1、Designation: E2079 07 (Reapproved 2013)Standard Test Methods forLimiting Oxygen (Oxidant) Concentration in Gases andVapors1This standard is issued under the fixed designation E2079; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the determination of thelimiting oxygen (oxidant) concentration of mixtures of oxy
3、gen(oxidant) and inert gases with flammable gases and vapors at aspecified initial pressure and initial temperature.1.2 These test methods may also be used to determine thelimiting concentration of oxidizers other than oxygen.1.3 Differentiation among the different combustion regimes(such as the hot
4、 flames, cool flames and exothermic reactions)is beyond the scope of these test methods.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 These test methods should be used to measure anddescribe the properties of materials
5、, products, or assemblies inresponse to heat and flame under controlled laboratory con-ditions and should not be used to describe or appraise the firehazard or fire risk of materials, products, or assemblies underactual fire conditions. However, results of this test may be usedas elements of a fire
6、risk assessment which takes into accountall of the factors which are pertinent to an assessment of thefire hazard of a particular end use.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to
7、establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E1445 Terminology Relating to Hazard Potential of Chemi-cals2.2 NFPA Publication:3NFPA 69 Standard on Explosion Prevention Systems2.3
8、NTIS Publications:4Bulletin 503 Coward, H.F., and Jones, G.W., Bureau ofMines, “Limits of Flammability of Gases and Vapors,”NTIS AD701575, 1952Bulletin 627 Zabetakis, M.G., Bureau of Mines, “Flamma-bility Characteristics of Combustible Gases and Vapors,”NTIS AD701576, 1965Bulletin 680 Kuchta, J.M.,
9、Bureau of Mines, “Investigationof Fire and Explosion Accidents in the Chemical, Mining,and Fuel-Related Industries A Manual,” NTISPB87113940, 19853. Terminology3.1 DefinitionsSee also Terminology E1445.3.1.1 flammablecapable of propagating a flame.3.1.2 ignitionthe initiation of combustion.3.1.3 lim
10、it of flammabilitythe boundary in compositionspace dividing flammable and nonflammable regions.3.1.4 limiting oxygen (oxidant) concentration (LOC) of afuel-oxidant-inert systemthe oxygen (oxidant) concentrationat the limit of flammability for the worst case (most flammable)fuel concentration.3.1.4.1
11、 DiscussionLimiting oxygen (oxidant) concentra-tion is also known as minimum oxygen (oxidant) concentrationor as critical oxygen (oxidant) concentration.4. Summary of Test Method4.1 A mixture containing one or more flammable compo-nents (fuel), oxygen (oxidant) and inert gas(es) (such asnitrogen, ca
12、rbon dioxide, argon, etc.) is prepared in a suitabletest vessel at a controlled initial temperature and made to thespecified initial pressure. Proportions of the components aredetermined by a suitable means. Ignition of the mixture isattempted and flammability is determined from the pressurerise pro
13、duced. The criterion for flammability is a pressure rise1These test methods are under the jurisdiction of ASTM Committee E27 onHazard Potential of Chemicals and are the direct responsibility of SubcommitteeE27.04 on Flammability and Ignitability of Chemicals.Current edition approved Oct. 1, 2013. Pu
14、blished October 2013. Originallyapproved in 2000. Last previous edition approved in 2007 as E2079 07. DOI:10.1520/E2079-07R13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information,
15、 refer to the standards Document Summary page onthe ASTM website.3Available from National Fire Protection Association (NFPA), 1 BatterymarchPark, Quincy, MA 02169-7471, http:/www.nfpa.org.4Available from National Technical Information Service (NTIS), 5285 PortRoyal Rd., Springfield, VA 22161, http:/
16、www.ntis.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1of 7 % above the initial absolute test pressure. Fuel, oxygen(oxidant), and inert gas proportions are varied between trialsuntil:4.1.1 LThe lowest oxygen (oxidant) concentra
17、tion forwhich flame propagation is possible for at least one combina-tion of fuel and inert gas (the “worst case” or most flammablefuel concentration range), and4.1.2 HThe highest oxygen (oxidant) concentration forwhich flame propagation is not possible for the same worstcase fuel concentration rang
18、e, are identified.NOTE 1The 7 % pressure criterion may not be appropriate for certainfuel and oxidant mixtures. This is also the case if the test enclosure volumeis small, or when the ignition energy is substantially larger than 10 J. It istherefore a prudent practice to perform exploratory tests in
19、 the vicinity oflimit mixtures to evaluate the validity of the selected pressure risecriterion. See, for example (1).55. Significance and Use5.1 Knowledge of the limiting oxygen (oxidant) concentra-tion is needed for safe operation of some chemical processes.This information may be needed in order t
20、o start up or operatea reactor while avoiding the creation of flammable gas com-positions therein, or to store or ship materials safely. NFPA 69provides guidance for the practical use of LOC data, includingthe appropriate safety margin to use.5.2 Examples of LOC data applications can be found inrefe
21、rences (2-4).NOTE 2The LOC values reported in references (5-7), and relied uponby a number of modern safety standards (such as NFPA 69 and NFPA 86)were obtained mostly in a 5-cm diameter flammability tube. This diametermay be too small to mitigate the flame quenching influence impedingaccurate deter
22、mination of the LOC of most fuels. The 4-L minimumvolume specified in Section 7 would correspond to a diameter of at least20 cm. As a result, some LOC values determined using this standard areapproximately 1.5 vol % lower than the previous values measured in theflammability tube, and are more approp
23、riate for use in fire and explosionhazard assessment studies.5.3 Much of the previous literature LOC data (5-7) weremeasured in the flammability tube.6. Limitations6.1 These test methods are not applicable to mixtures whichundergo spontaneous reaction before ignition is attempted.6.2 These test meth
24、ods are limited to mixtures which havemaximum deflagration pressures less than the maximum work-ing pressure of the test apparatus.6.3 These test methods may be used up to the temperaturelimit of the test system.6.4 Measurements of flammability are influenced by flame-quenching effects of the test v
25、essel walls. Further surfaceeffects due to deposits of carbon or other materials cansignificantly affect limits of flammability, especially in thefuel-rich region. Refer to Bureau of Mines Bulletin 503 andBulletin 627. For certain chemicals (for example, ammonia,halogenated materials, and certain am
26、ines) which have largeignition-quenching distances, tests may need to be conductedin vessels larger than that specified below.7. Apparatus7.1 The test vessel must have a volume of at least 4 L.NOTE 3A survey of practitioners of this method indicates that testvessels in the size range of 4 to 35 L ar
27、e used.7.2 Test vessels must be nearly spherical. The maximumaspect ratio of the test vessel (the ratio of largest to smallestinternal dimension) must be smaller than or equal to two.7.3 Test vessel may be equipped with a means of mechani-cal agitation to ensure uniform mixing of components beforean
28、 ignition attempt.7.4 If tests are to be conducted at an elevated temperature,the test vessel may be heated using a heating jacket, heatingmantle or placed inside a heated chamber. The heating systemmust be capable of controlling the gas temperature inside thetest vessel to within 63C both temporall
29、y and spatially. Anappropriate device such as a thermocouple should be used tomonitor the gas temperature within the test vessel.7.5 Ignition point must be positioned near the center of thevessel and away from any surfaces or obstacles inside the testvessel.7.6 One design of an acceptable test vesse
30、l is described inAppendix X1.7.7 The maximum allowable working pressure (MAWP) ofthe test vessel at the maximum test temperature must exceedthe maximum expected deflagration pressure.7.8 Pressure Transducers:7.8.1 Low-Range TransducerA low-range pressure trans-ducer may be used for the purpose of ma
31、king partial pressureadditions of gases and vapors to the test vessel. The transducerand its signal conditioning/amplifying electronics should havean accuracy, precision and repeatability sufficient to accuratelyresolve the required changes in the gas partial pressure for thecomponent used in lowest
32、 concentration. The transducershould be protected from deflagration pressures by means of anisolation valve. A pressure gage may be used if an erroranalysis is performed to demonstrate that the internal volumeof the pressure gage and piping will not significantly affect thetest mixture.7.8.2 High-Ra
33、nge TransducerThis transducer has the pur-pose of measuring the pressure rise on ignition of the gasmixture. It should have sufficient range to withstand the highestpressure it is expected to experience while also having suffi-cient accuracy and resolution to measure small pressure rises ofthe order
34、 of 7 % of the initial absolute test pressure.7.8.3 The pressure transducer and recording equipmentmust have adequate time resolution to capture the maximumrate of pressure rise developed by the combustion event.7.8.4 Calibration of the pressure transducer and data acqui-sition system must be verifi
35、ed over the range of pressures atwhich the system is expected to operate.7.9 Ignition SourceSeveral possible means of ignitionmay be used which include those described below. The meansof ignition used must be described in the test report.5The boldface numbers in parentheses refer to the list of refe
36、rences at the end ofthis standard.E2079 07 (2013)27.9.1 Fuse WireAfuse wire igniter can be constructed, forexample from a piece of No. 40 (0.076-mm diameter) copper,nichrome, or platinum wire fastened to power supply terminalsin such manner as to leave a filament of wire between theterminals approxi
37、mately 10 mm long. A 500 VA/115 Visolating transformer, or a properly sized discrete dischargecapacitor circuit will serve as an adequate igniter energysupply.7.9.2 Carbon SparkFour 2-mm diameter graphite rodswrapped by the leads coming from an electrical pulse genera-tor. The two electrical leads a
38、re separated bya6to10-mmdistance. The resulting discrete spark is in the form of a surfacedischarge over the graphite rods.7.9.3 Continuous Electric ArcAn electric arc igniter mayconsist of a pair of electrodes (steel or graphite) spacedapproximately 6 mm apart across which a 30 mA arc oftypically l
39、ess than 1 s duration can be supplied from a115/15 000 volt transformer (so-called luminous tube trans-former).7.9.4 Discrete Electric SparkAn electric spark igniter mayconsist of a pair of electrodes (steel or graphite) spacedapproximately 6 mm apart across which a short duration spark(lasting for
40、typically 1 ms or less) is caused to occur upon asingle discharge of a capacitor. The electrical energy stored onor discharged from the capacitor, or both, should be measuredand reported. The energy dissipated in the spark gap may alsobe measured by appropriate means. Use of at least 10 Joules ofnom
41、inal (stored) spark energy is recommended.NOTE 4Electric arcs and sparks listed in 7.9.3 and 7.9.4 may fail todischarge when testing fuels with high dielectric strength and during testsconducted at a high initial pressure.7.9.5 Chemical IgniterSome materials (such as chloro-fluoro-carbons) require a
42、 higher ignition energy than that canbe provided by the electrical means described above. In thatcase, tests with chemical igniters (for example, electricmatches, electrically activated kitchen match heads, or Sobbeigniters) may be necessary to determine the true limitingoxidant concentration (or th
43、e flammability limit) as opposed toan “ignitability limit.” If tests are conducted in a sufficientlylarge vessel, electric matches or Sobbe igniters may be used.However, it should be kept in mind that these igniters producesignificantly larger and sometimes multiple ignition kernelsthan the electric
44、al ignition sources. Chemical igniters are likelyto overdrive combustion events in small test vessels, and in thatcase, measured LOC values are expected to be lower than theactual LOC values. If a chemical igniter is used, the pressurerise from the igniter, by itself, must be determined. During ates
45、t, there is also an additional pressure generated by thecombustion of the fuel gas within the igniter flame, eventhough there is no propagation. One way to partially correct forthese igniter effects is to use a more stringent ignition criterionthan the standard 7 % pressure rise. Appropriate ignitio
46、ncriterion may be determined from a series of baseline testsconducted on actual fuel-oxidant-diluent mixtures chosen nearthe non-flammable vicinity of the composition H defined inSection 4.NOTE 5Igniters dissipating large quantities of energy (especiallychemical igniters) are capable of producing a
47、finite pressure rise in thesmaller test vessels, even in the absence of flammable test mixtures. Thepressure rise due to igniter must be quantified before the LOC testing, andmust be subtracted from the peak pressure rise measured at each test (see10.1.11). If the pressure rise due to igniter is a n
48、on-negligible fraction ofthe absolute pressure of the test mixture, the accompanying compressiveheating of the test mixture must be considered.NOTE 6Some igniters may not be capable of dissipating all or any oftheir rated energy at the extremes of pressure and temperature. If there isany doubt, the
49、reliability of the igniter function must be demonstrated atthe test conditions.8. Safety Precautions8.1 Adequate shielding must be provided to prevent injuryin the event of equipment rupture. The apparatus should be setup so that the operator is isolated from the test vessel while thevessel contains a charge of reactants, including the time whilethe vessel is being filled. The test apparatus should be equippedwith interlocks so that the ignition source cannot be activatedunless the operator has taken necessary steps to protectpersonnel and equipment. Acti
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