Came across this old report from 2004:
SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain Airbus Model A319, A320, and A321 series airplanes. This
proposed AD would require modification of certain auxiliary power unit
(APU) alternating current (AC) generators. This proposed AD is prompted
by a report of an explosion in the APU compartment, which blew open the
compartment doors. We are proposing this AD to prevent oil vapor
leakage from the APU AC generator, which, when combined with an
electric arc at the electrical receptacle, could result in a fire or
explosion in the APU compartment during flight.
Federal Register, Volume 69 Issue 194 (Thursday, October 7, 2004)
No idea if any relevance - just thought I'd put it out here for the experts to comment on.