q100 - same as a Ten. The No.2 and APU shared fuel line runs L/H fuselage inside pressurised area lower aft/centre cargo pits. If they do leak/break they are protected in a 20 gauge shroud tube vented to outside in two places. Just the sidewalls separate this from the upper deck compartment. On that piece of knowledge I'd say fire first, fuel contributed (much) later.
Disclaimer - if indeed de dah de dah de dah.........................
