Document jYjNDBabV9m6Do8vkgp8oqJN

34--Welding and Cutting until all fire and explosion hazards have been eliminated All of the surrounding premises should be thoroughly ventilated, and frequent gas testing provided Sufficient draft should be maintained to prevent accumulation of ex plosive concentrations Local exhaust equip ment should be provided for removal of haz ardous gases, vapors, and fumes (present in the surroundings or generated by the welding or cutting operations) that ventilation fails to dispel Drums, tanks, and dosed containers Closed containers that have held flammable liquids or other combustibles should be thoroughly cleaned before welding or cutting Sometimes containers which cannot be re moved and handled properly for standard cleaning procedures are purged with an inert gas (Fig 34-11) or filled with water to within an inch or two of the place where the work is to be done, with a vent left open Either of these two measures may also be employed as an added precaution after cleaning according to recommended methods (See American Welding Society Safe Practices for Welding and Cutting Containers That Have Held Combustibles, A6 1 See also National Fire Protection Association, Cleantng or Safeguard ing Small Tanks and Containers, Standard No 327 Also see Chapter 42, "Flammable and Combustible Liquids," in this Manual ) The accepted method for preparing tanks and drums for welding is 1 Remove all sources of ignition (open flames, unguarded electric lights, etc) from the vicinity of the drums to be cleaned 2 Remove the bung with a special longhandled wrench 3 Examine the inside for rags, waste, or other debns which might interfere with free draining Use a portable electric hand lamp that is listed for hazardous locations, or an electric extension lamp protected by a guard of spark-resistant matenal 4 Place the drums on a steam rack with the bung holes at the lowest possible point, and let the drums dram for 5 minutes 5 Steam the drums for at least 10 minutes 968 Drums that have contained shellac, tur pentine, or similar materials require longer steaming 6 Remove the drums from the steaming rack, and fill them part way with caustic soda or soda ash solution Rotate the drums for at least 5 minutes Light ham mering with a wood mallet will help to loosen scale 7 Thoroughly flush the drums for at least 5 minutes with boiling water A water spray nozzle placed 6 or 8 in inside the drum can be used Drums should be so placed that water can dram out the bung openings during this operation. 8 Wash down the outside of the drum with a hose stream of hot water 9 Dry the drum thoroughly by circulating warm air throughout the inside 10 Thoroughly inspect the interior of the drum, using a light that is listed for haz ardous locations, and a small mirror If it is not clean, repeat the cleaning process VENT Fic 34-11 --As an added precaution after clean ing, a container to be welded or cut may be filled with either carbon dioxide or nitrogen to dilute any combustible gas or vapor remaining-dilute it enough to render it nonhazardous Courtesy American Welding Society