If it is necessary to enter an aircraft's fuel tank, which procedure should be avoided?

Question

BlackTom AI · Accepted Answer

Conducting defueling and tank purging inside an air‑conditioned building should be avoided because the HVAC system can trap and recirculate flammable fuel vapors, creating an explosive atmosphere and increasing ignition risk.

1. Relevant knowledge points and concepts
- Confined-space entry and tank entry hazards: fuel vapors are flammable and can reach explosive concentrations; oxygen levels and toxic vapors must be monitored. 
- Ventilation principles: effective purging requires positive displacement of vapors to a safe location (usually outdoors) and continuous removal of vapors during work. 
- Electrical/spark sources: air‑conditioning and building electrical equipment are typically not explosion‑proof and can ignite flammable mixtures.
- Rescue/readiness: an external attendant and rescue plan are required for safe entry.

2. Step‑by‑step reasoning
- If defueling/purging is done inside an AC building, vapors displaced from the tank can accumulate in the enclosed space.
- The AC system may recirculate air rather than exhaust it, so vapors are not reliably removed.
- Recirculation plus non‑explosion‑proof fans or motors creates ignition sources.
- Therefore, performing these operations indoors increases fire/explosion risk compared with outdoor controlled ventilation or dedicated exhaust systems.

3. Intermediate safety steps (operational checks)
- Verify atmosphere with gas detectors (LEL, O2, toxic gases) before and continuously during entry.
- Supply continuous purge (preferably inert gas or forced ventilation) and exhaust outdoors.
- Ensure electrical equipment is rated for hazardous atmospheres.
- Have an attendant outside and rescue equipment ready.

4. Why the correct answer is correct
- “Conduct the defueling and tank purging operation in an air conditioned building.” is the unsafe procedure to be avoided because it promotes vapor accumulation and introduces non‑intrinsically‑safe electrical equipment and recirculated air, both increasing ignition/explosion risk.

5. Why the other options are incorrect (i.e., are safe practices)
- “Station an assistant outside the fuel tank access to perform rescue operations” is proper confined‑space practice and should be done.
- “Continue purging the tank during the entire work period” is correct because continuous purging prevents re‑accumulation of flammable vapors.

6. Conclusion
- The unsafe procedure to avoid is conducting defueling and tank purging in an air‑conditioned building, which matches the provided correct answer.

If it is necessary to enter an aircraft's fuel tank, which procedure should be avoided?单项选择题

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