A BOEING 737-200 RECEIVED AN INTERMITTENT APU FIRE WARNING AND DISCHARGED THE APU FIRE BOTTLE AT DFW.

Narrative

I JUST HAPPENED TO LOOK UP AND SAW THE APU LOW OIL PRESSURE LIGHT ILLUMINATED. I REACHED UP AND MOVED THE APU SWITCH TO 'OFF.' ABOUT 4 SECONDS LATER WE GOT AN APU FIRE WARNING INDICATION BUT IT WAS UNUSUAL IN THAT IT WAS WEAK AND INTERMITTENT. I TOLD THE FO TO DECLARE AN EMER AND ROLL THE TRUCKS WHILE I PROCEEDED TO USE THE OVERRIDE BUTTON TO PULL THE APU FIRE HANDLE THEN ROTATED THE HANDLE TO BLOW THE BOTTLE. WE GOT A BOTTLE DISCHARGE LIGHT AND ABOUT 5 SECONDS LATER THERE WAS NO MORE INDICATION OF FIRE. THE FO HAD A LOT OF DIFFICULTY GETTING A WORD TO THE TWR; THERE WAS A STUCK MIKE BLOCKING THEIR NORMAL FREQ; WE WERE ON A BACKUP FREQ. IN ALL THE EXCITEMENT WHEN THE FO DID GET THROUGH TO TWR HE FORGOT TO DECLARE AN EMER BUT DID ADVISE THEM OF OUR SIT AND REQUESTED ANY INFO THEY COULD SEE ON OUR SIT AND TO GET THE FIRE TRUCKS TO US. TWR AND MANY ACFT AROUND US COULD NOT SEE ANYTHING UNUSUAL. THE FIRE TRUCK PROBABLY GOT TO US IN ABOUT 3 MINS AND QUICKLY CONFIRMED ALL APPEARED NORMAL. DURING THIS 3 MINS WE ALSO CALLED THE CABIN CREW TO ADVISE THEM OF WHAT HAD HAPPENED AND TO GET THEIR INPUT AS TO WHAT WAS GOING ON IN THE CABIN. THEY RPTED AN EXHAUST TYPE OF SMELL BUT OTHER THAN THAT ALL WAS NORMAL.