[GingisK]

The tank was almost empty and filled with fumes. It was also heated by ambient temperatures and the air conditioning packs below it.

I keep forgetting the other issue. All sensors related to fuel systems are "intrinsically safe". They cannot make a spark or a wire hot enough to ignite the fuel even in the presence of oxygen.

[Moonman62]

I keep forgetting the other issue. All sensors related to fuel systems are “intrinsically safe”. They cannot make a spark or a wire hot enough to ignite the fuel even in the presence of oxygen.

...

As indicated in the NTSB report, the “safe” wires going into the tank shared a raceway with high voltage wires and there was evidence that shorting could have happened.