For those interested, the listed links describe the results of FAA funded research that showed the conductive residues sometimes present in the center wing fuel tanks of commercial aircraft can produce long term (10 - 20 seconds), high temperature (>800C) hot spots capable of igniting fuel if exposed to low dc power due to a short(e.g. short to float level switch wiring).
for a newspaper account go to
http://www.udri.udayton.edu/ResearchInstitute/
For two technical papers by UDRI and ASU go to
http://www.fire.tc.faa.gov/2001Conference/html/systems/protection.htm