OSHA Confined Spaces Quiz — 29 CFR 1926.1200-1213 Practice Questions (Subpart AA) — Page 4 of 4
Free OSHA 30-Hour Construction confined spaces practice test with 40 realistic scenarios. Permit-required spaces, atmospheric testing, ventilation, attendant duties, rescue, and entry permits with 29 CFR 1926 Subpart AA references. (Page 4 of 4)
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Q31/ 40
A worker wearing a half-face air-purifying respirator enters a manhole where organic solvents have been used for waterproofing application. After 30 minutes, the worker notices the respirator cartridges are becoming harder to breathe through. What should the worker do?
✅ Correct Answer: B
1926.1204(h)(2): 'Where air-purifying respirators are used, the entry permit shall include the means for determining that the cartridge or canister has not exceeded its service life.' 1910.134(d)(3)(iii)(B)(2): The employer must implement a cartridge change schedule based on objective data. Increased breathing resistance is a warning sign of cartridge loading — it indicates either particulate clogging or organic vapor saturation. Importantly, for many organic solvents, the worker CANNOT smell breakthrough until well after the exposure limit is exceeded (olfactory thresholds for many solvents are ABOVE the PEL). 1926.1209(e): Any condition that may compromise respiratory protection is a prohibited condition requiring immediate evacuation. Cartridge change must occur OUTSIDE the confined space.
Q32/ 40
The entry permit for a confined space lists the time of entry as 07:00 and the authorized duration as 4 hours (until 11:00). At 11:15, the work is 90% complete and atmospheric monitoring shows all parameters within limits. The entrants want to finish. What must happen?
✅ Correct Answer: B
1926.1203(h)(1): 'The entry supervisor shall terminate entry and cancel the permit when operations are completed or a condition that is not allowed under the permit arises.' 1926.1203(h)(2): 'The employer shall retain each canceled permit for at least 1 year.' 1926.1203(g) requires the entry supervisor to sign and authorize the permit for a specified duration. When the authorized duration expires, the permit is no longer valid — continuing entry is a violation regardless of atmospheric readings. The entry supervisor must re-evaluate the space, re-test, re-verify all conditions and procedures, and re-authorize with a new or updated permit. This rule prevents the normalization of deviance where 'just a few more minutes' becomes routine and hazards are overlooked.
Q33/ 40
During excavation, a backhoe bucket strikes an unmarked underground storage tank containing residual heating oil. The tank is breached, creating a 2-foot opening. The operator immediately backs away. A laborer approaches the opening to look inside. Is the tank now a confined space requiring permit entry?
✅ Correct Answer: B
1926.1202 defines a confined space by physical and atmospheric criteria, not by how it was created or discovered. The tank is: (1) large enough to enter (breached opening provides access), (2) limited means of egress (single breach point), (3) not designed for continuous occupancy. Heating oil residue contains benzene, naphthalene, and other VOCs — all heavier than air, accumulating at the tank bottom. Additionally, the steel tank interior is rusted (oxygen consumed by oxidation = O2 deficiency). 1926.1203(a): 'Before entry, the space must be evaluated.' The tank is a permit-required confined space until testing proves otherwise. The breach does not make it 'not a confined space' — it creates a new entry point into an existing confined space.
Q34/ 40
A contractor is working in a 6-foot-deep trench in an area known to have methane from a nearby former landfill. The competent person tests the atmosphere with a 4-gas meter every morning. The readings are always 0%. On Friday, they decide to skip testing 'since it's always zero.' At 11 AM, a worker using a propane-powered saw collapses at the trench bottom. What is the most likely cause?
✅ Correct Answer: B
This is a classic confined space scenario: a trench functions as a confined space because gases heavier than air (CO from the saw exhaust, density ~0.97 of air) can accumulate in low areas. 1926.1204(b) requires initial testing and 1926.1204(f) requires CONTINUOUS monitoring when conditions can change — using an internal combustion engine INSIDE the trench creates a changing atmospheric hazard. The daily methane check was irrelevant to the actual hazard (CO from the saw). This is factually based on the pattern of many fatal trench incidents: workers test for one hazard but introduce another. 1926.1204(c)(2) requires testing for 'atmospheric conditions that exist or may develop' — exhaust gases from a running engine inside the trench 'may develop' and must be tested for.
Q35/ 40
A horizontal lifeline is rigged inside a storage tank. The entrant will use a 6-foot shock-absorbing lanyard attached to a back D-ring, connected to the horizontal lifeline. The anchor points are at the tank's overhead manway flange, rated for 5,000 lbs each. The lifeline is installed with approximately 18 inches of sag (deflection). The entrant weighs 220 lbs plus 30 lbs of tools. In a fall, what is the critical factor that must be calculated?
✅ Correct Answer: B
1926.502(d)(15): 'Anchorages used for attachment of personal fall arrest equipment shall be independent of any anchorage being used to support or suspend platforms and capable of supporting at least 5,000 pounds per employee attached.' For a horizontal lifeline, the anchor force during a fall is: F_anchor = F_fall ÷ (2 × sin θ), where θ is the sag angle. With only 18 inches of sag in a typical tank span, the sin θ is very small (~0.1-0.15), meaning the anchor force multiplier is 3-10×. A 220+30=250 lb worker generating ~2,500-3,600 lbs of fall arrest force (MAF) could produce anchor loads of 7,500-36,000 lbs — far exceeding the 5,000-lb anchor rating. 1926.502(d)(8) requires that horizontal lifelines be designed, installed, and used under the supervision of a qualified person, as part of a complete personal fall arrest system which maintains a safety factor of at least two.
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Q36/ 40
A non-entry rescue is planned for a 15-foot-deep valve pit using a tripod and mechanical winch. The entrant wears a full-body harness with a dorsal D-ring. The rescue line is attached to the dorsal D-ring. During a drill, the rescuer operates the winch to lift an unconscious mock entrant. The winch lifts the entrant's upper body, but the legs drag and catch on the ladder rungs inside the pit. What is missing from the rescue plan?
✅ Correct Answer: A
1926.1211(e): 'The employer shall ensure that rescue systems are used in accordance with manufacturer's specifications.' 1926.1211(b): 'The employer shall ensure that the means for rescuing entrants are provided.' A single-point dorsal D-ring attachment for vertical retrieval produces a 'jackknife' position — the upper body lifts but the legs dangle and catch on obstructions (ladder rungs, pipe flanges, valve stems). A Y-lanyard connecting both the dorsal D-ring and a chest/waist attachment point (or a spreader bar between two shoulder D-rings) distributes the lifting force and raises the entrant in a more vertical orientation. This equipment must be specified in the rescue plan and available on site. The drill revealed a real deficiency — which is exactly why drills are required.
Q37/ 40
A confined space entry is planned inside a degreaser tank. The MSDS for the degreaser solvent lists: TLV-TWA = 50 ppm, vapor density = 4.8 (heavier than air), flash point = 105°F, LEL = 1.2%, UEL = 7.5%. The tank will be emptied and purged with steam for 2 hours. After purging, the tank interior temperature measures 110°F. The LEL meter reads 0%. The competent person approves entry based on these readings. Is a hot work permit required?
✅ Correct Answer: B
1926.352(b): 'Drums, containers, or hollow structures which have contained toxic or flammable substances shall be thoroughly cleaned, ventilated, and tested before welding, cutting, or heating is undertaken.' 1926.1203(d)(5)(iii): When hot work is performed, the employer shall verify that conditions in the permit space are safe for entry throughout the hot work operation. The flash point (105°F) is the temperature at which the liquid gives off sufficient vapor to form an ignitable mixture near the surface. The tank interior is at 110°F — ABOVE the flash point — meaning any residual liquid or soaked scale is actively generating flammable vapor. LEL meters are calibrated for specific gases at specific temperatures; high temperatures can affect sensor accuracy. 1926.1206(c) requires that all sources of ignition be controlled. Hot work in a tank that held flammable liquid requires specific pre-entry procedures.
Q38/ 40
A worker enters a manhole where a gasoline-powered pump had been running 30 minutes earlier. The pump has been shut off and removed. The 4-gas meter reads: O2 = 20.9%, LEL = 4%, CO = 25 ppm, H2S = 0 ppm. The competent person notes that the LEL is below the 10% alarm threshold and approves entry. Is this correct?
✅ Correct Answer: B
1926.1203(e)(2)(vi) requires the permit to specify acceptable entry conditions. OSHA's permit-required confined space standard (and industry practice based on 1910.146) considers any detectable flammable gas above 0% LEL to require investigation and explanation — 4% LEL means there IS flammable vapor present, and the source must be identified. If the concentration is rising, 10% LEL could be reached and exceeded. Additionally, 4% LEL from a gasoline-powered pump means gasoline vapors or CO from incomplete combustion is present. 1926.1204(c)(2) requires testing for all conditions that exist or may develop. A reading of 4% LEL is not the same as 'the space is safe' — it's a warning that the space is not clean and the source of flammable vapor must be identified, ventilated, and re-tested to 0% before entry.
Q39/ 40
The employer's written confined space program lists the competent person by name (John Smith) and describes his qualifications. John Smith leaves the company mid-project. For two weeks, entries continue without a designated competent person listed in the program while HR hires a replacement. Is this compliant?
✅ Correct Answer: B
1926.1203(a): 'Before any employee enters a confined space, the employer shall designate a competent person to evaluate the confined space and identify all existing and potential hazards.' 1926.1203(b): 'The employer shall develop and implement a written confined space program that is made available to each employee who may enter a confined space.' The program must identify the competent person who will evaluate the spaces. For two weeks, entries occurred without a designated competent person — meaning the hazard evaluation required by 1926.1203(a) was not performed by a qualified individual. The written program must be maintained current — this includes updating the identity of the competent person. A gap of even one day is a violation.
Q40/ 40
A contractor is doing spot-repair welding inside a 3,000-gallon stainless steel water tank at a hospital. The tank is continuously ventilated with an electric blower. The welder uses an argon-CO2 shielding gas mix. After 45 minutes of welding, the atmospheric monitor shows O2 dropping from 20.9% to 20.1%, trending downward. The welder wants to finish the seam (about 10 more minutes of work). What should the entry supervisor do?
✅ Correct Answer: B
1926.1204(f): 'The atmosphere shall be continuously monitored...' 1926.1209(e): 'If the attendant detects a prohibited condition, the attendant shall order the entrants to evacuate immediately.' The key insight is the TREND, not just the absolute reading. Argon is heavier than air (density 1.38) — it accumulates at the bottom of the tank, gradually displacing oxygen upward. An O2 drop from 20.9% to 20.1% in 45 minutes means a loss rate of ~0.018% per minute. In 10 more minutes, that would reach ~19.9% — still hypothetically above 19.5%. BUT: (1) the rate may accelerate as argon accumulation continues, (2) the O2 sensor may be at a different elevation than the welder's breathing zone, (3) the 19.5% threshold is for entry authorization, not an 'evacuate at 19.5%' — any developing hazardous atmosphere trend is a prohibited condition. 1926.1203(h)(1) requires permit cancellation when a prohibited condition arises. Welding can be resumed after re-evaluation and implementation of additional ventilation or supplied-air respiratory protection.