TM 1-1500-204-23-4 (6)  Ensure  that  all  unauthorized  personnel are  clear  of  area  before  opening  valves  or  energizing electrical circuits for starting machinery. (7)   Suitable   mechanical   guards,   such   as enclosures or barricades, shall be permanently installed on   all   machinery   not   already   equipped   with   such   to eliminate danger of injury from moving parts. (8)     Machinery     shall     not     be     adjusted, repaired, oiled, or cleaned while machine is in operation or power is on. (9)   Personnel    operating    machinery    shall wear   protective   clothing   as   prescribed.      A   protective face  shield  or  goggles  shall  be  worn  when  operating  a grinder  regardless  of  whether  grinder  is  equipped  with attached shields. (10)    Jewelry     shall     not     be     worn     while performing any maintenance. (11)   All   electrical   binding   posts   shall   be insulated, covered, and clearly marked with voltage and current values. (12) Do not lay soldering irons down except on   a   holder.      Always   unplug   soldering   irons   before leaving  work  stations.    Soldering  irons  shall  not  be  left on for extended periods. (13)   Shop   humidity   should   not   be   higher than 50 percent, and temperature should be maintained at approximately 77 °F (25 °C). (14)  Shop  must  be  kept  as  clean  and  dust- free as possible. d.    Fire  Safety.    A  constant  vigilance  must  be maintained  to  seek  out  fire  hazards.    Fire  hazards  are constantly present in the shop where sparks, friction, or careless   handling   can   cause   an   explosion   that   may destroy    equipment    or    buildings,    and    injure    or    kill personnel.    The  following  fire  safety  practices  shall  be observed: (1)  NO  SMOKING  signs  shall  be  placed  in areas where smoking could create a fire hazard. (2)  Personnel  shall  be  trained  in  the  use, knowledge, and location of shop fire fighting equipment. (3)  Each  shop  shall  be  equipped  with  fire extinguishers suited for type fire most likely to occur. (4) Use correct fire extinguisher for class of fire as follows: · Class  A  fire  (wood,  paper,  trash, etc). Use water or bromotrifluoromethane fire extinguisher. · Class    B    fire    (oil,    paint,    fuel, grease, etc.). bromotrifluoromethane  or  carbon dioxide  fire    extinguisher,  or  dry chemical  extinguisher  with  Class B rating. · Class C fire (electrical equipment). Use bromotrifluoromethane  or  carbon dioxide  fire    extinguisher,  or  dry chemical  extinguisher  with  Class C rating. · Class D fire (combustible metals) magnesium,   titanium,   zirconium, sodium,   lithium,   and   potassium. Use dry powder-type fire extinguisher. (5) Oily waste, rags, and similar combustible materials    shall    be    discarded    in    self-closing    metal containers which shall be emptied daily. (6) Flammable materials shall not be stored in the shop. (7) Use only approved cleaning solvents. 4-2.  Maintenance of Shop Equipment.   Maintenance of instrument shop equipment is covered in the following paragraphs.        The    instructions    and    procedures    are general   in   nature.      Specific   maintenance   instructions that    apply    to    particular    pieces    of    equipment    are contained in applicable operation and service instructions manuals. a.      Manometers.      A   manometer,   as   shown   in figure  4-1,  measures  pressures,  and  is  used  for  testing and     calibrating     differential     and     absolute     pressure instruments such as altimeter, airspeed indicators, rate- of-climb  indicators,  and  suction  gauges.    Exercise  care when  reading  a  manometer,  because  curvature  of  the liquid  level  varies  for  mercury  and  water,  as  shown  in figure 4-2. (1)   Inspection.      Inspect   manometers   for damage using the following procedures: (a) Inspect glass cover for breaks and chips. (b)  Inspect   glass   tube   for   scratches and dirt. 4-2