Human Factors in Aircraft Fuel Systems

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Primary Hazards related to Fuel Tank Working

There are a number of potential hazards which fuel-tank maintenance personnel may experience whilst engaged in Fuel Tank Work however the 2 primary hazards are:

a) Chemical
b) Physical

Considering Chemical Hazards and their Consequences - Fuel

Off course the most commonly recognized hazard is the jet fuel itself which is a flammable liquid and will ignite if the temperature of the fuel is such that vapour is created. (The temperature at which the vapours of a flammable liquid can ignite is known as the "flash point".)

Aviation Jet fuel, may also present toxic or irritant hazards. At high concentrations, jet fuel and other hydrocarbons can affect the nervous system, causing headache, dizziness, and lack of coordination.

The terms used in relation to the flammability are known as the lower flammability limit (LFL) or lower explosive limit (LEL). (Usually expressed as a percentage by volume.)

One of the best ways to control unwanted fires and explosions is to keep the fuel vapor concentration below the LFL/LEL, preventing it from reaching its flammable range.

Considering Chemical Hazards and their Consequences - Cleaning Chemicals

Chemicals may also cause chronic health problems, such as liver and kidney damage. Cleaning solvents, sealants, lubricants, and other chemicals used in fuel-tank work can also cause irritating effects to the skin if not controlled.

Chemicals with a low flash point (less than 70ºF (21ºC)), such as methyl ethyl ketone (MEK), are even more hazardous than jet fuel, and their use must be strictly controlled.

Considering Physical Hazards and their Consequences

Entry into most aircraft fuel tanks is through an oblong access panel which is less than two ft (0.6 m) long and one ft (0.3 m) wide.

The physical form of the tank can potentially create hazards and also play a role in the potential exposure leading to fire, explosion, and toxicity hazards.

The center wing tank in widebody jets is typically the largest, however it only needs a relatively small amount of a chemical inside one of these enclosed spaces (providing the temperature is conducive to the creation of vapour) to create significant levels of flammable or toxic vapor.

On many aircraft the inboard portion of the wing tank provides just enough clearance for a maintenance person's head, shoulders, and upper body, leaving the legs protruding outside of the access point.

Aircraft Wing Fuel Tanks becomes smaller as they progress outboard on the wing, at this point it may only be possible to accommodate the maintenance staff’s head and shoulders. Or if smaller - Arms and Hands - A challenge to see what you are doing - mirror may be required.

Sofema Aviation Services www.sassofia.com and our sister online training portal Sofema Online www.sofemaonline.com offer both classroom and online (with voice over) training compliant with the requirements of both EASA and FAA SFAR 88. For details please see our websites or email office@sassofia.com or online@sassofia.com

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