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Course 802 - Trench and Excavation Safety

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

Methods of Protection

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All excavations are hazardous because they are inherently unstable. If they are restricted spaces, they present the additional risks of oxygen depletion, toxic fumes, and water accumulation. If you are not using protective systems or equipment while working in trenches or excavations at your site, you are in danger of suffocating, inhaling toxic materials, fire, drowning, or being crushed by a cave-in.

OSHA standard 1926.652, Requirements for protective systems, details four types of protective systems.

  1. Sloping and Benching. This method is considered the safest of the four methods. It involves cutting back the trench wall at an angle inclined away from the excavation.
  2. Timber shoring. This method requires installing aluminum hydraulic, pneumatic, other types of supports to shore up the trench face prevent movement of soil.
  3. Shielding. This method is the most common system used and protects workers with trench boxes or other types of supports to prevent soil cave-ins.
  4. Engineered design. A licensed engineer designs protection systems for large complex construction projects.

Designing a protective system can be complex because you must consider many factors: soil classification, depth of cut, water content of soil, changes due to weather or climate, surcharge loads such as spoil and other materials used in the trench, and other nearby operations such as heavy equipment and vehicle traffic.

Click on the buttons below to see definitions and rule requirements.

Requirements

1926.652(a) Protection of employees in excavations.

(1)Each employee in an excavation shall be protected from cave-ins by an adequate protective system designed in accordance with paragraph (b) or (c) of this section except when:

  • (i)Excavations are made entirely in stable rock; or
  • (ii)Excavations are less than 5 feet (1.52m) in depth and examination of the ground by a competent person provides no indication of a potential cave-in.

(2) Protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied or transmitted to the system.

See Requirements for Protection Systems" for detailed slope configurations.

Appendix B Requirements and Definitions

(a) Scope and application. This appendix contains specifications for sloping and benching when used as methods of protecting employees working in excavations from cave-ins. The requirements of this appendix apply when the design of sloping and benching protective systems is to be performed in accordance with the requirements set forth in 1926.652(b)(2).

(b) Definitions.

Actual slope means the slope to which an excavation face is excavated.

Distress means that the soil is in a condition where a cave-in is imminent or is likely to occur. Distress is evidenced by such phenomena as the development of fissures in the face of or adjacent to an open excavation; the subsidence of the edge of an excavation; the slumping of material from the face or the bulging or heaving of material from the bottom of an excavation; the spalling of material from the face of an excavation; and ravelling, i.e., small amounts of material such as pebbles or little clumps of material suddenly separating from the face of an excavation and trickling or rolling down into the excavation.

Maximum allowable slope means the steepest incline of an excavation face that is acceptable for the most favorable site conditions as protection against cave-ins, and is expressed as the ratio of horizontal distance to vertical rise (H:V).

Short term exposure means a period of time less than or equal to 24 hours that an excavation is open.

1. Which of the following is considered the safest of the four methods to prevent an excavation wall collapse?

a. Engineered design
b. Timber shoring
c. Sloping/benching
d. Shielding

Next Section

Sloping Systems

As mentioned earlier, sloping is one of the most common protection systems used. It is by sloping the sides of the trench to a safe angle. The trench is sloped on both sides. The safe angle to slope the sides of an excavation varies with different kinds of soil.

The safe angle must be determined with each individual project. the safe angle must be more gradual when an excavation:

  • is near water,
  • has silty material or loose boulders, or
  • when it is being dug in areas where erosion, deep frost, or sliding is probable.
Type C sloping
Click to enlarge.

The example in the image to the right shows the sloping requirements for Type C soil. Note the ratio of the slope is 1½:1. For every 1½ feet horizontally, the height of the slope increases by 1 foot. The angle of the slope in this example is 34 degrees. (Click the Appendix B button below to see the Maximum Allowable Slope chart. )

Click on the buttons below to see definitions and sloping and benching system requirements.

1926.652(b) Design of sloping and benching systems. The slopes and configurations of sloping and benching systems shall be selected and constructed by the employer or his designee and shall be in accordance with the requirements of paragraph (b)(1); or, in the alternative, paragraph (b)(2); or, in the alternative, paragraph (b)(3), or, in the alternative, paragraph (b)(4), as follows:

  • (1) Option (1)-Allowable configurations and slopes
    • (i) Excavations shall be sloped at an angle not steeper than one and one-half horizontal to one vertical (34 degrees measured from the horizontal), unless the employer uses one of the other options listed below.
    • (ii) Slopes specified in paragraph (b)(1)(i) of this section, shall be excavated to form configurations that are in accordance with the slopes shown for Type C soil in appendix B to this subpart.
  • (2) Option (2)-Determination of slopes and configurations using Appendices A and B. Maximum allowable slopes, and allowable configurations for sloping and benching systems, shall be determined in accordance with the conditions and requirements set forth in appendices A and B to this subpart.
  • (3) Option (3)-Designs using other tabulated data.
    • (i) Designs of sloping or benching systems shall be selected from and be in accordance with tabulated data, such as tables and charts.
    • (ii) The tabulated data shall be in written form and shall include all of the following:
      • (A) Identification of the parameters that affect the selection of a sloping or benching system drawn from such data;
      • (B) Identification of the limits of use of the data, to include the magnitude and configuration of slopes determined to be safe;
      • (C) Explanatory information as may be necessary to aid the user in making a correct selection of a protective system from the data.
    • (iii) At least one copy of the tabulated data which identifies the registered professional engineer who approved the data, shall be maintained at the jobsite during construction of the protective system. After that time the data may be stored off the jobsite, but a copy of the data shall be made available to the Secretary upon request.
  • (4) Option (4)-Design by a registered professional engineer.
    • (i) Sloping and benching systems not utilizing Option (1) or Option (2) or Option (3) under paragraph (b) of this section shall be approved by a registered professional engineer.
    • (ii) Designs shall be in written form and shall include at least the following:
      • (A) The magnitude of the slopes that were determined to be safe for the particular project;
      • (B)The configurations that were determined to be safe for the particular project; and
      • (C) The identity of the registered professional engineer approving the design.
    • (iii) At least one copy of the design shall be maintained at the jobsite while the slope is being constructed. After that time the design need not be at the jobsite, but a copy shall be made available to the Secretary upon request.

1926.652(f) Sloping and benching systems. Employees shall not be permitted to work on the faces of sloped or benched excavations at levels above other employees except when employees at the lower levels are adequately protected from the hazard of falling, rolling, or sliding material or equipment.

(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 1/2 horizontal to one vertical (1/2H: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 (90°)
3/4:1 (53°)
1:1 (45°)
1 ½:1 (34°)

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 (63°) 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 (53°).

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.

2. Type C soil must have a slope no greater than _____.

a. 1:1.5 or 66 °
b. ¾:1 or 53 °
c. 1:1 or 45 °
d. 1½:1 or 34 °

Next Section

Benching Systems

Benching
Example of simple benching.

There are two basic types of benching: simple and multiple. The type of soil determines the horizontal to vertical ratio of the benched side.

  • As a general rule, the bottom vertical height of the trench must not exceed 4 feet. However, subsequent benches may be up to a maximum of 5 feet vertical in Type A soil and 4 feet in Type B soil.
  • All subsequent benches must be below the maximum slope allowed for that soil type.
  • In Type B soil, the trench excavation is permitted only in cohesive soil.

Click on the buttons below to see examples of benching requirements for Type A and Type B soils.

Type A Soil Benching

Type B Soil Benching

Click on the buttons below to see definitions and sloping and benching system requirements.

Definitions.

Actual slope means the slope to which an excavation face is excavated.

Distress means that the soil is in a condition where a cave-in is imminent or is likely to occur. Distress is evidenced by such phenomena as the development of fissures in the face of or adjacent to an open excavation; the subsidence of the edge of an excavation; the slumping of material from the face or the bulging or heaving of material from the bottom of an excavation; the spalling of material from the face of an excavation; and ravelling, i.e., small amounts of material such as pebbles or little clumps of material suddenly separating from the face of an excavation and trickling or rolling down into the excavation.

Maximum allowable slope means the steepest incline of an excavation face that is acceptable for the most favorable site conditions as protection against cave-ins, and is expressed as the ratio of horizontal distance to vertical rise (H:V).

Short term exposure means a period of time less than or equal to 24 hours that an excavation is open.

Requirements

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

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

Actual slope. The actual slope shall not be steeper than the maximum allowable slope. 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.

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).

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.

3. As a general rule, the bottom vertical bench height of a multiple-benched trench must not exceed _____.

a. 2 feet
b. 3 feet
c. 4 feet
d. 5 feet

Next Section

Sloping and Benching Problems

Example of sloping
Note collapse of the benching. The grade may be too steep for Type C soil.

Although sloping and benching is a good method for excavations, there are still some problems you may encounter. For example wide excavation areas can:

  • expose footings or cause damage to the walls of the adjacent structure and pose additional hazards to employees;
  • expose or place utilities (such as electrical power, water, and gas lines) above the angle for a safe slope; and
  • cause damage from the movement of the equipment across a larger excavation.

To prevent the collapse of an unsupported bench in an excavation 8 feet or less in depth, the allowable height of a bench at the base of an excavation must be 3 1/2 feet or less. The collapse of one bench into a lower bench can, in turn, cause a lower bench to fail in a situation where many benches have been created.

Preparing to Slope or Bench

Before the start of sloping or benching, the contractor needs to:

  • determine soil types at the excavation site using the soil classification system;
  • consider potential sloping and benching problems; and
  • identify all protective measures necessary to ensure safe working conditions, and
  • determine which protection method is the best to use at the site.

4. What is a common hazard when multiple benches have been created for an excavation?

a. The collapse of one bench into a lower bench
b. Multiple subsidence occurs in Type A soil
c. The slope tends to deform near the top of the trench
d. Entry and exit from the trench is difficult due to benching

Next Section

Shoring Systems

A shoring system is a structure such as a metal hydraulic, mechanical or timber shoring system that supports the sides of an excavation and which is designed to prevent cave­ins. Shoring or shielding is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical.

hydraulic shoring
Timber Shoring Components

Timber Shoring. Timber shoring systems are very versatile since they are custom built to fit the trench. Deep and long trenches are probably better suited to timber shoring than any other form of protective system. It is suited well for excavations where significant time is to be spent in one area.

Hydraulic Shoring. This seems to be more of a trend today. Hydraulic shoring, a pre-fabricated strut and/or wale system made from aluminum or steel. Hydraulic shoring provides a critical safety advantage over timber shoring because workers do not have to enter the trench to install or remove hydraulic shoring. All shoring should be installed from the top down and removed from the bottom up. Hydraulic shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and any other damaged or defective parts.

Pneumatic Shoring. Pneumatic shoring works in a manner similar to hydraulic shoring. The primary difference is pneumatic shoring uses air pressure in place of hydraulic pressure. However, you need to have an air compressor on site when using pneumatic shoring. Compressed air is used instead of hydraulic fluid to expand the trench jacks into position.

hydraulic shoring
Hydraulic Shoring Types

Screw Jack systems. Screw jack systems differ from hydraulic and pneumatic systems in that the struts of a screw jack system must be adjusted manually. This creates a hazard because the worker is required to be in the trench in order to adjust the strut. In addition, uniform "preloading" cannot be achieved with screw jacks, and their weight creates handling difficulties.

Single-Cylinder Hydraulic Shores. Shores of this type are generally used in a water system, as an assist to timber shoring systems, and in shallow trenches where face stability is required.

Underpinning. This process involves stabilizing adjacent structures, foundations, and other intrusions that may have an impact on the excavation. As the term indicates, underpinning is a procedure in which the foundation is physically reinforced. Underpinning should be conducted only under the direction and with the approval of a registered professional engineer.

Click on the buttons to see 1926.652(c) requirements, Appendix C and D requirements, and a video on sloping and shoring.

1926.652(c) Design of support systems, shield systems, and other protective systems.

Designs of support systems, shield systems, and other protective systems shall be selected and constructed by the employer or his designee and shall be in accordance with the requirements of paragraph (c)(1); or, in the alternative, paragraph (c)(2); or, in the alternative, paragraph (c)(3); or, in the alternative, paragraph (c)(4) as follows:

  • (1) Option (1)-Designs using appendices A, C and D. Designs for timber shoring in trenches shall be determined in accordance with the conditions and requirements set forth in appendices A and C to this subpart. Designs for aluminum hydraulic shoring shall be in accordance with paragraph (c)(2) of this section, but if manufacturer's tabulated data cannot be utilized, designs shall be in accordance with appendix D.
  • (2) Option (2)-Designs Using Manufacturer's Tabulated Data.
    • (i) Design of support systems, shield systems, or other protective systems that are drawn from manufacturer's tabulated data shall be in accordance with all specifications, recommendations, and limitations issued or made by the manufacturer.
    • (ii) Deviation from the specifications, recommendations, and limitations issued or made by the manufacturer shall only be allowed after the manufacturer issues specific written approval.
    • (iii) Manufacturer's specifications, recommendations, and limitations, and manufacturer's approval to deviate from the specifications, recommendations, and limitations shall be in written form at the jobsite during construction of the protective system. After that time this data may be stored off the jobsite, but a copy shall be made available to the Secretary upon request.
  • (3) Option (3)-Designs using other tabulated data.
    • (i) Designs of support systems, shield systems, or other protective systems shall be selected from and be in accordance with tabulated data, such as tables and charts.
    • (ii) The tabulated data shall be in written form and include all of the following:
      • (A) Identification of the parameters that affect the selection of a protective system drawn from such data;
      • (B) Identification of the limits of use of the data;
      • (C) Explanatory information as may be necessary to aid the user in making a correct selection of a protective system from the data.
    • (iii) At least one copy of the tabulated data, which identifies the registered professional engineer who approved the data, shall be maintained at the jobsite during construction of the protective system. After that time the data may be stored off the jobsite, but a copy of the data shall be made available to the Secretary upon request.
  • (4) Option (4)-Design by a registered professional engineer.
    • (i) Support systems, shield systems, and other protective systems not utilizing Option 1, Option 2 or Option 3, above, shall be approved by a registered professional engineer.
    • (ii) Designs shall be in written form and shall include the following:
      • (A) A plan indicating the sizes, types, and configurations of the materials to be used in the protective system; and
      • (B) The identity of the registered professional engineer approving the design.
    • (iii) At least one copy of the design shall be maintained at the jobsite during construction of the protective system. After that time, the design may be stored off the jobsite, but a copy of the design shall be made available to the Secretary upon request.

(c) Appendix C, Timber Shoring for Trenches

(a) Scope. This appendix contains information that can be used when timber shoring is provided as a method of protection from cave-ins in trenches that do not exceed 20 feet (6.1 m) in depth. This appendix must be used when design of timber shoring protective systems is to be performed in accordance with 1926.652(c)(1). Other timber shoring configurations; other systems of support such as hydraulic and pneumatic systems; and other protective systems such as sloping, benching, shielding, and freezing systems must be designed in accordance with the requirements set forth in 1926.652(b) and 1926.652(c).

(b) Soil Classification. In order to use the data presented in this appendix, the soil type or types in which the excavation is made must first be determined using the soil classification method set forth in appendix A of subpart P of this part.

(c) Presentation of Information. Information is presented in several forms as follows:

  • (1) Information is presented in tabular form in Tables C-1.1, C-1.2 and C-1.3, and Tables C-2.1, C-2.2 and C-2.3 following paragraph (g) of the appendix. Each table presents the minimum sizes of timber members to use in a shoring system, and each table contains data only for the particular soil type in which the excavation or portion of the excavation is made. The data are arranged to allow the user the flexibility to select from among several acceptable configurations of members based on varying the horizontal spacing of the crossbraces. Stable rock is exempt from shoring requirements and therefore, no data are presented for this condition.
  • (2) Information concerning the basis of the tabular data and the limitations of the data is presented in paragraph (d) of this appendix, and on the tables themselves.
  • (3) Information explaining the use of the tabular data is presented in paragraph (e) of this appendix.
  • (4) Information illustrating the use of the tabular data is presented in paragraph (f) of this appendix.
  • (5) Miscellaneous notations regarding Tables C-1.1 through C-1.3 and Tables C-2.1 through C-2.3 are presented in paragraph (g) of this Appendix.

(d) Basis and limitations of the data.

(e) Use of Tables.

(f) Examples to Illustrate the Use of Tables C-1.1 through C-1.3.

(g) Notes for all Tables.

All shoring should be installed from the top down and removed from the bottom up. Hydraulic shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and other damaged or defective parts.

More requirements for hydraulic shoring.

5. Hydraulic shoring provides a critical safety advantage over timber shoring when installing shoring because _____.

a. the wood tools are not required
b. workers do not have to enter the trench
c. the screw jacks might break the wales
d. workers trust hydraulic jacks more

Next Section

When a trench is excavated, employees who work in the area MUST be protected from cave-ins.
Trench box with ladder. Notice space between the box side and trench face.

Shielding Systems

In this method, a trench box or shield designed or approved by a registered professional engineer is used. Timber, aluminum, or other suitable material may be used in the construction. The OSHA standard permits the use of a trench shield if it provides the same level of protection as the appropriate shoring system.

Employers can choose the most practical method for the particular circumstance, but that system must meet the required performance criteria. The standard doesn't require a protective system when an excavation is made entirely in stable rock or is less than five feet deep. However, in this case, a competent person must examine the ground and find no indication of a potential cave-in.

When installing a trench shield, the contractor should excavate a wider area than the necessary minimum. This provides a more comfortable working environment for your employees in the trench.

When a trench is excavated, employees who work in the area MUST be protected from cave-ins.
Notice space below sides of trench box. Is this allowed?

This extra working area may provide a way for workers to escape an unexpected crisis, such as falling objects or debris. Contractors should also reduce risk by limiting the number of workers in the trench. The only workers allowed in the trench should be those who are absolutely needed to perform the task at hand.

As the trench is backfilled, the braces and planks can be removed to be used at another site. If installed and removed correctly, vertical planks and trench braces may be used several times!

Click on the buttons below to see the rule and appendix requirements.

1926.652(g) Shield systems-

  • (1) General.
    • (i) Shield systems shall not be subjected to loads exceeding those which the system was designed to withstand.
    • (ii) Shields shall be installed in a manner to restrict lateral or other hazardous movement of the shield in the event of the application of sudden lateral loads.
    • (iii) Employees shall be protected from the hazard of cave-ins when entering or exiting the areas protected by shields.
    • (iv) Employees shall not be allowed in shields when shields are being installed, removed, or moved vertically.
  • (2) Additional requirement for shield systems used in trench excavations. Excavations of earth material to a level not greater than 2 feet (.61 m) below the bottom of a shield shall be permitted, but only if the shield 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 shield.

See Appendix B for detailed slope configurations.

6. When is a protective system NOT required for an excavation?

a. When the excavation is dug in undisturbed soil
b. When the excavation is dug in Type A or Type B soil
c. When the excavation is dug in loose rock
d. When the excavation is less than five feet deep

Next Section

Selecting Protective Systems

The following figures are a graphic summary of the requirements contained in subpart P for excavations 20 feet or less in depth. Where the working area of an excavation is constantly moving, as in laying a conduit, shield systems or trench boxes may be the more appropriate protective devices to use.

Protective systems for use in excavations more than 20 feet in depth must be designed by a registered professional engineer in accordance with Sec. 1926.652 (b) and (c).

Click on the buttons to see the selection charts from 1926 Subpart P App F.

Figure 1. Preliminary Decisions

  • Is the excavation more than 5 feet deep?
    • YES - Is it entirely in stable rock?
      • YES - Excavation may be made with vertical sides
      • NO - Excavation must be sloped, shored, or shielded
    • NO - Is there a potential for cave-in?
      • NO - Excavation may be made with vertical sides
      • YES - Excavation must be sloped, shored, or shielded
    • If you choose to use sloping, go to Figure 2
    • If you choose to use shoring or shielding to Figure 3

Figure 2. Sloping Options

Sloping is selected as the method of protection.

  • Will soil classification be made in accordance with Sec. 1926.652 (b)?
    • YES - Excavation must comply with one of the following three options:
      1. Option 1: Sec. 1926.652(b)(3) which requires Appendices A and B to be followed
      2. Option 2: Sec. 1926.652(b)(3) which requires other tabulated data to be followed.
      3. Option 3: Sec. 1926.652(b)(4) which requires the excavation to be designed by a registered professional engineer.
    • NO - Excavation must comply with Sec. 1926.652(b)(1) which requires a slop of 1 1/2H:1V (34 deg.).

Figure 3. Shoring or Shielding Options

Shoring or shielding selected as the method of protection.

Soil Classification is required when shoring or shielding is used. The excavation must comply with one of the following four options in Sec. 1926.652 (b) and (c):

  1. Option 1: Sec. 1926.652(c)(1) which requires Appendices A and C to be followed (e.g. timber shoring).
  2. Option 2: Sec. 1926.652(c)(2) which requires manufacturers data to be followed (e.g. hydraulic shoring, trench jacks, air shores, shields).
  3. Option 3: Sec. 1926.652(c)(3) which requires tabulated data (see definition) to be followed (e.g. any system as per the tabulated data).
  4. Option 4: Sec. 1926.652(b)(4) and Sec. 1926.652(c)(4) which require the excavation to be designed by a registered professional engineer (e.g. any designed system).

7. Protective systems for use in excavations more than 20 feet in depth must be designed by _____.

a. a certified safety professional
b. a qualified person
c. a competent person
d. a registered professional engineer

Next Section

Case Studies

The following case reports of trenching accidents investigated by OSHA only illustrate how seemingly innocent workplace activities can have deadly consequence, especially when it comes to excavation work.

Example of fine-grained soil
  • Two employees were installing 6" PVC pipe in a trench 40' long x 9' deep x 2' wide. No means of protection was provided in the vertical wall trench. A cave-in occurred, fatally injuring one employee and causing serious facial injuries to the other.
  • An inadequately protected trench wall collapsed, killing one employee who had just gotten into the trench to check grade for installation of an 8" sewer line. The trench was 20-25 feet deep and had been benched about one bucket-width (4 feet) on each side. At the time of the collapse, a backhoe was still extracting soil from the trench.
  • Four employees were in an excavation 32' long x 7' deep x 9' wide boring a hole under a road. Eight-foot steel plates used as shoring were placed against the side walls of the excavation at about 30-degree angles. No horizontal bracing was used. One of the plates tipped over, crushing an employee.
Example of fine-grained soil
  • An OSHA investigator was performing a worksite inspection on a 10 ft deep trench being dug by ABC Construction. He directed an employee to exit the trench believing collapse was imminent. Within five minutes, the collapse occurred and could have buried the worker under six to seven feet of soil. Workers were ordered out of the trench just moments before a portion collapsed avoiding possible injury or loss of life. OSHA standards mandate that all excavations 5 feet or deeper be protected against collapse.

8. OSHA standards mandate that all excavations _____ be protected against collapse.

a. 4 feet deep
b. 5 feet or deeper
c. more than 6 feet deep
d. of any depth

Check your Work

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