pressure from exceeding container test pressure in the event  of exposure to excessive temperatures.  [Figure 9-9] classification Group 61). Noncorrosive, Halon 1301 does not  affect the material it contacts and requires no clean-up when  discharged. Halon 1301 is the current extinguishing agent for  commercial aircraft, but a replacement is under development.  Because Halon 1301 depletes the ozone layer only recycled  Halon 1301 is currently available. Halon 1301 is used until  a suitable replacement is developed. Some military aircraft  use HCL-125, which the Federal Aviation Administration  (FAA) is testing for use in commercial aircraft. Discharge valves are installed on the containers. A cartridge  (squib) and frangible disk type valve are installed in the  outlet of the discharge valve assembly. Special assemblies  having solenoid-operated or manually-operated seat type  valves are also available. Two types of cartridge disk-release  techniques are used. Standard release type uses a slug driven  by explosive energy to rupture a segmented closure disk.  For high temperature or hermetically sealed units, a direct  explosive impact type cartridge is used, which applies  fragmentation impact to rupture a prestressed corrosion- resistant steel diaphragm. Most containers use conventional  metallic gasket seals that facilitate refurbishment following  discharge.  [Figure 9-10] On many aircraft, means are usually provided for rapid access  to the compressor, tailpipe, or burner compartments. Many  aircraft systems are equipped with spring-loaded or pop-out  access doors in the skin of the various compartments. Internal  engine tailpipe fires that take place during engine shutdown  or false starts can be blown out by motoring the engine with  the starter. A running engine can be accelerated to rated  speed to achieve the same result. If such a fire persists, a fire  extinguishing agent can be directed into the tailpipe. It should  be remembered that excessive use of CO$_{2}$, or other agents  that have a cooling effect, can shrink the turbine housing on  the turbine and cause the engine to disintegrate. A wide range of diagnostics are utilized to verify the fire  extinguisher agent charge status. A simple visually indicated  gauge is available, typically a vibration-resistant helical  bourdon-type indicator.  [ see  Figure 9-9] Fire extinguisher containers (HRD bottles) store a liquid  halogenated extinguishing agent and pressurized gas  (typically nitrogen) normally manufactured from stainless  steel. Depending upon design considerations, alternate  materials are available including titanium. Containers are  also available in a wide range of capacities and are produced  under Department of Transportation (DOT) specifications or  exemptions. Most aircraft containers are spherical in design,  which provides the lightest weight possible. However,  cylindrical shapes are available where space limitations are  a factor. Each container incorporates a temperature/pressure  sensitive safety relief diaphragm that prevents container  A complete line of two-way check valves is available,  manufactured from either lightweight aluminum or steel.  A combination gauge switch visually indicates actual  container pressure and also provides an electrical signal if  container pressure is lost, precluding the need for discharge  indicators. A ground checkable diaphragm-type low-pressure  switch is commonly used on hermetically sealed containers. The Kidde system also has a temperature compensated  pressure switch that tracks the container pressure variations  with temperatures by using a hermetically sealed reference  chamber. Figure 9-9.  Fire extinguisher containers (HRD bottles). 9-9 CAUTION Mounting lug Data plate Weldment Caution plate Discharge outlet  Cartridge Caution tag Nameplate Fill fitting Pressure device (pressure switch and gauge guard) Two-Way Check Valve Containers  Pressure Indication Turbine Engine Ground Fire Protection Discharge Valves