assist with tarp or tent placement.

• Establish water diversion systems.

• Assist operations- or technician-level rescuers with de-watering activities.

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Potential Secondary Collapse Signs (1 of 2)

• Fissures parallel to or in face of excavation• Subsidence of edge of trench• Overhanging loose cantilevers of trench wall• Bulging of trench walls• Proximity of spoil pile to trench• Heaving or boiling of trench floor• Spalling of face of trench• Water in the trench

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Potential Secondary Collapse Signs (2 of 2)

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Trench Collapse Hazards (1 of 2)

• Water:– Flooding, seeping groundwater,

freezing/thawing

• Soil:– Mixing soil types

• Superimposed loads:– Causing secondary collapse

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Trench Collapse Hazards (2 of 2)

• Broken or damaged underground utilities:– Causing electrocution, fire, flooding,

drowning, secondary collapse

• Unanticipated atmospheric hazards:– Leaking hazardous materials from

underground storage tanks or pipelines or spreading methane gas and other toxic gases

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Minimize Risks at Trench Collapse (1 of 2)

• Recognize and avoid trenching hazards.

• Limit exposure to hazardous areas by denying entry into those sites.

• Control vibration sources by shutting down heavy vibration sources located within 500-feet radius (152.4 m) of trench

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Minimize Risks at Trench

Collapse (2 of 2)

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Patient Care Considerations (1 of 2)

• Provide care for walking wounded. • Request adequate EMS resources. • Assess and mitigate immediately life-

threatening hazards. • Mark victim’s location and lower a rope

adjacent to victim.• Provide initial medical and protective

support for accessible victims without entering trench.

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Patient Care Considerations (2 of 2)

• Provide initial medical and protective support for accessible victims without entering unprotected trench area.– Provide O2 to conscious, partially buried

victim.– Lower helmet or hard hat to mobile victim.

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Clues for Locating Buried Victim

• Interview information• End of pipe string• Grease can, brush used to lubricate

concrete pipe • Beverage bottles, drinking cups• Laser targets and grade poles• Cat or tire tracks• Large-diameter pipe

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Summary

• Trench rescue events vary in size and complexity.

• Only responders trained in trench rescue should enter excavation area.

• ICS is critical to trench collapse management.• Initial hazard control may include removing

unnecessary personnel, establishing control zones, installing barrier tape, and controlling vibration sources.