several small lightweight torches of this type that are ideal  for aviation welding projects. The Smith Airline™ and the  Meco Midget™ torches are small enough to be used in close  confined areas, lightweight enough to reduce fatigue during  long welding sessions yet, with the appropriate tips, are  capable of welding 0.250-inch steel. The injector torch uses fuel gas at pressures between just  above 0 and 2 psi. This torch is typically used with propane  and propylene gas. High-pressure oxygen comes through  a small nozzle inside the torch head and pulls the fuel gas  along with it via a venturi effect. The low-pressure injector  torch is more prone to flashback.  The cutting torch is an attachment added to the torch handle  that allows the cutting of metal. The cutting process is  fundamentally the rapid burning or oxidizing of the metal  in a localized area. The metal is heated to a bright red color  (1,400 °F to 1,600 °F), which is the kindling temperature,  using only the preheat jets. Then, a jet of high-pressure  oxygen released by the lever on the cutting attachment is  directed against the heated metal. This oxygen blast combines  with the hot metal and forms an intensely hot oxide. The  molten oxide is blown down the sides of the cut, heating the  metal in its path to the kindling temperature as the torch is  moved along the line of the desired cut. The heated metal  also burns to an oxide that is blown away on the underside  of the piece.  [Figure 5-17] The torch tip delivers and controls the final flow of gases.  It is important that you use the correct tip with the proper  gas pressures for the work to be welded satisfactorily. The  size of the tip opening—not the temperature—determines  the amount of heat applied to the work. If an excessively  small tip is used, the heat provided is insufficient to produce  penetration to the proper depth. If the tip is too large, the heat  is too great, and holes are burned in the metal.  Torch tip sizes are designated by numbers. The manufacturer  can provide a chart with recommended sizes for welding  specific thicknesses of metal. With use, a torch tip becomes  clogged with carbon deposits. If it is allowed to contact the  molten pool, particles of slag may clog the tip. This may  cause a backfire, which is a momentary backward flow of  the gases at the torch tip. A backfire is rarely dangerous, but  molten metal may be splattered when the flame pops. Tips  should be cleaned with the proper size tip cleaner to avoid  enlarging the tip opening. Protective eyewear for use with oxy-fuel welding outfits is  available in several styles and must be worn to protect the  welder’s eyes from the bright flame and flying sparks. This  eyewear is not for use with arc welding equipment.  Some of the styles available have individual lenses and  include goggles that employ a head piece and/or an elastic  head strap to keep them snug around the eyes for protection  from the occasional showering spark.  [Figure 5-18]  Another  popular style is the rectangular eye shield that takes a standard  2-inch by 4.25-inch lens. This style is available with an  elastic strap but is far more comfortable and better fitting  when attached to a proper fitting adjustable headgear. It can be worn over prescription glasses, provides protection from  Welding Eyewear Cutting Torch Torch Tips Injector Torch Figure 5-17. Torch handle with cutting, heating, and welding tips. Figure 5-16. Flashback arrestors. Figure 5-18.  Welding goggles. 5-9