TM 1-1500-204-23-3 c. Repairing Fuel Cell. (1) Internal Blister Repair. WARNING Acetone  and  repair  adhesives  are flammable  and  toxic.    Keep  away from heat, sparks and open flame. Wear  safety  glasses,  gloves  and protective     clothing     to     prevent contact.  Wear a NIOSH approved air-purifying respirator for organic vapors and work in a well ventilated area.  If contact occurs, flush   areas   with   water   and   get medical   attention.      If   ingestion occurs   get   medical   attention   at once. (a)    Cut the blister open.  The cut should resemble a "T' or "Y'.  Remove any fluid inside of blister. (b)    Clean interior area of blister using a piece    of    clean    cheesecloth    (item    16,    table    2-11) dampened   with   acetone   (item   3,   table   2-11).      Wear gloves (item 4, table 2-11). (c)    Lightly, hand buff all bonding surfaces of the blister using emery cloth (120 grit) (item 17, table 2-11). (d)    Clean  buffed  areas.    Use  a  clean piece  of  cheesecloth  (item  16,  table  2-11)  dampened with acetone (item 3, table 2-11).  Wear gloves (item 4, table 2-11). WARNING Repair adhesive is flammable and should   be   kept   away   from   any ignition source. NOTE Adhesive materials should be kept tightly sealed in individual containers in a cool, dry place. (e)    Prepare   repair   adhesive   (item   18, table   2-11).      Repair   adhesive   is   shipped   as   a   two component   kit.      Part   number   22-20556   (shelf   life   6 months)  is  the  masterbatch  and  part  number  22-20555 (shelf life 12 months) is the catalyst solution.  Stir each component   well   before   mixing.      Mix   the   two   parts together  and  thoroughly  blend  as  follows:  90%  of  22- 20556  (Masterbatch)  to  10%  of  22-20555  (Catalyst)  by weight.    Stir  mixture  for  10-15  minutes.    The  adhesive now  should  be  labeled  "PU-459".    Maximum  shelf  life after mixing is 6 hours. NOTE The    adhesive    should    be    used sparingly.        Two    (2)    thin,    even coats will provide better adhesion than   two   thick,   puddled   coats. Acetone  is  used  as  a  solvent  for the adhesive and, when the cemented  surface  appears  dry  to touch,   it   may   be   freshened   or made  tacky  again  by  application of this solvent. (f)    Brush-coat buffed surfaces of blister with   one   coat   of   adhesive   (item   18,   table   2-11)   and allow to dry 20-60 minutes. NOTE To determine if adhesive is tacky, test    it    by    pressing    a    knuckle gently against the cemented surface    and    withdrawing    it    (if practical).      Proper   tackiness   is achieved  when  a  few  threads  of adhesive    stick    to    the    knuckle. This  procedure  is  referred  to  as the knuckle test. (g)    Apply   a   second   coat   of   adhesive (item  18,  table  2-11)  to  buffed  areas  and  allow  to  dry until  tacky.    Adhesive  can  become  tacky  within  2  to  4 minutes,     depending     on     ambient     temperature     and humidity.  Perform knuckle test. (h)    Press cemented surfaces together. (i)    If  necessary  to  restore  tack  to  the cemented  surfaces,  use  a  piece  of  dean  cheesecloth (item   16,   table   2-11)   dampened   with   acetone,   lightly wipe over cemented areas.  Allow solvent to evaporate 10   to   20   seconds   or   until   cemented   areas   become "tacky." Change 2  2-57