Excavations and Trenching: Protective Systems and Daily Inspections

The main hazard here is the cave-in: soil or rock that separates from the side of an excavation, or soil lost from under a trench shield or support system, and moves into the excavation suddenly, in enough quantity to entrap, bury, or otherwise injure and immobilize a person (1926.650(b)). The rules ask you to protect employees with sloping, benching, a support system, or a shield, to control the other hazards around the dig, and to have a competent person inspect daily.

Who it applies to

Subpart P applies to all open excavations made in the earth's surface, and excavations include trenches (1926.650(a)). The scope paragraph lists no exclusions.

Four definitions drive the rest (1926.650(b)):

• Excavation: any man-made cut, cavity, trench, or depression in an earth surface, formed by earth removal.
• Trench: a narrow excavation (in relation to its length) made below the surface of the ground. In general the depth is greater than the width, but the width (measured at the bottom) is not greater than 15 feet (4.6 m). A wider excavation is also considered a trench if forms or other structures installed in it reduce the distance from the form or structure to the side of the excavation to 15 feet (4.6 m) or less, measured at the bottom.
• Competent person: one who is capable of identifying existing and predictable hazards in the surroundings, or working conditions that are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them.
• Protective system: a method of protecting employees from cave-ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of adjacent structures.

What the standard requires

Cave-in protection

Each employee in an excavation must be protected from cave-ins by an adequate protective system designed under 1926.652(b) or (c), except when (1926.652(a)(1)):

• the excavation is made entirely in stable rock (1926.652(a)(1)(i)); or
• the excavation is less than 5 feet (1.52 m) in depth and examination of the ground by a competent person provides no indication of a potential cave-in (1926.652(a)(1)(ii)).

Stable rock is natural solid mineral material that can be excavated with vertical sides and will remain intact while exposed (1926.650(b)). Protective systems must 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 (1926.652(a)(2)).

Design options

You or your designee must select and construct the system under one of four options.

Sloping and benching (1926.652(b)):

1. Slope no steeper than one and one-half horizontal to one vertical, 34 degrees from the horizontal (1926.652(b)(1)(i)).
2. Follow Appendix A (Soil Classification) and Appendix B (Sloping and Benching) (1926.652(b)(2)).
3. Use other tabulated data, such as tables and charts (1926.652(b)(3)(i)).
4. Have the system approved by a registered professional engineer (1926.652(b)(4)(i)).

Support systems, shield systems, and other protective systems (1926.652(c)):

1. Follow appendices A and C for timber shoring in trenches, and appendix D for aluminum hydraulic shoring when manufacturer's tabulated data cannot be utilized (1926.652(c)(1)).
2. Follow the manufacturer's tabulated data. Deviation is allowed only after the manufacturer issues specific written approval (1926.652(c)(2)(i), (c)(2)(ii)).
3. Use other tabulated data (1926.652(c)(3)(i)).
4. Have the system approved by a registered professional engineer (1926.652(c)(4)(i)).

So an engineer is required when you use none of the first three options. Depth matters too, and the 20 foot figure is in the appendices, not in 1926.652 itself. The slope table in Appendix B covers excavations less than 20 feet deep, and its note says sloping or benching for excavations greater than 20 feet deep must be designed by a registered professional engineer (Appendix B to Subpart P, Table B-1, Note 3). The timber shoring and aluminum hydraulic shoring appendices cover trenches that do not exceed 20 feet (6.1 m) in depth (Appendix C to Subpart P, paragraph (a); Appendix D to Subpart P, paragraph (a)).

Shield systems

Shields must not be subjected to loads exceeding those the system was designed to withstand (1926.652(g)(1)(i)). Employees must be protected from cave-ins when entering or exiting the areas protected by shields (1926.652(g)(1)(iii)).

Site conditions

• Surface encumbrances located so as to create a hazard to employees must be removed or supported, as necessary (1926.651(a)).
• Underground installations. Before opening an excavation, determine the estimated location of utilities that reasonably may be expected to be encountered (1926.651(b)(1)). Ask the utility companies or owners to establish the location before actual excavation starts. If they cannot respond within 24 hours (unless state or local law requires a longer period), or cannot establish the exact location, you may proceed with caution, using detection equipment or other acceptable means (1926.651(b)(2)). As digging approaches the estimated location, determine the exact location by safe and acceptable means (1926.651(b)(3)).
• Access and egress. Trench excavations 4 feet (1.22 m) or more in depth must have a stairway, ladder, ramp, or other safe means of egress located so employees need no more than 25 feet (7.62 m) of lateral travel (1926.651(c)(2)).
• Vehicular traffic. Employees exposed to public vehicular traffic must be provided with, and wear, warning vests or other suitable garments marked with or made of reflectorized or high-visibility material (1926.651(d)).
• Falling loads. No employee is permitted underneath loads handled by lifting or digging equipment (1926.651(e)).
• Hazardous atmospheres. Where oxygen deficiency (less than 19.5 percent oxygen) or a hazardous atmosphere exists or could reasonably be expected to exist, test the atmosphere before employees enter excavations greater than 4 feet (1.22 m) in depth (1926.651(g)(1)(i)).
• Water. Employees must not work in excavations with accumulated or accumulating water unless adequate precautions have been taken (1926.651(h)(1)).
• Adjacent structures. Where excavation endangers the stability of adjoining buildings, walls, or other structures, provide support systems such as shoring, bracing, or underpinning (1926.651(i)(1)).
• Spoil and equipment. Keep excavated or other materials and equipment at least 2 feet (.61 m) from the edge, use retaining devices sufficient to keep them from falling or rolling in, or combine both if necessary (1926.651(j)(2)).
• Walkways must be provided where employees or equipment are required or permitted to cross over excavations, with guardrails complying with 1926.502(b) where walkways are 6 feet (1.8 m) or more above lower levels (1926.651(l)).

Daily inspections

A competent person must inspect excavations, the adjacent areas, and protective systems daily for evidence of possible cave-ins, indications of failure of protective systems, hazardous atmospheres, or other hazardous conditions. Inspect prior to the start of work, as needed throughout the shift, and after every rainstorm or other hazard increasing occurrence. These inspections are only required when employee exposure can be reasonably anticipated (1926.651(k)(1)).

Where the competent person finds such evidence, exposed employees must be removed from the hazardous area until the necessary precautions have been taken to ensure their safety (1926.651(k)(2)).

Training

Sections 1926.650, 1926.651, and 1926.652 contain no employee training paragraph. Look instead to the competent person duties: the ground examination (1926.652(a)(1)(ii)) and the inspections (1926.651(k)).

Written programs and records

These sections require no written excavation program, and paragraph (k) does not say inspections must be recorded. The written items are tied to design. Tabulated data, engineer-approved designs, and manufacturer's data used under 1926.652(c)(2) must be in written form, with a copy at the jobsite while the system is being constructed. After that, a copy must be made available to the Secretary upon request (1926.652(b)(3)(ii), (b)(3)(iii), (b)(4)(ii), (b)(4)(iii), (c)(2)(iii), (c)(3)(ii), (c)(3)(iii), (c)(4)(ii), (c)(4)(iii)).

Easy-to-miss requirements

• Egress starts at 4 feet in trenches, shallower than the 5 foot figure in the cave-in exception (1926.651(c)(2), 1926.652(a)(1)(ii)).
• Stay out of a moving shield. Employees are not allowed in shields when shields are being installed, removed, or moved vertically (1926.652(g)(1)(iv)).
• Digging below a shield is limited. Excavating no more than 2 feet (.61 m) below the bottom of a shield is 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 (1926.652(g)(2)).
• Pumps need watching. If water removal equipment is used to control water, a competent person must monitor the equipment and operations to ensure proper operation (1926.651(h)(2)).

Related guides

• Ladders
• Confined spaces
• Fall protection

Source

This guide is based on the text of 29 CFR 1926.651 and 29 CFR 1926.652, with definitions from 29 CFR 1926.650, the title of Appendix A to Subpart P, one table note from Appendix B to Subpart P, and the scope paragraphs of Appendix C and Appendix D, as published on osha.gov. The regulation itself always controls. States that run their own OSHA-approved State Plans may have additional or stricter rules.