1.1* Scope. This standard shall apply to Class A, Class B, Class C, and Class D ovens, dryers, and furnaces; thermal oxidizers; and any other heated enclosure used for processing of materials and related equipment. A.1.1 Explosions and fires in fuel-fired and electric heat utilization equipment constitute a loss potential in life, property, and production. This standard is a compilation of guidelines, rules, and methods applicable to the safe operation of this type of equipment. Conditions and regulations that are not covered in this standard — such as toxic vapors, hazardous materials, noise levels, heat stress, and local, state, and federal regulations (EPA and OSHA) — should be considered in the design and operation of furnaces. Most failures can be traced to human error. The most significant failures include inadequate training of operators, lack of proper maintenance, and improper application of equipment. Users and designers must utilize engineering skill to bring together that proper combination of controls and training necessary for the safe operation of equipment. This standard classifies furnaces as follows: (1) Class A ovens and furnaces are heat utilization equipment operating at approximately atmospheric pressure wherein there is a potential explosion or fire hazard that could be occasioned by the presence of flammable volatiles or combustible materials processed or heated in the furnace. Such flammable volatiles or combustible materials can originate from any of the following: (a) Paints, powders, inks, and adhesives from finishing processes, such as dipped, coated, sprayed, and impregnated materials (b) Substrate material (c) Wood, paper, and plastic pallets, spacers, or packaging materials (d) Polymerization or other molecular rearrangements Potentially flammable materials, such as quench oil, water-borne finishes, cooling oil, and cooking oils, that present a hazard are ventilated according to Class A standards. (2) Class B ovens and furnaces are heat utilization equipment operating at approximately atmospheric pressure wherein no flammable volatiles or combustible materials are being heated. (3) Class C ovens and furnaces are those in which there is a potential hazard due to a flammable or other special atmosphere being used for treatment of material in process. This type of furnace can use any type of heating system and includes a special atmosphere supply system(s). Also included in the Class C classification are integral quench furnaces and molten salt bath furnaces. (4) Class D furnaces are vacuum furnaces that operate at temperatures that exceed ambient to over 5000°F (2760°C) and at pressures from vacuum to several atmospheres during heating using any type of heating system. These furnaces can include the use of special processing atmospheres. During gas quenching, these furnaces can operate at pressures from below atmospheric to over a gauge pressure of 100 psi (690 kPa). 1.1.1 The terms ovens, dryers, and furnaces are used interchangeably and shall also apply to other heated enclosures used for processing of materials. 1.1.2* Within the scope of this standard, a Class A, Class B, or Class C oven is any heated enclosure operating at approximately atmospheric pressure and used for commercial and industrial processing of materials. A.1.1.2 The following types of industrial systems are generally considered to be among those covered by NFPA 86 where the fuel is covered by the standard: afterburners, ammonia dissociators, annealing furnaces, arc melting furnaces, atmosphere generators (endothermic, exothermic), autoclaves, bakery ovens, batch furnaces, bell furnaces, belt furnaces, blast furnaces, brazing furnaces, brick kilns, car-bottom kilns, casting furnaces, catalytic thermal oxidizers, cement kilns, chemical vapor deposition furnaces, crematories, crucible furnaces, cupola furnaces, drying ovens, electric arc furnaces, electron beam melters, flameless thermal oxidizers, fume incinerators, glass melting furnaces, heat treating furnaces, heating cover furnaces, indirect-fired furnaces, induction furnaces, inert-atmosphere furnaces, integral quench furnaces, kilns, lime kilns, melting kettles/pots, muffle furnaces, open hearth furnaces, ovens, oxygen-enriched furnaces, paint drying ovens, paper drying ovens, plasma melting furnaces, pusher furnaces, reduction furnaces, refining kettles, regenerative thermal oxidizers, reheat furnaces, retort furnaces, reverberatory furnaces, roasting ovens, rotary calciners, rotary dryers, rotary kilns, shaft furnaces, shaft kilns, shuttle kilns, sintering furnaces, slag furnaces, smelting furnaces, solvent atmosphere ovens, special atmosphere furnaces, sweat furnaces, textile dryers, thermal oxidizers, tube furnaces, tunnel kilns, vacuum furnaces, vaporizers, and wood-drying kilns. 1.1.3 AClassAoven shall be permitted to utilize a low-oxygen atmosphere. 1.1.4 This standard shall apply to bakery ovens and Class A ovens, in all respects, and where reference is made to ANSI Z50.1, Bakery Equipment — Safety Requirements, those requirements shall apply to bakery oven construction and safety. 1.1.5 This standard shall apply to atmosphere generators and atmosphere supply systems serving Class C furnaces and to furnaces with integral quench tanks or molten salt baths. 1.1.6* This standard shall apply to Class D ovens and furnaces operating above ambient temperatures to over 5000°F (2760°C) and at pressures normally below atmospheric to 108 torr (1.33 × 106 Pa). A.1.1.6 Vacuum furnaces generally are described as cold-wall furnaces, hot-wall furnaces, or furnaces used for casting or melting of metal at high temperatures up to 5000°F (2760°C). There can be other special types. For more detailed information on the various types of furnaces, see Table A.1.1.6. See Figure A.1.1.6(a) through Figure A.1.1.6(c) for examples of a cold-wall, horizontal, frontloading vacuum furnace; a cold-wall, induction-heated vacuum furnace; and a hot-wall, single-pumped, retort vacuum furnace. Table A.1.1.6 Vacuum Furnace Protection Operating and Subject Safety Devices Cold Wall Hot Wall Casting and Melting Induction Resistance Electron Beam Gas- Fired Electric Induction Electron Beam Electric Arc Plasma Arc A. Vacuum System yes yes yes yes yes yes yes yes yes Vacuum chamber yes yes yes yes yes yes yes yes yes Roughing pump yes yes yes yes yes yes yes yes yes Diffusion pump op op yes op op op yes op no Holding pump op op op op op op op op no Retort no no no yes yes no no no no Multichamber op op op op op op op op op Internal fan (temp. uniformity) no op no op op no no no no B. Heating System yes yes yes yes yes yes yes yes yes High voltage no no yes no no no yes yes yes High current yes yes no no yes yes yes yes yes C. Cooling System Work cooling yes yes yes op op op op no yes Gas quench op op op op op op op no no Oil quench op op no no no no no no no Water quench op op no no no no op no no Fans, blower op op op op op op op no op Port-bungs op op op op op no no no op External-internal heat exchanger op op op op op op op op op Water-cooling equipment yes yes yes yes yes yes yes yes yes D. Process Atmosphere Cycle Hydrogen op op no op op no no no op Nitrogen op op no op op no no no op Methane op op no op op no no no op Argon op op no op op no no no yes Helium op op no op op no no no op E. Material Handling Internal yes yes yes yes yes yes yes yes yes External yes yes yes yes yes yes yes yes yes F. Instrument Controls Temperature yes yes yes yes yes yes yes yes yes Vacuum yes yes yes yes yes yes yes yes yes Pressure yes yes yes yes yes yes yes yes yes Flow yes yes yes yes yes yes yes yes yes Electrical yes yes yes yes yes yes yes yes yes G. Hazards of Heating System Gas-fired no no no yes no no no no no Electric heated yes yes yes no yes yes yes yes yes Cooling water to be circulating yes yes yes yes yes yes yes yes yes Overheating yes yes yes yes yes yes yes yes yes Steam buildup yes yes yes yes yes yes yes yes yes Diffusion pump element yes yes yes yes yes op yes op no Pump element overheating yes yes yes yes yes op yes op no Accumulation of air yes yes yes yes yes yes yes yes yes Hydrogen accumulation op op op op op no no no no Other combustibles no no no no no no no no no Water in oil explosion no yes no no yes no no no no Radiation no no yes no no no yes yes yes Water sentinel yes yes yes yes yes yes yes yes yes Electrical short safety shutdown yes yes yes — yes yes yes yes yes H. Personnel Safety Hazards yes yes yes yes yes yes yes yes yes Yes: Equipment provided or condition present. Op: Optional; there might be a choice. ****INSERT FIGURE HERE**** FIGURE A.1.1.6(a) Example of a Cold-Wall, Horizontal, Front-Loading Vacuum Furnace. ****INSERT FIGURE HERE**** FIGURE A.1.1.6(b) Example of a Cold-Wall, Induction-Heated Vacuum Furnace. ****INSERT FIGURE HERE**** FIGURE A.1.1.6(c) Example of a Hot-Wall, Single-Pumped, Retort Vacuum Furnace. ****INSERT FIGURE HERE**** FIGURE A.1.1.6(d) Example of a Three-Torch Production Plasma Melter. Plasma Melting. Plasma melting is a process by which metal solids, powders, chips, and fines are consolidated into ingot or slab form. Melting is accomplished by use of an ionized gas that transfers heat from the plasma torch to the material. The gas might be oxidizing, reducing, or inert, depending on the process requirements. The temperature of the plasma gas is in excess of 3632°F (2000°C). Material consolidation might be in the form of an ingot, usually extracted from the bottom of the melt chamber, or a slab that is removed horizontally from the melt chamber. The melt chamber operating pressure might vary from 102 atmospheres to 2 atmospheres, making the process suitable for a wide variety of metals and alloys. Cleaning and refinement of the material might be accomplished by the use of hearth melting, stirring action by torch manipulation, inductive stirring coils, or vacuum/pressure cycling of the melt chamber. The melt chamber, torches, copper hearths, consolidation containment system, and power supplies are water cooled. Each water-cooled circuit is monitored for low flow and high temperature, with alarms for all circuits, power disruption for critical circuits, or both. Solid-state power supplies are utilized to provide power to the torches, which range in size from 47 Btu/hr (50 kW) for a small research unit to multiple torches of 948 Btu/hr (1000 kW) each for large production melters. The torches provide x, y, and z movements that are programmable or computer controlled. [See Figure A.1.1.6(d).] Electron-Beam (EB) Melting. Of all commercial melting techniques, electron-beam (EB) melting is capable of producing the highest refinement of end product. The beam of the electron gun can be focused to produce heat intense enough to vaporize even those metals with the highest melting points. Where combined with a vacuum atmosphere of approximately 104 torr (1.3 × 106 Pa), most impurities can be separated from the product being melted. EB melting is especially suited for refining refractory metals and highly reactive metals, but it also has applications in melting alloy steels. Commercial EB melters are available in a variety of sizes and configurations. Figure A.1.1.6(e) illustrates a vertical feed system that allows the molten metal to drop from the feed stock into a water-cooled copper retention hearth, where the molten metal is further refined by the oscillating beams of the two guns. The retention time of the metal in the hearth is controlled by adjusting the melt rate of the feedstock. The metal flows over a weir at the end of the hearth and falls into a water-cooled chill ring, where it solidifies into a billet as it is withdrawn downward from the chamber. Vaporized impurities condense on the cold inner walls of the vacuum chamber or on special collector plates that are easily removed for cleaning. Because of the intense heat needed for the melting and refining process, the vacuum chamber is usually of doublewall construction so that large quantities of cooling water can circulate through the passages of the chamber. Vacuum Arc Melting and Vacuum Arc Skull Casting. Vacuum arc melting is a high-volume production method for alloying and refining metals. Alloys can be produced by sandwiching and welding strips of different metals together to produce an electrode that, after melting, results in the desired alloy. Second and third melts are sometimes necessary to refine the alloy. Most arc melters are of the consumable electrode type; however, nonconsumable electrode melters are commercially available. Figure A.1.1.6(f) illustrates the principal components of one type of consumable electrode arc melter. In operation, dc voltage potential is established between the stinger rod, which has the electrode attached to it, and the water-cooled copper melt cup. The stinger rod is driven down until an arc is established between the electrode and a metal disk placed in the bottom of the melt cup. Once the arc has stabilized and melting begins, the voltage might be reduced, thus shortening the arc length and lessening the possibility of arcing to the water-cooled sidewall of the cup. Automatic control systems are available for controlling the arc length and melt rates. A mechanical booster pumping system provides vacuum operating levels of approximately 10-2 torr (1.3 × 10-4 Pa).Water-cooling circuits are provided for the stinger rod, head, melt cup, solid-state power supply, cables and connections, and vacuum pumping system. The vacuum arc skull caster is a variation of the vacuum arc melter, with the essential difference that, instead of melting the electrode into a copper cup and allowing the molten metal to solidify, the electrode is melted into a cold-wall copper crucible. The crucible then is tilted, allowing the molten metal to pour into a casting mold, leaving a solidified metal lining, or “skull,” in the crucible. Burn-throughs into water jackets, which allow water to come in contact with hot metal, are not uncommon in arc melting. Equipment damage can be minimized by providing overpressure-relief ports, reliable cooling water sources, well designed and monitored cooling circuits, and well-trained operators. Blast protection walls are frequently installed for personnel protection. ****INSERT FIGURE HERE**** FIGURE A.1.1.6(e) Example of an Electron-Beam (EB) Melter. ****INSERT FIGURE HERE**** FIGURE A.1.1.6(f) Example of a Vacuum Arc Melter. 1.1.7 This standard shall not apply to the following: (1)*Coal or other solid fuel–firing systems A.1.1.7(1) Designing coal or other solid fuel–firing systems requires special knowledge and experience with such solid fuel systems. As an example, different types of coal (anthracite vs. sub-bituminous)—and other solid fuels such as petroleum coke, wood chips, sawdust, other biomass, and combustible dusts such as medium density fiberboard dust — can introduce significantly different hazards and require significantly different handling systems and fuel delivery systems. Solid fuels present unique burner control challenges. For example, there might be challenges selecting and arranging flame supervision devices, selecting the method of fuel preparation and delivery, and determining actions to take in an emergency shutdown. The best guidance from NFPA for coal-fired systems (pulverized or aggregate) is NFPA 85, Boiler and Combustion Systems Hazards Code. Another resource is FM Global Property Loss Prevention Property Loss Prevention Data Sheet 6-17, “Rotary Kilns and Dryers.” Burning of other solid fuels is less standardized. An available resource is FM Global Property Loss Prevention Data Sheet 6-13, “Waste Fuel Fired Boilers.” Coordinating this guidance into the design of an oven or furnace requires special knowledge and experience so that the solid fuel system is integrated into the overall oven or furnace system while the intent of NFPA 86 with regard to other interlock and control requirements is maintained. (2) Listed equipment with a heating system(s) that supplies a total input not exceeding 150,000 Btu/hr (44 kW) (3) Fired heaters in petroleum refineries and petrochemical facilities that are designed and installed in accordance with API STD 560, Fired Heaters for General Refinery Services, 2007; API RP 556, Instrumentation and Control Systems for Fired Heaters and Steam Generators, 1997; and API RP 2001, Fire Protection in Refineries, 2005. (4)*Fluid heaters where either of the following conditions exists: (a) Fluid is flowing under pressure in tubes or pipes and is indirectly heated by combustion of liquid gas fuel or an electrical source. (b) Fluid is heated indirectly by products of combustion of liquid or gas fuel flowing through tubes (firetube). A.1.1.7(4) For information on fluid heaters, refer to NFPA87, Recommended Practice for Fluid Heaters. Fee may be required