DALLAS — Are you small and flexible? Do you enjoy crawling into confined, dark spaces? Do you want to work around toxic chemicals with the constant threat of exploding to death? If so, we have the job for you!

While not as glamorous as the description above makes it sound, the position of fuel tank maintenance person, or "tank diver," as it is sometimes called, is vital to the aviation industry. These are the men and women who crawl inside aircraft fuel tanks to find and repair leaks and other structural malfunctions.

According to www.dvidshub.net, fuel technicians handle all operations involving the pumps, valves, manifolds, and all other aspects that encompass the fuel cell. The system is made up of massive black bladders that hold jet fuel within the wings and run down the bottom of the aircraft fuselage.

A Risky Job

Boeing says the risks of this job involve

• Chemical Risks - the primary one being exposure to jet fuel that "can ignite in certain ambient conditions, primarily temperature and vapor concentration." You would also encounter other flammable chemicals with a lower flash/ignition point than fuel. This includes methyl ethyl ketone (MEK), a solvent used in the manufacture of synthetic rubber, paraffin wax, and other chemical products.
• Physical Risks - the primary one being confined into a small space from which it is difficult to escape in an emergency. The entryways into fuel tanks, in larger aircraft, measure about two feet wide by one foot high. There is usually one access hole between each rib section in the wing. Per Boeing: "The inboard portion of the wing tank offers just enough clearance inside of the tank for a maintenance person's head, shoulders, and trunk, leaving the legs outside of the access hole. The tank becomes smaller as it progresses farther outboard on the wing, until it may accommodate only a maintenance person's head and shoulders. The most outboard sections of the wing may only have enough room for a maintenance person's hands and arms."

Of course, there are several steps that must be followed prior to entering the tanks for maintenance.

• Electrically ground and defuel the airplane according to standard practices
• Make fire protection equipment readily available
• Deactivate fueling/defueling and fuel transfer systems
• Ensure adequate ventilation
• Properly monitor the air in fuel tanks

https://www.youtube.com/watch?v=FxfcmFOSh58

Take a look at the video on how to enter an aircraft fuel tank.

Breathe Easy

Ensuring proper ventilation is literally a deadly serious aspect of tank maintenance. Most manufacturers recommend fresh exterior air as the best choice. With higher levels of outside air pumped into the tank, there is less chance that any fuel vapors would ignite. While pumping nitrogen into the wing to totally eliminate the risk of fire might seem a logical thing to do, it's not really a best practice. That is unless you want to quickly kill your maintenance people inside due to oxygen starvation.

Normal sea-level oxygen concentration is around 21%. Boeing recommends an oxygen level inside the tanks of between 19.5% and 23.5%. Above that level, the oxygen-rich air dramatically increases the risk of ignition of residual fuel.

Maintenance workers typically wear respirators that purify the air and also use tools and monitoring equipment approved for use in a flammable environment. Even a small spark from an electric drill could mean disaster.

Below is the inside of a Boeing 747 wing, from the guys at the Delta Flight Museum.

https://www.youtube.com/watch?v=4ktqOWgZfEE

First, Do No Harm

In addition to all this, properly training the workers is paramount. As Boeing says, "The mating surfaces of the access hole and covers should be protected during entry so that the surfaces are not scratched or otherwise damaged."

The components inside fuel tanks, such as fuel pumps, fuel-quantity systems, and associated wiring and conduits, are also vulnerable to damage if they are stuck or dislodged. Finally, the containment properties of the fuel tank can be compromised if the sealant is damaged or dislodged or if fuel-tank bladders are penetrated."

Sound like fun?

Featured image: Airman 1st Class Emilee Sharp gets inside a fuel tank on the top of a C-17 Globemaster III on April 17, 2015, during a Fuel Tank Extraction exercise at Joint Base Charleston, S.C. The exercise simulated an Airman being overcome by fumes inside a fuel tank requiring first responders from the 628th Civil Engineering Squadron to conduct an extraction. (U.S. Air Force photo/Senior Airman Jared Trimarchi)