ANSI ISA TR12.13.01-1999 Flammability Characteristics of Combustible Gases and Vapors.pdf

1、 TECHNICAL REPORT ANSI/ISA-TR12.13.01-1999 (R2013) ANSI Technical Report prepared by ISA Flammability Characteristics of Combustible Gases and Vapors Reaffirmed Copyright g227g322013 by the International Society of Automation (ISA). All rights reserved.Printed in the United States of America. No par

2、t of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publisher.ISA67 Alexander DriveP.O. Box 12277Research Triangle Park, North C

3、arolina 27709ANSI/ISATR12-13-011999 (R2013)Flammability Characteristics of Combustible Gases and VaporsISBN: 3 ANSI/ISA-TR12.13.01-1999 (R2013) Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA-TR12.13.01-1999 (R2013). This d

4、ocument has been prepared as part of the service of ISA towards a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they

5、 be addressed to the Secretary, Standards and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Standards and Practices Department is aware of the growing need for attention to

6、the metric system of units in general, and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in th

7、eir business and professional dealings with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International Sy

8、stem of Units (SI): The Modern Metric System, published by the American Society for Testing ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709. As a service to industry, the accompanying document, Bureau of Mines Bulletin 627 - Flammability Characteristics of Combustible Gase

9、s and Vapors, by Zabetakis 1965, is hereby reprinted in its entirety. This compendium, formerly available from the U.S. Bureau of Mines, contains information essential to an understanding of detection, measurement and handling of flammable gases and vapors. For further information, refer to ANSI/ISA

10、TR12.13.02. The reader should be aware that more recent LFL/UFL figures are available in NFPA 497, and IEC 60079-20-1. ABSTRACT This technical report includes theoretical and practical work carried out and collected by the U.S. Bureau of Mines relating to ignition and explosive properties of flammab

11、le gas mixtures. Flammability limits, under varying conditions of proportion, temperature and pressure, are presented. While the primary emphasis is on methane-air mixtures as found in coal mines, a full treatment of many other gases and vapors is included. KEY WORDS Methane Fire Explosion Flammabil

12、ity limits Flammable Combustible LEL, UEL LFL, UFL Gas This page intentionally left blank. 13 ANSI/ISA-TR12.13.01-1999 (R2013)APPENDIX IThe following document, Flammability Characteristics of Combustible Gases and Vapors, is reprinted in its entirety by permission of the publisher, the Bureau of Min

13、es, U.S. Department of the Interior.ANSI/ISA-TR12.13.01-1999 (R2013) 14 Bulletin 627Bureau of MinesAD 701 576FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORS,U.S. Bureau of Mines, Bulletin 627By Michael G. Zabetakis 15 ANSI/ISA-TR12.13.01-1999 (R2013)This publication has been cataloged a

14、s follows:Zabetakis, Michael George, 1924-2005Flammability characteristics of combustible gases and vapors. Washington U.S. Dept. of the Interior, Bureau of Mines 1965121 p. illus., tables. (U.S. Bureau of Mines. Bulletin 627)Includes bibliography.1. Combustion gases. 2. Gases. 3. Vapors. I. Title.

15、II. Title: Combustible gases. (Series)TN23.U4 no. 627 622.06173U.S. Dept. of the Int. LibraryA.1ANSI/ISA-TR12.13.01-1999 (R2013) 16 FLAMMABILITY CHARACTERISTICS OF COMBUSTIBLE GASES AND VAPORSbyMichael G. Zabetakis“AbstractThis is a summary of the available limit of flammability, autoignition, and b

16、urning-rate data for more than 200 combustible gases and vapors in air and other oxidants, as well as of empirical rules and graphs that can be used to predict similar data for thousands of other combustibles under a variety of environmental conditions. Specific data are presented on the paraffinic,

17、 unsaturated, aromatic, and alicyclic hydrocarbons, alcohols, ethers, aldehydes, ketones, and sulfur compounds, and an assortment of fuels, fuel blends, hydraulic fluids, engine oils, and miscellaneous combustible gases and vapors.IntroductionPrevention of unwanted fires and gas explosion disasters

18、requires a knowledge of flammability characteristics (limits of flammability, ignition requirements, and burning rates) of pertinent combustible gases and vapors likely to be encountered under various conditions of use (or misuse). Available data may not always be adequate for use in a particular ap

19、plication since they may have been obtained at a lower temperature and pressure than is encountered in practice. For example, the quantity of air that is required to decrease the combustible vapor concentration to a safe level in a particular process carried out at 200C should be based on flammabili

20、ty data obtained at this temperature. When these are not available, suitable approximations can be made to permit a realistic evaluation of the hazards associated with the process being considered; such approximations can serve as the basis for designing suitable safety devices for the protection of

21、 personnel and equipment.The purpose of this bulletin is to present a general review of the subject of flammability, and to supply select experimental data and empirical rules on the flammability characteristics of various families of combustible gases and vapors in air and other oxidizing atmospher

22、es. It contains what are believed to be the latest and most reliable data for more than 200 combustibles of interest to those concerned with the prevention of disastrous gas explosions. In addition, the empirical rules and graphs presented here can be used to predict similar data for other combustib

23、les under a variety of conditions. This bulletin supplements Bureau bulletins (40)Nand other publications (158).“Physical chemist, project coordinator, Gas Explosion, Explosives Research Center, Bureau of Mines, Pittsburgh, Pa.Work on manuscript completed May 1964.NItalicized numbers in parentheses

24、refer to items in the bibliography at the end of this report. 17 ANSI/ISA-TR12.13.01-1999 (R2013)Basic knowledge of combustion is desirable for a thorough understanding of the material, which can be found in numerous publications (69, 199, 202). Therefore, only those aspects required for an understa

25、nding of flammability are considered here; even these are considered from a fairly elementary viewpoint.Definitions and TheoryLIMITS OF FLAMMABILITYA combustible gas-air mixture can be burned over a wide range of concentrationswhen either subjected to elevated temperatures or exposed to a catalytic

26、surface at ordinary temperatures. However, homogeneous combustible gas-air mixtures are flammable, that is, they can propagate flame freely within a limited range of compositions. For example, trace amounts of methane in air can be readily oxidized on a heated surface, but a flame will propagate fro

27、m an ignition source at ambient temperatures and pressures only if the surrounding mixture contains at least 5 but less than 15 volume-percent methane. The more dilute mixture is known as the lower limit, or combustible-lean limit, mixture; the more concentrated mixture is known as the upper limit,

28、or combustible-rich limit, mixture. In practice, the limits of flammability of a particular system of gases are affected by the temperature, pressure, direction of flame propagation, gravitational field strength, and surroundings. The limits are obtained experimentally by determining the limiting mi

29、xture compositions between flammable and non-flammable mixtures (244). That is,(1)and(2)where LT,Pand UT,Pare the lower and upper limits of flammability, respectively, at a specified temperature and pressure, Cgnand C1nare the greatest and least concentrations of fuel in oxidant that are nonflammabl

30、e, and C1fand Cgf are the least and greatest concentrations of fuel in oxidant that are flammable. The rate at which a flame propagates through a flammable mixture depends on a number of factors including temperature, pressure, and mixture composition. It is a minimum at the limits of flammability a

31、nd a maximum at near stoichiometric mixtures (130).The Bureau of Mines has adopted a standard apparatus for limit-of-flammability determinations (40). Originally designed for use at atmospheric pressure and room temperature, it was later modified for use at reduced pressures by incorporating a spark

32、-gap ignitor in the base of the 2-inch, glass, flame-propagation tube. This modification introduced a difficulty that was not immediately apparent, as the spark energy was not always adequate for use in limit-of-flammability determinations. Figure 1 illustrates the effect of mixture composition on t

33、he electrical spark energy requirements for ignition of methane-air mixtures (75). For example, a 0.2-millijoule (mj) spark is inadequate to ignite even a stoichiometric mixture at atmospheric pressure and 26C; a 1-mj spark can ignite mixtures containing between 6 and 11.5 volume-percent methane, et

34、c. Such limit-mixture compositions that depend on the ignition source strength may be defined as limits of ignitibility or more simply ignitibility limits; they are thus LTPg441/2 CgnC1f+g91g93,=UTPg441/2 CgfC1n+g91g93,=ANSI/ISA-TR12.13.01-1999 (R2013) 18 indicative of the igniting ability of the en

35、ergy source. Limit mixtures that are essentially independent of the ignition source strength and that give a measure of the ability of a flame to propagate away from the ignition source may be defined as limits of flammability. Considerably greater spark energies are required to establish limits of

36、flammability than are required for limits of ignitibility (218); further, more energy is usually required to establish the upper limit than is required to establish the lower limit. In general, when the source strength is adequate, mixtures just outside the range of flammable compositions yield flam

37、e caps when ignited. These flame caps propagate only a short distance from the ignition source in a uniform mixture. The reason for this may be seen in figure 2 which shows the effect of temperature on limits of flammability at a constant initial pressure. As the temperature is increased, the lower

38、limit decreases and the upper limit increases. Thus, since a localized energy source elevates the temperature of nearby gases, even a nonflammable mixture can propagate flame a short distance from the source. That is, a nonflammable mixture (for example, composition-temperature point A, fig. 2) may

39、become flammable for a time, if its temperature is elevated sufficiently (composition-temperature point B).Figure 1Ignitibility Curve and Limits of Flammability for Methane-Air Mixtures at Atmospheric Pressure and 26C.Flammable mixtures considered in figure 2 fall in one of three regions. The first

40、is left of the saturated vapor-air mixtures curve, in the region labeled “Mist“. Such mixtures consist of droplets suspended in a vapor-air mixture; they are discussed in greater detail in the section on formation of flammable mixtures. The second lies along the curve for saturated vapor-air 19 ANSI

41、/ISA-TR12.13.01-1999 (R2013)mixtures; the last and most common region lies to the right of this curve. Compositions in the second and third regions make up the saturated and unsaturated flammable mixtures of a combustible-oxidant system at a specified pressure.Figure 2Effect of Temperature on Limits

42、 of Flammability of a Combustible Vapor in Air at a Constant Initial Pressure.In practice, complications may arise when flame propagation and flammability limit determinations are made in small tubes. Since heat is transferred to the tube walls from the flame front by radiation, conduction, and conv

43、ection, a flame may be quenched by the surrounding walls. Accordingly, limit determinations must be made in apparatus of such a size that wall quenching is minimized. A 2-inch-ID vertical tube is suitable for use with the paraffin hydrocarbons (methane, ethane, etc.) at atmospheric pressure and room

44、 temperature. However, such a tube is neither satisfactory under these conditions for many halogenated and other compounds nor for paraffin hydrocarbons at very low temperatures and pressures (197, 244).Because of the many difficulties associated with choosing suitable apparatus, it is not surprisin

45、g to find that the very existence of the limits of flammability has been questioned. After a thorough study, Linnett and Simpson concluded that while fundamental limits may exist there is no experimental evidence to indicate that such limits have been measured (132). In a more recent publication, Mu

46、llins reached the same conclusion (154). Accordingly, the limits of flammability obtained in an apparatus of suitable size and with a satisfactory ignition source should not be termed fundamental or absolute limits until the existence of such limits has been established. However, as long as experime

47、ntally determined limits are obtained under conditions similar to ANSI/ISA-TR12.13.01-1999 (R2013) 20 those found in practice, they may be used to design installations that are safe and to assess potential gas-explosion hazards.Industrially, heterogeneous single-phase (gas) and multi-phase (gas, liq

48、uid, and solid) flammable mixtures are probably even more important than homogeneous gas mixtures. Unfortunately, our knowledge of such mixtures is rather limited. It is important to recognize, however, that heterogeneous mixtures can ignite at concentrations that would normally be nonflammable if t

49、he mixture were homogeneous. For example, 1 liter of methane can form a flammable mixture with air near the top of a 100-liter container, although a nonflammable (1.0 volume-percent) mixture would result if complete mixing occurred at room temperature. This is an important concept, since layering can occur with any combustible gas or vapor in both stationary and flowing mixtures. Roberts, Pursall, and Sellers (176-180) have presented an excellent series of review articles on the layering and