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To CLAS SI FICATION OF DUSTS RELATIVE TO ELECTRICAL EQUIPMENT IN CLASS II HAZARDOUS LOCATIONS Report of the Committee on Evaluation of Industria 1 Hazard s NATIONAL MATERIALS ADVISORY BOARD Commission on Engineering and Technical Systems National Re search Counc il National Academy of Sciences Publication NMAB 353-4 NAT IONAL ACADEMY PRESS Washi ngto n, D . C . 1982

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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the Councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the panel responsible for the report were chosen for their special competences and with regard for appropriate balance. _ The report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which established the Academy as a private, nonprofit, self-governing membership corporation. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences. This study by the National Materials Advisory Board was conducted under Contract No. J-9-F-5-0070 with the Occupational Safety and Health Administration and continued under Contract No. 210-78-0120 with the National Institute of Occupational Safety and Health. This report is for sale by the National Technical Information Service, Springfield, Virginia 22151. Printed in the United States of America. ii

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ABSTRACT Thi s document combines material presented in earlier National Materials Advisory Board reports and revises it to account for changes in the National Electrical Code that were made in 1981 and that reflect some of the recommendations of the Committee on Evaluation of Industrial Hazards. 111 l

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PREFACE The Occupationa 1 Saf ety and Health Administration ~ OSHA ~ of the U. S . Department of Labor requested that the Committee on Evaluation of Industrial Hazards of the National Research Council' s (NRC ) National Materials Advisory Board ~ NMAB )* classify several hundred gases, vapors, and dusts in accordance with the groupings i n Article 50 0 of the Nationa 1 Electrica 1 Code. ** The committee's expertise is comprised of chemistry; combustion phenomena; knowledge of codes, - standards, and regulations; electrical eng ineeri ng; a nd industri al practices . The committee established two panels to deal with combustible dusts--one to classify the dusts and one to recommend the test methods needed to determine dust classification parameters. The conclusions of the Panel on Dust Test Equipment, amended and approved by the co~runittee, were presented in 1979 in Te st Equipment for Use in Determining Classifications of Combustible Dusts ( Report NMAB 3 53-2 ) . one classy ~ ~ cat' on of dusts by the Panel on Classif ication of Combustible Dusts, amended and approved by the committee, was published in 1980 in C1 assif ication of Combustible Dust in Accordance with the National Electrica 1 Code ~ Report NMAB 353 -3 ~ . This document combine s the material presented in these earlier reports and revises it to account f or changes in the NEC that were made in 1981 and that reflect some of the recommendations of the committee . Thus, this report supersedes Reports NMAB 3 53-2 and NMAB 3 53-3 . The work of the committee relative to gases and vapors resulted in two reports: Matrix of Combustion-Relevant Properties and Classif ications of Gases, Vapors, and Selected Solids ~ Report NMAB 353-1) was published in 1979 and classif fed certain chemicals based on physical and f lamrnability data. Classif ication of Ga ses, Liquids, and Vo labile Solids Relative to Explosion-Proof Electrical Equipment ( Report NMAB 3 53-5 ) was published in 1982 and classifies additional chemical compounds. In addition, the committee is preparing another report, Rationale for Classification of Combustible Gases, Vapors, and DuStS with Reference to the National Electrical Code, ~ Report NMAB 353-6 ) which reviews the classification procedure s f or gases and vapors and f or dusts and recommends changes to improve the procedure s. v

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The chairman of the committee expresses his sincere thanks to all those participating in the study as well as to Stanley M. Barkin of the National Materials Advisory Board who provided staff support. Special thanks are given to Ernest C. Magison who prepared the first draft of this report and to Leland J. Hall and Peter J. Schram, respective chairmen of the Panel on Classification of Combustible Dust and the Panel on Dust Test Equipment. Homer W. Carhart, Chairman * The National Materials Advisory Board is a unit of the Commission on Engineering and Technical Systems of the National Research Council. Its general purpose is the advancement of materials science and engineering in the national interest. It fulfills that purpose by providing advice and assistance to government agencies and private organizations on matters of J ~ materials science and technology affecting the national interest, by focusing attention on the materials aspects of problems and opportunities, and by making appropriate recommendations for the solution of such problems , . . . . . J and tne exploitation of the opportunities. **The chemicals and materials to be classified originally included those subject to an earlier N~C study for the U.S. Coast Guard and those listed by OSHA in the Federal Register on June 27, 1974 (pp. 23541-31. The list subsequently was expanded (with additional support from the National Institute for Occupational Safety and Health) to include the gases and vapors listed in Fire Hazard Properties of Flammable Liquids, Gases, Volatile Solids, Manual 325M issued by the National Fire Protection Association (NFPA) in 1977. The dusts to be classified were those listed in 1976 in the NFPA'S Fire Protection Handbook (pp. 3-107 to 3-114~. vi

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COMMITTEE ON EVALUATION OF INDUSTRIAL HAZARDS Chairman HOMER W. CARHART, Naval Research Laboratory, Washington, D.C. Members FREDERICK R. EIRICH, Polytechnic Institute of New York, New York LELAND J. HALL, (retired, formerly with The Mill Mutuals, Chicago, Illinois) ERNEST C. MAGISON, Honeywell Inc., Fort Washington, Pennsylvania J. ARTHUR NICHOLLS, University of Michigan, Ann Arbor PETER J. SCHRAM, National Fire Protection Association, Quincy, Massachusetts ROGER A. STREHLOW, University of Illinois, Urbana-Champaign Li al son Repre sentative s PETER BOCHNAK, National Institute for Occupational Safety and Health, Morgantown, West Virginia CHIA CHEN, Occupational Safety and Health Administration, Washington, D.C. ANDREW M. COWAN, Department of Agriculture, Beltsville, Maryland JOHN A. GERARD, National Institute for Occupational Safety and Health, Morgantown, West Virginia RICHARD W. McQUAID, David W. Taylor Naval Ship Research and Development Center, Annapoli s, Maryland JOSEPH E. PIPKIN, Occupational Safety and Health Administration, Washi ngton, D . C. THOMAS H. SEYMOUR, Occupational Safety and Health Administration Washington, D.C. ~ V11 i

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Technica 1 Advisors ERMINE HARTON, (retired, formerly with the U.S. Department of Transportation Washington, D.C.) MlJRRAY JACOBSON, Mine Safety and Health Administration, Arlington, Virginia N=B Staf f STANLEY M . BAR=N, Staf f Scientist - viii 1

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Chai -an PANEL ON CLAS SIFICATION OF COMBUSTIBLE DUSTS LELAND J. HALL ~ retired, formerly with The Mill Mutuals, Chicago, Illinoi s Member s CHIA CHEN, Occupational Safety and Health Administration, U.S. Department of Labor, Washington, D.C. ANDREW M. COWAN, U.S. Department of Agriculture, Beltsville, Maryland FREDERICK R. EIRICH, Polytechnic Institute of New York, Brooklyn MURRAY JACOBSON, Mine Safety and Health Administration, U.S. Department of Labor, Arlington, Virginia PANEL ON DUST TEST EQUIPMENT Chai Oman PETER J. SCHRAM, National Fire Protection Association, Quincy, Massachusetts Member s LELAND J. HALL ~ retired, formerly with The Mill Mutuals, Chicago, Illinois) MU PRAY JACOBSON, Mine Saf ety and He alth Administration, Department of Labor, Arlington, Virginia ELTON LITCHFIELD ~ deceased, formerly with the Bureau of Mines, U. S. Department of the Interior, Pittsburgh, Pennsylvania) ERNEST C. MADISON, Honeywell Inc., Fort Washington, Pennsylvania ROGER A. STRE:HLOW, University of Illinoi s, Urbana-Champaign ix

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CONTENTS Chapte r 1 SUMMARY OF RECOMMENDATIONS Chapter 2 RATIONALE FOR CLASSIFICATION OF COMBUSTIBLE DUSTS Page 1 3 3 Introduction Premises for Classifying Dusts into Groups E, F. and G 4 Conseque nce s of These Premises Chapter 3 DUST CLASSIFICATION METHODS 4 9 Classifying using the 1981 NEC Resistivity Guidelines 9 Proposed New Classification of Dusts Te st Apparatu s Te sting and Re search Chapte r 4 CLAS SIFICAT ION OF VARIOUS DUSTS Appendixe s ma. A. Ignition and Explosion Ha zard of Dusts B. Layer Ignition Temperature C. E1 ectrical Re sistivity D. Dusts with Cloud Ignition Temperatures Lower Than Their Layer Ignition Temperature s Curricula Vitae of Committee Members 11 14 14 15 23 29 43 48 50

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