and   clearly,   when   called,   require   immediate investigation. BETWEEN 25,000 AND 30,000 FEET.— Between  25,000  and  30,000  feet,  collapse, unconsciousnes,   and   death   quickly   follow interruption  of  the  oxygen  supply.  Mask  leakage at these  altitudes  may  cause a degree  of  hypoxia that,  although  not  noticed   during   flight,   can produce  considerable  fatigue  and  have  serious cumulative   effects. ABOVE  30,000  FEET.—  Above 30,000 feet, unconsciousness  and  death  strike  rapidly  and often   without   warning.   At   such   altitudes, it  is  imperative  that  all  oxygen  equipment  be functioning  correctly  and  that  each  breath  be taken  through  a properly  fitted  oxygen  mask. Above a pressure altitude of 35,000 feet, pressure breathing oxygen equipment is required. GASEOUS OXYGEN SYSTEMS Learning  Objective:  Identify  safety  pre- cautions, components, typical systems, and maintenance   procedures   for   gaseous oxygen systems. Gaseous oxygen systems  are used primarily in large, multiplace aircraft where space and weight limitations   are   less   important   items  and   the systems are used only periodically. HANDLING/SAFETY   PRECAUTIONS The  pressure  in  gaseous  oxygen  supply cylinders  should  not  be  allowed  to  fall  below  50 psi. If the pressure falls much below this value, moisture is likely to accumulate in the cylinder and could be introduced into the oxygen system of the aircraft, causing component malfunction. All  oxygen  under  pressure  is  potentially  very dangerous   if   handled   carelessly.   Personnel servicing  or  maintaining  oxygen  systems  and components must be meticulously careful about preventing  grease,  oil,  hydraulic  fluid,  or  similar hydrocarbons as well as other contamination from coming  in  contact  with  lines,  hoses,  fittings,  and equipment  as  this  contact  presents  a  fire  and explosion hazard. If, because of hydraulic leaks or some other unpreventable   malfunction,   components   of the  oxygen  system  do  become  externally  con- taminated,  they  should  be  cleaned  using  only 4-4 approved oxygen system cleaning compounds. While some MIMs specify the use of  a variety  of cleaning  compounds,  the  preferred  compound  is oxygen  system  cleaning  compound  conforming  to Military Specification MIL-C-8638 or ultra clean solvent cleaning compound (type I, trichlorotri- fluoroethane) conforming to Military Specifica- tion   MIL-C-81302B. The following safety precautions should be adhered to: l  Under  no  circumstances   should   a non- approved  cleaning  compound  be  used  on  any oxygen lines, fittings, or components. . When handling oxygen cylinders, the valve protection  cap  should  always  be  in  place.  Before removing the cap and opening the valve, ensure that the cylinder is firmly supported. A broken valve  may  cause  a  pressurized  cylinder  to be propelled like a rocket. . Do NOT use oxygen in systems intended for other gases or as a substitute for compressed air. . Cylinders being stored for use on gaseous oxygen servicing trailers or any other use must always   be   properly   secured.   Do   not   handle cylinders or any other oxygen equipment with greasy hands, gloves, or other greasy materials. The   storage   area   should   be   located   so   that oil  or  grease  from  other  equipment  cannot  be accidentally  splashed  or  spilled  on  the  cylinders. Additional   safety   precautions   may   be found   in   the   publications   technical   manual NAVAIROSH   Requirements   for   the   Shore Establishment,  NAVAIR  A1-NAOSH-SAF-000/ P-5100;   Aviators  Breathing  Oxygen  (ABO) Surveillance  Program  Laboratory  Manual  and Field Guide, A6-332A0-GYD-000;  Aviation-Crew System,  Oxygen  Equipment, NAVAIR 13-1-6.4. SYSTEM   COMPONENTS Basically, all gaseous oxygen systems consist of the following: 1. 2. 3. Containers   (cylinders)   for   storing   the oxygen   supply Tubing to route the oxygen from the main supply to the user(s) Various  valves  for  directing  the  oxygen through  the  proper  tubing