TM 1-1510-218-10 2-133 Table 2-16.  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 MIL-F-5566). 2.   Heat mixture to a temperature of 82° to 93°C (180° to 200°F). 4.   If tires are frozen to ground, use undiluted defrosting   fluid   to   melt   ice   around   tire.   Move aircraft as soon as tires are free. 2-113.  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 the polarity of the external power source is the same as that of the aircraft before it is connected. Do not charge battery with GPU. An external 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 outboard side of the right engine nacelle. 2-114.  SERVICING OXYGEN SYSTEM. The  oxygen  system  furnishes  breathing  oxygen to   the   pilot,   copilot,   and   passengers.      Figure   2-33 shows the location of oxygen cylinder. a.   Oxygen System Safety Precautions.  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, gauges,   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.   Do    not    allow    foreign    matter    to    enter oxygen lines. 3.   Never  allow  electrical  equipment to come in contact with the oxygen cylinder. 4.   Never  use  oxygen  from  a  cylinder  without first    reducing    its    pressure    through    a regulator. WARNING