Sloping and benching requirements

The appendix applies when sloping or benching is used to protect workers and when the design of those systems is performed under 1926.652(b)(2). Appendix B states it "contains specifications for sloping and benching when used as methods of protecting employees working in excavations from cave-ins" and applies when designs follow 1926.652(b)(2) and the guidance in Appendix B to Subpart P of Part 1926.

• Use Appendix B when you are selecting slopes or bench sizes per the table and figures provided.
• If you are designing a protective system under 1926.652(b)(2), Appendix B gives prescriptive slope/bench limits to follow.

You must first classify the soil or rock according to the criteria referenced in Subpart P before selecting a slope or benching system. Appendix B requires that "Soil and rock deposits shall be classified in accordance with appendix A to subpart P of part 1926," and the protective system you choose must match that soil type as required by 1926.652(b)(2).

• A competent person should perform soil classification on site.
• The classification (Type A, B, C, or stable rock) determines the maximum allowable slopes listed in Appendix B's Table B‑1.

The maximum allowable slopes for excavations less than 20 feet deep are: Stable rock — vertical; Type A — 3/4:1 (H:V); Type B — 1:1 (H:V); Type C — 1½:1 (H:V). These values are listed in Table B‑1 of Appendix B to Subpart P; see Table B‑1 in Appendix B and the related requirements in 1926.652(b)(2).

• Angles in degrees are given in parentheses in Table B‑1 for reference.

Yes — for short-term exposures (24 hours or less) in Type A soil that are 12 feet deep or less, Appendix B allows a steeper short-term maximum slope of 1/2H:1V. Appendix B notes that "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," and references the general design rules in 1926.652(b)(2) and Appendix B itself (Appendix B to Subpart P).

• This exception only applies when the excavation is both short-term (≤24 hours) and ≤12 feet deep in Type A soil.

A registered professional engineer must design sloping or benching for excavations deeper than 20 feet. Appendix B states that "Sloping or benching for excavations greater than 20 feet deep shall be designed by a registered professional engineer," and that requirement is part of the prescriptive limits in Appendix B to Subpart P and the design option referenced in 1926.652(b)(2).

• For excavations ≤20 feet, the prescriptive table and figures in Appendix B can be used by a competent person; above 20 feet, engineer-designed plans are required.

"Distress" means the soil is in a condition where a cave-in is imminent or likely to occur, and it is shown by observable signs such as fissures in the excavation face, subsidence of the edge, slumping or bulging of material, spalling from the face, or ravelling (small pieces trickling down). Appendix B defines "distress" and lists these same signs; see Appendix B to Subpart P and apply the relevant protective options in 1926.652(b)(2).

• If any of these signs are present, Appendix B requires reducing the actual slope to be less steep than the maximum allowable slope.

If signs of distress are present, the slope must be cut back so the actual slope is at least 1/2H:1V less steep than the maximum allowable slope. Appendix B states: "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," and this prescriptive requirement accompanies the design option in 1926.652(b)(2).

• Example: If the maximum allowable slope for a soil type is 3/4:1, reduce it by at least 1/2:1 to determine the new actual slope.

A competent person must determine how much to reduce the actual slope when surcharge loads (stored material, equipment, traffic) are present and must ensure the reduction is achieved; adjacent structures must be evaluated in accordance with [1926.651(i)]. Appendix B requires a competent person to make this determination and refers specifically to evaluating surcharge loads, with adjacent-structure evaluation per 1926.651(i) and the design provisions in 1926.652(b)(2).

• The competent person should account for the weight and placement of nearby loads and equipment and adjust slopes or use alternative protective systems as needed.

For excavations 8 feet or less in depth with unsupported vertically sided lower portions, the maximum vertical side allowed is 3½ feet. Appendix B specifies: "All excavations 8 feet or less in depth which have unsupported vertically sided lower portions shall have a maximum vertical side of 3½ feet," and this is part of the slope/bench configurations illustrated in Appendix B and governed by 1926.652(b)(2).

• If the excavation includes deeper vertical lower portions or different soil types, other Appendix B provisions or engineer-designed systems may apply.

For excavations more than 8 feet but not more than 12 feet deep with unsupported vertically sided lower portions, the excavation must have a maximum allowable slope of 1:1 and a maximum vertical side of 3½ feet. Appendix B states these limits explicitly and they are to be used with the guidance in 1926.652(b)(2).

• These prescriptive dimensions apply only where the soil classification and other conditions meet Appendix B assumptions; otherwise, use other options in 1926.652(b).

If a vertically sided lower portion is supported or shielded in an excavation 20 feet or less deep, the support or shield must extend at least 18 inches above the top of the vertical side, and the maximum allowable slope for the rest of the excavation shall be 3/4:1. Appendix B states: "All excavations 20 feet or less in depth which have vertically sided lower portions that are supported or shielded shall have a maximum allowable slope of ¾:1. The support or shield system must extend at least 18 inches above the top of the vertical side," consistent with the design options in 1926.652(b)(2).

• Ensure shields/supports are properly installed and extend the required 18 inches above the vertical portion.

For benched excavations in Type B soil up to 20 feet deep, the maximum allowable slope is 1:1 and bench dimensions must follow Appendix B's bench figures. Appendix B states: "All benched excavations 20 feet or less in depth shall have a maximum allowable slope of 1:1 and maximum bench dimensions as follows," and provides the illustrative bench diagrams; see Appendix B to Subpart P and the design option in 1926.652(b)(2).

• Follow the bench width and vertical rise dimensions shown in Appendix B figures for Type B benched excavations.

The maximum allowable slope for Type C soil for excavations 20 feet or less in depth is 1½:1 (horizontal to vertical). Appendix B specifies: "All simple slope excavations 20 feet or less in depth shall have a maximum allowable slope of 1½:1" for Type C soil; refer to Appendix B to Subpart P and the related design option in 1926.652(b)(2).

• If vertically sided lower portions exist in Type C, the Appendix requires support or shielding extending 18 inches above the top of the vertical side.

When soils are layered, Appendix B requires applying the maximum allowable slope for each layer as shown in the layered-soil diagrams; the excavation must meet the slope limits for the combination of layers. Appendix B provides diagrams (e.g., B over A, C over B) showing allowable configurations and states "All excavations 20 feet or less in depth made in layered soils shall have a maximum allowable slope for each layer as set forth below," and this approach is used with the design option in 1926.652(b)(2) and Appendix B (Appendix B to Subpart P).

• Evaluate each layer’s type and thickness; use the Appendix diagrams to determine a safe overall slope or use engineer-designed measures if the situation is complex.

A competent person must perform on-site determinations such as soil classification and whether a selected slope or benching system is adequate. OSHA requires a competent person under 1926.651 to identify hazards and take corrective action, and Appendix B's sloping and benching provisions are applied using that soil classification and competent-person judgment when following 1926.652(b)(2).

• The competent person must also watch for signs of distress and change protection as needed.

1926.652(b) allows several protective systems: sloping, benching, support systems (shoring), shield systems (trench boxes), and other equivalent protective systems designed by a qualified person. The prescriptive sloping/benching guidance in Appendix B is one acceptable method; the broader regulatory options are in 1926.652 and the Appendix B prescriptive tables apply when design is done under 1926.652(b)(2).

• If you use supports, shields, or a custom engineered system, follow the specific design requirements and ensure competent persons or engineers determine adequacy.

Appendix B defines "short-term exposure" as a period of time less than or equal to 24 hours, and short-term status can allow steeper slopes in limited cases (for example, Type A soil ≤12 feet deep may use a 1/2H:1V slope). See the definition and the short-term exception in Appendix B to Subpart P and the implementing provisions in 1926.652(b)(2).

• Always confirm short-term conditions (≤24 hours) and soil type before applying the steeper short-term slope.

When there are no signs of distress or surcharge loads, the actual slope must not be steeper than the maximum allowable slope given in Table B‑1 for the soil type. Appendix B states "The actual slope shall not be steeper than the maximum allowable slope," and those maximums appear in Table B‑1 in Appendix B and are applied under 1926.652(b)(2).

• If site conditions change (distress, surcharge), the competent person must adjust slopes accordingly.

If adjacent structures create surcharge conditions, a competent person must evaluate the effect and determine how much to reduce the slope, and adjacent structures must be evaluated in accordance with [1926.651(i)]. Appendix B requires competent-person evaluation of surcharge loads and specifically refers to evaluating adjacent structures per 1926.651(i) while applying sloping/benching options in 1926.652(b)(2).

• Consider protective measures such as increased cutback, shoring, or shielding when adjacent structures increase risk.

You cannot have unsupported vertically sided lower portions beyond the prescriptive limits in Appendix B; if the excavation configuration exceeds the allowed unsupported vertical portions (for depth or vertical height), you must provide support or shielding or use sloping/benching options consistent with [1926.652(b)(2)]. Appendix B gives maximum vertical side limits (e.g., 3½ feet for certain depths) and requires support/shielding or alternative designs found in 1926.652 and Appendix B to Subpart P.

• Remedy: install supports/shields extending 18 inches above the vertical top or change to an approved sloped/benched configuration.

When site conditions are complex or change such that Appendix B prescriptive limits do not clearly apply, employers must use a competent person and, when necessary, a registered professional engineer to design an appropriate protective system per 1926.652(b)(2). Appendix B notes other options in 1926.652(b) and that excavations greater than 20 feet require engineer design; see 1926.652 and Appendix B to Subpart P.

• If in doubt about stability, stop work, consult a competent person, and obtain engineered design where prescriptive guidance doesn’t cover the condition.

Employers should use Figure B‑1 and the Appendix diagrams as prescriptive examples of acceptable slope and bench configurations for the specified soil types and depths; the appendix states that "Configurations of sloping and benching systems shall be in accordance with Figure B‑1" and these figures are intended to be used under the design option in 1926.652(b)(2).

• Match the excavation’s soil type, depth, and whether it’s short-term to the appropriate figure.
• If conditions differ from the figures, use a competent person’s judgment or an engineer-designed system per 1926.652.