APU FIRE WARNING.

Narrative

SHORTLY AFTER STARTING THE APU TO PERFORM PREFLT CHK; FIRE WARNING FOR APU CAME ON. APU WAS SHUTDOWN AND FIRE EXTINGUISHER WAS DISCHARGED. ADVISED CAPT; WHO WAS NOT ON THE AIRPLANE AT THE TIME. A MECH CHKED THE AIRPLANE AS PER A CONVERSATION WITH THE COMPANY DIRECTOR OF MAINT. NO INDICATION OF FIRE COULD BE FOUND AND WAS NOTED IN THE MAINT LOG. IN A CONVERSATION WITH THE CAPT; COMPANY DIRECTOR OF OPS AND DIRECTOR OF MAINT IT WAS DECIDED TO CONTINUE THE TRIP WITH PROVISIONS OF ACFT MEL. APU WAS PLACARDED AND WAS NOT USED FOR THE REMAINDER OF THE FLT TO THE HOME BASE FOR MAINT. SUPPLEMENTAL INFO FROM ACN 279626: HE MOST LIKELY; ACCIDENTALLY ENGAGED THE FIRE TEST ON THE APU. THIS HAS HAPPENED ON OTHER OCCASIONS WITH PLTS AND MAINT UNFAMILIAR WITH THE APU CTL PANEL. THERE WAS NO SIGN OF A FIRE OR ANY ABNORMALITY. THE FIRE BOTTLE SHOWED PRESSURE AND WAS NOT DISCHARGED. THE REASON BEING THE APU RPM'S MUST SPOOL DOWN BELOW 5 PERCENT BEFORE THE EXTINGUISHER SWITCH WILL FIRE THE BOTTLE. BEING THE FIRE EXTINGUISHER ARMING SWITCH WAS ACTIVATED; BY MR. X EARLIER; WHEN WE PUSHED THE FIRE TEST BUTTON; THE EXTINGUISHER SWITCH WAS ACCIDENTLY PUSHED AND THE FIRE BOTTLE WAS DISCHARGED AT THAT TIME. THE FIRE TEST BUTTON AND EXTINGUISHER BUTTON ARE NOT EVEN A THUMBS WIDTH AWAY FROM EACH OTHER. SO BOTH BUTTONS UNINTENTIONALLY WERE PUSHED SIMULTANEOUSLY.