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Course 802 - Trench and Excavation Safety

Safety guides and audits to make your job as a safety professional easier

Jobsite Safety and Training

Excavation worksite.

Excavation projects, large and small need planning, inspections, and training.

One of the most important responsibilities of field and office management is planning for safety. Most on-the-job problems and accidents directly result from improper planning. Correcting mistakes in sloping, shoring and/or shielding after work has started slows down the operation, adds to the cost and increases the possibility of an excavation failure.

Contractors should develop safety checklists to make certain there is enough information about the jobsite and all needed items, such as safety equipment, are on hand.

To help ensure safety in trenching and excavation operations before the start of trenching or excavation, the contractor will need to take these specific conditions into account:

  • Soil types and layers
  • Traffic
  • Nearness of structures and their condition
  • Surface and ground water conditions
  • The water table evaluation
  • Overhead and underground utilities (check with utility companies)
  • Weather

These and other conditions can be determined by jobsite studies, observations and consultations with local officials and utility companies.

1. The contractor must always contact the utility companies involved and inform them of the work _____.

a. to let them know work has been completed
b. if an emergency occurs during normal work hours
c. before starting the trench or excavation
d. when suggested by the project safety manager

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Access and Egress

Means of Access and Egress
Means of access and egress. Did a competent person design this project?

A stairway, ladder, ramp or other safe means of access and egress must be located in trench excavations that are 4 feet (1.22 m) or more in depth so as to require no more than 25 feet (7.62 m) of lateral travel for employees.

Structural Ramps and Runways

  • Structural ramps that are used solely by employees as a means of access or egress from excavations must be designed by a competent person.
  • Structural ramps used for access or egress of equipment must be designed by a competent person qualified in structural design, and must be constructed in accordance with the design.
  • Ramps and runways constructed of two or more structural members must have the structural members connected together to prevent displacement.

Structural Members for Ramps and Runways

  • Structural members used for ramps and runways must be of uniform thickness.
  • Cleats or other appropriate means used to connect runway structural members must be attached to the bottom of the runway or must be attached in a manner to prevent tripping.
  • Structural ramps used in lieu of steps must be provided with cleats or other surface treatments on the top surface to prevent slipping.

2. Structural ramps that are used solely by employees for access or egress from excavations _____.

a. may be designed by employees working in the excavation
b. are not allowed in Type B or C soil
c. are not required for excavations less than 10 feet in depth
d. must be designed by a competent person

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Surface Crossing of Trenches

Means of Access and Egress
Crosswalks must have guardrails.

Surface crossing of trenches should be discouraged; however, if trenches must be crossed, they are only permitted under the following conditions:

  • Vehicle crossings must be designed and installed under the supervision of a registered professional engineer.
  • Walkways or bridges must be provided for foot traffic. These structures must:
    • Have a minimum clear width of 20 inches
    • Be fitted with standard rails
    • Extend a minimum of 24 inches past the surface edge of the trench

3. Each of the following is a requirement for trench walkways or bridges EXCEPT _____.

a. they must be fitted with standard rails
b. they must be made with reinforced metal plates
c. they must have a minimum width of 20 inches
d. they must extend at least 24 inches past the surface edge

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Employees must be protected from loads or objects falling from lifting or digging equipment.
Employees must be protected from loads or objects falling from lifting or digging equipment.

Exposure to Falling Loads

Employees must be protected from loads or objects falling from lifting or digging equipment.

Here are some procedures to protect your employees:

  • Employees are not permitted to work under raised loads
  • Employees are required to stand away from the equipment that is being loaded or unloaded
  • Equipment operators or truck drives may stay in their equipment during loading and unloading, if the equipment has a cab shield or adequate canopy

Warning Systems for Mobile Equipment

The following steps should be taken to prevent vehicles from accidentally falling into the trench:

  • Barricades must be installed where necessary.
  • Hand or mechanical signals must be used as required.
  • Stop logs must be installed if there is a danger of vehicles falling into the trench.
  • Soil should be graded away from the excavation; this will assist in vehicle control and channeling of run-off water.

Click on the button to take a short exercise. What questions do you think a competent person should be see when approaching the situation in the image?

Employees must be protected from loads or objects falling from lifting or digging equipment.

Questions a competent person should ask:

  • Do you see any hazards and unsafe behaviors?
  • What is the soil classification (hint, the soil has been worked previously)?
  • Are those workers in the trench safe from cave-ins?
  • Is there a dangerous hazard of being struck by falling objects?
  • Is that supervisor being responsible, or does he have a total lack of consideration for the safety of his employees?
  • What violations would you cite if you were an OSHA inspector?

Any other questions?

4. Which of the following practices is NOT allowed while working in a trench?

a. Work in a sloped trench with Type C soil
b. Working under a raised load
c. Entering an unguarded 4 ft deep trench without shoring
d. Working in a trench without a coworker

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Underground Utilities

If there are any hazardous conditions, you must provide the employee controls, such as proper respiratory protection or ventilation.
Always check for and mark underground utilities.

There are important steps the employer should take to minimize the risk of unexpectedly encountering underground utilities such as sewer, telephone, fuel, electric, water lines, or any other underground installations that reasonably may be expected to be encountered during excavation work. Before starting work, the Excavation standards require employers to do the following:

  • Determine the approximate location(s) of utility installations. 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.
  • Contact and notify the utility companies or owners involved at least 2 days prior to the start of work to inform them of the proposed work.
  • Ask utility companies or owners to establish the location of underground installations prior to the start of excavation work. If they cannot respond within 24 hours (unless the period required by state or local law is longer) or cannot establish the exact location of the utility installations, employers may proceed with caution, which includes using detection equipment or other acceptable means to locate utility installations.
  • Determine the exact location of underground installations by safe and acceptable means when excavation operations approach the approximate location of the installations.
  • Ensure that while the excavation is open, underground installations are protected, supported or removed as necessary to safeguard workers.

5. If a utility company cannot establish the exact location of an underground utility, what action may the employer take?

a. Proceed with caution using an acceptable means of detection
b. Close down the project until the utility company arrives
c. Continue the excavation using experience and common sense
d. Get permission from OSHA to continue with the project

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If there are any hazardous conditions, you must provide the employee controls, such as proper respiratory protection or ventilation.
Forced-air ventilation is provided for this excavation. However, I would not go into this trench. Would you?

Hazardous Atmospheres In Excavations

Common hazardous atmospheres might be due to methane, hydrogen sulfide, and carbon monoxide. Precautions include providing workers with proper respiratory protection or forced air ventilation. Do not assume that natural ventilation (natural air movement across and into the excavation) is sufficient to keep an atmosphere safe in the trench.

Employees must not work in hazardous and/or toxic atmospheres including those with:

  • Less than 19.5% or more than 23.5% oxygen;
  • A combustible gas concentration greater than 20% of the lower flammable limit; and
  • Concentrations of hazardous substances that exceed those specified in the Threshold Limit Values for Airborne Contaminants established by the ACGIH (American Conference of Governmental Industrial Hygienists).

All operations involving hazardous atmospheres must be conducted in accordance with OSHA requirements for occupational health and environmental controls (see 29 CFR Part 1926 Subpart D) for personal protective equipment and for lifesaving equipment (see 29 CFR Part 1926 Subpart E). Engineering controls (e.g., ventilation) and respiratory protection may be required.

A competent person must test an excavation before employees enter an excavation greater than 4 feet (1.22 m) in depth for where hazardous atmospheres exist or could reasonably be expected to exist, such as in excavations in landfill areas or excavations in areas where hazardous substances are stored nearby.

When testing for atmospheric contaminants within excavations or confined spaces in excavations, the following should be considered:

  • Testing should be conducted before employees enter the trench and should be done regularly to ensure that the trench remains safe.
  • The frequency of testing should be increased if equipment is operating in the trench.
  • Testing frequency should also be increased if welding, cutting, or burning is done in the trench.

6. What is a primary control measure if a flammable/combustible atmosphere is detected in a trench?

a. Water suppression system
b. Forced air ventilation
c. Natural ventilation
d. Reduced work

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Confined space in an excavation
Confined space in an excavation.

Hazardous Atmospheres In Confined Spaces

29 CFR Part 1926, Subpart AA applies to non-excavation work within a confined space located in an excavation. These standards are intended to complement the excavation standard and address two distinct hazards:

  1. hazardous atmospheres in excavations and
  2. the additional hazards associated with confined spaces located within excavations.

For example, the Confined Spaces in Construction standard covers entry into a large prefabricated storm drain, other pipe, or manhole large enough for human occupation, even if located at the bottom of an open excavation.

If unhealthful atmospheric conditions exist or develop in an excavation or confined space, workers must exit immediately, and not reenter until testing proves safe levels have been achieved. Under no circumstance may workers enter an excavation when flammable/combustible atmospheres are present.

Emergency Rescue

Emergency rescue equipment is required when a hazardous atmosphere exists or can reasonably be expected to exist. Requirements are as follows:

  • Respirators must be of the type suitable for the exposure. Employees must be trained in their use and a respirator program must be instituted.
  • Attended (at all times) lifelines must be provided when employees enter bell-bottom pier holes, deep confined spaces, or other similar hazards.
  • Employees who enter confined spaces must be trained.

7. Which of the following is an example of a non-excavation confined space within an excavation?

a. A 2 ft wide pipe for electrical wiring
b. An area protected with a trench box
c. A large storm drain
d. A 10 ft excavation

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Real-Life Scenario

This worker is buried up to his neck.  The forces pushing on his body can be enormous.
This worker is buried up to his neck. The forces pushing on his body can be enormous.

Two employees were installing storm drain pipes in a trench, approximately 20-30 feet long, 12-13 feet deep and 5-6 feet wide. The side walls consisted of unstable soil undermined by sand and water. There was 3-5 feet of water in the north end of the trench and 5-6 inches of water in the south end. At the time of the accident, a backhoe was being used to clear the trench. The west wall of the trench collapsed, and one employee was crushed and killed.

Inspection Results

As result of the investigation, OSHA issued citations for one willful, one serious, and one-other-than-serious violation of its construction standards.

OSHA's construction safety standards include several requirements which, if they had been followed here, might have prevented this fatality.

Click on the button to see OSHA recommendations for this accident.

Accident Prevention Recommendations

  1. Employers must shore, slope sheet or brace sides of trenches in unstable material (29 CFR 1926.652(b) or 1926.651(c)).
  2. There must be a means of escape from a trench such as ladder (29 CFR 1926.652(h)).
  3. Trench work is to be inspected daily by a "competent person". When there's evidence of cave-ins or slides, all work must stop (29 CFR 1926.650(i)).
  4. Water must not be allowed to accumulate in a trench (29 CFR 1926.651(p)).
  5. Excavation material must be moved at least two feet from the edge of the trench (29 CFR 1926.651(i)).
  6. Where heavy equipment is operating near a trench, extra precautions must be taken due to the extra load imposed on the ground (29 CFR 1926.651(q)).

8. A trench is 12 feet deep and 5 feet wide. The unprotected walls consist of unstable soil with beginning to seep into the trench. You are the competent person. What are your actions?

a. Confer with the contractor for instructions
b. Order timber shoring for the trench
c. Tell the workers to monitor the seeping water
d. Tell the workers to exit the trench

Check your Work

Read the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.

Exercise

Exercise

This exercise is optional. To complete the exercise you must speak to trainer John and answer his questions. To do so, you will need to select a response at the bottom of the screen. Do your best to answer his questions. Good luck!

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