1、Designation: E 2079 07Standard Test Methods forLimiting Oxygen (Oxidant) Concentration in Gases andVapors1This standard is issued under the fixed designation E 2079; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 oxygen(oxidant) an
3、d 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 flames, cool f
4、lames and exothermic reactions)is beyond the scope of these test methods.1.4 These test methods should be used to measure anddescribe the properties of materials, products, or assemblies inresponse to heat and flame under controlled laboratory con-ditions and should not be used to describe or apprai
5、se 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 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、.5 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 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Do
7、cuments2.1 ASTM Standards:2E 1445 Terminology Relating to Hazard Potential ofChemicals2.2 NFPA PublicationNFPA 69, Standard on Explosion Prevention Systems32.3 NTIS PublicationsCoward, H.F. and Jones, G.W., Bulletin 503, Bureau ofMines, “Limits of Flammability of Gases and Vapors,”NTIS AD701575, 195
8、24Zabetakis, M.G., Bulletin 627, Bureau of Mines, “Flamma-bility Characteristics of Combustible Gases and Vapors,”NTIS AD701576, 19654Kuchta, J.M., Bulletin 680, Bureau of Mines, “Investigationof Fire and Explosion Accidents in the Chemical, Mining,and Fuel-Related Industries - A Manual,” NTISPB8711
9、3940, 198543. Terminology3.1 Definitions: (see also Terminology E 1445):3.1.1 flammablecapable of propagating a flame.3.1.2 ignitionthe initiation of combustion.3.1.3 limit of flammabilitythe boundary in compositionspace dividing flammable and nonflammable regions.3.1.4 limiting oxygen (oxidant) con
10、centration (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 DiscussionLimiting oxygen (oxidant) concentra-tion is also known as minimum oxygen (oxidant) concentrationor as critical oxygen (
11、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, carbon dioxide, argon, etc.) is prepared in a suitabletest vessel at a controlled initial temperature and made to thespecified initi
12、al pressure. Proportions of the components aredetermined by a suitable means. Ignition of the mixture isattempted and flammability is determined from the pressurerise produced. The criterion for flammability is a pressure rise1These test methods are under the jurisdiction of ASTM Committee E27 onHaz
13、ard Potential of Chemicals and are the direct responsibility of SubcommitteeE27.04 on Flammability and Ignitability of Chemicals.Current edition approved Jan. 1, 2007. Published February 2007. Originallyapproved in 2000. Last previous edition approved in 2001 as E 207901.2For referenced ASTM standar
14、ds, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from National Fire Protection Association (NFPA), 1 BatterymarchPark, Quincy,
15、MA 02169-7471, http:/www.nfpa.org.4Available from National Technical Information Service (NTIS), 5285 PortRoyal Rd., Springfield, VA 22161, http:/www.ntis.gov.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.of $ 7 % above the initial
16、 absolute test pressure. Fuel, oxygen(oxidant), and inert gas proportions are varied between trialsuntil:4.1.1 LThe lowest oxygen (oxidant) concentration forwhich flame propagation is possible for at least one combina-tion of fuel and inert gas (the “worst case” or most flammablefuel concentration r
17、ange), and4.1.2 HThe highest oxygen (oxidant) concentration forwhich flame propagation is not possible for the same worstcase fuel concentration range, are identified.NOTE 1The 7% pressure criterion may not be appropriate for certainfuel and oxidant mixtures. This is also the case if the test enclos
18、ure volumeis small, or when the ignition energy is substantially larger than 10 J. It istherefore a prudent practice to perform exploratory tests in the vicinity oflimit mixtures to evaluate the validity of the selected pressure risecriterion. See, for example (1)5.5. Significance and Use5.1 Knowled
19、ge of the limiting oxygen (oxidant) concentra-tion is needed for safe operation of some chemical processes.This information may be needed in order to start up or operatea reactor while avoiding the creation of flammable gas com-positions therein, or to store or ship materials safely. NFPA 69provides
20、 guidance for the practical use of LOC data, includingthe appropriate safety margin to use.5.2 Examples of LOC data applications can be found inreferences (2, 3, 4).NOTE 2The LOC values reported in references (5, 6, and 7), andrelied upon by a number of modern safety standards (such as NFPA69 andNFP
21、A 86) were obtained mostly in a 5-cm diameter flammability tube.This diameter may be too small to mitigate the flame quenching influenceimpeding accurate determination of the LOC of most fuels. The 4-Lminimum volume specified in Section 7 would correspond to a diameterof at least 20 cm. As a result,
22、 some LOC values determined using thisstandard are approximately 1.5 vol.% lower than the previous valuesmeasured in the flammability tube, and are more appropriate for use in fireand explosion hazard assessment studies.5.3 Much of the previous literature LOC data (5, 6, 7) weremeasured in the flamm
23、ability tube.6. Limitations6.1 These test methods are not applicable to mixtures whichundergo spontaneous reaction before ignition is attempted.6.2 These test methods are limited to mixtures which havemaximum deflagration pressures less than the maximum work-ing pressure of the test apparatus.6.3 Th
24、ese 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 vessel walls. Further surfaceeffects due to deposits of carbon or other materials cansignificantly affect limits of flammability, especial
25、ly in thefuel-rich region. Refer to Bureau of Mines Bulletins 503 and627. For certain chemicals (for example, ammonia, haloge-nated materials, and certain amines) which have large ignition-quenching distances, tests may need to be conducted in vesselslarger than that specified below.7. Apparatus7.1
26、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 are used.7.2 Test vessels must be nearly spherical. The maximumaspect ratio of the test vessel (the ratio of largest to smallestinternal dimensi
27、on) 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 ignition attempt.7.4 If tests are to be conducted at an elevated temperature,the test vessel may be heated using a heating jacket, heatingman
28、tle or placed inside a heated chamber. The heating systemmust be capable of controlling the gas temperature inside thetest vessel to within 6 3C both temporally and spatially. Anappropriate device such as a thermocouple should be used tomonitor the gas temperature within the test vessel.7.5 Ignition
29、 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 vessel is described inAppendix X1.7.7 The maximum allowable working pressure (MAWP) ofthe test vessel at the maximum test temperature must exceedt
30、he 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 making partial pressureadditions of gases and vapors to the test vessel. The transducerand its signal conditioning/amplifying electronics shoul
31、d havean accuracy, precision and repeatability sufficient to accuratelyresolve the required changes in the gas partial pressure for thecomponent used in lowest concentration. The transducershould be protected from deflagration pressures by means of anisolation valve. A pressure gage may be used if a
32、n erroranalysis is performed to demonstrate that the internal volumeof the pressure gage and piping will not significantly affect thetest mixture.7.8.2 High-Range TransducerThis transducer has the pur-pose of measuring the pressure rise on ignition of the gasmixture. It should have sufficient range
33、to withstand the highestpressure it is expected to experience while also having suffi-cient accuracy and resolution to measure small pressure rises ofthe order of 7 % of the initial absolute test pressure.7.8.3 The pressure transducer and recording equipmentmust have adequate time resolution to capt
34、ure 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 verified over the range of pressures atwhich the system is expected to operate.7.9 Ignition SourceSeveral possible means of ignitionmay be used whi
35、ch include those described below. The meansof ignition used must be described in the test report.7.9.1 Fuse WireAfuse wire igniter can be constructed, forexample from a piece of No. 40 (0.076 mm diameter) copper,5The boldface numbers in parentheses refer to the list of refernces at the end ofthis st
36、andard.E2079072nichrome or platinum wire fastened to power supply terminalsin such manner as to leave a filament of wire between theterminals approximately 10 mm long. A 500 VA/115 Visolating transformer, or a properly sized discrete dischargecapacitor circuit will serve as an adequate igniter energ
37、ysupply.7.9.2 Carbon SparkFour 2 mm diameter graphite rodswrapped by the leads coming from an electrical pulse genera-tor. The two electrical leads are separated bya6to10mmdistance. The resulting discrete spark is in the form of a surfacedischarge over the graphite rods.7.9.3 Continuous Electric Arc
38、An electric arc igniter mayconsist of a pair of electrodes (steel or graphite) spacedapproximately 6 mm apart across which a 30 mA arc oftypically less 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
39、spark ignitermay consist of a pair of electrodes (steel or graphite) spacedapproximately 6 mm apart across which a short duration spark(lasting for 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 bo
40、th, should be measuredand reported. The energy dissipated in the spark gap may alsobe measured by appropriate means. Use of at least 10 Joules ofnominal (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 die
41、lectric strength and during testsconducted at a high initial pressure.7.9.5 Chemical IgniterSome materials (such as chloro-fluoro-carbons) require a higher ignition energy than that canbe provided by the electrical means described above. In thatcase, tests with chemical igniters (for example, electr
42、icmatches, electrically activated kitchen match heads, or Sobbeigniters) may be necessary to determine the true limitingoxidant concentration (or the flammability limit) as opposed toan “ignitability limit.” If tests are conducted in a sufficientlylarge vessel, electric matches or Sobbe igniters may
43、 be used.However, it should be kept in mind that these igniters producesignificantly larger and sometimes multiple ignition kernelsthan the electrical ignition sources. Chemical igniters are likelyto overdrive combustion events in small test vessels, and in thatcase, measured LOC values are expected
44、 to be lower than theactual LOC values. If a chemical igniter is used, the pressurerise from the igniter, by itself, must be determined. During atest, there is also an additional pressure generated by thecombustion of the fuel gas within the igniter flame, eventhough there is no propagation. One way
45、 to partially correct forthese igniter effects is to use a more stringent ignition criterionthan the standard 7 % pressure rise. Appropriate ignitioncriterion may be determined from a series of baseline testsconducted on actual fuel-oxidant-diluent mixtures chosen nearthe non-flammable vicinity of t
46、he composition H defined inSection 4.NOTE 5Igniters dissipating large quantities of energy (especiallychemical igniters) are capable of producing a finite pressure rise in thesmaller test vessels, even in the absence of flammable test mixtures. Thepressure rise due to igniter must be quantified befo
47、re 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 non-negligible fraction ofthe absolute pressure of the test mixture, the accompanying compressiveheating of the test mixture must be considered.NOTE 6Som
48、e 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 reliability of the igniter function must be demonstrated atthe test conditions.8. Safety Precautions8.1 Adequate shielding must be provided to prevent i
49、njuryin 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. Activation of the ignition sourceshould be possible only from a position shielded from the testvessel. The test vessel may be fitted with a rupture disk ventedto a
