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Breath of fresh air

Inspecting and repairing fuel tanks remains one of the most dangerous and uncomfortable maintenance tasks, but new technology from NanoVapor offers some relief. Ian Harbison reports

The biggest risk attached to working in aircraft fuel tanks is the presence of fuel vapour. As well as being a health hazard to maintenance personnel – requiring them to wear protective coveralls and breathing apparatus – it is also highly flammable and potentially explosive, meaning the use of intrinsically safe (or explosion-proof) electrical equipment is critical.


After an aircraft has been defuelled, it can take a considerable amount of time before the vapour has decreased to safe levels, even with forced air ventilation being blown through the tanks. This is because tanks often have awkward shapes and intrusions caused by the aircraft structure that can lead to fuel pooling in isolated corners.


NanoVapor, based in Houston, TX, has developed a system that uses proprietary chemical products that are non-toxic as well as both fuel- and water-soluble. When injected into the tanks as nano-molecules in a water-based fog, they form a monolayer barrier that covers all the inner surfaces, suppressing and capturing up to 99% of any vapour that may be produced. Even if disturbed, perhaps by personnel brushing against the surface, the chemicals have a tendency to quickly reform the layer. This can drastically reduce the waiting time for maintenance personnel. In trials carried out at Polar Air Cargo between 2008 and 2010, the system made the tanks of a Boeing 747 freighter safe to enter within 18 minutes, compared to a wait of up to 18 hours for the conventional defuel and degassing procedures in use at the time. A similar trial on a 737 produced a time of 13 minutes, compared to seven hours. Also on the 747 trials, an overnight test showed that no vapour growth was apparent after NanoVapor had been applied. 


Once maintenance work is complete, the aircraft can be refuelled as normal. The NanoVapor film breaks down and is dissolved into the fuel and burnt, with no side effects on pumps, filters or pipes. Residue levels in these elements have been found to be very low, typically with a maximum of 0.325ppm.


Although water is the carrier medium, it does not have any significant effect on the fuel, introducing only small changes to the relative humidity inside the tank – at 21°C and a relative humidity of 50%, the additional water is equivalent to raising the relative humidity to 60%. Nor is there any effect on fuel probes, which are sensitive to water contamination. Also, as tanks are open for less time, overall exposure to moisture is reduced. Evidence from Polar Air Cargo – which has degassed over 300 aircraft using NanoVapor systems – suggests that it can also reduce fuel probe failures, especially compared to conventional air blowers and venting.


The company has developed two models of the system. The first is mounted on a single axle towable trailer with dimensions of 4.4m long x 2.4m wide x 2.4m high, and an approximate weight of 1,000kg. A more portable unit has been developed in conjunction with a major US carrier, which is expected to be the launch customer with up to five units. The portable system measures 1.42m long x 80cm wide x 1.37m high and weighs less than 454kg. It can be fitted in the back of a pickup truck or used as a flyaway item for remote repairs, plus it can be deployed closer to the aircraft.


Hank Krakowski, President of NanoVapor, says the product has undergone some modifications since the Polar Air Cargo trials, to remove a potentially corrosive element, and has completed testing required by ASTM under the guidelines of D4054, Standard Practice for Qualification and Approval of New Aviation Turbine Fuels and Fuel Additives. It has been found to be both fuel compatible and fit-for-purpose and certification is imminent. A new trial is also scheduled to be carried out in New Mexico in the very near future.

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