Is it possible that one of the key benefits of the Boeing 787 Dreamliner, which is denser and more humid cabin air, is the factor that triggered the battery failures that lead to its grounding?

While the answer may be ‘No’ the question is a good one.

Two people who work for Boeing, one directly, one indirectly through a supplier, have raised the possibility in casual regular conversation.

The common reasoning comes from asking “What was so different in the early passenger service of the 787s, and the test and certification process during which nothing quite like the failure paths of the lithium-ion batteries in the JAL and ANA flights occurred?”

The difference is ‘Passengers’.

One of the highly desirable features of the high composite structure of the Dreamliners is that it is said to facilitate operating the airliner with a lowered cabin altitude, down to 6,500 feet or around 2000 metres instead of  just under 8000 feet (according to Boeing).

Now while Boeing may have been exaggerating the cabin altitude at which modern jets are pressurized or not, to make the differential with the 787 look more than it is, it ought to be pointed out that when the Boeing 707 came along in 1958, it usually operated at 7000 feet cabin pressurization, which was the same as turbo-prop and end-of-era piston engined airliners like the Douglas DC-7C.

Be that as it may, Boeing has the science of better cabin pressurization on its side, in that even a reduction of 1000 feet in effective altitude greatly enhances the retention in the cabin of humidity (or if we want to be direct about this, perspiration and expiration from the skin pores and lungs of those on board.)

And nothing perspires quite like a cabin full of tightly packed passengers, although the JAL and ANA configurations are in their long haul format, generous and comfortable the way an eight across economy cabin in a 787 was always promoted as being.

There may be another clue concerning the issue of high humidity inside 787s in the November 2010 emergency landing of a test fleet Dreamliner at Laredo, Texas, after a fire broke out in the rear under floor electricals near the seat of the JAL fire at Boston airport early in January.

After the Laredo incident, which was said to have most likely involved foreign object damage from something like a bit of metal left lying around which facilitated electrical arcing, Boeing was reported to have decided to install some additional heating to keep the location dry, or, drier.

That particular flight carried dozens of test flight personnel, as did many of them, but not several hundred people seated in the same intimately close confines as found even in a comfortable cabin like those flown by ANA and JAL.

The thought that more now needs to be done not just to contain lithium-ion batteries in the event of similar failures in the future, but to protect them and the electrical system in general from excess humidity, might be on the right track.

Or it could be completely wrong.  Yet the difference between the test experience of the 787s and in-service 787s is the obvious one of lots of people being in a more humid environment.   That might be the critical difference.

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