Excavation Hazards in Construction

This module will cover:

• The Federal OSHA excavation standard
• CFR 1926 Subpart P, Excavations

Upon completion of this module, you should be familiar with the hazards of trenching and related OSHA safety standards, including those regarding:

• Classification of soils
• Air monitoring
• Trench and excavation access
• Spoils piles
• Shoring and sloping

Learn how to identify and mitigate excavation hazards.

- Introduction

- What is a excavation Hazard?

ALL excavation related deaths are 100% PREVENTABLE!

What are the Major Types of excavation Hazards in Construction?

A. Unprotected edges

B. Fall hazards

C. Improper sloping or benching

D. Spoils mismanagement

E. Not properly classifying soils

F. Improper shoring systems

- How can I protect myself from excavation Hazards?

A. Minimum Training Requirements

B. Safety Requirements for excavations

C. Shoring systems

D. Benching and Sloping

E. Evaluating soils

- OSHA’s Excavation Safety Standards.

In place since 1989

37% of all trenching incidents occur at depths less than 5 feet!

Most fatalities occur in trenches 5-15 feet deep

Employers & Employees are responsible to ensure excavations are safe before entering

Safety Standards are designed to save your life!

- Trench or Excavation?

Trench: a cut in the earth that is deeper and longer than it is wide, but not wider than 15 feet

Excavation: any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal

Trenches and Excavations:

• Similar characteristics
• Equally dangerous
• Require worker protection

- What is an Excavation Hazard?

- Myths of Excavation.

• “If the trench is not deeper than 5 feet, I don’t have to shore or protect the excavation.”
• “Air monitoring is only for confined spaces, not excavations.”
•  “I can dig myself out if I am buried.”
• “Hitting utilities is simply part of the business!”
•  “If the soil looks pretty good, it must be type A.

- Myth 1: Under Five feet, Shoring Is Not Required.

The OSHA regulation actually says:

 Each employee shall be protected . . . Except when excavations are less than 5 feet and examination of the ground by a competent person provides no indication of a potential cave-in. Therefore, based on the competent person’s examination, shoring may still be required.

- Myth 2: Air Monitoring Is Not Required in Trenches.

OSHA requires air monitoring in confined spaces.

Includes trenches deeper than 4 feet, which present hazards such as:

•  Methane gas (landfills)
•  Flammable vapors (old gas stations)
• Carbon monoxide (your own equipment)
• Various chemicals (welding tasks, etc.)

- Myth 3: I Can Dig Myself Out.

Reality of a cave-in:

A cubic yard of soil can weigh as much as a small pickup truck.

Soil pressing on the chest can make it impossible to breathe.

Fine particles of dirt can clog your nose, mouth, and lungs.

- Myth 4: Hitting Utilities Is Part of the Business

• Live electrical lines in the ground can kill workers and cause significant property damage.
•  A gas line hit can lead to an explosion.
• A broken water line can fill a trench in seconds.
•  Contact with buried power cables can kill.

- Myth 5: If the Soil Looks Good, It Must Be Type A.

To be classified as Type A, the soil can NOT be:

•  Previously disturbed
•  Cracked or fissured
• Subject to vibration
•  Seeping water
• Part of a mixed layered system

 To be classified as Type A, the soil MUST be:

Fully tested by a competent person, every time.

- Types of Excavation Hazards.

- The Competent Person.

Capable of identifying existing and predictable hazards.

Authorized to take prompt corrective measures.

Specifically trained in:

• Soils analysis
• Protective systems & equipment
• OSHA standard requirements

- What causes Cave-ins?

 Characteristics of soil:

•  Lateral pressure up to 800 pounds per square foot
• Cubic yard can weigh 3000 pounds
• Cave-ins happened quickly with little warning
• Self-rescue nearly impossible due to the weight 

- Soil Failures.

Stress cracking near the edge of the excavation.

Caused by Soil Pressures or Equipment Vibrations

Indicative of Impending Failure

Competent Person required to:

•  Remove workers
•  Specify appropriate protective systems
•  Inspect daily for effectiveness

- Spoil Piles.

Spoils too close to the edge of the trench can:

• Slide in, on top of employees.
•  Put lateral pressure on side walls, causing failure.
• Piles must be kept at least 2 feet from the edge.

– Essential for preventing a cave-in

 Water saturation increases the risk of cave-ins.

- Soil and Soil Classification.

- Four Classes of Soils.

OSHA assigns the following 4 classifications of soil:

• Solid rock
• Type A
• Type B
• Type C

Solid Rock.

•  Natural solid mineral material.
•  Can be excavated with vertical sides.
•  Will remain intact while exposed.
• Identification often requires the help of a geologist.
•  If unsure, take the time to ask for a second opinion, lives may depend on it!

- Type A Soils

Type A Soils include:

• Various clays: silty clay, sandy clay, clay loam and others
• Cemented soils: caliche and hardpan

 No soil is Type A if:

•  The soil is fissured
•  The soil is subject to vibration
•  The soil has been previously disturbed
• Other factors exist that would classify it as a less stable material.

- Type B Soils.

Type B Soils include most granular soils that include:

• Angular gravel, silt, silt loam, sandy loam and, in some cases, silty clay loam and sandy clay loam.
•  Previously disturbed soils, except those which would otherwise be classified as type C.
•  Soil that would meet the requirements for type A but is in some way unstable.

- Type C Soils.

 Type C

• Typically, granular
• Gravel, sand, and loamy sand
•  Submerged soil
• Soil from which water is freely seeping
• Submerged rock that is not stable
•  High potential for instability and cave-ins.

- Classifying Soils.

Required Soil Tests

One visual and one manual test, by a competent person, on fresh soil unaffected by weather

Common tests

• Ribbon
• Thread
• Thumb
• Dry strength
• Sedimentation

- Critical to be “Correct”

No matter what type of process the competent person uses:

• Soil must be classified before a protective system decision can be made.
• Results must be correct; lives will depend upon it.
• Protection from Excavation Hazards.

Protective Systems Protecting Yourself from Harm:

Employees in a trench or excavation must be protected by a protective system.

Only two exceptions:

 Entirely stable rock

 Less than 5 feet without sign of potential cave-in.

- Types of Protective Systems.

• Sloping
•  Benching
• Wood shoring
•  Aluminum hydraulic shoring
• Waler systems
• Trench boxes
• Screw jacks
•  Engineered systems 

- Sloping and Benching.

The requirements of sloping and benching are detailed in link. Click on the link and review:

• Important information
• Charts and diagrams

Shoring and sloping are a preferred method for creating a safe excavation.

- Protective Systems.

- Sloping – Type A.

Type A soils:

• Strongest and most cohesive.
• The most sloping and benching options.
• Simple slope of ¾ to 1: every 1 foot down, soil must be excavated ¾ of a foot out from the toe. 

-Sloping & Benching – Type B Soils.

 Type B soils:

• Most common soil encountered.
• Four options for protecting workers.
• In a simple slope, 45-degree angle of repose.
• Rise and run of each bench will be equal.

- Sloping – Type C.

Type C soils:

• Poorest quality
• Sloping is still possible
• Angle of repose is very low (34 degrees)

- Aluminum Hydraulic Shoring.

• Lightweight aluminum frames.
• Patents first issued in Late 60’s and early 70’s.
• Sliding cylinders, hydraulic fluids.
• May be installed and removed by one person.
• Entering the trench not required.
  

- Aluminum Hydraulic Shoring.

Aluminum hydraulic shores: vertical, bearing fully on the side vertical walls of the trench.

Cylinders: maximum spacing of 4 feet vertically, bottom cylinder no more than 4 feet up.

Side rails: must extend to within 2 feet of the bottom to prevent kickout.

Shores pumped to a minimum of 750 pounds of pressure (1000 pounds is best practice).

1000 pounds of pressure translates to 3000 psi against side rails and into the soil.

- Waler Systems.

Type C soil:

 Walers must be used.

–Typically requires timber backing;

 Street plates or sheet pile can also be used.

- Many systems for protecting workers.

• Trench boxes
• Trench shields
• Slide rail systems
• Sheet pile
•  Screw jack systems

- Trench Boxes.

Trench shields or boxes:

• Protect against collapsing soil
• Do not prevent cave-ins
•  Available in a variety of dimensions
•  Usually aluminum or steel
• May be custom-built from tabulated data
•  Installed such that hazardous movement of the shield is restricted in sudden lateral pressures.

- Screw Jacks.

Screw jack systems:

• Struts adjusted manually
• Worker must be in the trench for adjustment
• No uniform preloading
• Weight creates handling difficulties

- Engineered Design.

Requires a Registered Professional Engineer

Allows deviations from OSHA standard

Allows greater flexibility in use

Required whenever using shores in a manner that differs from OSHA requirements

- Engineered Systems.

Registered professional engineer: person who is registered as a professional engineer in the state in which the work is to be performed; However, any state is acceptable within the meaning of this standard when approving designs for manufactured protective systems or tabulated data to be used in interstate commerce.

- New Employer Requirements.

 Employers Must Provide Protection

 Protection for employees entering trenches or excavations is required at all times.

 Employers Responsibility to provide you training, safe work procedures and the     right tools to get

 the job done safely

 It is YOUR responsibility to follow procedures and NEVER put your life at risk on   the job!

- Safe Planning of Work.

Proper planning and preparation required for anything that could create a hazard within the Zone of Influence, such as:

• Trees, spoil piles
• Curbs, gutters, sidewalks
•  Buildings, foundations, utility poles
•  Excavating equipment, dump trucks
• People

- Provide Location of Underground Installations.

 Underground utilities must be located and marked.

 Contact utility companies and owners in advance.

 After the allotted time, proceed with caution.

 Hand digging, potholing, equipment for detection

 Once cut is open, all underground installations must be protected, supported, or   removed.

 Each company (subcontractors) must receive a permit from the one-call     organization.

- Provide Safe Access and Egress.

Cuts over 4 feet deep: safe access and egress required within 25 feet of lateral travel.

When using ladders:

•  Must extend at least 3 feet over solid ground
•  Secure at 4 to 1 angle to prevent movement 

- Protection from Vehicular Traffic.

 In the presence of vehicular traffic:

• Highly visible clothing with reflective material
• Adequate signage, markings, and traffic control
• Lights at night
• Plan approved by local government

- Exposure to Falling Loads.

To avoid being struck:

• No work under overhead loads being transported by lifting or digging equipment
• Employees must stand away from vehicles being loaded or unloaded
• Stand clear of loads being lowered into the trench

- Warning Systems for Mobile Equipment.

 Equipment presents many hazards

 Falling into the trench

 Unexpected equipment failures or movements

 Warning system required when there is not a clear view of the ditch: barricades,     spotters with established hand signals, stop logs.

- Evaluating for Hazardous Atmospheres.

 If you suspect a hazard, test the area with a direct reading calibrated instrument or gas monitor.

The atmosphere must be declared safe before workers are allowed into the excavation.

See Confined Spaces Entry module for a more detailed discussion of identifying, controlling, and testing confined spaces.

- Protection from Water Accumulation Hazards.

 Do not work in excavations where there are signs of accumulating water.

May weaken the side walls

Protection requirements may include:

Special support or shield systems

Water removal (monitored by competent person) 

- Stability of Adjacent Structures.

Buildings, parallel utilities, utility poles, or sidewalks commonly exist near the excavation.

Threat of failure when exposed or undercut

Should be underpinned or cribbed

Enlist a registered professional engineer

- Competent Person Inspections.

Prior to work and as needed (e.g., after a change in conditions), competent person must inspect the site

Existing or predictable hazards

Indications of impending failure of protective systems (shoring, shielding, sloping)

Other potentially hazardous atmospheres

- Perimeter Access/Walkways.

Bridges or walkways must always be used when 

• Crossing an open cut
• Accessing a structure from the edge of the trench
• Walkways 6 feet up and more require handrails.
• Always use the walkway provided.
• Never jump across the trench as a shortcut.