As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON POSTFLIGHT, NOTICED SMOKE COMING FROM APU VENT. POWERED UP AIRPLANE AND APU FIRE BELL WITH LIGHT CAME ON FOR ABOUT FIVE SECONDS. POWER FUEL SWITCH WAS IN; I PRESSED OUT THE SWITCH. BOTTLE FIRED WHEN A/C WAS ADDED. REMOVED APU, INSPECTED FUEL MANIFOLD. REPLACED BOTH IGNITERS. PERFORMED LEAK CHECK WITH AIR OF FUEL SYSTEM. NO DEFECTS NOTED ON FUEL FEED SYSTEM. REINSTALLED APU PER CRJ MM 49-10-00.