Sheet 13Domain 2 of 5 · Hazard Identification and Control
Trenches and permit spaces: STSC excavation and confined-space rules
The excavator is down to shoulder height on a sewer lateral and the trench box is still on the lowboy. At 5 feet deep a trench needs a protective system, unless it is dug entirely in stable rock, and a competent person has to inspect it every day. The rest of this sheet covers soil, water, utilities and the way out, plus the confined spaces that have their own construction subpart.
Excavation sits in 29 CFR 1926 Subpart P (1926.650 to 1926.652). Two of its numbers sit a foot apart: 4 feet for a way out of the trench, 5 feet for a protective system. Keep them in their rows.
The competent person is the hinge of the subpart. Under Appendix A to Subpart P that person classifies the soil as stable rock, Type A, B or C, and the class decides which sloping or shoring options are allowed. Competent person vs qualified person explains where that person's authority ends and engineered design begins.
Confined spaces in construction have their own subpart too, 29 CFR 1926 Subpart AA (1926.1200 to 1926.1213), written for sites where several employers share one space. Test order and who signs the permit are on confined space entry and atmospheric testing.
Talking point 02
Trench numbers by depth
Excavation thresholds in 29 CFR 1926 Subpart Pscroll →
Depth or distance
What it triggers
Rule
Any depth
Utility locations estimated before digging; daily inspection by a competent person
1926.651(b)(1), 1926.651(k)(1)
4 ft deep
Stairway, ladder, ramp or other safe exit within 25 ft of lateral travel
1926.651(c)(2)
5 ft deep
Protective system: sloping, benching, shoring or shielding, unless the cut is entirely in stable rock
1926.652(a)(1)
2 ft back from the edge
Spoil and materials kept at least this far away, or held back by retaining devices, so they cannot fall or roll in
1926.651(j)(2)
Over 20 ft deep
Protective system designed by a registered professional engineer
1926.652(b) and (c)
Checked against eCFR on Oct 12, 2026.
Talking point 03
Confined space terms with construction meanings
Confined space
Large enough to enter and work in, with limited ways in or out, and not designed for continuous occupancy (29 CFR 1926.1202). Manholes, vaults, tanks, crawl spaces and pits all fit.
Permit-required confined space
A confined space with one or more of these: a hazardous atmosphere or the potential for one, material that can engulf an entrant, a shape that can trap or asphyxiate, or any other serious hazard.
Entry
Any part of the body passing through the opening. Leaning in to read a gauge counts.
Controlling contractor
The employer with overall responsibility for the site. Under 29 CFR 1926.1203(h) it passes what it knows about a space to each entry employer and coordinates entries when more than one employer works in or around the space.
Entry employer
Any employer whose own workers enter the space. It runs the permit program for its crew.
Talking point 04
Test yourself on trenches and tanks
Most of these cards put you at the edge of a trench that is already open; the rest go down a vault, into a tank or past a leaking drum.
Card 1 of 15 · 0 right
Card 1
Before a permit-space entry into a 12-ft-deep vertical vault, which rescue arrangement BEST meets OSHA's construction confined space standard?
Pick an answer. A short note for each option, A to D, appears here.
AAn outside rescue service must be evaluated in advance for response time and ability to handle the space's hazards.
BThe attendant never enters to rescue; untrained would-be rescuers entering a permit space often become victims themselves.
CCorrect: Non-entry retrieval is the default, and a vertical space more than 5 feet deep calls for a harness, retrieval line and mechanical retrieval device.
DA line held by hand without a mechanical device is not adequate to lift an unconscious entrant from a deep vertical vault.
Card 2
Workers are laying pipe in an 8-foot-deep trench with vertical walls and no protective system. The project manager insists the tie-in must be finished today. What should the supervisor do FIRST?
Pick an answer. A short note for each option, A to D, appears here.
AWritten approval to continue does not change how the soil behaves, and the workers stay exposed to a cave-in.
BA spotter cannot prevent or outrun a trench collapse, so it does not replace a protective system.
CCorrect: Trenches 5 feet or deeper need a protective system unless in stable rock, so the exposure ends first by getting workers out until protection is installed.
DA ladder within 25 feet is a real egress rule for deeper trenches, but egress does not prevent a cave-in.
Card 3
After heavy overnight rain, water has collected in the bottom of a 7-foot-deep trench protected by a trench box. The crew wants to start work. What should the supervisor do FIRST?
Pick an answer. A short note for each option, A to D, appears here.
ARubber boots address wet feet, not the softened walls or undermined soil that rain can create around and under the box.
BCorrect: A competent person must inspect after every rainstorm or other hazard-increasing event before workers enter, and remove workers if hazards are found.
CA trench box protects only when the surrounding soil and bottom are stable, which heavy rain can change overnight.
DPumping the water is a needed step, but starting work before the competent person's reinspection skips the required evaluation.
Card 4
A crane operator spots a drum leaking an unknown liquid in the laydown yard. The operator is trained only to the HAZWOPER first responder awareness level. What should the operator do?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: Awareness-level responders recognize the release, protect themselves and others, and notify trained responders without taking further action.
BPlugging the bung puts an awareness-level worker in contact with an unidentified liquid, which is operations- or technician-level work.
CMoving the drum brings the worker into contact with an unknown chemical and can worsen the leak.
DContainment of an unknown liquid is beyond awareness-level duties, and the leak is not an incidental release area workers can safely absorb.
Card 5
Utility paint marks show a gas line crossing the planned path of a trench. As the excavator nears the marks, what should the supervisor require?
Pick an answer. A short note for each option, A to D, appears here.
ALocator marks show an approximate location only, so digging by machine up to them risks striking the line.
BCorrect: As digging approaches a marked utility, its exact location must be found by safe means such as hand digging or vacuum excavation.
CA smooth bucket with a spotter still puts the machine into the uncertainty zone around the line.
DRe-marking is needed only when marks are missing or unclear; the line still has to be exposed by safe means.
Card 6
During a permit-required confined space entry, the attendant sees an entrant collapse inside the space. What should the attendant do?
Pick an answer. A short note for each option, A to D, appears here.
AThe attendant must stay at the post until relieved, so leaving abandons the entrants and delays rescue.
BCorrect: The attendant remains outside, summons rescue services and may perform non-entry retrieval as the rescue procedures provide.
CEntering without proper equipment and training is the leading way would-be rescuers die in confined spaces.
DAn escape respirator is designed for getting out, not for entering a space with an unknown atmosphere to perform a rescue.
Card 7
A trench being dug next to an old landfill could develop a hazardous atmosphere. What emergency equipment must be readily available under 29 CFR 1926.651?
Pick an answer. A short note for each option, A to D, appears here.
AA 10-B extinguisher is a fire-protection rule for flammable-liquid storage, not the rescue equipment required near hazardous atmospheres.
BAn AED and first aid help after a worker is reached, but neither lets anyone reach a collapsed worker in a bad atmosphere.
CAn eyewash and first aid kit address chemical splashes and minor injuries, not rescue from a hazardous trench atmosphere.
DCorrect: Where hazardous atmospheres exist or can reasonably be expected, emergency rescue equipment such as breathing apparatus, harness and line, or basket stretcher must be readily available.
Card 8
While digging a trench, a crew exposes an old cast-iron water main that now spans the open trench unsupported. What should the supervisor require?
Pick an answer. A short note for each option, A to D, appears here.
AThe utility owns the main, but the employer must still protect workers from an exposed installation while the trench is open.
BHanging the main from the bucket ties up the machine and creates a suspended load directly over workers.
CCorrect: Underground installations exposed in an excavation must be protected, supported or removed as needed to safeguard employees.
DPlastic sheeting protects the utility's coating, not the workers below a heavy main that could crack and fall.
Card 9
A supervisor inspects a 6-ft trench next to a leaking fuel line by looking from the surface only. Which hazard is this approach MOST likely to miss?
Pick an answer. A short note for each option, A to D, appears here.
ASpoil placement is visible from the surface during an ordinary walk-around inspection.
BStanding water at the bottom of the trench can be seen from the surface without entering.
CCorrect: Oxygen deficiency and flammable or toxic vapors are invisible, so near a fuel leak the atmosphere must be tested before workers enter.
DLadder placement within reach of workers is easy to confirm visually from the trench edge.
Card 10
A competent person measures an unconfined compressive strength of 1.6 tsf in a cohesive soil, but the new trench runs alongside an old backfilled utility trench. How should the soil be classified?
Pick an answer. A short note for each option, A to D, appears here.
AStrength alone does not make soil Type A; previously disturbed soil is excluded from Type A regardless of its test result.
BPreviously disturbed soil defaults to Type B, and it is Type C only if it otherwise meets the Type C criteria.
CCorrect: Soil that has been previously disturbed cannot be classified Type A, so cohesive soil of this strength beside an old utility trench is Type B.
DThe 24-hour condition applies to the short-term steeper slope allowed in Type A soil, not to how the soil is classified.
Card 11
A competent person classifies the soil for a 10-foot-deep trench as Type C. The crew will slope the walls instead of using shoring or a trench box. What is the maximum allowable slope?
Pick an answer. A short note for each option, A to D, appears here.
AA 1 to 1 slope, about 45 degrees, is the maximum for Type B soil, which is stronger than Type C.
BA 0.75 to 1 slope, about 53 degrees, is the Type A slope and is far too steep for Type C soil.
CCorrect: Type C is the weakest soil class, so walls up to 20 feet deep are sloped no steeper than 1.5 to 1, about 34 degrees.
DA 0.5 to 1 slope is allowed only for short-term cuts in Type A soil 12 feet deep or less.
Card 12
Laborers have been crossing an open 8-foot-deep trench on two loose planks to reach a material pile on the far side. What does OSHA require for this crossing?
Pick an answer. A short note for each option, A to D, appears here.
ABetter planks still leave open edges over an 8-foot drop. At this height the walkway needs guardrails.
BA ladder is not a walkway. Its rungs give poor footing and no edge protection over the trench.
CA spotter can warn but cannot stop a fall. The crossing itself must be a guarded walkway.
DCorrect: People crossing an excavation need a walkway, and at 6 feet or more above the bottom it needs guardrails.
Card 13
During the morning inspection of a 7-ft-deep trench, which observation is a warning sign of a possible cave-in?
Pick an answer. A short note for each option, A to D, appears here.
AKeeping spoil at least 2 feet back from the edge is good practice, so 3 feet is a sign of compliance, not distress.
BA shield extending above grade helps protect workers from rolling material, so it is not a warning sign.
CA ladder extending 3 feet above the top is proper egress, not a sign of an impending cave-in.
DCorrect: Tension cracks parallel to the edge show the trench face is pulling away, and evidence of a possible cave-in requires removing workers until it is addressed.
Card 14
Before workers enter a permit-required confined space on a construction site, who must sign the entry permit to authorize entry?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: the entry supervisor signs the permit to authorize entry after verifying that tests, isolation and equipment are in place.
BThe competent person identifies confined and permit spaces on the site, but identifying a space is not authorizing a specific entry.
CThe rescue service must be available and able to respond, yet it does not authorize entry into the space.
DThe attendant monitors entrants from outside and summons rescue; that role has no authority to approve the permit.
Card 15
During a site walk, a supervisor sees that a haul road beside an open 8-ft trench has been narrowed by a new spoil pile, pushing trucks toward the edge. Which hazard should be addressed FIRST?
Pick an answer. A short note for each option, A to D, appears here.
ACorrect: Trucks and spoil near the edge add surcharge that can collapse the trench wall or let a vehicle fall in, so this is the immediate threat.
BDust can reduce visibility and needs control, but it does not carry the immediate cave-in risk.
CCycle times are a production issue, not a safety hazard.
DPonding should be addressed, but it is less urgent than heavy loads pushing toward the trench edge.
Talking point 05
Shallow cuts, soil calls and confined-space scope
Can a trench shallower than 5 feet still need protection?
Yes. Under 29 CFR 1926.652(a)(1), a cut under 5 feet goes without a protective system only when a competent person examines the ground and finds no sign of a possible cave-in.
Who classifies the soil, and how?
The competent person, using at least one visual and at least one manual test under Appendix A to Subpart P. Without a classification, sloping has to follow the most conservative option, the one written for Type C soil (29 CFR 1926.652(b)(1)).
Is a trench a confined space under Subpart AA?
No. 29 CFR 1926.1201(b) leaves excavation work covered by Subpart P out of the confined space subpart, and the trench rules handle their own atmosphere hazards.