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34--Welding and Cutting Most welding and cutting processes--for construction, demolition, maintenance, and re pair-use portable, manually operated equip ment The major portion of this chapter discusses ways of minimizing the hazards encountered in this type of intermittent op eration Since production line welding and cutting equipment is usually permanently installed, the source of hazards can be mini mized through safe design The safety pro fessional, however, can use this chapter to help him check the operation and mainte nance of production line equipment The detailed specifications of ANSI Stand ard Z49 1, Safety in Welding and Cutting, should be followed In addition, city, state, and Federal codes and regulations, where applicable, should be consulted This chapter uses the American Welding Society's welding and cutting definitions A welder is "one who is capable of per forming a manual or semiautomatic welding operation." A welding operator is "one who operates machine or automatic welding equipment " Gas Welding and Oxygen Cutting A gas-welding process unites metals by heating them with the flame from the com bustion of a fuel gas or gases and sometimes includes the use of pressure and a filler metal An oxygen-cutting process severs or re moves metal by the chemical reaction of the metal with oxygen at an elevated temperature maintained with heat from the combustion of fuel gases In the powder-cutting process, a finely divided matenal, such as iron powder, is added to the cutting oxygen stream The powder bursts into flame in the oxygen stream and starts cutting without preheating the matenal to be cut Powder cutting is used on stainless and other steels, on many nonferrous metals, and on concrete in construction and demolition jobs Plasma arc cutting is now replacing powder oxy-fuel cutting Welding and cutting gases Oxygen is furnished to the consumer in steel cylinders, usually under a pressure of about 2200 psi at 70 F, or as a hquid to be gasified on the consumer's premises 948 Pure oxygen will not bum or explode It supports combustion, that is, it causes other substances to bum when they are raised to the kindling temperature Combusbble ma terials bum much more rapidly in oxygen than in air Oxygen forms explosive mixtures in certain proportions with acetylene, hydro gen, and other combustible gases Acetylene (C-H.) consists of 92 3 percent by weight of carbon and 7 7 percent by weight of hydrogen m chemical combination It contains stored-up energy which is released as heat when it bums, as in the welding flame This heat is m addition to that which would be obtained by combustion of equivalent amounts of elemental carbon and hydrogen Acetylene burned with oxygen can produce a higher flame temperature (approximately 6000 F) than any other gas used commercially Acetylene, like other combustible gases, ig nites readily, and in certain proportions forms a flammable mixture with air or oxygen The range of flammable limits of acetylene (2 5 to 81 percent acetylene in air) is greater than that of other commonly used gases, with con sequently greater hazard Acetylene is either supplied in cylinders or generated as needed It is a product of the reaction between water and calcium carbide, a gray crystalline substance made commer cially by fusing lime and coke in an electric furnace Calcium carbide itself is neither flammable nor explosive It is stored and sold in airtight and watertight cans or drums If the drums are damaged in handling and if water comes in contact with carbide, acetylene will be generated and there is then danger of ignition and explosion Hydrogen is furnished in cylinders under a pressure of about 2000 psi at 70 F. It may ignite in the presence of air or oxygen when in contact with a spark, open flame, or other source of ignition Hydrogen-air mixtures m the range from 4 1 to 74 2 percent hydrogen are flammable Other fuel gases are used with oxygen in torches, primarily for oxygen cutting For example, propane, butane, and their mixtures are supplied in cylinders m hquid form, gen erally under various trade names These gases