Confined Space and Trench Rescue Practice Questions

25 multiple-choice questions on Confined space and trench rescue for paramedic and EMT students, from Chapter 49 (Vehicle Extrication and Special Rescue). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. Under OSHA, a confined space is large enough to enter, has limited ways in or out, and:

   1. A. Is located below the level of the ground
   2. B. Has no natural or mechanical ventilation
   3. C. Is not designed for continuous occupancy
   4. D. Holds a known toxic or flammable gas
   Show answer

   Answer: C. Is not designed for continuous occupancy

   OSHA's definition has three parts: big enough to enter and work in, limited entry and exit, and not meant for continuous occupancy. Tanks, vaults, silos, and pipes fit, whether above or below ground; a toxic atmosphere makes it a permit-required space but is not part of the basic definition.

2. A confined space becomes a permit-required confined space when it:

   1. A. Is more than 1.5 m (5 ft) below the ground
   2. B. Has a serious hazard such as a toxic atmosphere
   3. C. Is entered more than once during each shift
   4. D. Has a single fixed ladder as its way in and out
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   Answer: B. Has a serious hazard such as a toxic atmosphere

   A permit-required space has, or may have, a hazardous atmosphere, an engulfment hazard, walls that narrow to trap an entrant, or another serious hazard. Depth and how often it is entered do not decide permit status.

3. A confined space atmosphere is considered oxygen deficient when the oxygen level is below:

   1. A. 19.5%
   2. B. 21.0%
   3. C. 16.0%
   4. D. 12.0%
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   Answer: A. 19.5%

   OSHA defines oxygen deficiency as less than 19.5%; normal air is about 20.9%. Symptoms such as impaired judgment appear around 16%, but by then an entrant is already in danger, so the safe limit is set higher.

4. A meter in a process tank shows 25% oxygen. This is dangerous mainly because it:

   1. A. Quickly causes oxygen toxicity
   2. B. Pushes carbon monoxide to the floor
   3. C. Shows toxic gases have been diluted
   4. D. Greatly raises the risk of fire
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   Answer: D. Greatly raises the risk of fire

   Above 23.5% oxygen, the atmosphere is oxygen enriched and materials, including clothing, ignite easily and burn fast. Oxygen toxicity takes much higher concentrations or longer exposure than an entrant would have.

5. You are with a rescue team at a 9-m (30-ft) deep vertical tank where a worker is down. Before entry, the atmosphere should be tested:

   1. A. At the entry opening alone
   2. B. At mid-depth inside the space
   3. C. At the top, middle, and bottom
   4. D. After the first rescuer enters
   Show answer

   Answer: C. At the top, middle, and bottom

   Gases layer by weight: methane rises, while hydrogen sulfide and many vapors sink, so a single reading can miss a deadly layer. Testing at several levels before anyone enters finds them.

6. When testing a confined space with a multigas meter, the usual order is:

   1. A. Toxic gases, then oxygen, then flammable gases
   2. B. Flammable gases, then toxic gases, then oxygen
   3. C. Oxygen, then flammable gases, then toxic gases
   4. D. Toxic gases, then flammable gases, then oxygen
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   Answer: C. Oxygen, then flammable gases, then toxic gases

   Oxygen is tested first because many flammable gas sensors need oxygen to read accurately, then flammability, which can kill quickly by explosion, then specific toxic gases. Testing toxics first can give a false sense of safety in an explosive space.

7. A sewer meter reads 15% of the lower explosive limit (LEL). By common standards, the space:

   1. A. Is too hazardous to enter without control
   2. B. Is safe, since 15% is far below 100%
   3. C. Has too little oxygen to permit entry
   4. D. Can be entered safely with a filter mask alone
   Show answer

   Answer: A. Is too hazardous to enter without control

   OSHA treats flammable gas above 10% of the LEL as a hazardous atmosphere, which builds in a margin before an explosive mix is reached. Thinking 15% is safe because it is well below 100% LEL is the common error.

8. Workers are running a gasoline-powered pump inside a below-grade vault. The gas most likely to build up is:

   1. A. Hydrogen sulfide
   2. B. Carbon monoxide
   3. C. Methane
   4. D. Chlorine
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   Answer: B. Carbon monoxide

   Engine exhaust in an enclosed space quickly raises carbon monoxide, which is colorless and odorless. Hydrogen sulfide and methane come from decaying organic matter in sewers and pits rather than from engines.

9. Why is an air-purifying respirator (APR) unsafe for entry into an oxygen-deficient space?

   1. A. It is too heavy to wear while climbing
   2. B. It cannot fit under a rescue helmet
   3. C. It blocks the voice radio system
   4. D. It filters air but supplies no oxygen
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   Answer: D. It filters air but supplies no oxygen

   An APR removes certain contaminants from the air around the wearer but cannot add oxygen, so it is useless at low oxygen levels. Entry into such spaces requires SCBA or supplied-air respirators.

10. NIOSH reviews of confined space deaths found that about 60% of those who died were:

    1. A. Workers with heart disease
    2. B. Workers younger than 20
    3. C. Would-be rescuers
    4. D. Supervisors on inspection
    Show answer

    Answer: C. Would-be rescuers

    Coworkers and untrained rescuers often enter to help a collapsed worker and are overcome by the same atmosphere. This is why entry is limited to trained, equipped rescue teams.

11. In a permit-required confined space entry, the attendant is the person who:

    1. A. Enters first to test the atmosphere inside it
    2. B. Stays outside to monitor and call for rescue
    3. C. Signs the permit to authorize the entry
    4. D. Goes in to help if an entrant collapses
    Show answer

    Answer: B. Stays outside to monitor and call for rescue

    The attendant stays outside, tracks the entrants, watches for hazards, and summons rescue; OSHA forbids the attendant to enter, so the attendant does not go in to test the air or to help a collapsed entrant. Atmospheric testing is done from outside before entry. Authorizing the entry is a separate role, not the attendant's.

12. In a permit-required confined space program, the person who authorizes entry and can end it is the:

    1. A. Entry supervisor
    2. B. Attendant
    3. C. Authorized entrant
    4. D. Retrieval operator
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    Answer: A. Entry supervisor

    The entry supervisor checks that the permit conditions are met, signs the permit, and can cancel the entry if conditions change. The attendant monitors from outside but does not authorize entry.

13. A worker has collapsed at the bottom of a 6-m (20-ft) vertical tank. He is wearing a harness attached to a line. Non-entry rescue is most often done with:

    1. A. A ladder and a two-person carry
    2. B. A rescuer entering on SCBA
    3. C. A rope lowered for him to climb
    4. D. A tripod and a retrieval winch
    Show answer

    Answer: D. A tripod and a retrieval winch

    Non-entry rescue pulls the entrant out with a harness, retrieval line, and mechanical winch, often on a tripod over the opening, so no rescuer enters. Sending a rescuer in on SCBA or carrying him up a ladder is entry rescue, not non-entry rescue, and a collapsed worker cannot climb a rope.

14. Before rescuers enter a tank fitted with mixer blades and feed pipes, the energy sources should be controlled by:

    1. A. Lockout/tagout of all power and lines
    2. B. A worker who keeps watch at the controls
    3. C. Switching the mixer off at its control panel
    4. D. A tag on the switch without a lock
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    Answer: A. Lockout/tagout of all power and lines

    Lockout/tagout physically locks switches and valves in the safe position, so machinery cannot start and materials cannot flow in while people are inside. A worker watching the controls can be distracted or misunderstand. Switching a machine off at the panel or tagging a switch without a lock leaves it free to be restarted, and feed lines must be blanked or blocked as well.

15. Rescuers plan to ventilate a confined space before entry. The best practice is to:

    1. A. Ventilate it once, then stop monitoring
    2. B. Blow fresh air in and keep monitoring
    3. C. Blow pure oxygen in to clear it out
    4. D. Rely on ventilation instead of SCBA
    Show answer

    Answer: B. Blow fresh air in and keep monitoring

    Forced fresh air lowers contaminants, but levels can change, so monitoring continues throughout the entry. Pure oxygen creates an oxygen-enriched fire hazard.

16. One cubic yard of soil, a common amount in a trench collapse, weighs about:

    1. A. 140 kg (300 lb)
    2. B. 360 kg (800 lb)
    3. C. 4,500 kg (10,000 lb)
    4. D. 1,400 kg (3,000 lb)
    Show answer

    Answer: D. 1,400 kg (3,000 lb)

    A cubic yard of soil weighs roughly 1,400 kg (3,000 lb), about the weight of a small car. Even partial burial puts enough pressure on the chest to stop breathing, which is why victims cannot simply be pulled out.

17. OSHA requires a protective system such as shoring or a trench box once a trench reaches a depth of:

    1. A. 0.6 m (2 ft)
    2. B. 3.0 m (10 ft)
    3. C. 1.5 m (5 ft)
    4. D. 6.0 m (20 ft)
    Show answer

    Answer: C. 1.5 m (5 ft)

    Trenches 1.5 m (5 ft) deep or more must have sloping, shoring, or shielding unless they are cut entirely in stable rock. A trench less than 5 ft deep needs a protective system only if a competent person sees signs of a possible cave-in, so 2 ft is not the rule, although shallow trenches can still collapse. At 10 ft the rule already applies, and 20 ft is the depth beyond which the protective system must be designed by a registered professional engineer.

18. OSHA requires that the spoil pile from an excavation be kept back from the trench edge at least:

    1. A. 0.6 m (2 ft)
    2. B. 0.15 m (6 in)
    3. C. 3.0 m (10 ft)
    4. D. 6.0 m (20 ft)
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    Answer: A. 0.6 m (2 ft)

    Keeping spoil at least 0.6 m (2 ft) from the edge reduces the extra weight on the trench lip and keeps dirt from rolling back in. Spoil piled at the edge is a common cause of wall collapse.

19. In a trench 1.2 m (4 ft) deep or deeper, OSHA requires a ladder or other way out within a lateral travel distance of:

    1. A. 1.5 m (5 ft)
    2. B. 15 m (50 ft)
    3. C. 7.6 m (25 ft)
    4. D. 30 m (100 ft)
    Show answer

    Answer: C. 7.6 m (25 ft)

    Workers in a trench 4 ft or deeper must be no more than 25 ft from a ladder, ramp, or other exit. A ladder too far away can trap workers when a wall starts to fail.

20. You arrive at a collapsed trench where a worker is partly buried. To walk up to the trench, rescuers should approach from:

    1. A. The sides, where the lip is wider
    2. B. The spoil pile, for better footing
    3. C. Any side, as long as they go slowly
    4. D. The ends, not along the sides
    Show answer

    Answer: D. The ends, not along the sides

    The weight of a rescuer on the lip along the sides can start a secondary collapse, so approach is made from the ends, where the walls are less likely to fail. The spoil pile is loose and adds weight to the edge.

21. You arrive at a trench collapse with one worker buried. The ambulance and other heavy apparatus should be parked:

    1. A. Near the lip so that the patient carry is shorter
    2. B. Well away, to limit vibration on the walls
    3. C. Next to the spoil pile to shield the crew
    4. D. Wherever an engine can idle nearest to it
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    Answer: B. Well away, to limit vibration on the walls

    Vehicle weight and engine vibration can shake loose the walls, so apparatus is parked away and nearby heavy equipment is shut down. Saving a few steps on the carry is not worth a second collapse.

22. A worker is buried to the chest in a collapsed trench. He is conscious but breathing fast and shallow. The main threat from the soil around him is:

    1. A. Rapid heat loss into the cold, damp soil around him
    2. B. Pressure on the chest that limits breathing
    3. C. Infection from soil entering his wounds
    4. D. Toxic gas being released from the soil
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    Answer: B. Pressure on the chest that limits breathing

    The weight of soil around the chest prevents it from expanding, causing respiratory failure even without other injuries. Hypothermia and infection are later concerns, not the immediate threat.

23. Rescuers digging out a buried worker use hand tools and their hands near his body, rather than an excavator, mainly to:

    1. A. Remove soil faster than a machine could
    2. B. Meet OSHA rules that ban machines in trenches
    3. C. Allow the site to be preserved for the police inquiry
    4. D. Avoid injuring the patient hidden in the soil
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    Answer: D. Avoid injuring the patient hidden in the soil

    Heavy machinery cannot see a buried victim and can crush or cut him. Once rescuers are close to the patient, soil is removed by hand or with small tools. Hand digging is slower than a machine, not faster, and the reason is patient safety rather than a ban on machines.

24. A trench 2.4 m (8 ft) deep has partly collapsed on a worker. The walls are not shored, and his coworkers are digging him out from inside. You should:

    1. A. Stay out and urge the crew to leave the trench
    2. B. Climb in to help dig him out and assess his airway
    3. C. Lower a backboard and climb in after it
    4. D. Enter if a coworker watches the walls
    Show answer

    Answer: A. Stay out and urge the crew to leave the trench

    Unshored trench walls can collapse again without warning, burying the rescuers as well; no one enters until shoring is in place. A coworker watching the walls cannot give enough warning to escape.

25. Rescue crews make a collapsed trench safe for entry mainly by:

    1. A. Spraying water to firm up the walls
    2. B. Digging the walls straight down
    3. C. Installing shoring or a trench box
    4. D. Moving the spoil pile next to the lip
    Show answer

    Answer: C. Installing shoring or a trench box

    Shoring or a trench box holds the walls in place so rescuers can work at the bottom. Water weakens soil, vertical walls are the least stable shape, and spoil at the lip adds weight.