The Basics

Introduction

An excavation is any man-made cut, cavity, trench or depression in the earth's surface formed by earth removal.

Excavation and trenching are among the most hazardous construction operations. The Occupational Safety and Health Administration’s (OSHA) Excavation standards, 29 Code of Federal Regulations (CFR) Part 1926, Subpart P, contain requirements for excavation and trenching operations. The OSHA standard applies to all open excavations made in the earth's surface, which includes trenches.

Excavations and Trenches

Excavations. OSHA defines an excavation as any man-made cut, cavity, trench, or depression in the Earth’s surface formed by earth removal.

Trenches. A trench is defined as a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth of a trench is greater than its width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m).

The Dangers of Trenching and Excavation Operations

Trenching and excavation work presents serious hazards to all workers involved.

• Cave-ins pose the greatest risk and are more likely than some other excavation-related incidents to result in worker fatalities. One cubic yard of soil can weigh as much as a car. An unprotected trench can be an early grave. Employers must ensure that workers enter trenches only after adequate protections are in place to address cave-in hazards.
• Other potential hazards associated with trenching work include falling loads, hazardous atmospheres, and hazards from mobile equipment.

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OSHA Sticker.

The Standards

29 CFR 1926.650, 29 CFR 1926.651, and 29 CFR 1926.652 are applicable OSHA standards.

The standard also provides several appendices:

• Appendix A, Soil Classification;
• Appendix B, Sloping and Benching;
• Appendix C, Timber Shoring for Trenches;
• Appendix D, Aluminum Hydraulic Shoring for Trenches;
• Appendix E, Alternatives to Timber Shoring; and
• Appendix F, Selection of Protective Systems;

The Basic Strategies

OSHA has made reducing trenching and excavation hazards the Agency's Priority Goal. Trench collapses, or cave-ins, pose the greatest risk to workers' lives. To prevent cave-ins:

1. SLOPE or bench trench walls by cutting back the trench wall at an angle inclined away from the excavation;
2. SHORE trench walls by installing aluminum hydraulic or other types of supports to prevent soil movement; or
3. SHIELD trench walls by using trench boxes or other types of supports to prevent soil cave-ins.

Employers should also ensure there is a safe way to enter and exit the trench. Keep materials away from the edge of the trench. Look for standing water or atmospheric hazards. Never enter a trench unless it has been properly inspected.

Competent Person (CP) Responsibilities

Proper selection and installation of trench protection measures require the involvement of a competent person (CP). OSHA defines competent person as:

"one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them."

The CP has important excavation inspection responsibilities:

• Determine cave-in potential to assess the need for shoring or other protective systems;
• Classify soil and rock deposits;
• Determine the appropriate slope of an excavation to prevent collapse;
• Assess entry and exit methods such as ladders and structural ramps;
• Inspect the excavation and protective system at least daily before the start of work and as needed throughout a workshift.
• Inspect when any hazard-increasing occurrence (such as a rainstorm) takes place.
• Remove employees from the danger area if evidence of a possible cave-in, protective system failure or any other hazardous condition, exists.
• Monitor water removal equipment and operations and inspect excavations subject to runoff from heavy rains

Preplanning

Even the simplest jobs require preplanning.

No matter how many trenching, shoring, and backfilling jobs an employer has done in the past, it is important to approach each new job with care and preparation. Many on-the-job incidents result from inadequate initial planning. Waiting until after the work starts to correct mistakes in sloping, shoring, or shielding slows down the operation, adds to the cost of the project, and makes a cave-in or other excavation failure more likely.

Before preparing a bid, employers should know as much as possible about the jobsite and the materials they will need to have on hand to perform the work safely and in compliance with OSHA standards. For instance, if you were bidding on a job to replace an underground utility line, you might assume that the soil covering the line would not be Type A (more on soil types in Module 3) because it is previously disturbed soil. However, you would always want to analyze the soil just to make sure.

Employers can gather the information they need through jobsite studies, observations, test borings for soil type or conditions, and consultations with local officials and utility companies. This information will help employers determine the amount, kind, and cost of safety equipment they will need to perform the work safely.

Employers should do what's necessary to avoid hitting underground utility lines and pipes during excavation work. One common industry practice is to call 811, the "Call Before You Dig" number, to establish the location of any underground utility installations in the work area.

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Safety Factors to Consider When Bidding

Consider safety factors when bidding.

Before preparing a bid, employers should know as much as possible about the jobsite and the materials they will need to have on hand to perform the work safely and in compliance with OSHA standards. A checklist may prove helpful to identify safety requirements for new projects.

A safety checklist may prove helpful when employers are considering new projects. You can view an example of an excavation checklist at OSHA's Guide for Daily Inspection of Trenches and Excavations.

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Employers can gather the information they need through jobsite studies, observations, test borings for soil type or conditions, and consultations with local officials and utility companies. This information will help employers determine the amount, kind, and cost of safety equipment they will need to perform the work safely.

Written Policies

Shield it, Shore it, or Slope it.

Many companies have established a written policy that outlines specific safe trenching practices in detail. An effective policy should ensure adequate support for the trench is installed and that frequent inspections of the excavation site are conducted to detect any change in the soil conditions.

Field and office personnel should become familiar with the company policies and guidelines outlined in the company safety program. The program may be put into writing to communicate the company’s position regarding jobsite safety. An example of a company safety and health program in action is a written policy that ensures all employees in all excavations will be protected from cave-ins. When this type of policy is enforced, all employees understand their responsibilities and that helps to avoid unsafe practices.

Sound policies can be grouped into three major categories. Write policies to:

• Prepare a safe trench. Provide safe entry and exit before starting work. Keep materials at least 2 feet away from the edge.
• Protect workers from a cave-in by using protective systems. Sloping or benching trench walls, shoring the trench walls with supports, or shielding trench walls with trench boxes.
• Inspect the trench for hazards. Look for standing water and other environmental hazards. Never enter a trench unless it has been inspected and approved by the competent person.

Download a sample Excavation Safety Program from the Texas Dept. of Insurance.

Scenario

Any soil that has been worked is Class C and subject to cave-ins.

Two construction laborers died when the trench they were working in experienced a cave-in. The victims were members of a crew installing conduit in an eight-foot-deep by two-foot-wide trench.

When work started, the jobsite foreman instructed the crew leader to operate a backhoe to dig the trench. The foreman then left the site to check on another job. After approximately an hour, the crew leader grounded the bucket, turned the machine off and walked to the company trailer to check blueprints.

As he was looking at the blueprints, he heard loud voices outside the trailer from the direction of the ditch. As he exited the trailer, he was informed that the trench had collapsed and the two employees were buried.

The crew leader summoned the emergency medical services (EMS) who responded within minutes.

Coworkers uncovered the victims and removed them from the trench as the EMS arrived. However, the victims could not be revived.

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Video

VIDEO

Watch this excellent video on excavation and trenching safety by Marko Kaar.

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