Free Trench Safety Practice Test (OSHA Subpart P)

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Trench safety practice test: 20 random questions

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Question 1 How does OSHA define an excavation?

Any digging deeper than 5 feetAny man-made cut, cavity, trench or depression in an earth surface formed by earth removalAny trench that workers enterAny hole made with powered equipment

Question 2 Which description best matches OSHA's definition of a trench?

Any excavation deeper than 4 feetAn excavation that is wider than it is deepA narrow excavation, generally deeper than it is wide, no more than 15 feet wide at the bottomAny excavation made for underground utilities

Question 3 Forms are built inside a 30-foot-wide excavation, leaving 4 feet between the forms and the excavation wall. How should that 4-foot space be treated?

As stable rockAs a trenchAs a confined space onlyAs an area exempt from Subpart P

Question 4 Which section of Subpart P sets out when protective systems are required and how they may be designed?

1926.6501926.6511926.6521926.21

Question 5 Roughly how much can one cubic yard of soil weigh?

About 300 poundsAbout 800 poundsAbout 3,000 pounds, roughly the weight of a carAbout 10,000 pounds

Question 6 Which appendix to Subpart P explains how to classify soil?

Appendix AAppendix BAppendix CAppendix F

Question 7 Why can a partial burial, with the worker's head still above the soil, be fatal?

It cannot. Only full burial is fatalSoil pressure on the chest and abdomen can prevent breathing and cause crush injuriesSoil is always contaminated with toxic gasesPartial burials only cause minor injuries

Question 8 A trench wall slab tips into the trench after cracks open parallel to the edge. What type of failure is this?

Bottom heaveBoilingToppling caused by tension cracksSpalling from vibration

Question 9 Which of the following is an excavation hazard?

Cave-insHazardous atmospheresFalling loadsAll of the above

Question 10 At what depth does OSHA generally require a protective system against cave-ins?

3 feet or deeper4 feet or deeper5 feet or deeper, unless the excavation is entirely in stable rock20 feet or deeper

Question 11 How far from the edge must spoil and materials be kept, if no retaining device is used?

6 inches1 footAt least 2 feetAt least 10 feet

Question 12 A loaded bucket swings over the trench. What does OSHA require?

Workers in the trench must wear hard hatsNo employee may be underneath loads handled by lifting or digging equipmentWorkers may stay if they are inside a trench boxThe operator must sound the horn

Question 13 When must the atmosphere in an excavation be tested?

Only when workers report an odorOnly in excavations deeper than 20 feetBefore entry into excavations deeper than 4 feet where a hazardous atmosphere exists or could reasonably be expectedNever; atmospheric testing only applies to confined spaces

Question 14 An excavator operator cannot see the edge of the trench while backing up. What is required?

A warning system such as barricades, hand or mechanical signals, or stop logsA second operator in the cabNothing, if the operator is experiencedA trench box at that location

Question 15 Workers exposed to public vehicular traffic must wear what?

Steel-toe bootsWarning vests or other garments marked with or made of reflectorized or high-visibility materialHearing protectionA full-body harness

Question 16 You notice a crack opening in the ground parallel to the trench edge. What should you do?

Keep working and mention it at lunchFill the crack with spoilGet out of the trench and tell the competent personMove the spoil pile closer to the edge to hold the wall

Question 17 Which list puts OSHA's categories in order from most stable to least stable?

Type A, stable rock, Type B, Type CStable rock, Type A, Type B, Type CType C, Type B, Type A, stable rockType A, Type B, Type C, stable rock

Question 18 What is the minimum unconfined compressive strength for Type A soil?

0.5 tsf1.0 tsf1.5 tsf3.0 tsf

Question 19 A clay trench next to a busy highway has a UCS of 2.0 tsf. Why can't it be Type A?

Clay is never Type AThe soil is subject to vibration from heavy trafficThe strength is too high for Type AHighway trenches are always Type C

Question 20 Water is freely seeping from the trench wall. How must the soil be classified?

Type AType BType CStable rock

Question 21 How is a layered soil system classified?

By the strongest layerBy the weakest layerBy the layer at the bottom of the trenchBy averaging all the layers

Question 22 Backfill around an existing sewer line has been dug before. What is the best possible classification?

Type AType B, unless it would otherwise be Type CStable rockIt does not need to be classified

Question 23 Which is the maximum allowable slope for Type C soil in an excavation under 20 feet deep?

¾:1 (53°)1:1 (45°)1½:1 (34°)Vertical

Question 24 How many analyses does Appendix A require before a competent person classifies soil?

One visual test onlyOne manual test onlyAt least one visual and at least one manual analysisA laboratory test for every excavation

Question 25 What is the minimum number of tests Appendix A requires to classify soil?

One test of any kindAt least one visual and at least one manual analysisTwo manual testsA laboratory test plus a visual test

Question 26 In the plasticity test, what result indicates cohesive soil?

The sample crumbles when rolledAt least a 2-inch length of ⅛-inch thread can be held on one end without tearingThe sample can be formed into a 1-inch ballWater seeps out when the sample is squeezed

Question 27 A fresh clump can be indented by the thumb but penetrated only with very great effort. What does this suggest?

Type A soil, about 1.5 tsfType C soil, about 0.5 tsfGranular soilSaturated soil

Question 28 A sample can be easily penetrated several inches by the thumb and molded with light finger pressure. What does this suggest?

Stable rockType A soilType C soilCemented soil

Question 29 What does a pocket penetrometer estimate?

Moisture contentUnconfined compressive strength in tons per square footSoil temperatureThe depth of the water table

Question 30 During the drying test, a sample cracks as it dries. What does that indicate?

The soil is granularSignificant fissures are presentThe soil is Type AThe sample was too wet to test

Question 31 Why should manual tests be performed on fresh samples as soon as practical?

OSHA requires a 10-minute time limitSamples that dry out or are exposed for long periods can give misleading resultsFresh samples are lighter to carryOld samples are always Type A

Question 32 Which observation is part of a visual analysis?

Rolling the soil into a threadPressing a penetrometer into a clumpLooking for cracks, layers, water seepage, previously disturbed soil and vibration sourcesDrying a sample for 24 hours

Question 33 What is the maximum allowable slope for Type B soil in an excavation 20 feet deep or less?

½:1¾:11:1 (45°)1½:1

Question 34 A Type C trench is 8 feet deep with a 3-foot-wide bottom. What is the minimum top width if it is sloped at the maximum allowable slope?

11 feet19 feet27 feet35 feet

Question 35 Who must design sloping or benching for an excavation deeper than 20 feet?

The competent personThe equipment operatorA registered professional engineerThe utility owner

Question 36 Under what conditions does Appendix B allow a ½:1 slope?

In any soil for excavations under 5 feetIn Type A soil, for excavations 12 feet deep or less that are open 24 hours or lessIn Type B soil if no one is in the trenchIn Type C soil with a dewatering system

Question 37 In which soil type is benching never allowed?

Type ACohesive Type BType CStable rock

Question 38 A Type B slope at 1:1 begins to show cracks and sloughing. What must happen?

Nothing, as long as workers stay out of the middleAdd water to stabilize the soilCut the slope back to at least ½H:1V flatter than the maximum, such as 1½:1Steepen the slope to reduce the load

Question 39 If an employer has not classified the soil, what is the steepest slope allowed under 1926.652(b)(1)?

¾:11:11½:1 (34°)Vertical

Question 40 A trench with a shielded vertical lower portion in Type C soil is sloped above the shield. How far must the shield extend above the top of the vertical side?

It may stop at the vertical side6 inchesAt least 18 inchesAt least 4 feet

Question 41 What is the main difference between shoring and a trench shield?

Shoring supports the walls to prevent a cave-in, while a shield protects workers inside it if a cave-in happensShields are only used in Type A soilShoring is only used deeper than 20 feetThere is no difference

Question 42 Which component runs horizontally across the trench and pushes the two walls apart?

UprightWaleCross braceSheeting

Question 43 Why is aluminum hydraulic shoring often preferred for utility trenches?

It never needs tabulated dataIt can be installed and removed from outside the trench and it preloads the soilIt is allowed in excavations of any depth without an engineerIt does not need to be inspected

Question 44 Which appendix to Subpart P contains tables for timber shoring?

Appendix AAppendix BAppendix CAppendix F

Question 45 A crew wants to use a manufacturer's hydraulic shores in a way the tabulated data does not cover. What is required?

The competent person's verbal approvalThe manufacturer's specific written approvalNothing, as long as the trench is under 10 feetA second set of shores

Question 46 In what order must support systems be removed?

From the top downFrom the bottom of the excavation upward, with backfilling progressing together with removalIn any order, as long as workers are outAll at once, as quickly as possible

Question 47 How far below the bottom of a support system may a trench be excavated?

Not at allUp to 2 feet, if the system is designed for the full depth and there is no sign of soil lossUp to 4 feet in any soilAny depth if the competent person agrees

Question 48 Where must manufacturer's tabulated data be kept while the shoring is in use?

At the main officeAt the jobsiteWith the equipment rental companyIt does not need to be kept

Question 49 What does a trench shield (trench box) do?

Prevents the trench walls from movingWithstands the forces of a cave-in to protect the workers inside itRemoves water from the trenchReplaces the need for a competent person

Question 50 When are workers prohibited from being inside a shield?

During lunch breaksWhile the shield is being installed, removed or moved verticallyWhenever the trench is deeper than 10 feetOnly during rain

Question 51 Under what conditions may a trench be dug up to 2 feet below the bottom of a shield?

Any time the soil is Type AOnly if the shield is designed for the full depth of the trench and there is no sign of soil loss from behind or below itOnly if the competent person is in the trenchNever

Question 52 A shielded lower portion is combined with a sloped upper portion. How high must the shield extend above the top of the vertical side?

It does not need to extend above itAt least 6 inchesAt least 18 inchesAt least 3 feet

Question 53 Where should the ladder be placed when a crew works inside a trench box?

Inside the protected area of the box, so workers enter and exit while protectedAt the end of the box in the unprotected trenchOutside the trench onlyAnywhere within 50 feet

Question 54 A crew wants to weld a bracket onto a trench box side wall. What is required?

Nothing if the weld is smallThe manufacturer's written approval, since it deviates from the tabulated dataThe operator's approvalPaint over the weld

Question 55 Which area is not protected by a standard two-sided trench box?

The space between the side wallsThe open ends of the boxThe area under the spreadersThe inside floor of the box

Question 56 Why should the gap between a trench box and the trench wall be kept small?

To make the box easier to dragA large gap lets a collapsing wall hit the box with momentum and can allow hazardous lateral movementOSHA requires a gap of exactly 6 inchesTo keep water out of the box

Question 57 At what trench depth does OSHA require a means of egress such as a ladder?

2 feet4 feet or more5 feet or more20 feet or more

Question 58 What is the maximum lateral travel distance to the nearest means of egress in a trench 4 feet or deeper?

10 feet25 feet50 feet100 feet

Question 59 How far must ladder side rails extend above the top of the trench, if no grab rail is used?

1 footAt least 3 feet6 feetThey don't need to extend above the top

Question 60 What is the minimum distance spoil must be kept from the edge of an excavation if no retaining device is used?

1 foot2 feet4 feet10 feet

Question 61 Who must design a structural ramp used only by employees for access to an excavation?

The equipment operatorA competent personThe utility locatorAny crew member

Question 62 When do walkways over excavations require guardrails?

AlwaysWhen the walkway is 6 feet or more above lower levelsOnly at nightOnly when the public uses them

Question 63 Why does a large spoil pile right next to a trench increase cave-in risk even if it doesn't roll in?

It blocks the operator's viewIt adds surcharge load that pushes on the soil supporting the trench wallIt keeps the soil too dryIt doesn't increase risk

Question 64 A crew needs to dig below the footing of an adjacent building. Which condition would allow it under 1926.651(i)?

The building is unoccupiedThe trench is less than 10 feet deepA support system such as underpinning is provided, or a registered professional engineer approves the workThe crew works quickly

Question 65 When must the estimated location of underground utilities be determined?

After the trench is openedBefore opening the excavationOnly if the trench is deeper than 5 feetOnly on public property

Question 66 What color marks indicate a gas line?

RedBlueYellowGreen

Question 67 What do red marks indicate?

Electric power lines, cables, conduit and lighting cablesProposed excavationPotable waterSewer lines

Question 68 What should you use to expose a line inside the tolerance zone?

An excavator with a smooth bucketA trencher on its lowest settingHand tools or vacuum excavationA rock breaker

Question 69 Which lines are commonly NOT marked by the 811 process?

Main gas distribution linesPublic water mainsPrivate lines such as sewer laterals, site lighting and irrigationTelecommunication trunk lines

Question 70 If a utility owner cannot respond within 24 hours, what does OSHA allow?

Digging with no precautionsProceeding with caution, using detection equipment or other acceptable means to locate the utilityWaiting indefinitelyAsking the crew to guess the location

Question 71 Your bucket scrapes the coating on a steel gas line but nothing leaks. What should you do?

Backfill and keep workingWrap it with duct tapeStop work and report the damage to the facility owner as required by state lawIgnore it if there is no odor

Question 72 What does OSHA require for underground installations exposed while the excavation is open?

NothingThey must be protected, supported or removed as necessary to safeguard employeesThey must be painted whiteThey must be cut and capped

Question 73 Before entering an excavation of what depth must the air be tested where a hazardous atmosphere could reasonably be expected?

Any depthMore than 2 feetGreater than 4 feetGreater than 20 feet

Question 74 Below what oxygen level does OSHA consider an atmosphere oxygen-deficient?

23.5%21%19.5%16%

Question 75 What flammable gas limit does 1926.651(g) set for excavations?

5% of the lower flammable limit10% of the lower flammable limit20% of the lower flammable limit100% of the lower flammable limit

Question 76 A gas-powered trash pump runs at the edge of a deep, narrow trench. Which gas is the main concern?

Oxygen enrichmentCarbon monoxideNitrogenHelium

Question 77 Where hazardous atmospheres may develop, what must be true of emergency rescue equipment?

It must be stored at the main officeIt must be readily available and attended when in useIt is only required in trenches over 20 feetIt must be locked up

Question 78 Who must monitor water removal equipment used to control water in an excavation?

The pump rental companyA competent personThe utility locatorAny laborer

Question 79 Water is freely seeping from a trench wall that was classified as Type B. What happens to the classification?

It stays Type BIt becomes Type AIt becomes Type CIt becomes stable rock

Question 80 When must a competent person inspect an excavation in relation to rain?

Only after a flood warningAfter every rainstorm or other hazard-increasing occurrenceOnce a week during the rainy seasonRain does not require an inspection

Question 81 What two things make someone a competent person under OSHA's definition?

The ability to identify existing and predictable hazards and the authority to take prompt corrective measuresA college degree and 10 years of experienceA state license and a trench boxBeing the oldest worker on site and having a cell phone

Question 82 When must the competent person inspect an excavation?

Once a weekOnly after an incidentBefore work starts, as needed throughout the shift, and after every rainstorm or hazard-increasing occurrenceOnly when OSHA visits

Question 83 What must the competent person do on finding evidence of a possible cave-in?

Note it for tomorrow's inspectionRemove exposed employees from the hazardous area until precautions are takenLet workers decide whether to stayCall the utility company

Question 84 Who decides whether a trench less than 5 feet deep needs a protective system?

The equipment operatorThe competent person, based on whether there is any indication of a potential cave-inNobody; trenches under 5 feet never need protectionThe building inspector

Question 85 Who designates the competent person on a jobsite?

OSHAThe training providerThe employerThe local building department

Question 86 Which of these is a warning sign of a potential cave-in?

Dry, firm spoil far from the edgeTension cracks in the ground surface parallel to the trenchA ladder placed every 25 feetA properly installed trench box

Question 87 Which task does Subpart P assign to the competent person?

Approving tabulated data for trench boxesMonitoring water removal equipment and operationsDesigning sloping for excavations over 20 feetIssuing 811 locate tickets

Question 88 Daily inspections under 1926.651(k) are required when:

The trench is deeper than 20 feetEmployee exposure can be reasonably anticipatedThe weather forecast calls for rainA new worker joins the crew

Question 89 A co-worker is partially buried in an unprotected trench. What should you do first?

Jump in and start digging with your handsUse the excavator bucket to remove the soil quicklyCall 911, report a trench collapse, and keep others out of the unprotected trenchPull the worker out by the arms

Question 90 Why are untrained rescuers at high risk after a cave-in?

The disturbed walls are likely to collapse again, burying the rescuersSoil becomes harder after a collapseRescuers are never at risk if they move fastOSHA prohibits rescue

Question 91 Why should you stop excavators and other equipment near a collapsed trench?

To save fuelVibration and weight near the edge can trigger a secondary collapseSo the operator can help digOSHA requires equipment to be removed from the site

Question 92 How do professional trench rescue teams typically recover a buried worker?

By pulling with a rope from the surfaceBy using an excavatorBy shoring the trench first, then digging carefully by handBy flooding the trench to loosen the soil

Question 93 Within what time must an employer report a work-related fatality to OSHA?

24 hours8 hours7 days30 days

Question 94 Within what time must an employer report an in-patient hospitalization, amputation or loss of an eye?

8 hours24 hours72 hoursAt the end of the year

Question 95 Where hazardous atmospheres could develop in an excavation, which equipment must be readily available?

A second excavatorEmergency rescue equipment such as breathing apparatus, a harness and line, or a basket stretcherA fire hydrantA spare trench box

Question 96 A trench wall sloughs off while nobody is inside. What is the right response?

Nothing happened, so keep workingTreat it as a near miss: stop, find out why, and correct the protective system before re-entryHave the crew dig fasterRemove the ladder

Last reviewed: October 25, 2026 · Free general education based on OSHA 29 CFR 1926 Subpart P. It does not replace the site-specific training and competent person your employer must provide, and it does not issue a certificate. Nothing you enter on this page is saved or sent.

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