TM 1-1500-204-23-8 (1) Personnel protective equipment. Suitable personal protective clothing and equipment shall be worn by  personnel  performing  welding  operations.    Helmets, shields,   aprons,   gloves,   gauntlets,   or   other   items   of clothing of approved design may be used.  Goggles shall be carefully selected on the basis of lens shade which will provide complete protection for type of welding involved. (2)   Ventilation.  Forced ventilation should be provided when natural ventilation is inadequate to keep concentration   of   injurious   fumes   produced   in   welding operation   below   harmful   levels.      Suitable   respiratory equipment  shall  be  worn  when  concentration  of  injurious fumes     cannot     be     kept     below     maximum     allowable concentrations. (3)   Fire hazard.  Welding shall not be permitted in the vicinity of flammable or explosive substances.  A suitable fire extinguisher shall be provided for all welding units. (a)   Flammable  material.    All  flammable  material shall  be  removed  from  the  immediate  vicinity  of  welding operations.        Wooden    floors    and    other    combustible material  which  may  be  subjected  to  excessive  heat  or contact   with   the   flame   shall   be   adequately   protected. Where  removal  of  flammable  material  is  impractical,  a suitable   fire-resistant   shield   shall   be   placed   between flammable  material  and  welding  operation.    A  thorough inspection    of    surrounding    area    shall    be    made    upon completion of a welding operation to detect any potential fire. (b)   Explosive hazards. Welding shall be prohibited  where  flammable  liquids  and  gases  create  a fire    or    explosion    hazard.        In    confined    areas    with inadequate   ventilation,   it   is   possible   for   the   welding operation itself to produce flammable and explosive gases. (c)   Fire     protection.          Where     a     fire     hazard continues    to    exist    despite    reasonable    precautionary measures,    a    fire    guard    provided    with    suitable    fire extinguishing  equipment  shall  be  stationed  near  welding location. (4)      Welding   of   containers.      Tanks,   cylinders,   and other  containers  shall  never  be  welded  until  it  has  been ascertained    that    they    do    not    contain    flammable    or explosive substances. (a)   Sealed  containers.    Sealed  containers  shall not   be   worked   on   until   it   has   been   determined   that their  contents  do  not  present  a  hazard  and  venting  is provided. (b)   Draining.      Prior   to   welding   gas   tanks   and other containers which have contained flammable liquids, all liquid shall be drained from tank.  Precautions shall be taken   to   prevent   draining   process   from   creating   a   fire hazard.      The   tank   shall   then   be   thoroughly   washed, steamed, and filled with water.  Provide a vent to permit release of pressure which is generated in tank by heat of welding process.  Accomplish repairs as soon as possible after tank has been drained and cleaned. 3-3.  Types of Welding.  There are three general types of welding: gas, electric arc, and spot welding. The following paragraphs describe the three types. a.   Gas Welding.   Gas  welding  is  accomplished  by heating the ends or edges of metal parts to a molten state with  a  high  temperature  flame.    The  flame  is  produced with   a   torch   burning   pure   oxygen   with   acetylene   or hydrogen.      The   metals,   when   in   a   molten   state,   flow together to form a union. (1)   Gas    welding    precautions.        The    oxygen, acetylene,  and  the  flame  used  in  oxyacetylene  welding requires   careful   handling   to   prevent   injury   or   damage. Observe the following precautions: Do    not    allow    oil    or    grease    to    contact    welding apparatus.      Oil   or   grease   in   contact   with   oxygen equipment,  in  particular,  is  extremely  dangerous  and may result in fire or explosion. Do  not  use  acetylene  from  cylinders  at  pressures  in excess of 15 psi.  The special T-wrench provided for opening acetylene cylinders will be left in place while cylinder   is   in   use   to   permit   quick   shutoff   in   an emergency. Acetylene and oxygen cylinders will be hand- led with care  to  prevent  damage  to  cylinders,  regulators,  or valves.    Cylinder  valves  will  be  in  an  immediately accessible   location   when   cylinders   are   in   use   to permit quick shutoff in an  emergency.    All  cylinders  to  which  a  hose  is  not attached will be provided with protective caps. Protect  hose  from  mechanical  damage  or  con-  tact with   hot   metal,   open   flame,   and   other   destructive agents.        Inspect    hose    periodically    for    leaks    by submerging  in  water.    Do  not  use  a  flame  to  test  for leaks.  Use only standard ferrules or clamps to secure hose to nipples. 3-2