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Course 802 - Trench and Excavation Safety

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Scope and Application of OSHA Standard

OSHA revised the excavations standard in 1989, with focus on the existing standard to simplify many of the existing provisions, add and clarify definitions, eliminate duplicate provisions and ambiguous language, and give employers added flexibility in providing protection for employees.

In addition, the standard provides several new appendices. Appendix A to 1926.652 provides a consistent method of soil classification. Appendix B to 1926.652 provides sloping and benching requirements. Other appendixes (appendices C-F) provide pictorial examples of shoring and shielding devices, timber tables, hydraulic shoring tables, and selection charts that provide a graphic summary of the requirements contained in the standard.

For more information on the details of proper installation, please refer to the OSHA standard on excavation (29 CFR 1926 Subpart P, which includes 650-652 and appendices A-F).

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

Applying OSHA Standard

The OSHA standard applies to all open excavations made in the earth's surface, which includes trenches. According to the OSHA construction safety and health standards, a trench is referred to as a narrow excavation made below the surface of the ground in which the depth is greater than the width (the width not exceeding 15 feet or 4.5 meters).

An excavation is any man-made cut, cavity, trench or depression in the earth's surface formed by earth removal. This can include excavations for anything, from cellars to highways.

The standard does not apply to house foundation/basement excavations (including those that become trenches by definition when formwork, foundations or walls are constructed) when all of the following conditions are present:

  • The house foundation/basement excavation is less than 7 1/2 feet (2.5 meters) deep or is benched for at least 2 feet (0.61 meters) horizontally for every 5 feet (1.52 meters) or less of vertical height.
  • The minimum horizontal width (excavation face to formwork/wall) at the bottom of the excavation is as wide as practicable but not less than 2 feet (0.61 meters).
  • There is no water, surface tension cracks or other environmental conditions present that reduce the stability of the excavation.
  • There is no heavy equipment operating in the vicinity that causes vibration to the excavation while employees are in the excavation.
  • • All soil, equipment and material surcharge loads are no closer in distance to the top edge of the excavation than the excavation is deep; however, when front end loaders are used to dig the excavations, the soil surcharge load must be placed as far back from the edge of the excavation as possible, but never closer than 2 feet (0.61 meters).
  • Work crews in the excavation are the minimum number needed to perform the work.
  • The work has been planned and is carried out in a manner to minimize the time employees are in the excavation.

The standard provides several options for designing trench protection measures. Under certain conditions, the design of the trench protection measures must be prepared by a registered professional engineer.

Competent Person and the Standard

Proper selection and installation of trench protection measures are very important. To comply with the standard, the employer must have a competent person:

“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.”

This competent person has critical inspection responsibilities regarding excavations. This person must inspect every excavation and protective system under his or her care daily, including areas adjacent to any excavation. Additional inspections must be conducted before starting work and as needed through a shift, for example, when any hazard-increasing occurrence (such as a rainstorm) takes place. When the competent person finds any evidence of a situation that could result in a cave-in, protective system failure or any other hazardous condition, employees are to be immediately removed from the danger area until the problem is fixed.

image of chemicals in the workplace

Competent Person and the Standard (continued...)

The items below discuss more trenching and excavation activities where a competent person is necessary:

  • Protective Systems or Equipment
    • Monitoring water removal equipment and operations
    • Inspecting excavations subject to runoff from heavy rains
    • Determining cave-in potential to assess the need for shoring or other protective systems
    • Classifying soil and rock deposits
    • Determining the appropriate slope of an excavation to prevent collapse
  • Inspecting Trench and Protective Systems
    • Authorizing immediate removal of employees from an area where there is evidence of a possible cave-in, a failure of protective systems, and where hazardous atmospheres exist.
  • Unsafe Access/Egress
    • Designing structural ramps used only by employees as a means of access or egress. Structural ramps used for access or egress of equipment must be designed by a competent person qualified in structural design.

Written Policies

Many companies have established a written policy that outlines specific safe trenching practices in detail. Such a policy should ensure adequate support for the trench and frequent inspections of the excavation site 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.

Scenario

Image of a trench being dug by a backhoe.

On January 28, 2003, two Hispanic construction laborers [15 and 16-year-old brothers] 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 by one of the workers that the trench had collapsed and that the two employees had been covered up.

The emergency medical squad (EMS) was summoned and responded within minutes.

Coworkers had uncovered the victims and removed them from the trench as the rescue squad arrived. The victims could not be revived and the county coroner was summoned to the scene where he pronounced the victims dead.

Location of Victims
Location of victims.
Click to enlarge.

NIOSH investigators concluded that, to help prevent similar occurrences, employers should:

  • Ensure that a competent person conducts daily inspection of excavations, adjacent areas, and protective systems and takes appropriate measures necessary to protect workers.
  • Ensure that workers are protected from cave-ins by an adequate protective system.
  • Develop, implement, and enforce a comprehensive written safety program for all workers which includes training in hazard recognition and the avoidance of unsafe conditions.
  • Ensure that workers who are part of a multilingual workforce comprehend instructions in safe work procedures for the tasks to which they are assigned.
  • Ensure that only qualified rescue personnel who have assumed responsibility for rescue operations and site safety should attempt rescue operations.

Congratulations! You've read through the course material for Module 1. Now you just need to watch the video and take the quiz :-)

VIDEO

Instructions

Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

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

2. When does the OSHA standard NOT apply to house foundation/basement excavations?

3. All of the following are requirements for a “competent person”, EXCEPT ________.

4. According to the OSHA Construction Safety and Health Standards, which choice is a characteristic of a trench?

5. When a competent person finds any evidence of a situation that could result in a cave-in the competent person should __________.


Have a safe day!

Important! You will receive an "error" message unless all questions are answered.