1、Designation: E2931 13Standard Test Method forLimiting Oxygen (Oxidant) Concentration of CombustibleDust Clouds1This standard is issued under the fixed designation E2931; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast 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 This test method is designed to determine the limitingoxygen concentration of a combustible dust dispersed in amixture
3、of air with an inert/nonflammable gas in a near-spherical closed vessel of 20 L or greater volume.1.2 Data obtained from this method provide a relativemeasure of the deflagration characteristics of dust clouds.1.3 This test method should be used to measure and describethe properties of materials in
4、response to heat and flame undercontrolled laboratory conditions and should not be used todescribe or appraise the fire hazard or fire risk of materials,products, or assemblies under actual fire conditions. However,results of this test may be used as elements of a fire riskassessment that takes into
5、 account all of the factors that arepertinent to an assessment of the fire hazard of a particular enduse.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns
6、, 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. Specific precau-tionary statements are given in Section 8.2. Referenced Documents2.1
7、ASTM Standards:2D3173 Test Method for Moisture in the Analysis Sample ofCoal and CokeD3175 Test Method for Volatile Matter in the AnalysisSample of Coal and CokeE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE177 Practice for Use of the Terms Precisio
8、n and Bias inASTM Test MethodsE1226 Test Method for Explosibility of Dust CloudsE1515 Test Method for Minimum Explosible Concentrationof Combustible DustsE2079 Test Methods for Limiting Oxygen (Oxidant) Con-centration in Gases and Vapors2.2 NFPA Publications:3NFPA 69 Standard on Explosion Prevention
9、 Systems2.3 CEN/CENELEC Publications:4EN 140344 Determination of the explosion characteristicsof dust cloudsPart 4: Determination of the limitingoxygen concentration LOC of dust clouds3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 dust concentrationthe mass of dust divided by
10、 theinternal volume of the test chamber.3.1.2 limit of flammabilitythe boundary in compositionspace dividing flammable and nonflammable regions.3.1.3 limiting oxygen (oxidant) concentration (LOC) of afuel-oxidant-inert systemthe oxygen (oxidant) concentrationat the limit of flammability for the wors
11、t case (most flammable)fuel concentration.3.1.3.1 DiscussionThe Limiting Oxygen (oxidant) Con-centration is sometimes also known as Minimum Oxygen(oxidant) Concentration or as Critical Oxygen (oxidant) Con-centration.3.1.4 Pignitionthe absolute pressure at the time the ignitoris activated, see Fig.
12、1.3.1.5 Pignitorthe pressure rise in the chamber due to theignitor by itself in air at atmospheric pressure.3.1.6 Pex,athe maximum explosion pressure (absolute)reached during the course of a single deflagration test.1This test method is under the jurisdiction of ASTM Committee E27 on HazardPotential
13、 of Chemicals and is the direct responsibility of Subcommittee E27.05 onExplosibility and Ignitability of Dust Clouds.Current edition approved June 1, 2013. Published July 2013. DOI: 10.1520/E2931-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
14、e 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, MA 02169-7471, http:/www.nfpa.org.4Available from European Committee for
15、 Standardization (CEN), AvenueMarnix 17, B-1000, Brussels, Belgium, http:/www.cen.eu.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.7 pressure ratio (PR)defined asPR5Pex,a2Pignitor!Pignition.3.1.8 (dP/dt)exthe maximum rate of pre
16、ssure rise duringthe course of a deflagration test. The rate of pressure rise canbe size-normalized by multiplying by the cube root of thechamber volume, giving dPdt!ex3V13.4. Summary of Test Method4.1 A dust cloud is formed in a closed combustion chamberby dispersion of the material with air and an
17、 inert gas (such asnitrogen, carbon dioxide, argon, etc.). The test is normallymade at atmospheric pressure and ambient temperature. Pro-portions of the gaseous components (oxygen and inert gas) aredetermined by a suitable means.4.2 Ignition of the mixture is attempted after a specifieddelay time, a
18、nd flammability is determined from the pressurerise produced. Fuel, oxygen (oxidant), and inert gas propor-tions are varied between trials until the following are deter-mined:4.2.1 LThe lowest oxygen (oxidant) concentration forwhich flame propagation is possible for at least one dustconcentration (t
19、ypically the “worst case” or most flammablefuel concentration range), and4.2.2 HThe highest oxygen (oxidant) concentration forwhich flame propagation is not possible for the same “worstcase” fuel concentration range.5. Significance and Use5.1 This test method provides a procedure for performinglabor
20、atory tests to evaluate relative deflagration parameters ofdusts.5.2 Knowledge 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, shut downor operate a process while avoiding the creation of fla
21、mmabledust-gas atmospheres therein, or to pneumatically transportmaterials safely. NFPA 69 provides guidance for the practicaluse of LOC data, including the appropriate safety margin touse.5.3 Since the LOC as measured by this method may varywith the energy of the ignitor and the propagation criteri
22、a, theLOC should be considered a relative rather than absolutemeasurement.5.4 If too weak an ignition source is used, the measuredLOC would be higher than the “true” value and would not besufficiently conservative. This is an ignitability limit rather thana flammability limit, and the test could be
23、described as“underdriven.” Ideally, the ignition energy is increased untilthe measured LOC is independent of ignition energy (that is,the “true” value). However, at some point the ignition energymay become too strong for the size of the test chamber, and thesystem becomes “overdriven.” When the igni
24、tor flame be-comes too large relative to the chamber volume, a test couldappear to result in an explosion, while it is actually just dustburning in the ignitor flame with no real propagation beyondthe ignitor (1-3).5This LOC value would be overly conserva-tive.5.5 The recommended ignition source for
25、 measuring theLOC of dusts in 20-L chambers is a 2500-J pyrotechnicignitor.6This ignitor contains 0.6 g of a powder mixture of 40% zirconium, 30 % barium nitrate, and 30 % barium peroxide.Measuring the LOC at several ignition energies will provideinformation on the possible overdriving of the system
26、 toevaluate the effect of possible overdriving in a 20-L chamber,comparison tests may also be made in a larger chamber such asa 1-m3chamber (1-3).5.6 The values obtained by this testing technique are spe-cific to the sample tested (particularly the particle size distri-bution) and the method used an
27、d are not to be consideredintrinsic material constants.NOTE 1Much of the previously published LOC data (4). wereobtained using a spark ignition source in a 1.2-L Hartmann chamber andmay not be sufficiently conservative. The European method of LOCdetermination EN 140344 uses two 1000-J pyrotechnic ig
28、niters in the20-L chamber.6. Interferences/Limitations6.1 Unburned dust or combustion products remaining in thechamber or disperser from a previous test may affect results.The chamber and disperser should both be cleaned thoroughlybefore each test is made.6.2 Carbon dioxide should not be used as the
29、 diluent gaswhen determining the LOC for most metal dusts because itmay react with the metal. Some diluent gases might react withthe material to be tested. For example, it is known that carbondioxide will react with some metals such as aluminum,magnesium, titanium and zirconium.6.3 This test method
30、is limited to mixtures which havemaximum deflagration pressures less than the maximum work-ing pressure of the test apparatus.5The boldface numbers in parentheses refer to a list of references at the end ofthis standard.6The sole source of supply of the pyrotechnic ignitors known to the committeeat
31、this time is Cesana Corp., P.O. Box 182, Verona, NY 13478, or Fr. Sobbe, GmbH,Beylingstrasse 59, Postfach 140128, D-4600 Dortmund-Derne, Germany. If you areaware of alternative suppliers, please provide this information to ASTM Interna-tional Headquarters. Your comments will receive careful consider
32、ation at a meetingof the responsible technical committee,1which you may attend.FIG. 1 Typical Data for a Weak Dust Deflagration in a 20-L Cham-berE2931 1326.4 This test method may be used up to the temperaturelimit of the test system. Note that the ignitors may melt at someelevated temperatures if t
33、he test is not performed quicklyenough.7. Apparatus7.1 The equipment consists of a closed steel combustionchamber with an internal volume of at least 20 L, spherical orcylindrical (with a length to diameter ratio between 1.3:1 and0.7:1) in shape.7.2 The vessel should be designed and fabricated in ac
34、cor-dance with the ASME Boiler and Pressure Vessel Code,Section VIII. A maximum allowable working pressure(MAWP) of at least 15 bar is recommended.7.3 A dispersion reservoir contains the pressurized gas usedto disperse the dust.7.4 The apparatus must be capable of generating a well-dispersed dust cl
35、oud of the material.7.5 Optical dust probes, such as those described in Refs. (5)and (6), may be used to monitor the uniformity of the dustdispersion.7.6 The pressure transducer and recording equipment musthave a combined response rate that is greater than the maxi-mum measured rate of pressure rise
36、.7.7 An example of a chamber and specific procedures thathave been found suitable are shown in Appendix X1. Addi-tional information and details about suitable chambers may befound inAppendix X1 of Test Method E1226 (Siwek chamber)and Appendix X1 of Test Method E1515 (additional informa-tion on Burea
37、u of Mines chamber).7.8 An analyzer or sensor may be used to verify the oxidizercontent of the final pre-ignition gas mixture of a blank test (thatis, no ignitor or dust present).8. Safety Precautions8.1 Prior to handling a dust, the toxicity of the sample andits combustion products must be consider
38、ed. This informationis generally obtained from the manufacturer or supplier.Appropriate safety precautions must be taken if the materialhas toxic or irritating characteristics. Tests using this apparatusshould be conducted in a ventilated hood or other area havingadequate ventilation.8.2 Before init
39、iating a test, a physical check of all gasketsand fittings should be made to prevent leakage.8.3 If chemical ignitors are used as an ignition source, safetyin handling and use is a primary consideration. Prematureignition by electrostatic discharge or other means must beconsidered a possibility. Whe
40、n handling these ignitors, eyeprotection must be worn at all times. A grounded, conductivetabletop is recommended for preparation. Federal, state, andlocal regulations for the procurement, use, and storage ofchemical ignitors must be followed.8.4 All testing should initially be conducted with smallq
41、uantities of sample to prevent overpressurization due to highenergy material.8.5 Explosive, highly reactive, or easily decomposed mate-rials should not be tested unless they have been characterizedby prior testing. Procedures such as the use of barricades,hoods, and personal protective equipment sho
42、uld be used asjudgment indicates.8.6 It is recommended that LOC evaluations be performedat atmospheric pressure prior to conducting evaluations atelevated initial pressure. This measure should provide baselinedata which will help to avoid unexpectedly energetic explo-sions at high initial pressure.8
43、.7 Where the LOC is expected to exceed 21 %, testingshould begin with air at 21 % oxygen, and the oxygenconcentration should be increased in small increments.8.8 Where oxidizers stronger than air are used, the potentialsafety consequences of enhanced reactivity must be addressed.8.9 Compressed gas c
44、ylinders should be secured by meansappropriate to the size of cylinder. Gas cylinder valves shouldbe closed when not in use. Gas cylinders should be fitted withpressure regulators of the correct pressure range and typesuited for use with the gas contained therein. Regulatordelivery pressure should b
45、e set to the lowest value required forefficient gas transfer. The use of check valves in gas supplylines is recommended. All connections in gas transfer linesshould be checked for tightness.9. Sampling, Test Specimens, and Test Units9.1 It is not practical to specify a single method of samplingdust
46、for test purposes because the character of the material andits available form affect selection of the sampling procedure.Generally accepted sampling procedures should be used asdescribed in the Manual on Test Sieving Methods, MNL 32.79.2 Tests may be run on an as-received sample. However,due to the
47、possible accumulation of fines at some location in aprocessing system, it is recommended that the test sample be atleast 95 % minus 200 mesh (75 m).9.3 To achieve this particle fineness (95 % minus 200mesh (75 m), the sample may be ground or pulverized or itmay be sieved.NOTE 2The operator should co
48、nsider the thermal stability and thefriction and impact sensitivity of the dust during any grinding orpulverizing operation. In sieving the material, the operator must verify thatthere is no selective separation of components in a dust that is not a puresubstance.9.4 Dust samples that are much finer
49、 than 200 mesh (75 m)may have even lower LOC values.NOTE 3It may be desirable in some cases to conduct dust deflagrationtests on materials as sampled from a process because process dust streamsmay contain a wide range of particle sizes or have a well-defined specificmoisture content, materials consisting of a mixture of chemicals may beselectively separated on sieves and certain fibrous materials which maynot pass through a relatively coarse screen may produce dust deflagra-tions. When a material is tested in the as-received state, it should berecognized
