TM 55-1510-222-10 Table  2-12.  Recommended Fluid Dilution Chart AMBIENT TEMPERATURE (°F) PERCENT DEFROSTING FLUID BY VOLUME PERCENT WATER BY VOLUME FREEZING POINT OF MIXTURE (°F) APPROXIMATE) 30°  and above 20 80 10° 20° 30 70 0° 10° 40 60 -15° 0° 45 55 -25° -10° 50 50 -35° -20° 55 45 -45° -30° 60 40 -55° NOTES: 1. Use anti-icing and deicing fluid (MIL-A-8243) or commercial fluids. 2. Heat Mixture to a temperature of 82°  to 93°  C (180 to 200 F). B100201 b. Spray diluted, hot fluid in a solid stream (not over   15   gallons   per   minute).      Thoroughly   saturate aircraft surface and remove loose ice.  Keep a sufficient quantity  of  diluted,  hot  fluid  on  aircraft  surface  coated with  ice,  to  prevent  liquid  layer  from  freezing.  Diluted, hot  fluid  should  be  sprayed  at  a  high  pressure,  but  not exceeding 300 PSI. c. When facilities for heating are not available and it is deemed necessary to remove ice accumulations from aircraft surfaces, undiluted defrosting fluid may be used.  Spray undiluted defrosting fluid     at     15     minute     intervals     to     assure     complete coverage. Removal of ice accumulations using undiluted defrosting fluid is expensive and slow. d. If  tires  are  frozen  to  ground,  use  undiluted defrosting fluid to melt ice around tire.  Move aircraft as soon as tires are free. 2-100. APPLICATION OF EXTERNAL POWER. CAUTION Before   connecting   the   power   cables from the external power source to the aircraft,   ensure   that   the   GPU   is   not touching the aircraft at any point.  Due to  the  voltage  drop  in  the  cables,  the two ground systems will be of different potentials.  Should they come in contact while the GPU is operating, arcing    could    occur.        Turn    off    all external   power   while   connecting   the power  cable  to,  or  removing  it  from, the  external  power  supply  receptacle. Be certain that polarity of the external power  source  is  the  same  as  that  of the   aircraft   before   it   is   connected. Minimum   GPU   requirements   are   as follows:  400-amperes,  28V  continuous output   DC   and   11   5V,   3   phase,   400 cycle, 3 KVA continuous output AC. An   external   power   source   is   often   needed   to supply  the  electric  current  required  to  properly  ground service the aircraft electrical equipment and to facilitate starting  the  aircraft's  engines.    An  external  DC  power receptacle is installed on the underside of the right wing stub, just outboard of the engine nacelle. An external AC power receptacle is installed on the underside of the left wing stub, just outboard of the engine nacelle. 2-101. SERVICING OXYGEN SYSTEM. The oxygen system furnishes breathing oxygen to the pilot, copilot and first aid position.  Oxygen cylinder location is shown in figure 2-22. a. Oxygen System Safety Precautions. WARNING Keep  fire  and  heat  away  from  oxygen equipment.        Do    not    smoke    while working with or near oxygen equipment,    and    take    care    not    to generate sparks with carelessly handled   tools   when   working   on   the oxygen system. (1) Keep oxygen regulators, cylinders, gages, valves, fittings, masks, and all other components of the oxygen   system   free   of   oil,   grease,   gasoline,   and   all other readily combustible substances.  The utmost care shall be exercised in servicing, handling, and inspecting the oxygen system. 2-87