not  reach  electrical  machinery  or  wiring;  and (3)  ensuring  that  safety  guards  are  provided  at potential  danger  points,  such  as  rotating  and reciprocating  equipment. For  personnel  and  machinery  safety,  you  must adhere   to   the   following   safety   precautions specifically  related  to  the  engineering  department: Do  not  attempt  to  operate  equipment by   overriding   automatic   shutdown   or warning devices. Tag-out and disconnect batteries or other sources   of   electrical   power   before   per- forming   maintenance.   This   prevents injuries from short circuits and accidental start-up  of  equipment. Avoid  holding  or  touching  spark  plugs, ignition units, or high-tension leads while they are energized. Do  not  use  oxygen  to  pressure  test  fuel lines and equipment. Take precautions to avoid inhaling vapors of  lacquer  thinner,  trichlorethylene,  and similar solvents. Do  not  wear  jewelry  or  watches  while working  in  machinery  spaces. Take   precautions   to   avoid   touching exposed  hot  parts  of  an  engine.  Do  not perform maintenance work until the engine has  been  shut  down  and  cooled. Wear  proper  ear  protection  in  all  main machinery  spaces. It is the responsibility of supervisory personnel to  ensure  that  their  subordinates  are  instructed  in and carry out the applicable safety precautions. Each  individual  is  responsible  for  knowing  and observing  all  safety  precautions  applicable  to  their living  or  working  spaces.  Refer  to  Navy  Safety Precautions  for  Forces  Afloat,  OPNAVINST 5100.19. SHIPS’   MAINTENANCE   AND MATERIAL  MANAGEMENT (3-M) SYSTEMS The Ships’  Maintenance  and  Material  Manage- ment   (3-M)   Manual,   OPNAVINST    4790.4, describes  in  detail  the  Ships’  3-M  Systems.  The primary  objective  of  the  Ships’  3-M  Systems  is to  provide  for  managing  maintenance  and  mainte- nance  support  in  a  way  to  ensure  maximum equipment operational readiness. The Ships’ 3-M Systems is divided into two subsystems. They are the planned maintenance system (PMS) and the maintenance  data  system  (MDS). PURPOSES OF PMS The  PMS  was  established  for  the  following purposes: To  reduce  complex  maintenance  to  sim- plified  procedures  that  are  easily  identified and managed at all levels To  define  the  minimum  planned  mainte- nance  required  to  schedule  and  control PMS   performances To  describe  the  methods  and  tools  to  be used To  provide  for  the  detection  and  prevention of  impending  casualties To  forecast  and  plan  personnel  and material requirements To  plan  and  schedule  maintenance  tasks To  estimate  and  evaluate  material readiness To  detect  areas  requiring  additional  or improved   personnel   training   and/or improved   maintenance   techniques   or attention To provide increased readiness of the ship BENEFITS OF PMS The  PMS  is  a  tool  of  command.  By  using PMS,   the   commanding   officer   can   readily determine  whether  the  ship  is  being  properly maintained.   Reliability   and   availability   are improved.  Preventive  maintenance  reduces  the need for major corrective maintenance, increases economy,  and  saves  the  cost  of  repairs. The PMS assures better records because the shipboard maintenance manager has more useful data.  The  flexibility  of  the  system  allows  for programming  of  inevitable  changes  in  employ- ment  schedules.  This  helps  to  better  plan preventive maintenance. 1-9