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Risk Management Department

Excavation

Safety

May, 2008

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Excavation Safety

Introduction

In order to prevent injuries and improve work productivity, APS has developed this training to provide you the knowledge to stay safe when working in and around excavations.

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Excavation Safety

Introduction About 400 U.S. workers die in trench-related

accidents each year

About 6,400 are seriously injured

For this reason it is important to understand how to stay safe in and around excavations

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Excavation Safety

Introduction

In this training we will cover:

What is a trench? Soil characteristics Collapse types Shoring techniques Safety requirements

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Excavation Safety

What is a Trench?

A narrow excavationthat is deeper than it is wide

No more than 15 feet wide at bottom

Walls will eventually fail

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Excavation Safety

What is a Trench?

Failure of trench walls results in 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

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Excavation Safety

What is a Trench?

Cave-ins are dangerous to workers:

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

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Excavation Safety

Soil Characteristics

Type A (most stable) — dense and heavy clay

Type B — silt, sandy loam, medium clay

Type C (least stable) — gravel, loamy sand, soft clay

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Excavation Safety

Soil Characteristics

Factors affecting soil strength: Water Vibrations Erosion and Weathering Excavation Depth Slope Steepness Degree of Soil Compaction

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Excavation Safety

Soil Characteristics

Signs of impending collapse:

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

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Excavation Safety

Collapse Types

There are four types of trench collapses:

Spoil Pile Slide

Side Wall Shear

Slough–in

Rotation

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Excavation Safety

Collapse Types

Spoil Pile Slide -Collapse of material that hasbeen removed from the trench back into the trench

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Excavation Safety

Collapse Types

Side Wall Shear -Collapse of side wallfrom the top into trench

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Excavation Safety

Collapse Types

Slough-in - Collapse of side wallfrom middle of wall

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Excavation Safety

Collapse Types

Rotation -Collapse of bottom thirdof trench wall causingsecondary wall collapse

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Excavation Safety

Shoring Techniques

Engineers are often required to design shoring, which is a construction procedure used specifically to maintain the stability of the walls of an excavation and provide protection to workers who may enter the excavation

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Excavation Safety

Shoring Techniques

To mitigate the danger of cave-ins, there are 4 main techniquesto shore trench walls:

Wood Support

Screw Jacks

Hydraulic Shores

Trench Cages

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Excavation Safety

Shoring Techniques

Wood Support

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Excavation Safety

Shoring Techniques

Screw Jacks

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Excavation Safety

Shoring Techniques

Hydraulic Shores

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Excavation Safety

Shoring Techniques

Trench Cages

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Excavation Safety

Safety Requirements

At least one worker in each work crew must be experienced in the type of work being performed in excavations

At least one worker should be trained in first aid

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Excavation Safety

Safety Requirements

Protecting the area around the excavation:

All work areas must be adequately guarded or barricaded by fences, guardrails or a covering sufficient to prevent persons from falling into the excavation

Excavations might endanger stability of buildings, walls, other structures

Sidewalks, pavement not undermined unless supported to prevent collapse on excavation workers

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Excavation Safety

Safety Requirements

Protecting workers in excavations:

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 at least 3 feet from edge

• Use retaining devices

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Excavation Safety

Safety Requirements

Protecting workers in excavations:

Excavation sites cannot be covered with anything such as piles of excavated material or excavation equipment which might accidentally fall into the excavation

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Excavation Safety

Safety Requirements

Protecting workers in excavations:

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

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Excavation Safety

You are finished!

You have finished the Excavation Safety training.

Download the quiz from the Risk Management website’s training page.

Print the form and be sure to write your name, location and employee number in the spaces provided.

Complete the ten questions and have your supervisor send it to the Risk Management office