it stops when the fire switch is pulled. The fire switch isolates  the APU from the airplane systems. If the fire warnings do not go away with the switch out,  put the switch to the left or right DISCH position. Hold the  switch against the discharge stop for one second. This fires  the bottle squib and releases the fire extinguishing agent into  the APU compartment. Verify that the APU bottle discharge  light comes on.  [Figure 9-29] Fire Bottle Discharge A A A A Pressure switch Test button APU bottle discharge Master Dim &  Test APU fire switch  disch  disch  In  Out  Fire/Overheat test APU fire extinguishing bottle Cargo fire/engine control panel (P5) APU bottle discharge APU fire shutdown Bottle discharged Fire bottle armed AIMS cabinet (2) P40 service and APU shutdown panel P310 standby power management panel 10 seconds delay APU EXT shutdown APU  remote  warning Fire alarm 1 Unattended fire alarm APU fuel system & ELMS Fire EXT APU 28V DC hot battery bus APU RMT fire indicator/auto discharge arm 28V DC hot battery bus Figure 9-29.  APU fire extinguishing circuit. 9-20