8501-1997.pdf

NFPA 8501Standard for Single Burner Boiler Operation 1997 Edition National Fire Protection Association, 1 Batterymarch Park, PO Box 9101, Quincy, MA 02269-9101 An International Codes and Standards Organization Copyright  National Fire Protection Association, Inc. One Batterymarch Park Quincy, Massachusetts 02269 IMPORTANT NOTICE ABOUT THIS DOCUMENT NFPA codes, standards, recommended practices, and guides, of which the document contained herein is one, are developed through a consensus standards development process approved by the American National Standards Institute. This process brings together volunteers representing varied viewpoints and interests to achieve consensus on fire and other safety issues. While the NFPA administers the process and establishes rules to promote fairness in the development of consensus, it does not independently test, evaluate, or verify the accuracy of any information or the soundness of any judgments contained in its codes and standards. The NFPA disclaims liability for any personal injury, property or other damages of any nature whatsoever, whether special, indirect, consequential or compensatory, directly or indirectly resulting from the publication, use of, or reliance on this document. The NFPA also makes no guaranty or warranty as to the accuracy or completeness of any information published herein. In issuing and making this document available, the NFPA is not undertaking to render professional or other services for or on behalf of any person or entity. Nor is the NFPA undertaking to perform any duty owed by any person or entity to someone else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. The NFPA has no power, nor does it undertake, to police or enforce compliance with the contents of this document. Nor does the NFPA list, certify, test or inspect products, designs, or installations for compliance with this document. Any certification or other statement of compliance with the requirements of this document shall not be attributable to the NFPA and is solely the responsibility of the certifier or maker of the statement. NOTICES All questions or other communications relating to this document and all requests for information on NFPA procedures governing its codes and standards development process, including information on the procedures for requesting Formal Interpretations, for proposing Tentative Interim Amendments, and for proposing revisions to NFPA documents during regular revision cycles, should be sent to NFPA headquarters, addressed to the attention of the Secretary, Standards Council, National Fire Protection Association, 1 Batterymarch Park, P.O. Box 9101, Quincy, MA 02269-9101. Users of this document should be aware that this document may be amended from time to time through the issuance of Tentative Interim Amendments, and that an official NFPA document at any point in time consists of the current edition of the document together with any Tentative Interim Amendments then in effect. In order to determine whether this document is the current edition and whether it has been amended through the issuance of Tentative Interim  Amendments, consult appropriate NFPA publications such as the National Fire Codes Subscription Service, visit the NFPA website at www.nfpa.org, or contact the NFPA at the address listed above. A statement, written or oral, that is not processed in accordance with Section 5 of the Regulations Governing Committee Projects shall not be considered the official position of NFPA or any of its Committees and shall not be considered to be, nor be relied upon as, a Formal Interpretation. The NFPA does not take any position with respect to the validity of any patent rights asserted in connection with any items which are mentioned in or are the subject of this document, and the NFPA disclaims liability for the infringement of any patent resulting from the use of or reliance on this document. Users of this document are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, is entirely their own responsibility. Users of this document should consult applicable federal, state, and local laws and regulations. NFPA does not, by the publication of this document, intend to urge action that is not in compliance with applicable laws, and this document may not be construed as doing so. Licensing Policy This document is copyrighted by the National Fire Protection Association (NFPA). By making this document available for use and adoption by public authorities and others, the NFPA does not waive any rights in copyright to this document. 1. Adoption by Reference—Public authorities and others are urged to reference this document in laws, ordinances, regulations, administrative orders, or similar instruments. Any deletions, additions, and changes desired by the adopting authority must be noted separately. Those using this method are requested to notify the NFPA (Attention: Secretary, Standards Council) in writing of such use. The term "adoption by reference" means the citing of title and publishing information only. 2. Adoption by Transcription—A. Public authorities with lawmaking or rule-making powers only, upon written notice to the NFPA (Attention: Secretary, Standards Council), will be granted a royalty-free license to print and republish this document in whole or in part, with changes and additions, if any, noted separately, in laws, ordinances, regulations, administrative orders, or similar instruments having the force of law, provided that: (1) due notice of NFPA's copyright is contained in each law and in each copy thereof; and (2) that such printing and republication is limited to numbers sufficient to satisfy the jurisdiction's lawmaking or rule-making process. B. Once this NFPA Code or Standard has been adopted into law, all printings of this document by public authorities with lawmaking or rule-making powers or any other persons desiring to reproduce this document or its contents as adopted by the jurisdiction in whole or in part, in any form, upon written request to NFPA (Attention: Secretary, Standards Council), will be granted a nonexclusive license to print, republish, and vend this document in whole or in part, with changes and additions, if any, noted separately, provided that due notice of NFPA's copyright is contained in each copy. Such license shall be granted only upon agreement to pay NFPA a royalty. This royalty is required to provide funds for the research and development necessary to continue the work of NFPA and its volunteers in continually updating and revising NFPA standards. Under certain circumstances, public authorities with lawmaking or rule-making powers may apply for and may receive a special royalty where the public interest will be served thereby. 3. Scope of License Grant—The terms and conditions set forth above do not extend to the index of this document. (For further explanation, see the Policy Concerning the Adoption, Printing, and Publication of NFPA Documents, which is available upon request from the NFPA.) Revisions were adopted in 1967. 1997. and acted on by the National Fire Protection Association.000 lb of steam per hour. Standard for Single Burner Boiler Operation. and 1973. NFPA 85A was completely revised. . Major revisions in 1982 included changes to the scope of the standard so that it applied to boilers with fuel input that was greater than 12. which are referred to as the NFPA 85 series. This edition of NFPA 8501 was approved as an American National Standard on August 15. this standard was adopted at the 1964 Annual Meeting as NFPA 85A and covered natural gas–fired units. at its Annual Meeting held May 19–22. Foremost was the renumbering and retitling of the document to NFPA 8501. In 1982. 1997. CA. with an effective date of August 15. covering fuel oil–fired units. the committee suggested that the document be renumbered to 85A to distinguish it from the remainder of the Boiler-Furnace standards. released by the Technical Correlating Com- mittee on Boiler Combustion System Hazards. Tentative Standard NFPA 85C-T–1964. In 1987. Inc.500. Standard for Single Burner Boiler Operation. 1997. and supersedes all previous editions. was prepared by the Technical Committee on Single Burner Boilers.000 Btu/hr (3663 kW) rather than 10. Various technical changes were incorporated. 1997. Included are new or revised definitions. new appendix material. The 1992 edition was a partial revision and included a variety of changes. was combined with NFPA 85A and the combined standard was issued as NFPA 85. These lines are included as an aid to the user in identifying changes from the previous edition.. 1972. This was consistent with an initiative by the NFPA Boiler project to remove the letter designations and use shorter document titles. 8501–1 Copyright © 1997 NFPA. and other revisions were made to conform with the NFPA Manual of Style. Origin and Development of NFPA 8501 Originally. It was issued by the Standards Council on July 24. This latest edition is a partial revision that includes changes to improve the standard. Changes other than editorial are indicated by a vertical rule in the margin of the pages on which they appear. and revised requirements for logic control systems. All Rights Reserved NFPA 8501 Standard for Single Burner Boiler Operation 1997 Edition This edition of NFPA 8501. At the 1965 Annual Meeting. in Los Angeles. Babcock & Wilcox Co. TX [M] Donald J. CT [M] [M] (Alt. Sherman. Assn. DE [U] Michael C. Inc. L. VA [SE] Masaaki Kinoshita.. Axtman. NC Merton W. American Petroleum Inst. CT [I] Steven K. Inc.. TX [U] Rep. Exxon Research and Engr. Factory Mutual Research Corp. OH [M] Francis X. Union Carbide Corp. Cioffi) Kenneth N. MD [SE] Gordon G. Elek) (Alt. Wachter. S. Raytheon Engr & Constructors. CT Paul L..and multiple-burner boilers with a heat input rate of 12. Qilin. MA Courtney D.8501–2 SINGLE BURNER BOILER OPERATION Technical Correlating Committee on Boiler Combustion System Hazards Dale E.. MO [U] Merton W. MO Thomas B. C. Funk. to J. NFPA Staff Liaison Committee Scope: This Committee shall have primary responsibility for documents on the reduction of combus- tion system hazards in single. Wong. Lawrence. Underwriters Laboratories Inc. Babcock & Wilcox Co. Funk) Nonvoting Shelton Ehrlich. Henry K. WV [U] William H... Inc. deRuyter. L. Gray Gull Assoc. to M. Industrial Risk Insurers Rep.. to S.. Mitsubishi Heavy Industries Ltd. Nonvoting Secretary Nat’l Fire Protection Assn. Japan [M] Johnny W. Lutherville. CT [I] Dennis P. NJ [U] (Alt... K. The DuPont Co. Kemper Nat’l Insurance Cos. Yeich. American Boiler Mfrs... NC [I] (Alt. NJ [M] Alternates Tetsuya Fujino. Alvey. Gaetke. Dressel. OH [M] [I] William E. VA [M] [SE] Jerry J.. Waung. ABB Combustion Engr. and stoker-fired boilers. (Bill) Bass. Inc.. Inc. to R. 1997 Edition . IL [RT] Peter B.. Inc. MA Russell N. Industrial Risk Insurers. CA Robert P.000 Btu/hr and above. Industrial Risk Insurers.. Polagye. Bunker. PA [M] William G. Lin. Inc. Moskal.. Hartford Steam Boiler Insp. Forney Int’l. heat recovery steam generators. PA [M] Thaddeus Bukowski.. Mosher. OH [I] Peter J. MA [I] Robert S.. fluidized-bed boilers. Honeywell. Bailey Controls Co. to P. Gore Willse) J.500. M&M Protection Consultants. MD [U] Ronald E. Moskal) (Alt.. Hamilton. Co. Chair Monsanto Co. This Committee also is responsible for documents on the reduction of hazards in pulverized fuel systems. Maskol.. ABB Combustion Engr. CA John P. Foster Wheeler Energy Corp. Elek. O’Rourke. OH [I] James L. J.. Kinoshita) Richard J. Bostick. X. & Ins. Kaltenbach.. The DuPont Co. Maskol) (Alt. Fringeli. Hamilton Consulting Services. Cunningham. Mitsubishi Heavy Industries America. CT [M] John C. Gore Willse. Bunker.. Kemper Nat’l Insurance Cos. to F. TX [SE] James R.. at any heat input rate.. Jenkins. Inc. Honeywell. Palo Alto. OH [M] (Alt. Co. Baltimore Gas & Electric Co. Cioffi. to P. J. Matthews. This includes all fuels. Burns & McDonnell Engr. COMMITTEE PERSONNEL 8501–3 Technical Committee on Single Burner Boilers Peter J. Inc. American Risk Consultants Corp. Herdman) (Alt. MD [SE] John J. Gore Willse. Williams. Landis & Gyr. Babcock & Wilcox Co. CT [M] Tim McCarthy. Doran.. Lawrence. Herdman.. Clark. TN [U] William H. This list represents the membership at the the Committee was balloted on the text of this edition. Axtman. Dressel. NOTE: Membership on a committee shall not in and of itself constitute an endorsement of the Association or any document developed by the committee on which the member serves. Fireye. CT [I] Dale E. A.. Lawrence) Nonvoting Russell N. to K. VA [SE] Robert J. American Boiler Mfrs. N. VA Merton W. Inc. 1997 Edition . Inc. Since that time.. OH [I] Thaddeus Bukowski. IL [M] J. changes in membership may have occurred. DuPont Engr. Honeywell.000 Btu/hr and above. MO [U] Courtney D. OH [E] Jacques van Heijningen.. Bunker. Eibl. to R.. Lutherville. NJ [M] James C. Assn.. Inc. ABB Combustion Engr. GA [I] Alternates Ian M. Inc. IL [RT] Robert M. NFPA Staff Liaison Committee Scope: This Committee shall have primary responsibility for documents on the reduction of combus- tion system hazards and the prevention of boiler furnace explosions in single burner boilers with a heat input rate of 12. ABB Combustion Engr. Vice Chair Monsanto Co. Chair Industrial Risk Insurers. Honeywell. MN [M] (Alt. M. The Nat’l Board of Boiler & Pressure Vessel In- spectors.. A key to classifications is found at the back of this document. CA [M] Kenneth N. DeLacy. Alvey. “Red” Wagner....500. This includes all fuels. PA [M] Lee J.. Underwriters Laboratories Inc. Gross. Mosher. CT [M] John M.. The Coen Co. Gray Gull Assoc. Inc. . . 8501–16 1-2 Purpose . Logic . . . . . . . . 8501–13 Appendix A . . . . . . . . 8501– 6 6-8 Soot Blowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–29 1997 Edition . . . . . . . . . . 8501– 7 Chapter 8 Simultaneous Firing of Oil and Gas for Fuel Transfer Only . . . . . . 8501– 7 8-1 Transfer Without Shutdown . . . . . . . . . 8501–21 Chapter 6 Operating Systems . . . . . 8501–12 Single Burner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–21 5-1 General . . . . . . . . . . . . . . . . . . . . . . Construction. . . . . . . . . . . . . . . . . . . . . . . . . 8501–18 and Operation . . . . . . . . . . . . . . . . . . 8501–13 Chapter 11 Referenced Publications . . . . . 8501–12 9-1 General . . . 8501–18 2-5 Maintenance Organization . . . . . . . 8501–15 Appendix B Referenced Publications . . . . . . . . . . . . . . . 8501–10 8-3 Single Fuel Firing Without Airflow Biasing . . . . . . . 8501–12 10-2 Inspection and Maintenance Schedule . . . . . . . . . . . . . . . . . . . . 8501–21 6-3 Automatic (Nonrecycling) Systems for Watertube Boilers . . . . . 8501–19 Chapter 4 Equipment Requirements . . . . 8501–17 2-1 Furnace Explosions . . . . . . . 8501–11 Chapter 9 Dual Oil Atomizers in a 4-6 Combustion Control System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–12 9-2 Changeover Procedures . . . . . . . . 8501–19 4-3 Alternate Fuel Firing . . . . . . . . . . . . . . . . . . . . . . . 8501–18 2-3 Installation . . . . . . . . . . 8501–20 4-8 Flame Safety Shutdown System . . . . . . . . . . . . . . . . . . . 8501–15 Index . . . . . . . . . . . 8501–18 2-4 Coordination of Design. . . . . . . . . . . . . . . . . . . . . . . 8501– 5 6-6 Supervised Manual Systems for Oil-Fired 1-1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–10 8-4 Single Fuel Firing with Airflow Biasing . . . . . . . . . . . . . . . . . . . . . . . 8501–20 4-7 Interlock System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 7 Simultaneous Firing of Oil and and Engineering . . . . . . . . . . . . . . . 8501– 9 Continuous Basis . . . . 8501–19 4-2 Fuel Supply (Gas) . . . . . . . . . . . . . . . . . . . . . . 8501– 7 7-3 Light-Off Cycles . . . . . . . 8501–21 5-3 Oil-Fired Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–19 Chapter 3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . 8501– 7 2-7 Gas and Oil Firing—Special Problems . . 8501– 5 Watertube Boilers . . . . . . . . . 8501– 5 6-7 Supervised Manual Systems for Gas-Fired Watertube Boilers . . . . . . . . . . . . . 8501–20 4-4 Fuel-Burning Equipment . . . . . . . . . . . . Design. . . . . . . . . . . . . . . . . . . . . 8501–21 6-2 Automatic (Recycling) Systems for Watertube Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–21 5-2 Gas-Fired Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–12 Chapter 10 Inspection and Maintenance . . . . . . . . . . . . . 8501–17 Chapter 2 General . . 7-2 Continuous Firing . . . . . . . . . . . . 8501– 7 7-4 Normal Shutdown Procedure . . . . 8501–13 6-1 General . . . 8501–28 6-4 Automatic (Recycling) Systems for Firetube Boilers . . . 8501– 6 Gas Fuels . . . . . . 8501– 6 7-1 General . . . . . . . . . . . . . . . . . . 8501–12 Chapter 5 Starting a Cold Boiler . . . . . . . . . . . . . . . . . . 8501–12 10-3 Familiarity with Equipment and Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–18 2-6 Basic Operating Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501– 5 6-5 Automatic (Nonrecycling) Systems for Firetube Boilers . . . . . . . . . . . 8501–10 4-5 Burner Management System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501– 6 2-2 Manufacture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8501–16 Chapter 1 Introduction . . . . . . . . . . . . . 8501–12 10-1 General . 8501–20 4-9 Electrical Equipment . . . . . . . . . 8501– 9 8-2 Simultaneous Firing on a 4-1 Fuel Supply (Oil) . .8501–4 SINGLE BURNER BOILER OPERATION Contents Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 000 Btu/hr (3663 kW) or greater. 1-1.1 The purpose of this standard is to establish minimum uncontrollable condition or in a masked failure of a micropro. related systems to contribute to safe operation and. Chapter 9 applies to dual atomizers in a single burner. such as those of process heaters that are used even more important that only highly trained individuals be in chemical and petroleum manufacture wherein steam gen- employed in the translation of these guidelines into operating eration is incidental to the operation of a processing system. Therefore. alarms. Chapter 8 applies to fuel trans. 1-2. In such cases. It is vital that the designer of the safety 1-1.5 Revisions to this document reflect the current state of knowledge and do not imply that previous editions were When applying any type of equipment to a safety system. and maintenance of single burner firetube and 1-2.or gas-fired watertube boilers. operation.1 This standard applies to boilers with a fuel input rating of forced draft fan inlet through the stack. combustion control equipment.3 Furnaces. Such coordination shall include requirements for ensuring a continuous flow path from the 1-1. Chapter 6 applies to operating systems. Each type of hardware has its own unique features are not covered by this standard. 2. the designer is cau- (b) Detailed sections that are specific to the particular tioned that the standard is not a design handbook and does operation described (Chapter 5 applies to starting up a cold not do away with the need for competent.4 The effect of gas cleanup systems that are located down- stream of the post–combustion gas passes of the boiler is Chapter 1 Introduction known to be significant. This document is to be used for the design. make it 1-1. cable to new installations and to major alterations or exten- sions of existing equipment for the preparation and burning of fuel that are contracted for use subsequent to the date of FOREWORD this standard. and in particular the persuasiveness of microprocessor-based hardware.2* This standard is not retroactive.2* No standard that will guarantee the elimination of fur- watertube boilers and their burner management and combus. flue gas path is required. the specific hardware as well as possess a thorough under- Nevertheless. those features of this standard that are considered applicable It is neither possible for these standards to encompass specific and reasonable for existing installations. The standard is organized as follows: is under constant development. Chapter 10 applies to inspection and maintenance. ferring.4 Since this standard is based on the present state of the system be completely familiar with the features and foibles of art. operation that is described. Technology in this area tion control systems. 1-1. their fuel-burning systems.) 1-2. The user of this standard must recognize the (a) Introduction and common sections that apply to all complexity of fuel firing as to the type of equipment and the fired fuels covered in this standard (Chapters 1 through 4) characteristics of the fuel. operating companies are encouraged to adopt standing of these standards and their intent. including auto. nance of single burner boilers. the system and the safety of the unit and personnel. its application to existing installations is not mandatory. ity of the approach. the designer is responsible for the valid- simultaneous firing of fuels. engineering judg- boiler. reflected in part by revisions to this standard. Coordination of the operating proce- dures and designs of the boiler and air quality system’s air/ 1-1 Scope. INTRODUCTION 8501–5 NFPA 8501 (a) Natural gas as defined in Chapter 3 (b) Other gas having a Btu value and characteristics that Standard for are similar to natural gas Single Burner Boiler Operation (c) Fuel oil of No. Technological advances in recent years. systems. 4. It is intended that a designer who is capable of applying matic recycling and automatic nonrecycling systems for both more complete and rigorous analysis to special or unusual watertube and firetube boilers and supervised manual systems problems shall have latitude in the development of such for oil. in partic- ular. hardware applications nor should these standards be considered a “cookbook” for the design of a safety system. or 6 grade (d) Gas and oil that are fired simultaneously for fuel transfer 1997 Edition (e) Gas and oil that are fired simultaneously and continu- NOTICE: An asterisk (*) following the number or letter des- ignating a paragraph indicates that explanatory material on ously the paragraph can be found in Appendix A. to the prevention of furnace explosions. 5. This standard offers 12. designer must carefully consider all of the possible failure modes and the effect that each might have on the integrity of 1-2 Purpose. installation. 1997 Edition .500. standards for the design. operation. This standard is appli- Information on referenced publications can be found in Chapter 11 and Appendix B. nace explosions can be promulgated. the inadequate. and other related controls that used in conjunction with the sections covering the specific are essential to safe boiler operation. the common sections should be safety interlocks. This standard applies only the general requirements of these systems because of the only to boilers using single burners that fire the following fuels: many variations of the designs. and mainte- cessor-based system that could result in the operator unwit. installation. ment. Chapter 7 applies to designs. When using this standard. trips. no single point failure should result in an unsafe or 1-2. In partic- ular. and tingly taking action that could lead to an unsafe condition. and operational modes.3 Emphasis is placed on the importance of operation and maintenance procedures. 1 The boiler shall not be released for operation before the tion of the accumulation by a spark or other ignition source. in cooper- 2-1 Furnace Explosions. will allow the operator to avoid unsafe conditions. upset conditions or control malfunction be reached on its suitability in advance of start-up. and the igni. installing temporary understanding of the problem by both designers and opera.3 An evaluation shall be made to determine the optimum will result in rapid or uncontrolled combustion when an igni. including “furnace puffs. ensure that the unit is not defi- cient in any apparatus that is required for proper operation. (c) An environment conducive to proper decisions and nition of an accumulation actions.3 The purchaser.” are the result 2-2. improper tion.2 A dangerous combustible mixture within the boiler burner. ditions such as the following: (b) In-service maintenance and checking of system func- (a) An interruption of the fuel or air supply or ignition tions without impairing the reliability of the overall control energy to the burners that is sufficient to result in momentary system. Any such temporary system shall be reviewed nace explosions. by the purchaser. with respect to pressure parts. ducts. 2-3.5 The burner front piping and equipment shall be the accumulation by a spark or other source of ignition designed and constructed to prevent the formation of hazard- (c) Repeated. tems and devices during the normal operating life of the These accumulations can ignite with explosive force in the plant. proper operating sequences. the equip- has been far more frequent than is usually recognized. and an examination ratus is installed and connected properly. or equipment or con. (d) The accumulation of an explosive mixture of fuel and air as a result of a complete furnace flameout. interlocks and instrumentation to meet these requirements tors can greatly reduce the risks and actual incidences of fur. 2-1. Usable displays of variables shall be provided that operation of a boiler that will produce common explosive con.4 The conditions that are favorable to a furnace explosion installation of the equipment shall see that all pertinent appa- as described in 2-1. (b) Fuel leakage into an idle furnace and the ignition of 2-2.3 Numerous situations can arise in connection with the situation. and the operating company shall avoid believed that improved instrumentation.5 In a boiler. The does not necessarily provide for maximum overall safety. of numerous reports of furnace explosions suggests that the occurrence of small explosions. and a clearer ate properly as a system. air and fuel metering. Dead pockets could exist in the be tested jointly by the organization with responsibility for the boiler enclosure or other parts of the unit where combustible system design and those who operate and maintain such sys- mixtures can accumulate under upset furnace conditions. furnace puffs. The trend toward more complex plants or increased design of equipment or control system. enclosure consists of the accumulation of an excessive quan- tity of combustibles that are mixed with air in proportions that 2-2. explosive mixture 2-3 Installation.3 are typical examples. Some magnitude and intensity of the explosion will depend on both trip actions result in additional operations that increase expo- the relative quantity of combustibles that has accumulated and sure to hazards. installation and checkout of the required safeguards and such as that from attempting to light a burner instrumentation system. These tests and checks shall be accomplished before ini- presence of an ignition source. fuel-burn- an accumulated combustible mixture within the confined ing equipment. A furnace explosion can result from ing the advantages and disadvantages of each trip function.2 The constructor who is responsible for the erection and 2-1. the equipment manufacturer. and Engineering.1 The purchaser or the purchaser’s agent shall. the proportion of air that is mixed therewith at the moment of ignition. ignition of this accumulation if the quantity of combustible mixture and the proportion of air to fuel are such that an NOTE: The maximum number of automatic trip features explosive force is created within the boiler enclosure. (a) Information about significant operating events permit- ting the operator to make a rapid evaluation of the operating 2-1. tial operation. Design.8501–6 SINGLE BURNER BOILER OPERATION Chapter 2 General 2-2 Manufacture. could be necessary. and agreement shall 2-1. Explosions. and the operating company. ation with the manufacturer. could lead to an air/fuel mixture that could result in a flame- out that is followed by reignition after a combustible air/fuel 2-3. 2-2. 1997 Edition . loss of flames and is followed by restoration and delayed reig. maintenance of a stable flame. safety interlocks and boiler operation until such safeguards have been tested to oper- protective devices. 2-3. or near misses 2-3.4 The safety interlock system and protective devices shall ratio has been reestablished. and safe lighting and space of the furnace or within the associated boiler passes. integration of manual and automatic safety features.4 This standard requires a minimum degree of automa- of improper procedures by operating personnel. resulting in the accumulation of an under normal operating conditions.1 The basic cause of furnace explosions is the ignition of so far as is practical. automation requires added provisions for the following: trol system malfunction. the engineering consultant. unsuccessful attempts to light off without ous concentrations of combustible gases that could exist appropriate purging. 2-2. It is ment manufacturer. the engineering consultant. and fans that convey the gases of combustion to the stack. In some instances.2 All fuel systems shall include provisions to prevent for- eign substances from interfering with the fuel supply to the 2-1. consider- tion source is supplied. turbu- lence. Boiler. rigidly enforced. NOTE: This is not “Air-Rich” as previously defined. liquid. Automatic. or any combination thereof (a) Establish operating procedures that will result in the by the application of heat from combustible fuels in a self-con- minimum number of manual operations. and individual responsible for approving equipment.1 Statistics indicate that human error can be a contribut- ing factor in the majority of furnace explosions. of fuel and air into a furnace at the required velocities. (b) Periodic analysis to compare the plant to evolving tech. for operator guidance shall be provided for achieving these basic operating objectives. See Burner Management System. A ratio of air to fuel supplied to a furnace that pro- vides less air than that required for an optimum air/fuel ratio. Mechanical. Chapters 5 and 6 describe operating Burner. Air Change. It is particularly important that purge and start. Alarm. (c) Lack of functional coordination of the various compo. Frequently. fuels. safeguards. amount of air that is required for complete combustion of a 2-4. (See Chapter 10. A closed vessel in which water is heated. or a procedure. Authority Having Jurisdiction. that pro- 2-4. revealed human error and has overlooked completely the Excess Air. grated. or failure to use. Burner Management System. controls.3 In the planning and engineering phases of plant construc. The use of inter. An audible or visible signal indicating an off-stan- ment. 2-4.1 Basic operating objectives shall include the following: generated. The device in an oil burner that (c) Maintaining documentation of plant equipment. terms shall have the fol- operating procedures. design shall be coordinated with operating personnel. (b) Standardize all operating procedures. dedicated to boiler safety. Each of these fuels has special hazards that relate to its physical characteristics. ment or its controls that is equal to the volume of furnace and boiler gas passes. Consideration shall be given to the ergonomics that will exist during the operating life of the system. interlocks. A supplementary fluid. operator and dard or abnormal condition. such as steam or 2-5 Maintenance Organization. and communication and training— Alteration. An air/fuel ratio. including the combustion con- and to stop sequences when conditions are not proper for trol system but not the burner management system. The control system that is tions shall be described. the service requirements. A change or modification in a boiler system that shall be the responsibility of the operating company and shall results in a deviation from the original design specifications or be accomplished by the following steps: criteria.2 Furnace explosions have occurred as a result of unfavor. and equipment lowing meanings. office. The physical boundary for all boiler pres- up procedures with necessary interlocks be established and sure parts and for the combustion process. for the maintenance of equipment at intervals that are consis. which consist of the boiler. DEFINITIONS 8501–7 2-4 Coordination of Design. Construction. provided through the burner. Atomizing Medium. tained or attached furnace. 1997 Edition . steam is 2-6. Air/Fuel Ratio. sys. Boiler Control System. that assists in breaking down oil into a finely divided state. Boiler Enclosure. However. vides more air than that required for an optimum air/fuel able functional design. steam is superheated. and maintenance atomizing medium. it is important to consider whether the error is also a result of the Chapter 3 Definitions following: (a) Lack of understanding of. maintenance functions. the design. Therefore. an installa- the manufacturer’s recommendations. the investigation has ratio. (a) Providing design and operating personnel who possess Annunciator. operator assistance in the starting and stopping of fuel preparation and burning equipment. or tent with the type of equipment. A quantity of air. The group of control systems that locks is essential to minimize improper operating sequences regulates the boiler process. proper For the purpose of this standard. nents of the steam-generating system and its controls Air-Rich. emits liquid fuel in a finely divided state without using an tem. and safety devices. 2-6 Basic Operating Objectives. and Operation. A program shall be provided air. required to bring about these objectives Approved. Fuel-Rich. continuation. 2-4. Common hazards the prevention of misoperation of and damage to fuel prepa- are involved in the combustion of solid. Theoretical Air (Stoichiometric Air). A device or group of devices for the introduction sequences that have proven to be effective in boiler operation.2 Written operating procedures and detailed checklists tion of fuel within the furnace.4 The proper integration of the various components— given quantity of a specific fuel. The device in an oil burner that emits liquid fuel nology so that improvements can be made to make the plant in a finely divided state. safer and more reliable Atomizer. fuel and air supply equip. A device indicating an off-standard or abnor- a high degree of competence in this field and who are mal condition by both visual and audible signals. The chemically correct tion. Air supplied for combustion in excess of theo- chain of causes that triggered the operating error. Atomizer. and 2-7* Gas and Oil Firing—Special Problems.* The organization. (b) Unfavorable operating characteristics of the equip. or gaseous ration and fuel-burning equipment.* Acceptable to the authority having jurisdiction.) tion. supplied to a furnace. and concentration to maintain ignition and combus- 2-6. All manual and automatic func. retical air. and functional objectives of the over- all system of the components and their controls shall be inte. burner. installation. A pressure-actuated device that uation of services. 1. proper procedures. locks are included to ensure that the operation follows estab. The control system that regu. See definition of Purge. and by whose labeling the manufacturer indicates cal process of rapidly converting fuel and air into products of compliance with appropriate standards or performance in a combustion. air quality control. See definitions of LP-Gas and Natural Gas. ated device that is arranged to effect a safety shutdown of the Labeled. A pressure-actuated sense a limit or off-limit condition or improper sequence of device that is arranged to effect a safety shutdown of the events and to shut down the related equipment or to prevent burner when the steam pressure exceeds a preset pressure. Operating systems and logic software when the water temperature exceeds a preset temperature. and stopped automat. through the burner under prescribed light-off conditions. electrical igniter that is capable of directly ignit- the boiler in accordance with demand. that maintains peri- not limited to. Low Gas Pressure Switch. or service meets identified standards or when the gas pressure exceeds the preset value. and 6 fuel oils as defined in Light-Off Time Limit Timer. A temperature-actu. production of listed equipment or materials or periodic eval- High Gas Pressure Switch. rials. High Oil Temperature Switch. Inerting is cleanout and drain connections. steam pressure exceeds a preset pressure. The dilution of the oxygen content of an air/fuel Drip Leg. The visible or other physical evidence of the chemi. The establishment of the combustion of fuel absence of flame and provides a usable signal. Fuel Oil. so that liquids and solids are trapped. Class 3 Special (Direct Electric Igniter). also used to support ignition under low load or certain adverse Manual. symbol. generally in arranged to effect a safety shutdown or to prevent starting excess of 10 percent of fuel load burner input. A pressure-actuated device that is Class 1. condition. A system by which a furnace is purged input. Numbers 2. High Water Temperature Switch. and stopped automat. such as. A device or group of devices that are arranged to Excessive Steam Pressure Switch. has been tested and found suitable for a specified purpose. materials. 1997 Edition . A device that is used on super- ASTM D 396. A system by which a furnace is purged and a operating conditions. Individual devices and intercon- ommended by the burner manufacturer. and stopped manually. A device that senses the presence or Light-Off. It is ically but does not recycle automatically. but and concerned with product evaluation. ignited. A temperature-actuated Logic System. Class 2 igniters shall be permitted to be operated as and a burner is started. the limits that are required to maintain the viscosity range rec- (a) Hard-Wired Systems. An addition to the boiler system. attached a label. A system by which a furnace is both fuel and air above the minimum ignition temperature. and stopped manually. nization that is acceptable to the authority having jurisdiction Extension. light-off conditions. ity having jurisdiction and concerned with evaluation of prod- Furnace Purge. specified manner. Class 3 igniters. An igniter that is applied to ignite the fuel input arranged to effect a safety shutdown or to prevent starting through the burner and to support ignition under any burner when the gas pressure falls below the preset value. An enclosure that is designed for the combustion published by an organization that is acceptable to the author- of fuel. light-off or operating conditions. The decision-making and translation ele- device that initiates a signal when oil temperature rises above ments of the burner management system. entering the furnace. burners to ignite the fuel input to the burner under prescribed Combustion Control System. that maintains periodic inspection of Gas. Interlock.* Equipment. with suitable mixture to a point where it is no longer explosive. ignited. ignited. generally 4 percent to 10 percent of full load burner fuel Supervised Manual. into which gas is discharged accomplished through the addition of an inert gas or vapor. Automatic (Nonrecycling). result of an interlock or operator action. or services included in a list Furnace. 4. A pressure-actuated device that is such that it will provide sufficient ignition energy. The range of capacity of such igniters is burner is started. Computer hardware.8501–8 SINGLE BURNER BOILER OPERATION Types of systems used in this document include the following: burner to raise any credible combination of burner inputs of Automatic (Recycling). odic inspection of production of labeled equipment or mate- Flame. purged and a burner is started. The automatic shutoff of a specific fuel as the than five minutes. Low Fire. Class 3 igniters. ucts or services. material. This control system ing the main burner fuel. An igniter that is applied to ignite the fuel input purged and a burner is started. Flame Detector. The capacity of such igniters generally does lates the furnace fuel and air inputs to maintain the air/fuel not exceed 4 percent of the full load burner fuel input. and whose listing states that either the is arranged to effect a safety shutdown or to prevent starting equipment. Inter. at its associated when the oil pressure falls below the preset value. Standard Specifications for Fuel Oils. This time shall be no more Fuel Trip. High Steam Pressure Switch. necting wiring. I/O devices. A chamber of ample volume. An igniter that is applied particularly to gas and oil lished. ratio within the limits that are required for continuous com. ignited. immediately light off the main burner. A special Class 3. 5. Listed. A temperature-actuated and interconnections between these items device that is arranged to effect a normal burner shutdown 2. proceeding in an improper sequence to avoid a hazardous Excessive Water Temperature Switch. Equipment or materials to which has been burner when the water temperature exceeds a preset temper. Class 3. The minimum fire rate that results in stable Igniter. Its location and capacity are Low Oil Pressure Switch. Inerting. vised manual systems that limits the allowable time between completion of purge and light-off. bustion and stable flame throughout the operating range of high-energy. A device that provides proven ignition energy to combustion. A pressure-actuated device that is arranged to effect a normal burner shutdown when the (b) Microprocessor-Based Systems. includes the furnace draft control where applicable. Class 1 igniters shall be permitted to also operate as Class 2 or ically and recycles on a preset pressure range. power supplies. or other identifying mark of an orga- ature. A system by which a furnace is Class 2. heating. A fast-closing pressure in the system. Service Connection. A system that proves the leak tight- designed. to a predetermined low level. and interconnected so as to Safety Shutdown Trip Relay. Main Burner Establishing Period. The pressure at the fuel ser.3 MJ/m3). To establish by measurement or test the existence of a 4-1. propylene. and consumed. ated boiler passes. The region between the maximum fuel input and minimum fuel input in which the burner flame can be maintained continuous and stable. The ability of a device to maintain a constant 4-1. A flow of air through the furnace. tions in accordance with the applicable portions of NFPA 31. attention and to automatically initiate corrective action. Postpurge. chamber in a finely atomized form that can be ignited readily nal design specifications or criteria. per ft3(26. lines where heavy oil will tend to solidify. and butylenes. Cold oil may prevent satis- functions that conventionally are attributed to “semiautomatic. level. 1997 Edition .1 MJ/m3 and 55. Relief valves shall be installed after the pump to prevent over- Safety Shutoff Valve (Safety Trip Valve). sages. The interval of Natural Gas. n-butane. normal or a safety shutdown signal. that is used to trip all required equipment simultaneously. the oil service connection under anticipated operating condi- Purge. pressure. ducts. See Burner Management System. and straining the fuel from storage to the service connection Restart. Prove. sized. Operating Range. The flue gas pressure at the outlet of the last convection pass of the boiler. To sense and indicate a condition requiring of the following hydrocarbons or mixtures of them: propane. ing automatic corrective action. Repeatability. time during light-off in which a safety control circuit permits sisting mostly of a mixture of organic compounds—normally the main burner fuel safety shutoff valve(s) to be opened methane.9 MJ/m3). air to clean heat-absorbing surfaces. ensure that the interlocks and instruments reflect correct val- Set Point. and fans that convey the gases of Normal Fuel Supply Pressure. isobutane. The Btu value of nat. tion system is required to supervise the igniter flame. An electromechanical relay provide a suitable fuel supply over a full range of conditions. See Burner Management System. range recommended by the burner manufacturer. To gradually vary the fuel and air flows to the ing light-off in which a safety control circuit permits the igniter burner in accordance with load demand. Indicates a mandatory requirement.4 All equipment that is associated with pumping. fuel safety shutoff valve(s) to be opened before the flame detec- Monitor. care shall be taken to ment. ethane. 4-1. the majority averaging Unit. and butane. tion for Shutdown. A purge performed after a burner is shut down. LP-Gas. before the flame detection system is required to supervise the ural gases varies between about 700 Btu per ft3 and 1500 Btu main burner flame only. 4-1 Fuel Supply (Oil). A process that returns the boiler system to its origi. EQUIPMENT REQUIREMENTS 8501–9 Low Oil Temperature Switch. The terms “automatic (nonrecycling)” and NOTE: Excessively heated oil may create vapor-lock. and associated flues and ducts that will effectively Standard for the Installation of Oil-Burning Equipment. A device that is arranged to effect a Normal. A material that is composed predominantly of any Supervise. A-10(b)1. A device that is arranged to and ignition energy to the furnace by means of a safety inter- effect a safety shutdown [requires manual reset (see the defini. propane. or position. A gaseous fuel occurring in nature and con. Manual. Safety. and delivered to specified condition such as flame. The interval of time dur- Modulate. Low Water Cutout. Trial-for-Ignition Period (Main Burner). Supervised Manual. A mechanical device for introducing steam or the boiler falls to a predetermined low level.2 Operation of the burner shall not be attempted until a Purging also can be accomplished by an inert medium. A predetermined value to which an instrument is ues of the variable being measured. Semiautomatic. or power is connected to the boiler. Recycle. See definition of Fuel Oil. Chapter 4 Equipment Requirements Outlet Draft. firing equip. To sense and indicate a condition without initiat. ness of all safety shutoff valves and prevents main burner or Oil. See definitions for Trial.5 Fuel being burned shall be delivered to the burner at ply to the main burner(s) or the igniter(s) in response to a proper temperature and pressure.1 Fuel shall be properly stored. 4-1. Stopping burner operation by shutting off all fuel Auxiliary Low Water Cutout. satisfactory fuel supply is assured. valve that automatically and completely shuts off the fuel sup- 4-1. A start-up that is initiated by steam pressure or water temperature following a normal shutdown.3 Fuel shall be delivered continuously to the combustion Repair. remove any gaseous combustibles and replace them with air. Shutdown. set point characteristic. A temperature-actuated Shall. Indicates a recommendation or that which is below the limits that are required to maintain the viscosity advised but not required. vice connection for which the fuel burning system has been Valve-Proving System. which “supervised manual” are used in this standard to describe the can prevent continuous operation. Stopping burner operation by shutting off all shutdown of the burner when the water level in the boiler falls fuel and ignition energy to the furnace.” factory atomization. A manually initiated start-up. or controlled devices. boiler gas pas. particularly in dead-end adjusted and at which it shall perform its intended function. A person meeting the requirements of for-Ignition Period. device that initiates a signal when the oil temperature falls Should. Trained Operator. prepared. Safety)] of the burner when the water level in Soot Blower.6 Where the fuel must be heated. The confined spaces of the furnace and the associ- 1000 Btu per ft3 (37. flow. Trial-for-Ignition Period (Igniter). 4-1. igniter light-off if the test is not satisfied. A point at which fuel. combustion to the stack. an atomizing medium. lock or interlocks and requiring a manual restart. shall be properly designed. This is 4-2. Either the main CAUTION: Means shall be provided to prevent or re. 4-4. These tests shall be performed without the igniter in service and shall include the intended range and 4-3. lieve excess pressure between these valves. 4-3 Alternate Fuel Firing. from the main burner under light-off conditions.8* Two safety shutoff valves in series. The An automatic vent valve shall be provided between the two use of such igniters to support ignition or to extend the valves. each with proof of to ensure that the main flame is self-supporting. the igniter shall be 4-2. Where oil and gas are to be the igniter and main burner flames. Where oil and gas are to be grade of fuel(s). the main burner.1 The main burner shall direct the fuel and air into the Leakage-tightness tests of the main safety shutoff valves shall furnace so as to provide a stable flame and efficient combus- be conducted at least annually.1. and other equipment that operate at speeds faster than of oil and gas fuels.3* Two safety shutoff valves in series shall be provided in 2. 4-4. between venting systems of different boilers. each with proof of closure switches. compatible with the selected mode of operation. Valve proving shall be performed either after every burner shutdown or prior to every burner light-off. shall be provided in the the discharged gas being drawn into the air intake. flame shall be proven by a flame detector. to burn heated and unheated oils shall include a procedure to 4-4. supervised by a atmosphere shall be located so that there is no possibility of listed automatic valve-proving system.2 Automatic Fuel Selection. The main flame authority having jurisdiction. the charge of fuel to the furnace in the event that ignition 4-2* Fuel Supply (Gas). (See A-4. ventilating gas line to the main burner. energy to provide immediate ignition of all fuel discharge and debris shall be removed from the gas piping. mined by tests. the automatic vent valve is prohibited by the authority having 4-2. either after every burner shutdown or prior to every burner The discharge shall be extended sufficiently above the boiler light-off. For simultaneous firing ers.1. a manually positioned.1.1 The main burner shall be equipped with a perma- tions shall include the intended routing of recirculated oil.1 The gas supply at the gas service connection shall be then the main burner flame shall be proven by a flame scan- controlled at the pressure for which the fuel-burning system ner independently of the igniter. burned alternately.1 Where a Class 1 igniter is used. chips. burned alternately. time trial-for-ignition of the main burner has expired.1. 4-2. nently installed igniter.) the line to the gas igniter.1 Manual Fuel Selection.1.9 Oil piping materials and system design shall be in accor- The burner shall be operated under controlled conditions to dance with NFPA 31. One safety shut- 4-2. damp- accordance with 4-3.2 Gas piping shall be of ample size to maintain the desired shut down as a part of the burner light-off procedure when the constant pressure for the maximum burner flow.1. tion over its entire operating range. supervised by a listed auto. the speed of response of other components in the system.2 The igniter flame or arc shall impinge on the main burner air/fuel mixture and shall supply sufficient ignition 4-2. each with proof of 4-4. shall be provided in the gas line to burner flame shall be proven by a flame scanner.1.2 The burner shall be provided with at least one conve- nient observation port of a size to permit visual inspection of 4-3.5 A drip leg shall be provided in the gas piping. does not occur during light-off.7* The discharge from atmospheric vents and vents to the jurisdiction. 1997 Edition . is stable.3 Where a Class 3 igniter is used. 4-2.1 and Chapter 8.1. National Fuel Gas Code. two safety shutoff valves in series. Standard for the Installation of Oil-Burning limit the potential for abnormal operation as well as to limit Equipment.2 Where a Class 2 igniter is used. ensure that the proper type of oil. 4-4. There shall be no cross connection cleaning. an automatic change from one fuel to the The tests shall verify that transients that are generated in the other shall be accomplished only after a shutdown. scale. 4-4. (See also A-4-2. Precau. shall be provided in the gas line to the main burner.2.1. off valve shall be provided in the line to the oil igniter. 4-1. 4-4.1* Ignition. it shall not be used to ignite main fuel under uncontrolled or abnormal conditions.6 Gas piping materials and system design shall be in accor. the main matic valve-proving system.4 The igniter shall be designed for periodic removal.1.2.2 Main Burner. An automatic vent valve shall be pro- vided between the two valves for gas igniters.8501–10 SINGLE BURNER BOILER OPERATION 4-1.8 Permanent means shall be provided for making leakage- tightness tests of the main burner gas safety shutoff valves.1. 4-4. the main burner closure. 4-1. If the Class 2 igniter is not shut down once the main flame sequence is successfully completed. or windows of the boiler room or adjacent buildings. had been designed.1.) and adjacent structures so that gaseous discharge does not 4-4. Where dance with NFPA 54. is not dependent upon ignition support from the igniter. see Chapter 7. for manual changeover of the system shall be provided in Such transients are generated by burner control valves. fuel selector switch shall be provided to permit operation of the necessary interlocks. Provisions fuel and air systems do not adversely affect burner operation. 4-4.3 and A-4-4. 4-4.4 Where a Class 3 Special igniter is used. and maintenance. is being supplied to the burner.3 The limits of stable flame for the burner shall be deter- fuel safety shutoff valves.4 Foreign matter such as welding beads. two safety shutoff valves in series. shall be proven by a flame scanner.1. shall be provided in the oil line to the main burner.3* Two safety shutoff valves in series.3. and closure. Valve proving shall be performed system. dust. 4-2. present a fire hazard.2. Where the automatic vent valve is prohibited by the burner control range shall be prohibited. flame or the igniter flame shall be proven. and controls for the fuel to be fired. 4-4. 4-4.7 The operation of a burner system that has the capability 4-4 Fuel-Burning Equipment. requirements of 4-4. (j) Timer failure 4-4. (b) Logic system failure shall not preclude proper opera- tion of the burner flame and furnace.g. operation.1 Failure Effects. excursions.. and maintenance.6 Any procedure for clearing the atomizer and piping (c) Other appropriate means into the furnace prior to shutdown shall be accomplished Exception: Dampers are not required on the outlet of boilers of a type in while the fan is operating and the igniter is re-established or which maintenance operations are performed from outside of the boiler.2 shall be provided to permit observa.2.2. The logic system for burner management shall of contaminants that could cause an interruption of service. 4-4.6 Combustion Products Removal. be designed specifically so that a single failure in that system shall not prevent an appropriate shutdown. This shall be accomplished by one of the following means: 4-4. and NFPA 54.1 Where the fuel is to be atomized with the assistance of in a particular sequence in response to external inputs and another medium. 4-5. the following 4-4. A logic system provides outputs 4-4. (h) The operator shall be provided with a dedicated man- sible operating and locking devices. This equipment shall be ual switch(es) that shall independently and directly actuate compatible with the combustion control system of the boiler.4.4 Each manual adjustment feature on the burner shall be interlock nonfunctional if the linkage becomes disconnected.4.2 Design. (c) Logic shall be protected from unauthorized changes.2. (f) Addressing errors 4-4. tions adversely affecting flame stability and could re.2.2 At least one observation port in addition to the processor logic functionability. (d) Logic shall not be changed when the associated equip- ing combustion products without adversely affecting stable ment is in operation. 4-5.2 Specific Requirements. ate the failure modes of components when considering the design application of the system. (f) Noise immunity shall be adequate to prevent false quire special draft control provisions. As a minimum. National Fuel Gas Code.3. (g) Processor faults tion shall be interlocked with the burner so that airflow is (h) Relay coil failure proven during equipment operation.3.3.4 Combustion Air Supply.2. each connection shall be equipped with a damper shall not prevent a mandatory safety shutdown trip. (e) System response time (i.2 Provisions shall be made for periodic cleaning of the failure effects shall be evaluated and addressed: combustion air supply equipment. relay. throughput) shall be suffi- CAUTION: Tall stacks can produce furnace draft condi. cleaning.5 Furnace. NOTE: Some items are not applicable to specific types of 4-4. 4-5 Burner Management System. ciently short to prevent negative effects on the application. tor intervention. All boiler outlet dampers shall be equipped with acces.6. 4-4. (c) Information transfer corruption and losses 4-4. As a minimum. 1997 Edition .5 The atomizing equipment for oil burners shall be (a) Placing the interlock on the driven member designed for periodic removal.2. (d) Inputs and outputs “fail-on.2 Where two or more boilers are connected to a com.1 The combustion air supply equipment shall be capa- ble of supplying combustion air for the optimum air/fuel ratio 4-5. burner stability while minimizing zones that cannot be purged. recoveries. burner management. (a) Diagnostics shall be included in the design to monitor 4-4. (b) Utilizing a furnace pressure switch 4-4.2. enter the atomizing medium line during or after operation.” “fail-off” tion or interlocked with the equipment so that they are opened automatically or manually during equipment opera. logic systems.1 General Requirements. EQUIPMENT REQUIREMENTS 8501–11 4-4.4. flame conditions. Standard for the Installation (b) Memory corruption and losses of Oil-Burning Equipment. 4-4. 4-4.3. e.3 Atomizing Medium for Oil Burners. The interlock shall be placed on the driven member.4. the main flame is proven continuously during this operation. (a) Interruptions. system. 4-4.1 Louvers and grilles shall be fixed in the open posi.e. Logic. the safety shutdown trip relay.1 The outlet draft equipment shall be capable of remov.3 The requirements for the availability of combustion air and partial losses of power shall be determined from NFPA 31. (g) A single component failure within the logic system mon stack. dips. transients.3.5.3 Provisions shall be made to ensure that fuel cannot burner management meets the intent of these standards.7 Clearing of the oil passages of the atomizer into the section is to provide guidance in the use of logic systems in furnace immediately after a shutdown shall be prohibited. provided with means for securing it in its intended position. The intent of this 4-4.2 Fans supplying air to the boiler room for combus. this atomizing medium shall be supplied free internal logic. 4-4..1 The furnace shall be designed to promote main 4-5.4. Provisions shall be made to prevent rendering the be reached in case of emergency. (e) Signals that are unreadable or not being read tion. 4-4.6. (i) Relay contact failure (fail-on or fail-off) 4-4.2 The atomizing medium shall be provided at the pres- sures that are required for proper operation. At least one identified manual Interlocks shall be provided to prevent firing against a closed switch shall be located remotely from the boiler where it can damper.5. The logic system designer shall evalu- over the entire operating range of the burner. the following shall be included in the design to ensure that a logic system for 4-4. ted to be bypassed for blowdown purposes only. the failure modes shall be evaluated and addressed. 5-3.g. 4-5.2.1. of the safety shutoff valves shall not exceed four seconds. vibra. but not be limited to.1. 5-1.2. 4-7.8.6 Data highway communications between the burner management and boiler control system and other systems shall Chapter 5 Starting a Cold Boiler be permitted. Where grounding is not include. shall have switching contacts in one side of the line and shall and flame monitoring.8501–12 SINGLE BURNER BOILER OPERATION 4-5. The procedures of Chapter 6 shall be followed for starting a cold gas-fired boiler.3 Requirement for Independence. as an atomizing medium.1 The combustion control system shall maintain air/fuel dance with the boiler manufacturer’s instructions.1 The logic system performing the safety functions for burner management shall not be combined with any other Exception: See 4-7. National Electrical Code®. and with the burner management system only where the fuel/air ratio is shall be protected with a suitable fuse or circuit breaker in the controlled externally from the boiler control system (e.2. condition without a trained operator present. design of the system.2 The system shall provide limits on fuel and air to prevent reducing furnace input below the point of stable burner oper. logic or control system. 4-5.3. 5-3. (c) Compressed air supply (d) Check valves in steam and air lines to the atomizer 4-7.6 Each safety control ac circuit shall be two wire. 4-7. 4-6 Combustion Control System. 5-3. proper purge interlocks and possible and the circuit voltage exceeds 50 volts.3. culating system. 1997 Edition . 4-7. Where remote I/O communication 5-1 General. repair. inadvertent tenance. using auxiliary heater and recir- shall be of a type that is temporarily held during blowdown. independent 4-9 Electrical Equipment. NFPA 70.1. When steam is not available for heat- ation.2 The burner management safety functions shall in 4-7. another boiler system). 4-8 Flame Safety Shutdown System. tion. (a) An atomizing air supply. 4-7. This bypass (a) Circulate and heat oil.2. and corrosive agents. humidity. (See A-4-1.. 5-3.1 Starting of a cold boiler shall be accomplished in con- formance with the manufacturer’s recommendations. In no 4-5.2 or verified by operational tests.1 Auxiliary Air Atomizing of Oil.) 4-7. 5-3. 4-5. input/output systems.3. shall be provided with independent logic.2 Each interlock shall be provided with a method of estab. 5-2 Gas-Fired Boilers.2.3. one side Exception: Boiler control systems shall be permitted to be combined grounded. between a logic system processor and its input/output devices are used. mixtures at pre-established ratios throughout the operating range of the burner and during changes in the firing rate.3 shall be used.3. The set point shall be repeatable within prescribed limits.3.e. the circuit timing.2 Applicable start-up procedures for the provided boiler shall be followed.4 and Chapter 5.3. and independent internal power sup- plies and shall be functionally and physically separate from 4-9. The firing rate shall be limited in accor- 4-6. to satisfy all interlocks.7 Safety control dc circuits shall be arranged as called for 4-5. or for driving auxiliary equip- operation shall be defined by the burner manufacturer and ment.2 Required Facility. be provided with ground-fault circuit-interrupters.5 Interlocks shall not be manually bypassed at any time during normal operation. agement system.1 The response time from flame failure to de-energization more than one boiler where separated from the burner man. Boiler control systems shall be permitted to be combined for 4-8. such as temperature. 4-7 Interlock System. (b) Approved auxiliary oil heater for start-up fuel flow with a capacity not less than that required for minimum fire with 4-7. 4-8.2 The response time from de-energization of the safety 4-5. (a) Forced draft (FD) fan bling any of the interlock devices. stable flame lishing the set point.2 Special fuels or applications could require components used for burner management and boiler control systems as is for hazardous location and shall be reviewed during the used for other logic systems. where included.2. or extended shutdown be started from a cold reopening of the main or igniter fuel valves.1. locked fuel/air hot side only. 5-1.4 The interlocks on the low water cutouts shall be permit.3 The logic system shall be limited to one boiler only.4 The burner management and boiler control system shutoff valves to full closure shall not exceed one second.7 No logic sequences or devices shall be permitted case shall a boiler that has been taken out of service for main- that allow momentary closing and subsequent.5 The same hardware type shall be permitted to be 4-9. The minimum and maximum points of stable burner ing oil. trial timing for ignition. 5-3.6 where grounding is possible.2. mandatory safety shutdowns.3 Starting Procedure.1 The system shall be equipped with a method of deter- mining the operating state of each interlock without disassem. Signals that initiate mandatory safety shutdowns shall be hard wired. 4-5.1 Required Equipment. 4-6.. ratio with mechanical positioning type system). one of the starting methods described in 5-3.1* All electrical equipment and wiring shall conform to other logic systems (i.3 Interlock devices shall be designed for anticipated envi- ronmental conditions. preferably not exceeding nominal 120 volts. 5-3 Oil-Fired Burners.2. (d) Follow normal start-up procedure as described in Chapter 6. 5-3.2.4.e. and supervised manual systems to meet the intent of this standard. firing condition. [See 5-3. 6-2 Automatic (Recycling) Systems for Watertube Boilers. Airflow interlock 1997 Edition . 5-3. Air pressure and “open damper” interlocks for all (d) Open light oil supply into the system.1 Required Equipment. nonrecycling).3.) equivalent protection and meet the intent of this standard. (m)Follow normal start-up procedure. admit medium to main burner. adequate for heating and atomizing the heavy oil. 5-3. while not recommended.e.2. is optional. Different arrangements are permissible if they provide ator with adequate warning devices. A-4-2.3 An igniter as specified in 4-4. shut down in in Chapter 6. and the manual burner valve(s) shall be closed. (f). (l) Open heavy oil supply to the system. shut down in 6-2.3. (a) FD fan Chapter 6 Operating Systems (b) Approved auxiliary oil heater for start-up fuel flow with a capacity not less than that required for minimum fire with 6-1* General. (a) FD fan (c) Start fan. 2. (c) Modulation.2 It is further assumed that the fuel to be fired has been man- ually selected.e. (g) When steam pressure is raised to a point where it is (c) Set combustion control at light-off firing rate. described in Chapter 6. (b) Mechanical atomizer (d) Satisfy fan interlock. satisfy atomizing operator with adequate warning devices. recycling).1 Prefiring Cycle. In this section. shut down (d) When steam pressure is raised to a point where it is in accordance with normal shutdown procedure as described adequate for heating and atomizing the oil. (b) Light-off cycle (i) Make atomizing medium interlocks operable. where included. (k) Make oil and atomizing medium interlocks operable (f) Change over from auxiliary oil heater to steam oil heater. set pressure and perform four major functions as follows: (g) Remove mechanical atomizer.2.) medium interlocks.. where provided (j) Change over from auxiliary oil heater to steam oil (d) Shutdown cycle heater. (h) Prove purge airflow by satisfying one of the following (b) Insert mechanical atomizer. two items: (c) Bypass oil and atomizing medium interlocks. Chapter 6 and Figures A-4-1.2 Starting Procedure.1 shall be provided. (g) Follow normal start-up procedure. accordance with the normal shutdown procedure as (h) Shut off light oil supply to the system.1 Required Equipment. (i) Remove mechanical atomizer. and (g) in the sequence 5-3.1 illustrate typical arrangements of operating systems for (c) Mechanical atomizer automatic (i. (f) When steam pressure is raised to a point where it is adequate for heating and atomizing the oil. accordance with the normal shutdown procedure as 6-2. using air as the atomizing medium. and A- stable flame 4-4. dampers in the flow path (e) Follow normal start-up procedure described in Chapter 6. it is assumed that the unit is hot and that steam (c) Insert mechanical atomizer. The prefiring cycle shall accomplish the following in the listed order: 5-3. pressure and operating water level have been established. 6-2.. automatic (i. 1.4 An automatic (i.1. making certain that dry steam is available. (a) Shut off heavy oil to system. (g) Satisfy appropriate fuel interlocks. recycling) unit shall recycle on a pre- described in Chapter 6. (a) A light oil supply NOTE: The order of items (e). (c) Check valves in the heavy and light oil lines (e) Where atomizing medium is used and if not already (d) Means to bypass oil and atomizing medium interlocks on. 5-3. (The fact that these are bypassed shall be made evident to the (f) Where atomizing medium is used. 5-3. supply.3. (a) Prefiring cycle (h) Insert steam atomizer.2 Auxiliary Mechanical Atomizing of Heavy Oil.. by removing bypasses. Chapter 6. 6-2.8. (k) Follow normal start-up procedure. (b) Prove no flame is present at the burner.3. (a) Prove the main fuel safety shutoff valves are closed. are discussed in A- fact that these are bypassed shall be made evident to the oper- 6-1. (d) Means to bypass atomizing medium interlocks (The Manual systems. as described in (f) Set combustion control at light-off rate. 6-2. (e) Close atomizing air supply and open atomizing steam (j) Insert steam atomizer.2 Required Facility. recycling) unit shall not be started (b) Bypass atomizing medium interlocks. The alternate fuel system shall be placed in a non- (e) Set combustion control at light-off firing rate.1 An automatic (i.] from a cold condition unless a trained operator is present.1(d). OPERATING SYSTEMS 8501–13 (b) Follow the normal start-up procedure.e. (a) Circulate and heat oil using auxiliary heater and recir- culating systems to satisfy oil interlocks.3 Auxiliary Mechanical Atomizing of Light (Unheated) Oil.3 Starting Procedure.. 4. prove the main flame. cle until a trained operator determines the cause of the shut- lowing in the listed order: down and takes the necessary corrective action to assure that safe operating conditions prevail before restarting: (a) Energize igniter. where provided. 2 and (e) Where the inerting system is used. 4. establish safety shutdown. Low fuel pressure 1.4.6 For automatic (i. water cutout 2. proof of igniter operation shall not be if in operation..High temperature of heated oil (a) Shut off fuel supply to main burner.4. Shut off atomizing medium. Low gas pressure (c) For oil: 3.4. vided. if in 1. Loss of control system actuating energy (d) Where gas is used. establish safety shutdown. If not proven. Power failure valves shall be vented to the atmosphere. open recirculating valve. (c) For oil: 1. determined by the auxiliary low water cutout) shall accom- (j) Set controls to light-off position. Excessive steam pressure or water temperature shall accomplish the following in the listed order: 10. admit fuel to main burner.7(a). gas piping between safety shutoff 6. shut off igniter. oil-recirculating flow. Low water level as determined by the auxiliary low tion where provided. establish safety shutdown. gas piping between safety shutoff 2. 5 and 6 oils. water temperature. has returned to within the preset operating range. Excessive steam pressure or water temperature 1997 Edition .7 Safety Shutdown Cycle. Low water level as determined by the auxiliary low (e) Perform a postpurge of the boiler furnace enclosure. Loss of or failure to establish flame 2. 6-2. 1. release to modulating control where pro. either one accomplished by a combustion control system.2 Light-Off Cycle. The light-off cycle 6-2. if desired. (h) Require manual reset. at an airflow rate not exceeding that at which the unit was shut flow required at maximum continuous capacity of the unit. Loss of control system actuating energy oils or 15 seconds for Nos. 7.5 Normal Shutdown Cycle. of which shall initiate a safety shutdown on low pressure. If proven. Where used. 6-2. If proven. or low water level (not the time for eight air changes. The dura- valves to the atmosphere. 5. Low temperature of heated oils recirculating flow. Power failure 1. The light-off cycle safety shutdown. gas igniters. valves shall be vented to the atmosphere. shall accomplish the following in the listed order and shall lowing in the listed order: activate an alarm: (a) Energize igniter. as inter- locked by flow or two pressure switches (One located at the 6-2.4. (b) Prove igniter flame is within 10 seconds. where used. (i) The purge shall be sufficient for at least eight air (f) Shut down fan.8501–14 SINGLE BURNER BOILER OPERATION Purge airflow shall reach no less than 70 percent of the air.4. Loss of or failure to establish flame (c) After a maximum of 10 seconds for gas and Nos. 5 and 6 oils. simultaneously shut off 2. if desired. 3. high water temperature. 2 and 4 5. Airflow during the time to open the damper and 6-2. simultaneously shut off 2. down.8* Any of the following conditions shall accomplish a 6-2. If not proven. or water level position. If proven. Modulation. Where used.) 6-2. burner other than return flow type. (a) Shut off fuel supply to main burner. 2. 1. (d) Where gas is used. If proven. vent the gas piping between igniter safety shutoff (f) Perform a postpurge of the boiler enclosure. Loss of atomizing medium. release to combustion control for modula. Loss of combustion air supply 1. 2. 4.e. water cutout The duration of the postpurge shall be no less than 15 seconds 8. recycling) boilers. Intermittent Igniter. (b) For gas: (b) Interrupt spark and shut off fuel supply to igniter. shut off atomizing medium. changes. and the burner shall not be allowed to recy- for a burner with an intermittent igniter shall accomplish the fol. 7. The normal shutdown cycle 9.4. if desired. admit fuel to main burner.4. 6. shut down fan. If not proven. The safety shutdown cycle for a burner with an interrupted igniter shall accomplish the fol. (c) After a maximum of 10 seconds for gas and Nos.3 Light-Off Cycle. plish a normal shutdown.4 Modulation. For an oil 1. establish safety shutdown. (a) For oil: (b) Prove igniter flame is within 10 seconds. open recirculating valve. If not proven. For simultaneously with 6-2. (g) After postpurge. For direct (b) Shut off fuel supply and interrupt spark to the igniter electric igniter. it shall be energized 4 oils or 15 seconds for Nos. Where used. For an oil burner other than return flow type. Interrupted Igniter. tion of the postpurge shall be no less than 15 seconds at an air- (d) Prove main flame. flow rate not exceeding that at which the unit was shut down. High gas pressure operation. shall be service connection and the other at the burner. if desired. the high steam return it to light-off position can be included in computing pressure. Loss of combustion air supply 2. required. and the burner shall be allowed to (k) Prove dampers and fuel control valve are in light-off recycle when steam pressure. 8. or water level has been established. satisfy atomizing if in operation.7 Any of the following conditions shall accomplish a during the time to open the damper and return it to light-off safety shutdown. 1. Airflow interlock. medium interlocks.3.e. 5 and 6 oils. if desired. (c) Modulation.7(a). Low temperature of heated oils (b) Prove igniter flame is within 10 seconds.2 An automatic (i. gas igniters. vided. Low water level as determined by the auxiliary low 2. 5. Air pressure and “open damper” interlocks for all (f) Perform a postpurge of the boiler enclosure.2.2.2. OPERATING SYSTEMS 8501–15 CAUTION: Excessive recycling to achieve a burner (c) After a maximum of 10 seconds for gas and Nos. gas piping between safety shutoff valves shall be vented to the atmosphere. For direct 3. the (h) Require manual reset. Low oil pressure (a) Energize interrupted igniter. and that the operating allowed to recycle when steam pressure.1 In this section. shut off atomizing medium. flow rate not exceeding that at which the unit was shut down. 6-3.4. shall accomplish the following in the listed order: (e) Where atomizing medium is used and if not already (a) Shut off fuel supply to main burner. The light-off cycle shall accomplish (a) For oil: the following in the listed order: 1. Where used. gas piping between safety shutoff valves shall be vented to the atmosphere. Loss of or failure to establish flame required. and 6-2. accomplished by a combustion control system. down and takes the necessary corrective action to assure that (j) Prove control system is in light-off position. that the boiler has been placed in accomplish a normal shutdown. tion of the postpurge shall be no less than 15 seconds at an air- 2. 2.4 shall apply.2. establish safety shutdown. shut off igniter. 6-2. A trained operator shall initiate the restart. admit fuel to main burner. (d) Prove main flame. Where used. it is assumed that the equipment is in water (not determined by the auxiliary low water cutoff) shall accordance with Chapter 4. 6-4. flow rate not exceeding that at which the unit was shut down. if desired. 6-2. 2 and light-off can lead to accumulation of a hazardous 4 oils or 15 seconds for Nos.6 shall not apply. release to modulating control where pro- Exception: 6-2.4 High steam pressure. (f). and (g) in the sequence is optional. proof of igniter operation shall not be 4. (d) Where gas is used. The normal shutdown cycle set pressure or temperature and perform four major functions shall accomplish the following in the listed order: as follows: (a) Shut off fuel supply to main burner. The safety shutdown cycle (d) Satisfy fan interlock. 1. If not proven. open recirculating valve. recycling) unit shall recycle on a pre. (c) Start fan. 2. establish safety shutdown.6 Safety Shutdown Cycle. The dura- the following in the listed order: tion of the postpurge shall be no less than 15 seconds at an air- (a) Prove the fuel safety shutoff valves are closed.4. 6-4. During the purge.2. 6-3 Automatic (Nonrecycling) Systems for Watertube Boilers. 6-4 Automatic (Recycling) Systems for Firetube Boilers. NOTE: The order of items (e). 6-3. (a) Prefiring cycle (b) For oil: (b) Light-off cycle 1. air damper shall be driven to the full open position. Loss of combustion air supply electric igniter. or low 6-4. if desired.. high water temperature. shall be be allowed to recycle.2 When high steam pressure. open recirculating valve. safe operating conditions prevail before restarting: 6-4. If not proven. If proven. (h) Prove purge airflow by satisfying one of the following (e) Where the inerting system is used. shut down fan.2. where provided 2. high water temperature. water level establishes a normal shutdown. 6. admit medium to main burner.1 The provisions of 6-2. For amount of fuel in the furnace and shall be avoided. where provided.2 Light-Off Cycle.1 Prefiring Cycle. if desired. 6-4. the burner shall not 6-4. Where used. water temperature. on. (i) The purge of the furnace and boiler gas passes shall be (g) After postpurge. The prefiring cycle shall accomplish (d) Perform a postpurge of the boiler enclosure. water cutout 1997 Edition . sufficient for at least four air changes. If proven. shut off atomizing medium. water level has returned to within the preset operating range. Loss of control system actuating energy 1. The dura- dampers in the flow path.2.2. 1.5 Normal Shutdown Cycle. vent the gas piping between igniter safety shutoff valves to the atmosphere. 6-4. (b) Shut off fuel supply and interrupt spark to the igniter (f) Where atomizing medium is used.2. and the burner shall not be allowed to recy- position can be included in computing the time for four air cle until a trained operator determines the cause of the shut- changes. (e) After postpurge. Airflow 6-4. it shall be energized two items: simultaneously with 6-2. (d) Shutdown cycle (c) Where gas is used. (c) For oil: (g) Satisfy appropriate fuel interlocks. and the burner shall be service in accordance with Chapter 5. Modulation. or low 2. Where used. shut down fan. 6-4.3 Modulation. (b) Prove no flame is present at burner. change to automatic Exception: 6-4. 6-6. 6-6. 2 and 4 oils or 6. or (b) Airflow. Perform a postpurge of 3. Operator Functions Interlock Functions 1. proof of igniter (b) For gas: operation shall not be 1.1(a). 5. Start purge timer. 1. Operator Functions Interlock Functions 1. It is assumed that fuel pressure and tem. power. control system energy. damper(s). vent 7. 4.1 and 6-4. None. are in light-off position. Damper and fuel control valve the boiler enclosure. main burner is closed.1(b).2. 6-5. Open fuel recirculating valve. shut off 3. Low water level as determined by the auxiliary low 15 seconds for Nos. 2. 1997 Edition . Loss of atomizing medium where used Table 6-6. None. or low water level establishes a normal shutdown. CAUTION: Excessive recycling to achieve a burner operating pressure at an light-off can lead to accumulation of a hazardous acceptable rate. 8. amount of fuel in the furnace and shall be avoided. and water level have been established. Low gas pressure valve to main burner. shut down. 2. 3. (a) Air pressure and open 2.High temperature of heated oil seconds. 6.4.1. With gas igniter. high water temperature. vent gas piping position. Open manual fuel shutoff 4. Loss of combustion air supply 3. None. After post purge. ratio. 4. shall not be allowed to recycle. (For direct electric ignition. Excessive steam pressure or water temperature gas piping between safety 8. 4. Spark and igniter and main the unit was shut down. None. None. Loss of or failure to establish flame where used.] the atmosphere. Remove fuel atomizer. 6-5. None.2 shall apply. Excessive steam pressure or water temperature Operator Functions Interlock Functions 9. 7. Shut off fuel supply to the main 2. Check that manual fuel 1. A trained operator shall initiate the restart. None.1(c). Power failure shutoff valves. seconds for Nos. and 6-6. 2. available. Fan is on. duration of the postpurge shall be no less than 15 6-6.1(c) Normal Shutdown Cycle (in listed order). Loss of control system actuating energy valve. None. in operation. Table 6-6. Open fuel safety shutoff 2. 3. 1. Energize igniter. Open damper(s) to purge 4. None. supervised manual unit. Close igniter safety shutoff valve(s). None. this fact shall be indicated to the operator. perature. atomizing medium. Close recirculating valve. 5. None. Atomizing medium supply is interrupt spark to the igniter if medium valve. 2. None.4 shall not apply. 4. satisfied at each step. Purge is complete. Where used. Table 6-6. None.1 The provisions of 6-4. 3. maintaining an optimum air/fuel 6-5 Automatic (Nonrecycling) Systems for Firetube Boilers. open atomizing 3. fan can be 4. fan can be 6. If light. Fuel safety shutoff valve(s) to 6-6 Supervised Manual Systems for Oil-Fired Watertube Boilers. Perform a postpurge of 5.2 Select the fuel to be fired. the burner Table 6-6.3 An igniter as specified in 4-4. The alternate fuel system shall seconds at an airflow rate be placed in a nonfiring condition.1(b) Light-Off Cycle (in listed order). 6-6. The valve in light-off position. 2. High gas pressure required. start light-off time seconds at an airflow rate limit timer.) 2. safety shutoff valves are ready 4.1(d)] shall be taken by the operator when starting a 3. for operation. range.2 When high steam pressure. Where used. Manual fuel shutoff valve(s) is Operator Functions Interlock Functions shutoff valve(s) is closed. Power failure 1. not exceeding that at which 7. 6.1(a) Prefiring Cycle (in listed order). combustion control.1 shall be provided. duration of the postpurge off airflow is less than purge shall be no less than 15 airflow rate. 6-6. Start fan. For gas igniter. The been satisfied. 5. and the indicated interlocks shall be atomizing medium. and the manual burner not exceeding that at which valve(s) shall be closed.1 The following steps [see Tables 6-6. main burner. When interlocks have the boiler enclosure. Prove igniter flame is within 10 10. where used. 4.1(h) and (i). After postpurge. None. Place damper and fuel control 6. the unit was shut down. Shut off fuel supply to the 1. Prove main flame is within 10 5.1(d) Safety Shutdown Cycle (in listed order). 1. between safety shutoff valves to [See 6-2. On reaching preset pressure 6. burner.8501–16 SINGLE BURNER BOILER OPERATION 7. shut down. shut off fuel supply and 3. closed. 5 and 6 water cutout oils. 5. 6. Bring unit to present 5. The duration of the postpurge (f) Low water level as determined by the auxiliary low shall be no less than 15 water cutout seconds at an airflow rate (g) Loss of atomizing medium not exceeding that at which the unit was shut down. Prove main flame is within 10 the boiler. None. Place damper and gas control 5.1(d)] shall be taken by the operator when starting a supervised manual unit. Operator Functions Interlock Functions shall sound alarms: 1.1(c) Normal Shutdown Cycle (in listed order). 6-8. 6-7.1(a).1(h) and (i). and interrupt spark. Open gas safety shutoff 2. Shut off gas supply to the 1.3 An igniter as specified in 4-4. valves to main burner. simultaneously energize 6-7 Supervised Manual Systems for Gas-Fired Watertube inerting system. shutdown: Operator Functions Interlock Functions (a) Low pressure in the fuel supply at the service connection 1. (a) Air pressure and open (d) Loss of or failure to establish flame purge position. atmosphere.1 The following steps [see Tables 6-7. Table 6-7. Check that gas safety 1. where oil heating is provided. 2. On reaching preset range.1. CAUTION: Excessive recycling to achieve a burner be shut down. start light-off time (h) Excessive steam pressure or water temperature limit timer. Prove igniter flame is within 10 seconds.1 Soot blowers shall be operated only while burners are pressure at an acceptable firing at rates that are sufficiently high to avoid extinguishing rate. OPERATING SYSTEMS 8501–17 6-6. if in operation. if this operation is not per- operation shall not be formed with an optimum air/fuel ratio. Start fan. and interrupt spark to the (b) High oil temperature igniter if in operation. Vent gas piping between safety (b) Loss of combustion air supply main burner and to the shutoff valves to the (c) Loss of or failure to establish flame igniter. Damper and fuel control valve (g) Low water level as determined by the auxiliary low valve in light-off position. None. None. or (b) Airflow. fan can 3.1 Soot blowing is necessary to maintain high thermal effi- ignition. this fact shall be indicated to the operator. 4.1(b) Light-Off Cycle (in listed order). (e) Power failure boiler enclosure. (d) Loss of control system actuating energy 2. 6-7. explosions can occur required. Fan motor is on. (h) Excessive steam pressure or water temperature 3. After postpurge. (For direct electric 6-8.2 Boilers that are equipped with automatic soot-blowing 4. Open damper(s) to 3. (f) Power failure 5.) from the formation and ignition of air-soot dust clouds within 2. Energize igniter.4. When interlocks valve(s) shall be closed. the burner flame.5 The following conditions.1(c). It is assumed that control system energy. and the indicated interlocks shall be 6-7.4 Any of the following conditions shall accomplish a safety shutdown: Operator Functions Interlock Functions (a) High gas pressure 1. Operator Functions Interlock Functions 6-8 Soot Blowing. 6-6. 1. If light- off airflow is less than purge water cutout airflow rate. [See 6-2. 6-7. 1. dampers(s). and the manual burner power. However. The alternate fuel system shall satisfied at each step.2 Select the fuel to be fired. None. None. CAUTION: Excessive recycling to achieve a burner light-off can lead to accumulation of a hazardous Table 6-7. closed. Purge is complete. 4.4 Any of the following conditions shall accomplish a safety Table 6-7. mum air/fuel ratio. Gas safety shutoff valves are shutoff valves are closed. amount of fuel in the furnace and shall be avoided. light-off can lead to accumulation of a hazardous amount of fuel in the furnace and shall be avoided. Vent gas piping between safety shutoff valves to the atmosphere.1(a) Prefiring Cycle (in listed order). 2. Shut off gas supply to the main (a) Low oil temperature burner. and 6-7. and water level have been established. are in light-off position. Where used.1. Perform a postpurge of the 2. light-off cycles. 6-7. Table 6-7. Start purge timer. None. 3. Bring unit to preset operating 3. proof of igniter ciency in oil-fired boilers. 1997 Edition .1. Boilers. equipment shall have their controls interlocked to prevent change to automatic operation when the burner is shut down or in the prefiring or combustion control.1(d) Safety Shutdown Cycle (in listed order).1(b). shut off fuel supply.1 shall be provided. maintaining an opti. 6-8. seconds. 6-7. 1. (c) Loss of combustion air supply 3. have been satisfied. 2. be placed in a nonfiring condition.] (e) Loss of control systems actuating energy 4. (b) Low gas pressure 2. . 7-4.2 The normal shutdown procedure for gas while continu- fected fuel in a stable manner. Provides for the introduction of the second fuel with. where used. on an interlock action peculiar to only one (g) Verify stable flame and proper air/fuel ratio of the gas of the fuels being fired. the following possibilities: (c) Open atomizing medium shutoff valve. 3. (f) Remove oil atomizer from burner if required. fire. (c) Verify stable flame and adjust air/fuel ratio in prepara- tion for purging oil atomizer. (b) Abrupt change in the air/fuel ratio (e) Open oil safety shutoff valve and establish oil flow through the burner. modate a fixed amount of secondary fuel without metering and totaling all fuels shall be acceptable. 7-2 Continuous Firing. 4. being fired. ing to fire oil shall be as follows: (a) Reduce gas flow to light-off rate. forming the following functions: (b) Place gas control valve in light-off position. tion 6-7 for gas. 7-3. range of the burner. (d) Verify stable flame and proper air/fuel ratio. (c) Over-firing of a boiler (f) Verify stable flame and proper air/fuel ratio. alone are included in Section 2-7 and A-2-7. (c) A safety interlock system with the following capabili- ties: (d) Purge oil passages of oil atomizer.3. Gas firing 7-4. (c) Verify stable flame and proper air/fuel ratio of the oil duced with their flow control valves in light-off positions.1 Hazards that are related to gas firing alone and oil firing (a) Establish oil fuel system to satisfy interlocks.3 When gas is introduced as the second fuel. (a) A fuel-rich condition (d) Place oil control valve in light-off position. down. (a) Low oil pressure 7. (a) A burner that is capable of burning either oil or gas 7-3. Proportioning total fuel input. Provides. 1. close vent valve. provided it main. out requiring a boiler prepurge. Provides that both the first and second fuels be intro.1 The normal shutdown procedure for oil while continu- the boiler. to total airflow to obtain a proper lish gas flow through the burner. Igniter flame (d) High temperature of heated oil b. air/fuel ratio. the simultaneous firing of gas and oil increases the potential for (b) Install oil atomizer. ing to fire gas shall be as follows: 3. fire. that this particular fuel shall auto. 2. 2. 7-3.1 Prefiring and light-off cycles for the initial fuel to be 7-1 General. (e) Place the combustion control system into the desired tains proper air/fuel ratios throughout the entire operating mode for controlling input rate of each fuel.e.1 Any of the following operating conditions shall accom- 5. the proce- dure shall be as follows: 7-1. The following equipment shall be (g) Place the combustion control system into the desired provided for continuous firing of both oil and gas: mode for controlling input rate of each fuel.8501–18 SINGLE BURNER BOILER OPERATION Chapter 7 Simultaneous Firing of Oil and Gas Fuels 7-3 Light-Off Cycles. the following equipment and procedure shall be used to avoid a hazardous furnace condition. 4. NOTE: Shutdown of both fuels is acceptable.. fuel trip): d. 7-4 Normal Shutdown Procedure. A control system that is designed to accom. Provides detector(s) to supervise any of the following (b) Low temperature of heated oils conditions: (c) Loss of atomizing medium a. each fuel individually (c) Open safety shutoff valves. 7-4. the proce- fuel individually or both fuels simultaneously dure shall be as follows: (b) A combustion control system that is capable of per.2 Either of the following conditions shall accomplish a c. (b) Shut off gas supply to the burner. Meets the requirements of Section 4-7 for each fuel (e) Shut off atomizing medium if required. Providing a stable return to proper air/fuel ratio valve. Limiting total fuel input to the maximum capacity of 7-4. Prohibits the simultaneous light-off of both fuels. Controlling minimum input rates of each fuel.3 Safety Shutdowns. Oil firing safety shutdown of the gas supply to the burner (i. 7-4. In addition. and estab- or in any combination. Combined gas and oil firing (a) High gas pressure 1997 Edition . after the trip of either one of the two fuels. When it is necessary or desirable to fire both oil fired shall be in accordance with Section 6-6 for oil and Sec- and gas simultaneously in a single burner boiler on a continu. Controlling a minimum airflow rate. (a) Establish gas fuel system to satisfy interlocks. Requires a manual reset following any interlock shut. fuel trip): 6. (b) Shut off oil supply to burner and open oil recirculating 5. plish a safety shutdown of the oil supply to the burner (i.2 When oil is introduced as the second fuel. (a) Reduce oil flow to light-off rate.3. matically shut down with operation continuing on the unaf.e. 1. ous basis. Provides an interlock action that will trip either fuel should its respective flow control valve leave a predeter.3. Provides for the introduction of the second fuel with. and an alarm for 8. Care satisfied. 7-4.3 Procedure required for changing from oil to gas: matically shut down with operation continuing on the unaf- fected fuel in a stable manner. of the fuels being fired. place it in ser- vice. of oil and gas fuels on a continuous basis. A control device. at all times by continuously observing the burner flame or by 3. Provides that both the first and second fuels be intro. SIMULTANEOUS FIRING OF OIL AND GAS FOR FUEL TRANSFER ONLY 8501–19 (b) Low gas pressure 6.1(b)3. A gas/oil-firing mode that permits simultaneous fir. Requires a manual reset following any interlock shut- down. if provided. 8-2 Simultaneous Firing on a Continuous Basis. (e) Reduce oil-firing rate to light-off flow. (g) Place fuel transfer–switching system in the gas/oil posi- out requiring a boiler purge. (m)Return the combustion control system and burner-fir- 2. During this period. 8-3. airflow is maintained at a constant rate ties: with only the manual fuel valves operated. At this point the gas flow rate is con- (a) A burner that is capable of firing the two fuels simulta. When it is necessary or (b) Check that the manual oil valve at the burner is closed. 4. (b) Check that the manual gas valve at the burner is closed. duced with their flow control valves in light-off positions. place it in ser- vice. (a) Loss of combustion air supply 8. (b) A fuel transfer system that includes the following: (k) Simultaneously and slowly close the manual gas valve 1. transfer timer. 5.3 Any of the following conditions shall accomplish a complete safety shutdown of the boiler: 7. vided. Gas firing (d) Power failure (e) Excess steam pressure or water temperature c. trolled by the manual valve instead of by the normal control neously during the transfer period valve. downstream (g) The occurrence of either the oil or the gas fuel trip of the safety shutoff valves in each fuel line when only that fuel is being fired f. desirable to transfer from one fuel to another without stop. fer combustion control system is designed for simultaneous firing (h) Place oil control valve in the normal light-off position. on an interlock action peculiar to only one ing rate to automatic operation. that this particular fuel shall auto. 3. The following equipment and procedures shall be used to (e) Open atomizing medium shutoff valve. (a) Where a Class 1 or 2 igniter is available. A pressure gauge in each fuel line downstream of the manual shutoff valve 8-3. tion. Meets the requirements of Section 4-7 for each fuel (l) Place the fuel transfer system in the oil position. to limit continuous operation in this mode observing the air/fuel ratio or oxygen indicator. A gas-firing mode in which oil cannot be fired while opening the manual oil valve to light the oil flame from the gas flame. provided all interlocks for both fuels are gas valve is closed and the manual oil valve is fully open. (c) A safety interlock system with the following capabili. (i) Place fuel transfer–switching system into oil/gas posi- 8-3 Single Fuel Firing Without Airflow Biasing. (d) Place combustion control system in manual position. Prohibits the simultaneous light-off of both fuels. Provides detector(s) to supervise any of the following (b) Loss of or failure to establish flame conditions: (c) Loss of control system actuating energy a. Fuel oil pressure now will be upstream of time and no capability of biasing the airflow upward is pro. Oil firing (f) Low water level as determined by the auxiliary low d. An oil-firing mode in which gas cannot be fired cutting back on the gas-firing rate to keep a constant heat 3. Igniter flame b. If the gas safety interlocks are satisfied. the manual oil valve at the burner. (c) Establish oil fuel system to satisfy interlocks. being fired. (f) Place combustion control system in manual position.2 Procedure required for changing from gas to oil: Chapter 8 Simultaneous Firing of Oil and Gas for Fuel Transfer Only (a) Where a Class 1 or 2 igniter is available. Continue to increase the oil-firing rate while 2. If the oil safety interlocks are satisfied. the oil safety shut- bustion control system is designed for firing only one fuel at a off valve will open. mined low rate during fuel transfer. ping the flow of fuel to the furnace. (j) Observe the gas pressure downstream from the man- ual gas shutoff valve and slowly close the valve until the gas 8-3. When a trans. tion. 8-1 Transfer Without Shutdown. Provides. including light-off position for both fuel valves must be taken to maintain an adequate amount of excess air 4. Manual shutoff valves at the burner. 1. the changeover shall be (d) Install oil atomizer.1 Required Equipment. avoid a hazardous furnace condition. accomplished in a manner to prevent a fuel-rich condition. the following equipment and procedures shall be used. (c) Establish gas fuel system to satisfy interlocks. pressure starts to drop. input of the combined fuels to the burner until the manual ing of both fuels. When a com. the gas safety 1997 Edition . (f) Place gas control valve in the normal light-off position. Combined gas and oil firing water cutout e. (g) Reduce gas-firing rate to light-off flow. NOTE: Shutdown of both fuels is acceptable. Chapter 7 shall apply. 1.1 Required Equipment.8501–20 SINGLE BURNER BOILER OPERATION shutoff valves will open. Provides for the introduction of the second fuel with. The following procedure for 5. valve is closed and the manual gas valve is fully open. if provided. a. airflow is being maintained at a constant (b) Install oil atomizer. if required. Provides. (a) A burner that is capable of firing the two fuels simulta. oil safety shutoff valve will now close.1(b)3] to simultaneously bias the airflow by a while cutting back on the oil-firing rate to keep a constant preset value and open the safety shutoff valve(s) of the fuel heat input of the combined fuel to the burner until the oil being introduced. place it in 6. 4. changing atomizers shall be followed: out requiring a boiler purge. Provides a momentary contact fuel transfer push but- from the oil flame. maintenance without affecting the boiler load. 8-4 Single Fuel Firing with Airflow Biasing. (l) Shut off atomizing medium. 1997 Edition . down. (except during fuel transfer) (f) Observe that gas firing has commenced. Care must be taken to maintain an adequate amount of excess air 8-4. Prohibits the simultaneous light-off of both fuels. Where a burner is equipped with main and aux- iliary oil atomizers for the purpose of changing atomizers for NOTE: Shutdown of both fuels is acceptable. which automatically transfer trips the oil safety shutoff valves. equipment and procedures shall be used.3 The following procedure is required for changing from oil to gas: 8-4. (h) Observe that oil firing has commenced. manual gas valve at the burner.2 The following procedure is required for changing from at all times by continuously observing the burner flame or by gas to oil: observing the air/fuel ratio or oxygen indicator. A momentary contact push button enabling fuel (h) Release fuel transfer push button. When a combus. Chapter 9 Dual Oil Atomizers in a Single Burner matically shut down with operation continuing on the unaf- fected fuel in a stable manner. which automatically tion control system is designed for firing only one fuel at a trips the gas safety shutoff valves. duced with their flow control valves in light-off positions. (e) Reduce gas-firing rate to light-off flow. (a) Establish gas fuel system to satisfy interlocks. Gas pressure now will be upstream of 7. (m)Remove oil atomizer from burner. (i) Return the combustion control system and burner-fir- ties: ing rate to automatic operation. that this particular fuel shall auto. Requires a manual reset following any interlock shut. (g) Depress fuel transfer push button. (a) Where an intermittent igniter is available. (k) Return the combustion control system and burner-fir- ing rate to automatic operation. rate with only the manual fuel valves operated. service. Provides detector(s) to supervise any of the following (h) Observe the oil pressure downstream from the manual conditions: oil shutoff valve and slowly close the valve until the oil pres. (b) Place combustion control system in manual position. (a) Establish oil fuel system to satisfy interlocks. if required. (j) Release fuel transfer push button. (j) Close atomizing medium shutoff valve. 3. Combined gas and oil firing while opening the manual gas valve to light the gas flame 9. if required. An oil-firing mode in which gas cannot be fired (except during fuel transfer) (g) Move fuel selector switch to the gas-firing position. Oil firing (i) Simultaneously and slowly close the manual oil valve d. (b) A fuel transfer system that includes the following: (d) Place gas control valve in the normal light-off position. the following ing rate to automatic operation. (c) Open atomizing medium shutoff valve. The (d) Place combustion control system in manual position. if required. Provides that both the first and second fuels be intro- ing conditions by a trained operator. neously during the transfer period (c) Reduce oil-firing rate to light-off flow. A gas-firing mode in which oil cannot be fired (e) Depress fuel transfer push button. mined low rate during fuel transfer as described in Section 8-4. (k) Remove oil atomizer. 2. (j) Place the fuel transfer system in the gas position. 8-4. Igniter flame sure starts to drop. time and the capabilities have been provided to enable the air- flow to be automatically biased up to a preset amount when (k) Return the combustion control system and burner-fir- either fuel is fired at a predetermined low rate. 8. Gas firing the manual valve instead of by the normal control valve. Provides an interlock action that will trip either fuel CAUTION: Care shall be taken to prevent a fuel-rich should its respective flow control valve leave the predeter. Continue to increase the gas-firing rate ton [see 8-4. (b) Install auxiliary atomizer. Meets the requirements of Section 4-7 for each fuel being fired. 2. on an interlock action peculiar to only one of the fuels being fired. c. (i) Move fuel selector switch to the oil-firing position. (c) A safety interlock system with the following capabili. condition during the changeover period. 9-2 Changeover Procedures. (f) Place oil control valve in the normal light-off position. At this point the oil flow is controlled by b. the changeover of atomizers shall be carried out under stable fir- 3. During this period. 9-1 General. 1. 2 Any defects found shall be corrected immediately. strictly applying the provisions of this main atomizer to the auxiliary atomizer until the main atom. Also. or interlocked to prevent a fuel-rich mixture. and the results shall gas firing that require special consideration are as follows: be recorded in the log book. (See The edition indicated for each referenced mandatory docu. Appendix A izer until pressure reaches that required for light-off. Some of these mandatory documents might gas can be either “wet” or “dry. The indi. comply with increasingly stringent emission limits.2 In existing units. National Fuel Gas Code. which may be characteristic of a purposes and. be capable of rendering sound judgment as to when equipment is 3. cause disproportionate effort or expense with little increase in protection. Potentially hazardous conditions are most likely to occur within buildings. Discharges from relief valves or any other form of atmospheric vents can become hazardous unless special ASTM D 396. This appendix con- tains explanatory material. West Conshohocken. combustion Chapter 11 Referenced Publications control systems that respond to reduced boiler steam pressure or steam flow with an impulse for more fuel. In the case of such a wet gas. Quincy. Thus.4. There are insufficient data and operating and maintenance schedule shall be established and performed on experience to justify changes to this standard. Outdoor boilers tend with all operating procedures and equipment functions and shall to minimize confined area problems. National Electrical Code®. Gas is colorless. An inspection not recommended. P. iliary atomizer until it ignites. furnace.” A wet gas usually implies also be referenced in this standard for specific informational the presence of distillate. Materials. particular source. or stack which could cas- cade into a progressively worse condition. tions should be taken with wet gas supply systems. Particularly with respect to natural gas systems. American Society for Testing and an equivalent change in airflow. details. Section 4-6 for requirements to avoid such hazards.1 Operability and set points on all devices. ade- viduals making inspections and tests shall be thoroughly familiar quate ventilation should be provided.) ment is the current edition as of the date of the NFPA issuance 4. Box 9101. (f) Divert the atomizing medium and oil flow from the A-1-1. standard is not always practical. tary flameout and possible reignition.2 Although NOx and other emissions during start-up control devices depends upon their ability to respond quickly and extremely low-load operation are low. 5.2 ASTM Publication. they might not to their activating impulses. Therefore. routed through confined areas. Standard Specifications for Fuel Oils. 1996 edition. see NFPA 54. Reignition could result in a furnace explosion. admitting oil to the aux- ble text paragraphs. over of distillate into the burners could result in a momen- 1 Batterymarch Park. cation of appropriate safeguards. from the light-off procedure. 1996 edition.8. departures from safe air/fuel ratios possible without any visi- ble evidence at the burners. remove auxiliary atomizer. and cleaning shall be performed during initial operation. repeat the procedure as outlined In existing units. Widely different characteristics of gas from either a NFPA 70. a leak usually cannot be 10-2. 6. 10-2. are not required. should be con- enced within this standard as mandatory requirements and sidered potentially hazardous. purge. the of this standard. 1996. 1. unless protected 11-1 The following documents or portions thereof are refer. (d) Slowly close manual fuel valve on main atomizer until Appendix A is not a part of the requirements of this NFPA document it is in control of oil flow. adjustment. National Fire Protection Association. 1997 edition. A-2-7 Gas and Oil Firing—Special Problems. 100 Barr Harbor Drive. Characteristics of gas and cable. where appli. therefore. the carry- 11-1. detected visually. the authority having jurisdiction (g) To place a main atomizer back into service and to should be satisfied that reasonable protection is provided. APPENDIX A 8501–21 (c) Slowly open atomizing medium valve to auxiliary atom.3 and A-6-2. Since the effective operation of all safety and A-1-2. numbered to correspond with the applica- (e) Slowly open the manual valve. precautions are taken. Modification of conditions that do not represent a significant threat. particularly where the gas piping is 10-3 Familiarity with Equipment and Procedures. but is included for informational purposes only.1. single source or multiple sources can result in a significant change in the Btu (kJ) input rate to the burner(s) without 11-1. In such cases. reliance cannot be placed on detec- tion of a gas leak by the presence of odor. substituting the main atom. ing without the above-mentioned interlocks or alarms. 2.1 NFPA Publications. a systematic and thorough inspec. shall be verified by periodic testing. and minimum airflow requirements defined in this standard to meet these limits is 10-2 Inspection and Maintenance Schedule. The nature of gas fuel makes experiencing severe in reliable operating condition. PA 19428-2959. even if such condi- tions are not in strict conformance with the requirements of Chapter 10* Inspection and Maintenance this standard.) NFPA 54. special precau- NFPA 31. Physical limitations could izer is out of service.3 Frequent inspection. (a) Hazards Peculiar to Gas Firing. Standard for the Installation of Oil-Burning Equip. boiler combustion system hazard should be mitigated by appli- izer for the auxiliary atomizer. any condition that represents a serious in Section 9-2(a) through 9-2(f). In the latter instance.O. Deviation tion and maintenance shall be performed.) 1997 Edition . therefore. are also listed in Appendix B. (See A-4-4. a periodic basis. 10-1 General. 10-2. The same applies to manual fir- shall be considered part of the requirements of this standard. National Fuel Gas Code. (For ment. MA 02269-9101. the burner front is not normally classified more restrictively than 2. plant are within the specific ranges of the fuel-handling and ous unless proper methods are used for purging and fuel-burning equipment. Purging the burner atomizer before removal will (iii) Rapid operation of regulating valve in the return minimize the probability for hazardous concentrations oil line from the burner header (on systems using of flammable vapors at the burner front during mainte- this type of control) nance operations. care Combustible Liquids Code.. limits to maintain proper atomization. Fuel oils have high volumetric heats of combustion. Maintenance and repair of gas piping can be hazard. Attempting to ing areas where fuel is stored. handled. or plugging of strainers. (ii) Rapid operation of burner shutoff valves e. flammable vapors or gases could be present in the ity. Flash point is an indicator of volatility and. Dif. fering characteristics. Flammable and ing difficulties and potential safety hazards. d. such systems include provisions for preheating these c. There is the ever-present hazard of inserting an c. most power boiler cosity of oil flowing to the burners should be held within fuel oil systems are designed for the heavier grades 5 and 6. Installations should conform to NFPA 30. new gas. On installations that are designed to fire both b. mechanical atomization) or oil piping supply to the burner as well as oil-recirculating by using steam or air to break up small oil streams.) defined in ASTM D 396. consideration should be that can be dangerous unless flowing velocities are lim. Currents. grades 1. fuel storage areas. forming solids. Recommended Practice for Protection atmosphere. thus. Fuel oil is a complex mixture of hydrocarbons of without an appropriate change in fuel oil temperature differing molecular weights and boiling and freezing to restore the flowing viscosity to the proper value. Thus. Water or sludge in fuel oil storage tanks or usually viscous fuels. respectively. Some fuel oils contain constituents that. lower viscosities and less water and sediment than grades 5 therefore. proper handling and burning.e. Similar consideration should be given to the fuel through small orifices (i. consideration should be extremely fine mist to mix intimately with the combus- given to the design of the burner management system to tion air to burn quickly and completely. This action can result in an unsafe pressure and fuel composition. sumps. Proper pumping and atomization of fuel oils are heated. could decompose. recharging the line. more care is of the fuel supply to the burners. when over- g. NFPA 31. Division 2. provides for classifying upon the following operations: such areas and defines requirements for electrical (i) Rapid operation of oil supply valve installations in the areas so classified. National Fuel Gas Code. Standard for the Installa- must be exercised to ensure that oils that are received at a tion of Oil-Burning Equipment. Furthermore. In power boilers ensure proper interlocks are activated for the selected this is accomplished by spraying high pressure drops fuel oil. Characteristics of fuel oil and fuel oil firing that cial provisions for storing. I liquids as defined in NFPA 30. operating condition. Fuel oil is introduced into the furnace as an heated and unheated fuel oils. Widely different characteristics of fuel oil from 4. The operating company is responsible for classify- for a specific range of oil characteristics. can result because of are supplied with grade 6 oil than with the other ASTM plugged strainers or burner tips. Clean distillate fuels have low conductivities and Combustible Liquids Code) or that could be heated will generate static electrical charges in the fuel stream above their flash point. Flammable and h. require special considerations include the following: and so forth. or burned and burn an oil whose characteristics differ widely from those for revising the classification if conditions are changed. gaseous. of potential for flammable vapors. When firing oils that require preheating. and API-RP 2003. or 6. atomizing. handling. The more important characteristics of fuel oils are the repairs. (b) Hazards Peculiar to Oil Firing. tics can cause a precipitation of sludge that can lead to thus. Typical locations are burner areas. Hence. (See NFPA 77. and solid fuels with hazards as described in A-2-7(b)1. (See NFPA 54. d. either required in the design and operation of fuel oil systems that immediately or at a later time. or burning fuel oils that tion of viscosity control systems should be followed for could have flash points below 100°F (38°C) (Class each fuel when the source or properties are variable. or could solidify dependent upon control of viscosity.c. grades. they require fewer special provisions to ensure b. rapid transients in oil flow through an operating burner National Electrical Code. Changes in viscosity when exposed to low ambient temperature. the vis. f. for which the system was designed can cause serious operat.) pits. creating new liquid. heating. The presence in relation to temperature vary for different oils and of such solids in the fuel could cause interruptions. unpredictable properties. Close attention to the design and opera. cate ease of atomization. Vis- piping to the fuel storage tanks. it is relatively simple to identify oils that require spe- 1. However. hence. When fuel oil is subjected to sufficiently high ferent shipments of fuel oil with dissimilar characteris. All of the following characteristics could have a bear- either a single source or multiple sources can result in a significant change in the Btu (kJ) input rate to the ing on the problem of properly and safely burning fuel oils: burner(s) without an equivalent change in airflow or a. and low spots where fuel leakage or i. National Elec- 1997 Edition . depending on the cosity and volatility are characteristics of the oil that indi- arrangement of the provided equipment. blends of oils. Against Ignitions Arising Out of Static Lighting and Stray fuel-handling equipment areas. (i) When storing. Article 500 of NFPA 70. and NFPA 70. A fuel oil burning system is designed f. even small leaks can create potential fire hazards. or sprayer plate. pumping. to avoid flameouts that improperly located suction takeoffs from the storage are attributed to interruptions or pulsation of the fuel sup- tank can result in hazardous interruptions or pulsations ply. Recommended Practice on Static Electric. given to electrical installations in areas where ited. The incompressibility of fuel oil can create very vapors can accumulate. oil gun in the burner assembly without a tip. before and after making 3. With such provisions. It is a function of kets. Generally speaking. e. and 4 have a. The term fuel oil refers to liquid fuels with widely dif. points. A flameout. Class I. temperature. or burner tips. Standard Specifications for Fuel Oils. 2. hence. it will partially decompose or vaporize.8501–22 SINGLE BURNER BOILER OPERATION 7. These methods can narrow the limits of stable flames that are produced by the burner system. recommen. regard to furnace safety. electrical ing new burner and furnace designs inspector.2. such as propane/air mixtures. require special consideration in storing. The A-4-2 For additional information. see NFPA 54. A-4-1. and. APPENDIX A 8501–23 trical Code. involving the introduction organization that is concerned with product evaluations and is of combustion air in two or more stages partly at the fuel noz. a second stage of air admission within the same burner housing A-3 Authority Having Jurisdiction. equipment should be addressed in this standard. For insurance purposes. plied to boilers typically is lighter than air and presents no spe- tion air. fined areas.e. NFPA or other appropriate standards. equipment should be provided to assure proper mixing and uni. at government installations. The authority having jurisdic- percent to 25 percent excess air) tion may also refer to the listings or labeling practices of an b. procedure. thus in a position to determine compliance with appropriate zle. and should be made to ensure the prescribed distribution of venting to prevent accumulations in depressions or in con- air and the recirculating flue gas/air mixture. nor does it approve or evaluate test- tions in some local areas require a reduction of NOx emis. 3. In many circumstances. 2. air quality regula. past operating procedures. installations meet NOx emission limits that are lower than emissions now obtained from many of the presently A-3 Approved. Multistage air admission. gases is to eliminate the vent valve from between the two main dations of the boiler. the commanding officer or departmental official may be the 1. Guidance can be obtained from API-RP 500. and NFPA 58. or flameouts.3 Main Burner Gas Supply. said authority may require evidence of proper a. the property flames. the d. The National Fire Protection Association does installed firing systems and furnace designs. the equipment manufacturers introduc. and instrument manufac. and so ture is introduced at the burner. it is important to trip fuel on loss of flame. Air pollution control regulations require that new location of flame detectors on existing units. In addition. Generally. c. In determining the acceptability of installa- sions from existing boilers. procedures. as do ondary air their responsibilities. refinery gases. the authority having jurisdiction may base acceptance on compliance with 2. and partly by standards for the current production of listed items. the effect of all of these methods is to pro- or other insurance company representative may be the author- duce lower flame temperatures and longer. The phrase “authority having jurisdiction” is used in NFPA documents in a broad c.3.3 and Table A-4-2. Fuel staging fire marshal. authority having jurisdiction. or certify any installations. or materials. To achieve these reductions. These heavier-than- culation is introduced so that only air and not the mix. which are specified in 4-4. which result in lower NOx. A-4-2. handling. less turbulent ity having jurisdiction. or use. an insurance inspection department. On new units. burner. ment. Liquefied Petroleum Gases. owner or his or her designated agent assumes the role of the (d) Hazards of Low NOx Firing Methods. should be repeated on existing units when any of these methods are Gas Code. d. rating bureau. Because of developing energy cost provided to monitor either the ratio of flue gas to air or considerations. In the absence of such lowing methods should be used: standards. independent admission through special furnace ports. Low excess air firing (i. When flue gas recirculation is used. or others having statutory authority. (See Figure A-4-2. which could be less than stoichiometric air. b. Therefore. which are using not approve. and can introduce unacceptable risks if proper precautions are A-3 Listed. The means for identifying listed equipment may not taken. Fuel-firing systems that are designed to reduce some organizations do not recognize equipment as listed NOx emissions tend to reduce the margins formerly unless it is also labeled. one or more of the fol. The authority having jurisdiction available to prevent or minimize accumulations of should utilize the system employed by the listing organization unburned fuel in the furnace during combustion upsets to identify a listed product. Where public safety is primary. chief of a fire prevention bureau.8. Any change in flame characteristics to reduce NOx (c) Low NOx Operation—Special Problems. particularly for existing units. building official. National Fuel tests. gases with heavier-than-air characteristics. or other regional department or individual such as a fire chief. Reduced secondary air temperature authority having jurisdiction may be a federal. proper provisions forth. manner. procedures. When flue gas recir. a. Most natural gas that is sup- form distribution of recirculated gas and the combus. or health department. e. Installations in Petroleum Refineries. less than the “normal” 10 installation. equipment. These methods can have important implications with authority having jurisdiction. or materials. since jurisdictions and approval agencies vary. air gases.8 See Figure A-4-1. ing laboratories. All of the methods tend to increase the possibility of an unstable flame and unburned combustibles An alternative to the automatic venting of heavier-than-air throughout the unit and ducts. labor depart- f. vary for each organization concerned with product evaluation. Flue gas recirculation into all or a portion of the sec. tions. inspect. emissions can require changing either or both the type and 1.3. local. gas safety shutoff valves. turers should be followed or tests should be conducted Recommended Practice for Classification of Areas for Electrical to verify operating margins. Standard for the Storage and Handling of employed. When flue gas recirculation is introduced into cial problems in the atmosphere over and above those the total combustion air stream. state. Thus.) 1997 Edition .. equipment. many boilers are using a gas or a mixture of the oxygen content of the mixture. 8 Typical fuel and atomizing medium supply systems and safety controls for oil burner. spring closing (NC) Safety shutdown interlocks (not shown) B Oil recirculation valve atomizing (NO) (optional for unheated oil) Flame detector(s) D Oil flow control valve Excessive steam pressure interlock F Low oil temperature switch (not applicable for unheated oil) Auxiliary low water cutoff (one required) G High oil temperature switch (not applicable for unheated oil) Combustion air supply interlock I Closed position interlock on safety shutoff valve J Atomizing medium differential control valve L Automatic atomizing medium shutoff valve M Oil meter (optional) N Low atomizing medium pressure switch O Oil strainer P Atomizing medium flow interlock differential switch. 1997 Edition .8501–24 SINGLE BURNER BOILER OPERATION Clearing line Z T S R U G F S PI PSL TI TSH TSL PI A A X I O D ZSC ZSC ZSC M T Oil * supply Z Recirc. to tank B T or pump inlet Z S Oil N PSL PI burner J Atomizing T Z T medium L P T supply Z W PSL Y Alternate T Z atomizing medium Trap supply Drain A Safety shutoff valve. or pressure interlock switch R Low pressure switch S Pressure gauge T Manual shutoff valve U Oil temperature gauge (optional for unheated oil) W Atomizing medium strainer X Low fire start switch Y Atomizing medium flow orifice Z Check valve * Caution: Means shall be provided to prevent or relieve excess pressure between these valves Figure A-4-1. these valves should be large enough to relieve 1. The manual sys- tems are not recommended. it is recognized that with A-4-2. lieve excess pressure between these valves. 11/4 in. This design minimizes the potential for leakage into a furnace. Many oil-fired boilers are equipped with propane or other liquefied Shutoff System Minimum petroleum gas–fired (LPG) igniters. gas to the atmosphere at a rate that is equal to the potential leak. propane. adequate and uninterrupted supplies of fuel and air.3 Typical fuel supply systems and safety controls for gas burner. Two automatic safety shutoff valves. to 3 in. 15% of supply line cross-sectional area A-6-1 Manual Systems for Watertube Boilers. 51/2 in.1. the cross-sectional area of the mediate spring opening automatic vent valve manifold pipe should be equal to or greater than the sum of the b. To (a) Controls and Interlocks. APPENDIX A 8501–25 Vent to atmosphere Vent to atmosphere S S R C Q PI PI PSL PSH PI S A A T T I K I X T T H ZSC L ZSC D ZSC M T J T Gas supply Main N L burner T To ignition system A Safety shutoff valve. in depressions or in confined areas. In absence of other justification. vent valve port diameters should conform to Table A-4-2. Interrupted or intermittent igniter. igniter vent valve from between the two igniter safety shutoff valves. 21/2 in. certain operating functions can be performed by a trained operator as off valves are intended to relieve any gas pressure that could well as by control devices. to 71/2 in. Special precautions are Gas Supply Line Size Vent Port and Line Size required in locating the vent pipe from the automatic bleed (11/2 in. vented gases do not accumulate 2 in.1 See Figure A-4-4.3 Heavier-than-Air Gases and Gas-Fired Igniters.1 Locations where natural gas. vent pipe sizes and a. 31/2 in. to 6 in. 2 in. However. Safety shutoff valves. shutoff valves in oil line to burner CAUTION: Means shall be provided to prevent or re- A-4-4. spring opening (NO) Flame detector(s) D Gas flow control valve Excessive steam pressure interlock H Gas strainer (excessive water temperature and pressure interlock I Closed position interlock on valves safety shutoff for hot water boilers) J Constant gas pressure regulator valve Auxiliary low water cutoff (one required) K Vent line manual shutoff valve for leakage testing (locked or sealed open) Combustion air supply interlock L Leakage test connection M Gas meter (optional) N Drip leg Q High gas pressure switch R Low gas pressure switch S Pressure gauge T Manual shutoff valve X Low fire start switch Note: NC = normally closed. 3/ 4 in. 2. Two automatic spring-closing safety cross-sectional areas of the two largest vents that are involved. Gas Firing. 4 in. with inter- When manifolding is allowed. 1 in. An alternative to the auto- 21/2 in. in gas line to the main burner. 11/2 in. Oil Firing. tems are installed in compliance with this standard normally 8 in. de-energized NO = normally open. de-energized Figure A-4-2.7 Atmospheric vent valves that are located between shut. as follows: age rate. 1997 Edition . or fuel oil sys- 61/2 in. spring-closing.3 Vent Line Sizes A-4-4. A-4-9. National Electrical Code. >8 in. are not considered hazardous locations for electrical equip- ment as defined in NFPA 70. valve so that heavier-than-air.3. spring closing (NC) Safety shutdown interlocks (not shown) B Vent valve. matic venting of heavier-than-air gases is to eliminate the 31/2 in. perform properly.1. Table A-4-2. to 5 in. 3 in. build up due to failure of the first (upstream) shutoff valve. slowly increase airflow until normal air/fuel ratio has been restored. d. Excessive recycling to achieve a optimum air/fuel ratio by the manipulation of a single con- burner light-off can lead to accumulation of a hazardous trol device. Therefore. spring closing (NC) C Vent valve. with light-off can lead to accumulation of a hazardous intermediate. the following condi- the burner. Manual shutoff valve(s) in the fuel line(s) adjacent to 7. spring opening (NO) (optional) H Gas strainer J Constant gas pressure regulator N Drip leg S Pressure gauge T Manual shutoff valve S PI V T O T Y Light oil Ignitor pilot supply O Ignitor oil strainer S Pressure gauge T Manual shutoff valve V Pilot oil safety shutoff valve. amount of fuel in the furnace and should be avoided. Low gas pressure sideration these potential variables. The minimum and maximum points of stable deficiency should develop while flame is maintained at the burner operation are defined by the burner manufacturer burners. Low oil temperature be opened. 3. de-energized NO = normally open. Changes in firing rate are made by the simultaneous A-6-2. For gas firing this shutoff valve should be tions sound an alarm: proved closed before the spark to the igniter can be ener- gized and the igniter and main gas safety shutoff valves can a. 6. Safety shutdown interlocks include the following: (c) Fuel Quality. Gas-Fired Igniter. spring closing (NC) Y Pilot oil pressure regulator (optional) Note: NC = normally closed. High gas pressure engineering systems and material designs must take into con- c. de-energized Figure A-4-4. reduce the fuel until the normal air/fuel ratio has and verified by operating investigation. Where oil heating is provided. Loss of combustion air supply Vent to atmosphere S C PI A A T H Natural T J gas Ignitor supply N A Safety shutoff valve. b. Low oil pressure available today contain unexpected constituents. adjustment of fuel and air supplies at a pre-established. 1997 Edition . If fuel flow cannot be reduced. High oil temperature 4. 5.8 Supplemental Recommendations and Precautions.1 Typical ignition systems for gas/oil-fired burner. Two spring-closing automatic CAUTION: Excessive recycling to achieve a burner safety shutoff valves in the gas line to the igniter. Limits on fuel and air to prevent reducing the fur- nace input below the point of stable burner operation are (b) Recovering from a Fuel-Rich Furnace Condition. It should be recognized that fuels that are a. spring-opening automatic vent valve amount of fuel in the furnace and should be avoided. b. If an air provided.8501–26 SINGLE BURNER BOILER OPERATION c.4. been restored. (a) Excessive Recycling. and tively perform any required maintenance tasks. continued reli. Adequate spare parts that are available. and Safety. (2) High and low fuel pressure interlocks able operation. (1) Fuel pressure and temperature interlocks (a) Maintenance. Any special techniques. the following typical schedule is a pressure. As a minimum.1 and 10-2. internal all installations. 1. This pro- sensing hardware. set points. to the involved equipment and consistent with safety requirements and manufacturer’s recommendations. (iv)High steam pressure interlock 2. b. cover routine and special techniques. Training. Compressed air should not be used to dislodge 1997 Edition . (i)Flame failure detection system d. In-service inspection of equipment should be estab. Therefore. Operator training. and efficient performance of equipment. Good housekeeping is essential for safe operation c. In-service inspections to identify conditions requiring corrective action or further study. and connections of all inter- locks and shutoff valves include the following: (v)Combustion control system a. and equipment manufacturer training. APPENDIX A 8501–27 A-10 Inspection and Maintenance. The training dusts. contaminated or oxygen-deficient atmosphere. the maintenance program should (iv)Piping. wiring. including logic. Creation of dust clouds should be minimized during (v)For oil: cleaning. Semiannually or annually as required program should be provided for the maintenance of equip. c. Procedures should be consistent with safety a. knowledgeable planning to allow use of trained personnel. operation and equipment involved. mented. Operating procedures should be directly related 3. without necessitating makeshift repairs. field train- ing. comprehen. and a. testing and field training. such as temperature. and equipment for an e. (vi)For gas: 1. set points. ment and hazards that are involved. Monthly and prevention of fires or explosions. ers. (i)Atomizers c. videotapes. (b) Training. such as temperature limitations. be established to prepare personnel to safely and effec- 6. Operation. and manufacturer’s specifications. Written comprehensive maintenance procedures incorporating manufacturer’s instructions to define a. Weekly (c) Housekeeping. keep them current with changes in equipment and per- ified by periodic testing and the results should be docu. sonnel. A formal training program should be established tasks and skills required. Maintenance training. procedures. videotapes. contami- 8. (vi)Calibration of indicating and recording instru- ments b. Special environmental factors ating manuals. Maintenance and repairs should be b. suitable for the work. e. among others. A formal maintenance training program should repairs should be documented. and manufacturer’s recommendations. Procedures should be reviewed periodically to keep them current with changes in equipment and per- (ii)Low water level cutoffs and associated alarms sonnel. The training program should be specific to the formed by trained personnel using tools and instruments involved equipment and to potential hazards. As required for oil firing efficient safe repair or modification. testing. Shutdown maintenance inspections. program should be consistent with the type of equip- and limited access or confined space requirements. (iii)Flame failure system components 2. maintenance work done. System configuration. and limited access or confined space require- guide only. Daily requirements and manufacturer’s recommendations. It is not practical to pre-establish a single schedule for nated or oxygen-deficient atmosphere. being evaluated and approved. subject to adjustment according to specific plant ments should be included. Any potential envi- mendations and applicable standards and codes. should be covered. Detailed. b. and repairs should be per. cover normal and emergency conditions. A d. such as to prepare personnel to safely and effectively operate nondestructive testing or those tasks requiring special equipment. programmed instruction. Use of comprehensive equipment history that (ii)Strainers records conditions found. Maintenance procedures should be established to performed in accordance with the manufacturer’s recom. provisions (i)Fan and airflow interlocks should be made for periodic cleaning of horizontal ledges (ii)Fuel safety shutoff valves for leakage or surfaces of buildings and equipment to prevent the accu- (iii)Low fire start interlock mulation of appreciable dust deposits. and date of each. This program can consist of review of oper- tools. changes made. normal operating conditions. Inspection.2. 2. among oth- 7. d. meeting shutdown procedures. d. adjustments. to cover all problem areas. Operating procedures should be established that sive in scope. lished and followed. should be defined. Defects should be reported and corrected. 5. ronmental factors.) c. should not be changed without the effect gram can consist of review of maintenance manuals. Therefore. dust. The objective of a maintenance program is to identify (1) Gas strainer and drip leg and correct conditions relating to the safety. Start-up and f. Inspections. to provide reliable service lockout procedures should be covered in detail. Procedures should be reviewed periodically to 4. (i)Igniter and burner operation 1. service requirements. and adjustments should be ver. programmed instruction. (See 10-2. (i)Igniter and burner components ment at intervals that are consistent with the type of equip- (ii)Combustion air supply system ment. or bins. American Petroleum Institute. Specific procedures. National Electrical Code. ited to. (ii)A careful inspection of all areas near where welding or cutting has been done. 19428-2959. 6 volt or 12 volt) extension tion. ASTM D 396. B-1 The following documents or portions thereof are refer- tain that no smoldering fires have developed. depleted of oxygen. NFPA 54. attendant should remain outside of the confined Standard for the Design and Installation of Oxygen-Fuel Gas space with appropriate rescue equipment and Systems for Welding. Standard for the Design and Installation of Oxygen-Fuel approved method. The safety a. Standard for the Installation of Oil-Burning Equip- are present.1 ASTM Publication. 1991. permits.. c. (ii)Access to or from the enclosure is by manhole. fined space entry. (iii)Prevent accidental closing of access doors or hatches.2. port. including the Appendix B Referenced Publications floors above and below. and Allied Processes. sphere may be stagnant. Box 9101. Confined space. 1994 edition. hot air. windboxes. Tests for an explosive or oxygen-deficient atmosphere should be made. 1996 edition. Recommended Practice on Static Electricity. 2. 1991. sure that no cartridges or charges are left in the work NFPA 51B. NW. 1996. Standard Specifications for Fuel Oils. and walls should be cleaned and all dust accumulation should be removed by an NFPA 51. floors. such use is practical. and where moisture could be a hazard. The edition indicat- present. steam. Protective clothing. ing Processes. MA 02269- cords and lighting should be used for all confined spaces 9101. 1 Batterymarch Park. and Allied Processes. ment. P. gases. tions without hitting the enclosure. water washing or vacuum clean. A careful check should be made to be Gas Systems for Welding. A confined space is any work location or enclo. (ii)Positively prevent inadvertent starting or mov- ing of mechanical equipment or fans. Where flammable dusts or dust clouds are standard unless also listed in Chapter 11. Flammable and Combustible Liquids Code. When these operations become necessary. or other relatively small opening that B-1. fine weld spatter or cutting sparks.2 API Publications. 1993 edition.8 m) tall cannot stand up in the middle of the space or extend his or her arms in all direc. sparking electrical tools must not be used. but are not lim. 1997 Edition . All ed here for each reference is the current edition as of the date lamps must be suitable for Class II. Quincy. 3. NFPA 58. oped and used for personnel entering a confined space: 1220 L. as follows.2 Other Publications. (v)Determine need for ventilation or self-con- tained breathing apparatus where the atmo- 1. includ. Special Safety Precautions. West Conshohocken. National Fire Protection Associa- approved low voltage (i. 51B. or ing but not limited to hard hats and safety glasses. and NFPA should be in contact. which should be properly tied off when ods should be used in such a manner as to con. B-1.8501–28 SINGLE BURNER BOILER OPERATION soot or dust accumulations. Recommended Practice for Protection Against Igni- tions Arising Out of Static Lighting and Stray Currents. Welding and flame cutting. Division 1 locations of the NFPA issuance of this standard. 1997 edition. General Safety Precautions. Welding Processes. 100 Barr Harbor Drive. Materials. (i)Positively prevent inadvertent introduction of fuel. or locks to cover con- ing methods are preferred. Street. enced within this standard for informational purposes only and are thus not considered part of the requirements of this b. National Electrical Code. as defined in NFPA 70. American Society for Testing and limits ingress and egress to one person at a time. (vi)Provide for a safety attendant. (d) Safety. Washington. National Fuel Gas Code. nesses. furnaces. Either ground fault protected or specially B-1.O. should be devel.2. DC 20005. b. dust collectors.1 NFPA Publications. 1995 edition (i)The dimensions are such that a person who is 6 NFPA 70. Standard for the Storage and Handling of Liquefied sure in which any of the following could exist: Petroleum Gases.e. Standard for Fire Prevention in Use of Cutting and Weld. B-1. Cutting. should contaminated with irritating or combustible be used by personnel during maintenance operations. (See also NFPA 51. preferably visual contact. cyclones. NFPA 30. Recommended Practice for Classification of Areas for Electrical Installations in Petroleum Refineries. NFPA 77. 1996 edition. ft (1. API-RP 500. hatch. 1996 edition. heaters. 1997 edition. Cutting. (iv)Include tags. d. or gas. all equipment. a.) (vii)Provide for use of proper safety belts or har- (i)Fire-resistant blankets or other approved meth. API-RP 2003. with those inside. PA (iii)Confined spaces can include. Standard for Fire Prevention in Use of Cutting and area. ducts. Explosion-operated tools and forming techniques should not be used where flammable dust or dust clouds NFPA 31. bunkers. should be made when the job is finished or interrupted and such areas patrolled for a period long enough to make cer.