For the FQIS to be a credible potential ignition source, two independent failures must occur. The leading scenario presented involved copper-sulfide deposits on the FQIS wiring inside the CWT and an induced voltage onto the FQIS system wiring outside the CWT created by switching on and off power in adjacent wiring. Specific knowledge of the melting temperature and boiling temperature of the deposits could be useful in assessing these deposits as possible ignition sources. These deposits must provide an electrical path to ground or to another wire for current to flow. As an example, a corona discharge may have more than the minimum ignition energy but not the energy density necessary to be an incendiary ignition source.
Corona discharges occur quite often during refueling operations.
A third scenario should also be considered involving the sulfide deposits heating the wire insulating material to its ignition temperature that in turn ignites the fuel vapors. I believe heat transfer calculations will show none of these three scenarios is possible with only 0.6 millijoules of total energy available. Another FQIS scenario needs some discussion. Either of these two events should independently provide some indication of a malfunction to the flight crew or maintenance personnel. The probability of these two events occurring simultaneously without some malfunction indication is astronomical.