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Course 802 - Trench and Excavation Safety

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

Employer Requirements

Materials and Equipment

Example of a shield that has not been maintained
Example of a shield that has not been maintained

The employer is responsible for maintaining materials and equipment used for protective equipment. Defective and damaged materials and equipment can cause failure of a protective system and other excavation hazards.

To avoid possible failure of a protective system, you must make sure that:

  • materials or equipment is not damaged or defective;
  • manufactured materials or equipment is used and maintained consistent with the manufacturer's recommendations;
  • a competent person examines all damaged materials and equipment; and
  • unsafe materials or equipment is removed from service until a registered professional engineer evaluates and approves it for use

1926.652(d) Materials and equipment.

(1) Materials and equipment used for protective systems shall be free from damage or defects that might impair their proper function.

(2) Manufactured materials and equipment used for protective systems shall be used and maintained in a manner that is consistent with the recommendations of the manufacturer, and in a manner that will prevent employee exposure to hazards.

(3) When material or equipment that is used for protective systems is damaged, a competent person shall examine the material or equipment and evaluate its suitability for continued use. If the competent person cannot assure the material or equipment is able to support the intended loads or is otherwise suitable for safe use, then such material or equipment shall be removed from service, and shall be evaluated and approved by a registered professional engineer before being returned to service.

See Appendix B for detailed slope configurations.

1. Who must examine all damaged excavation materials and equipment?

a. The project manager
b. A registered engineer
c. A competent person
d. The manufacturer

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Installing and Removing Protective Systems

Installing a trench shield.
Trench box being installed.

The Excavation standards require employers to take certain steps to protect workers when installing and removing support systems. For example:

  • Members of support systems must be securely connected to prevent sliding, falling, kickouts or predictable failure.
  • Support systems must be installed and removed in a manner that protects workers from cave-ins and structural collapses and from being struck by members of the support system.
  • Members of support systems must not be overloaded.
  • Before temporary removal of individual members, additional precautions are required, such as installing other structural members to carry loads imposed on the support system.
  • Removal must begin at, and progress from, the bottom of the excavation.
  • Members shall be released slowly so as to note any indication of possible failure of the remaining members of the structure or possible cave-in of the sides of the excavation.
  • Backfilling must progress together with the removal of support systems from excavations.

The standards permit excavation of 2 feet (0.61 meters) or less below the bottom of the members of a support system, but only if the system is designed to resist the forces calculated for the full depth of the trench and there are no indications, while the trench is open, of a possible loss of soil from behind or below the bottom of the support system. Employers must coordinate the installation of support systems with the excavation work.

2. Removal of excavation protective systems must _____.

a. be removed from the top down
b. occur quickly to protect workers
c. be approved by the site supervisor
d. begin at the bottom of the excavation

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Access and Egress

An excavation that has a depth of four feet or more must have a way to enter and exit the excavation.
Will this worker escape if there's a major collapse?

Worker safety may depend on how quickly they can climb out of an excavation. OSHA requires employers to provide ladders, steps, ramps, or other safe means of egress for workers working in trench excavations 4 feet (1.22 meters) or deeper.

  • The means of egress must be located so as not to require workers to travel more than 25 feet (7.62 meters) laterally within the trench.
  • Structural ramps used by workers to enter and exit the site must have non-slip surfaces and 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.
  • Structural members used for ramps or runways must be uniform in thickness and joined in a manner to prevent tripping or displacement.
  • A competent person must also evaluate ramps made from soil that are used to enter and exit an excavation.

3. The means of egress in a trench must be located within _____ laterally.

a. 15 feet
b. 25 feet
c. 30 feet
d. 35 feet

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If water is in the trench, classify the soil as Type C.
If water is in the trench, classify the soil as Type C.

Water Accumulation

The employer must prohibit employees from working in excavations where water has accumulated or is accumulating without adequate protection.

  • If water enters the excavation through the soil for any reason, the soil must be considered Type C and adequate protection must be provided.
  • If you use water removal equipment to control or prevent water accumulation, you must make sure a competent person monitors the equipment and its operation to ensure proper use.
  • If workers enter excavations, methods for controlling standing water and water accumulation must be provided and meet the following requirements:
    • use of special support or shield systems is approved by a registered professional engineer;
    • water removal equipment, i.e., well pointing, is used and monitored by a competent person;
    • safety harnesses and lifelines are used;
    • surface water is diverted away from the trench;
    • employees are removed from the trench during rainstorms; and
    • trenches are carefully inspected by a competent person after each rain and before employees are permitted to re-enter the trench.

OSHA standards also require the employer to use diversion ditches, dikes and other suitable means to prevent water from entering an excavation and to provide drainage of the adjacent area. A competent person must also inspect those excavations that are subject to runoffs from heavy rains.

4. If water enters the excavation through the soil for any reason, the soil must be considered _____.

a. Type A
b. Type B
c. Type C
d. Type D

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Fall Protection

Employers must ensure that any worker who enters a bell- bottom pier hole or similar deep and confined footing excavation wears a harness with a lifeline. The lifeline must be attached securely to the harness and must be separate from any line used to handle materials. Also, the lifeline must be individually attended by an observer at all times when the worker wearing the lifeline is in the excavation.

Falling Loads and Moving Equipment

Trench barrier
Make sure workers are not in danger of being struck from falling material or objects.

In addition to cave-ins and related hazards, workers involved in excavation work are exposed to hazards involving falling loads and mobile equipment. To protect workers from these hazards, OSHA requires employers to take certain precautions. For example, employers must:

  • Place spoils,
    spoils
    These spoils are spaced 2 feet or more from the trench.

    stored materials, and equipment at least 2 feet (0.61 meters) from the edge and/or by using a retaining device to keep the materials or equipment from falling or rolling into the excavation.
  • Provide a warning system (such as barricades, spotters using hand or mechanical signals.
  • Use stop blocks when mobile equipment must approach the edge of an excavation and the operator does not have a clear and direct view of the edge.
  • Protect workers from loose rock or soil that could fall or roll from an excavation face by scaling to remove loose material, installing protective barricades at appropriate intervals, or using other equivalent forms of protection.
  • Institute and enforce work rules prohibiting workers from working on faces of sloped or benched excavations at levels above other workers unless the workers at the lower levels are adequately protected from the hazards of falling, rolling, or sliding material or equipment.
  • Institute and enforce work rules prohibiting workers from standing or working under loads being handled by lifting or digging equipment.
  • Require workers to stand away from vehicles being loaded or unloaded to protect them from being struck by any spillage or falling materials. (Operators may remain inside the cab of a vehicle being loaded or unloaded if the vehicle is equipped, in accord with 29 CFR 1926.601(b)(6), to provide adequate protection for the operator.)
1926.652(e) Installation and removal of support-

(1) General.

  • (i) Members of support systems shall be securely connected together to prevent sliding, falling, kickouts, or other predictable failure.
  • (ii) Support systems shall be installed and removed in a manner that protects employees from cave-ins, structural collapses, or from being struck by members of the support system.
  • (iii) Individual members of support systems shall not be subjected to loads exceeding those which those members were designed to withstand.
  • (iv) Before temporary removal of individual members begins, additional precautions shall be taken to ensure the safety of employees, such as installing other structural members to carry the loads imposed on the support system.
  • (v) Removal shall begin at, and progress from, the bottom of the excavation. Members shall be released slowly so as to note any indication of possible failure of the remaining members of the structure or possible cave-in of the sides of the excavation.
  • (vi) Backfilling shall progress together with the removal of support systems from excavations.

1926.652(e)(2) Additional requirements for support systems for trench excavations.

  • (i) Excavation of material to a level no greater than 2 feet (.61 m) below the bottom of the members of a support system shall be permitted, but only if the system is designed to resist the forces calculated for the full depth of the trench, and there are no indications while the trench is open of a possible loss of soil from behind or below the bottom of the support system.
  • (ii) Installation of a support system shall be closely coordinated with the excavation of trenches.

(c) Requirements.

(1) Soil classification. Soil and rock deposits shall be classified in accordance with appendix A to subpart P of part 1926.

(2) Maximum allowable slope. The maximum allowable slope for a soil or rock deposit shall be determined from Table B-1 of this appendix.

(3) Actual slope.

(i) The actual slope shall not be steeper than the maximum allowable slope.

(ii) The actual slope shall be less steep than the maximum allowable slope, when there are signs of distress. If that situation occurs, the slope shall be cut back to an actual slope which is at least ½ horizontal to one vertical (½H:1V) less steep than the maximum allowable slope.

(iii) When surcharge loads from stored material or equipment, operating equipment, or traffic are present, a competent person shall determine the degree to which the actual slope must be reduced below the maximum allowable slope, and shall assure that such reduction is achieved. Surcharge loads from adjacent structures shall be evaluated in accordance with 1926.651(i).

(4)Configurations. Configurations of sloping and benching systems shall be in accordance with Figure B-1.

TABLE B-1
MAXIMUM ALLOWABLE SLOPES
SOIL OR ROCK TYPE MAXIMUM ALLOWABLE SLOPES (H:V)(1) FOR EXCAVATIONS LESS THAN 20 FEET DEEP(3)
STABLE ROCK
TYPE A (2)
TYPE B
TYPE C
VERTICAL (90º)
3/4:1 (53º)
1:1 (45º)
1 ½:1 (34º)

Footnote(1) Numbers shown in parentheses next to maximum allowable slopes are angles expressed in degrees from the horizontal. Angles have been rounded off.

Footnote(2) A short-term maximum allowable slope of 1/2H:1V (63º) is allowed in excavations in Type A soil that are 12 feet (3.67 m) or less in depth. Short-term maximum allowable slopes for excavations greater than 12 feet (3.67 m) in depth shall be 3/4H:1V (53º).

Footnote(3) Sloping or benching for excavations greater than 20 feet deep shall be designed by a registered professional engineer.

See Appendix B for detailed slope configurations.

5. What is the excavation requirement for spoils, materials, and equipment?

a. Locate them at either end of the trench
b. Place a barrier between them and the trench
c. Get approval for their placement away from the trench
d. Place them at least two feet from the trench

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Excavation Training

Trench barrier
Workers should be fully trained prior to entry into the trench.

Cooperation between employers and employees is necessary to make sure excavation safety training policies are developed and implemented effectively. Each project supervisor and competent person must understand their responsibility for providing effective safety training to ensure a safe working environment. Effective excavation training includes a hands-on practice component to make sure workers have adequate knowledge, skills, and the ability to perform tasks safely (KSAs).

Employee excavation training should include the following topic areas:

  1. Trenching and excavating hazards
  2. Soil identification
  3. Safe slopes for different soil types and conditions
  4. Stress patterns on trench walls from soil and spoil, equipment, and vibration caused by equipment and traffic
  5. Effects of nearby buried utilities, building foundations and lengthy exposure to the elements on trench side walls and other excavations
  6. Effects on trench and excavation conditions from severe weather (such as excess water, freezing temperatures, unexpected heat or long-term drying)
  7. Recognition of buried drums, containers, tanks and wells

Employees also need to be trained to follow the proper procedures to involve the electrical power company, health department and other agencies when they find unforeseen objects, such as wells, sewage disposal systems, cemeteries, and historical, architectural, and archeological artifacts.

6. Which component of excavation training helps to determine workers have adequate knowledge, skills, and abilities (KSAs) to complete tasks safely?

a. Attendance sheet signed by the supervisor
b. The OSHA 10-hour training module
c. At least one hour of classroom training
d. A hands-on practice component prior to work

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Look close. There is a worker partially buried by a collapse in this trench. Click to enlarge.
Trench next to adjacent structure.
There are NO support systems in a trench next to an adjacent structure. The worker is buried up to his waist beneath collapsing concrete and brick veneer.

Adjacent Structures

The Excavation standards require employers to provide support systems, such as shoring, bracing, or underpinning, when necessary to ensure that adjacent structures (including adjoining buildings, walls, sidewalks and pavements) remain stable for the protection of workers. The standards also prohibit excavation below the base or footing of any foundation or retaining wall that could be reasonably expected to pose a hazard to workers unless:

  • The employer provides a support system, such as underpinning;
  • The excavation is in stable rock; or
  • A registered professional engineer determines that the structure is far enough away from the excavation that it would not be affected by the excavation activity or that the excavation work will not pose a hazard to workers.

Excavations under sidewalks and pavements are prohibited unless you provide an appropriately designed support system or another effective means of support. There must not be any indications of a possible cave-in (while the trench is open) below the bottom of the support system. Also, you must coordinate the installation of support systems closely with the excavation work.

Once the work is finished, you are required to backfill the excavation when you take apart the protective system. After the excavation is cleared, remove the protective system from the bottom up.

7. In which situation would an excavation next to a foundation or retaining wall be initially prohibited?

a. The excavation is in stable rock
b. The excavation is approved by a registered professional engineer
c. The foundation or retaining wall creates a hazard
d. The employer has provided suitable underpinning

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Residential Construction

Trench next to adjacent structure.
Residential excavations must meet specific requirements to be exempt.

OSHA recognizes that residential construction sites can be very different from commercial sites as they relate to excavations. In 1995, OSHA suspended the requirements of 1926.652 to house foundation/basement excavations. (OSHA Letter of Interpretation 1995-06-30).

The exemption applies only if ALL six of the following conditions are present:

  1. the house foundation/basement excavation is less than 7½ feet in depth or is benched for at least 2 feet horizontally for every 5 feet or less of vertical height;
  2. the minimum horizontal width at the bottom of the excavation is as wide as needed, but not less than 2 feet;
  3. there is no water, surface tension cracks or other environmental conditions present that reduce the excavation stability;
  4. there is no heavy equipment operating in the vicinity that causes vibration to the excavation while employees are in the excavation;
  5. work crews in the excavation are the minimum number needed to perform the work; and
  6. the work has been planned and is carried out in a manner to minimize the time employees are in the excavation.

However, it's important to note that OSHA 1910.652 does still apply if any of the above conditions are not met.

This policy applies to all house foundation/basement excavations including those which become trenches by definition when formwork, foundations, or walls are constructed. This policy does not apply to utility excavations (trenches) where 29 CFR 1926.652 remains applicable.

8. Which of the following is TRUE regarding the residential basement/foundation exemption for excavations?

a. The exemption applies to all utility excavations
b. In 1995, OSHA reinstated the residential construction requirement
c. One of the six exemption conditions must be present
d. All six exemption conditions must be present

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On-site Inspection

Trench next to adjacent structure.
Inspectors must be competent persons.

The employer must ensure documented inspections are conducted by a competent person. The following guide specifies the frequency and conditions requiring inspections:

  • Daily and before the start of each shift;
  • As dictated by the work being done in the trench;
  • After every rainstorm;
  • After other events that could increase hazards, e.g. snowstorm, windstorm, thaw, earthquake, etc.;
  • When fissures, tension cracks, sloughing, undercutting, water seepage, bulging at the bottom, or other similar conditions occur;
  • When there is a change in the size, location, or placement of the spoil pile; and
  • When there is any indication of change or movement in adjacent structures.

If the inspector finds any unsafe conditions during an inspection, they must clear employees from the hazardous area until safety precautions are in place.

See a sample Excavation Safety Checklist that can help conduct inspections.

9. What must the inspector do if unsafe conditions in a trench are discovered during an inspection?

a. Note the condition on the inspection checklist
b. Immediately clear workers until the trench is safe
c. Ask for an OSHA consultation about the hazard
d. Hire a registered engineer to recommend a fix

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.

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VIDEO

This excerpt from NAHB Construction Safety & Health's Trenching & Excavation Safety Video highlights the most common hazards associated with residential trenching and excavation.

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