Hazards of Airplane Fuel Tank Entry
To ensure effective maintenance within the Fuel Tank Systems there is a need to develop procedures associated with Fuel Tank Entry, Personnel Protection, Working within the Fuel Tank Environment, and Fuel Tank Closure.
The separate elements to consider include fully understanding the potential hazards - Fire and explosion, toxic chemicals, as well as oxygen deficiency.
Procedures for entry within the tank, ensuring the safety of the environment for the maintenance worker.
Preparations include electrically grounding the aircraft, refueling in accordance with maintenance manual procedures, and deactivating all associated systems to ensure personnel safety.
Even though the tank has been fully purged, the use of chemicals (as part of the maintenance process) within the tanks may also provide a threat that needs to be mitigated.
Adequate ventilation is required throughout the maintenance process; it is also necessary to have a monitor “buddy” present to provide an additional safeguard.
Tank ventilation is normally achieved with the use of a blower forcing air into the tank and, at the same time, providing a separate “exit” vent point, typically venting to the atmosphere outside of the hangar. Maintaining a positive flow of fresh air will ensure that safety levels are maintained and the risk is kept at a minimum level.
We have to develop and test an Emergency Response Plan in respect of any perceived exposures.
Fuel vapour within the Fuel Tank poses a threat with the possibility of flammability; there are two terms we need to make people familiar with—the lower flammability limit (LFL) or lower explosive limit (LEL). Typically expressed as a percentage by volume. To ensure safety, we must ensure that fuel vapour concentration remains below the LFL/LEL.
Normal oxygen levels are approx. 21% and lower levels can lead to serious problems and ultimately fatal injury from hypoxia. Tank entry is not usually permitted where the oxygen level is below 19.5% and care should also be taken that the oxygen level is not too high as higher levels may increase the risk of fire and explosion.
Measuring equipment is required to monitor both oxygen concentration and flammable vapour concentration. Oxygen concentration is the most critical, as direct harm to individuals is possible.
Tooling & Lighting
All power tools and lighting equipment must be approved for use within the Fuel Tank Environment. Any pneumatic tools must only be powered by compressed air, as any inert gas could pose a risk to individuals by displacing the available oxygen within the tank.
FTS Initial and Recurrent training courses are available either classroom-based with Sofema Aviation Services or as online training.
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