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Flammable vapor limit during cabin cleaning

Aviation Mechanic General (AMG) practice question 10 of 31 on Cleaning and Corrosion Control. ACS element AM.I.G.R1 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic General (AMG) practice mode.

Question bank updated 2026-09-22

QUESTIONDuring cabin refurbishing with a flammable solvent, a vapor measurement taken 5 feet from the point of use shows 30 percent of the solvent's lower flammability limit. What does the handbook require?

  1. ANo action, because the reading is below 50 percent of the limit
  2. BContinue, but move the measuring point to 10 feet
  3. CEmergency revisions of the operations in progress
Show the answer and explanation

Correct answer: C. Emergency revisions of the operations in progress

  • A — incorrect The action threshold is 25 percent of the lower flammability limit, not 50 percent, so a 30 percent reading already requires action.
  • B — incorrect The measurement point specified is 5 feet from the location of use, and a reading above 25 percent there requires emergency changes, not relocation of the measurement.
  • C — correct An accumulation of flammable vapors above 25 percent of the lower flammability limit, measured 5 feet from the location of use, requires emergency revisions of the operations in progress; 30 percent exceeds that threshold.

BACKGROUND

Aircraft cabins are small enclosures where restricted ventilation can allow flammable vapor/air mixtures to build up quickly if flammable cleaning agents are used indiscriminately. The handbook requires cabins to have ventilation sufficient at all times to prevent accumulation of flammable vapors, with cabin doors open to take advantage of natural ventilation and approved mechanical ventilation used where natural airflow is insufficient. If flammable vapors accumulate above 25 percent of the lower flammability limit of the vapor in use, measured 5 feet from the location of use, emergency revisions of the operations in progress are required. Open flame and spark-producing equipment must also be shut down in the vapor hazard area.

STUDY TIP

Two numbers carry this rule: 25 percent of the lower flammability limit and a 5 foot measurement distance; compare any given reading against them.

KEY POINTS

  • Cabin ventilation must prevent flammable vapor accumulation at all times
  • Threshold: 25 percent of the lower flammability limit measured 5 feet from use
  • Exceeding it requires emergency revisions of the operation

SOURCES

  • FAA-H-8083-30B ch08 "Fire Prevention Precautions"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-30B Aviation Maintenance Technician Handbook – General, 14 CFR part 43 and part 65. Regulations and handbooks are revised; confirm details against the current edition.