1、Designation: E 1515 07Standard Test Method forMinimum Explosible Concentration of Combustible Dusts1This standard is issued under the fixed designation E 1515; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi
2、on. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis test method describes procedures for measuring the minimum concentration of a combustibledust (dispersed in air) that is ca
3、pable of propagating a deflagration. The tests are made in laboratorychambers that have volumes of 20 L or larger.1. Scope1.1 This test method covers the determination of the mini-mum concentration of a dust-air mixture that will propagate adeflagration in a near-spherical closed vessel of 20 L or g
4、reatervolume.NOTE 1The minimum explosible concentration (MEC) is also re-ferred to as the lower explosibility limit (LEL) or lean flammability limit(LFL).1.2 Data obtained from this test method provide a relativemeasure of the deflagration characteristics of dust clouds.1.3 This test method should b
5、e used to measure and describethe properties of materials in 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
6、 be used as elements of a fire riskassessment that takes into 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 as thestandard.1.5 This standard does not purport to address all of thesafety con
7、cerns, 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 Document
8、s2.1 ASTM Standards:2D 3173 Test Method for Moisture in theAnalysis Sample ofCoal and CokeD 3175 Test Method for Volatile Matter in the AnalysisSample of Coal and CokeE 681 Test Method for Concentration Limits of Flammabil-ity of Chemicals (Vapors and Gases)E 1226 Test Method for Pressure and Rate o
9、f Pressure Risefor Combustible Dusts3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 dust concentration, nthe mass of dust divided by theinternal volume of the test chamber.3.1.2 (dP/dt)ex, nthe maximum rate of pressure rise dur-ing the course of a single deflagration test.3.1.
10、3 minimum explosible concentration (MEC), ntheminimum concentration of a combustible dust cloud that iscapable of propagating a deflagration through a well dispersedmixture of the dust and air under the specified conditions oftest.3.1.4 Pignition, nthe absolute pressure at the time theignitor is act
11、ivated, see Fig. 1.3.1.5 DPignitor, nthe pressure rise in the chamber due tothe ignitor by itself in air at atmospheric pressure3.1.6 Pex,a, nthe maximum explosion pressure (absolute)reached during the course of a single deflagration test (see Figs.1 and 2).1This test method is under the jurisdictio
12、n of ASTM Committee E27 on HazardPotential of Chemicals and is the direct responsibility of Subcommittee E27.05 onExplosibility and Ignitability of Dust Clouds.Current edition approved Oct. 1, 2007. Published November 2007 . Originallyapproved in 1993. Last previous edition approved in 2003 as E 151
13、5 03a.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, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, P
14、O Box C700, West Conshohocken, PA 19428-2959, United States.3.1.7 pressure ratio (PR), ndefined as PR =(Pex,aDPignitor)/Pignition.4. Summary of Test Method4.1 A dust cloud is formed in a closed combustion chamberby an introduction of the material with air. The test is normallymade at atmospheric pre
15、ssure.4.2 Ignition of this dust-air mixture is then attempted after aspecified delay time by an ignition source located near thecenter of the chamber.4.3 The pressure time curve is recorded on a suitable pieceof equipment.5. Significance and Use5.1 This test method provides a procedure for performin
16、glaboratory tests to evaluate relative deflagration parameters ofdusts.5.2 The MEC as measured by this test method provides arelative measure of the concentration of a dust cloud necessaryfor an explosion.5.3 Since the MEC as measured by this test method mayvary with the uniformity of the dust dispe
17、rsion, energy of theignitor, and propagation criteria, the MEC should be consid-ered a relative rather than absolute measurement.5.4 If too weak an ignition source is used, the measuredMEC would be higher than the “true” value. This is anignitability limit rather than a flammability limit, and the t
18、estcould be described as“ underdriven.” Ideally, the ignitionenergy is increased until the measured MEC is independent ofignition energy. However, at some point the ignition energymay become too strong for the size of the test chamber, and thesystem becomes “overdriven.” When the ignitor flame be-co
19、mes too large relative to the chamber volume, a test couldFIG. 1 Typical Recorder Tracings for a Weak Dust Deflagration in a 20-L Chamber, using a 2500 J IgnitorFIG. 2 Typical Recorder Tracings for a Moderate Dust Deflagration in a 20-L Chamber, using a 2500 J IgnitorE1515072appear to result in an e
20、xplosion, while it is actually just dustburning in the ignitor flame with no real propagation beyondthe ignitor.5.5 The recommended ignition source for measuring theMEC of dusts in 20-L chambers is a 2500 or 5000 Jpyrotechnic ignitor.3Measuring the MEC at both ignitionenergies will provide informati
21、on on the possible overdrivingof the system.4To evaluate the effect of possible overdriving ina 20-L chamber, comparison tests may also be made in a largerchamber, such asa1m3-chamber.5.6 If a dust ignites with a 5000 J ignitor but not with a 2500J ignitor in a 20-L chamber, this may be an overdrive
22、n system.4In this case, it is recommended that the dust be tested with a10 000 J ignitor in a larger chamber, such asa1m3-chamber,to determine if it is actually explosible.5.7 The values obtained by this test method are specific tothe sample tested (particularly the particle size distribution)and th
23、e method used and are not to be considered intrinsicmaterial constants.6. Interferences6.1 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.7. Apparatu
24、s7.1 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 accor-dance with the ASME Boiler and Pressure Vessel
25、 Code,Section VIII.5A maximum allowable working pressure(MAWP) of at least 15 bar is recommended.7.3 The apparatus must be capable of dispersing a fairlyuniform dust cloud of the material.7.4 Optical dust probes, such as those described in Foot-notes6,77 and 8, may be used to monitor the uniformity
26、of thedust dispersion.7.5 The pressure transducer and recording equipment musthave a combined response rate that is greater than the maxi-mum measured rate of pressure rise.7.6 An example of a chamber and specific procedures thathave been found suitable are shown in Appendix X1.NOTE 2Another 20 L ch
27、amber design is described in Appendix X1 ofTest Method E 1226.8. Safety Precautions8.1 Prior to handling a dust, the toxicity of the sample andits combustion products must be considered. This informationis generally obtained from the manufacturer or supplier.Appropriate safety precautions must be ta
28、ken 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 initiating a test, a physical check of all gasketsand fittings should be made to prevent leakage.8.3 If chemical ignitors
29、 are used as an ignitor source, safetyin handling and use is a primary consideration. Prematureignition by electrostatic discharge must be considered a possi-bility. When handling these ignitors, eye protection must beworn at all times. A grounded, conductive tabletop is recom-mended for preparation
30、. Federal, state, and local regulationsfor the procurement, use, and storage of chemical ignitors mustbe followed.8.4 All testing should initially be conducted with smallquantities of sample to prevent overpressurization due to highenergy material.8.5 Explosive, highly reactive, or easily decomposed
31、 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 should be used asjudgment indicates.9. Sampling, Test Specimens, and Test Units9.1 It is not practical to specify a single method of
32、 samplingdust 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 MNL 32.89.2 Tests may be run on an as-received sample. However,due to the possible accumulation
33、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), the sample may be ground or pulverized or it may besieved.NOTE 3The operator should consider the thermal stabilit
34、y and thefriction and impact sensitivity of the dust during any grinding orpulverizing. In sieving the material, the operator must verify that there isno selective separation of components in a dust that is not a puresubstance.9.4 Dust samples that are much finer than 200 mesh (75 m)may have even lo
35、wer MEC values.NOTE 4It 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 b
36、eselectively separated on sieves and certain fibrous materials that may notpass through a relatively coarse screen may produce dust deflagrations.When a material is tested in the as-received state, it should be recognizedthat the test results may not represent the most severe dust deflagration3The p
37、yrotechnic ignitors are available commercially from Cesana Corp., POBox 182, Verona, NY 13478, or from Fr. Sobbe, GmbH, Beylingstrasse 59, Postfach140128, D-4600 Dortmund-Derne, Germany.4Cashdollar, K. L., and Chatrathi, K., “Minimum Explosible Dust Concentra-tions Measured in 20-L and 1-m3Chambers,
38、” Combustion Science and Technology,Vol. 87, pp. 157171, 19935Available from American Society of Mechanical Engineers, 345 E. 47th St.,New York, NY 10017.6Cashdollar, K. L., Liebman, I., and Conti, R. S., “Three Bureau of Mines DustProbes,” RI 8542, U.S. Bureau of Mines, 1981.7Conti, R. S., Cashdoll
39、ar, K. L., and Liebman, I., “Improved Optical Dust Probefor Monitoring Dust Explosions,” Review of Scientific Instruments, Vol 53, 1982, pp.311313.8MNL 32, Manual on testing Sieving Methods, is available from ASTMHeadquarters, 100 Barr Harbor Drive, West Conshohocken, PA 19428.E1515073possible. Any
40、process change resulting in a higher fraction of fines thannormal or drier product than normal may increase the explosion severity.9.5 The moisture content of the test sample should notexceed 5 % in order to avoid test results of a given dust beingnoticeably influenced.NOTE 5There is no single metho
41、d for determining the moisturecontent or for drying a sample. ASTM lists many methods for moisturedetermination in the Annual Book of ASTM Standards. Sample drying isequally complex due to the presence of volatiles, lack of or varyingporosity (see Test Methods D 3173 and D 3175), and sensitivity of
42、thesample to heat. Therefore, each must be dried in a manner that will notmodify or destroy the integrity of the sample. Hygroscopic materials mustbe desiccated.10. Calibration and Standardization10.1 Because a number of factors (uniformity of dispersion,ignition energy, sample age, etc.) can affect
43、 the test results, anytest vessel design other than that listed inAppendix X1 must bestandardized using dust samples whose minimum explosibleconcentrations are known. A minimum of five dust samplesover a range of MEC values is required. The MEC for eachdust must agree to within 610 % or 5 g/m3, whic
44、hever islarger. The comparison must be made using the same dust,ignitor energy, and chamber volume.10.2 Representative MEC data in grams per cubic metre(g/m3) for five dusts samples are listed as follows:Bureau of Mines Fike20-L ChamberA1m3ChamberB2500 J 5000 J 10 000 JBituminous coal, Pocahontas se
45、am 120 85 .Bituminous coal, Pittsburgh seam 80 60 80Lycopodium 45 30 42Gilsonite 35 30 36Polyethylene 32 28 .A20-L Chamber at Pittsburgh, PA. See Appendix X1 and Cashdollar, K. L. andHertzberg, M. “20-L Explosibility Test Chamber for Dusts and Gases,” Rev. Sci.Instrum., Vol 56, 1985, pp. 596602.B1-m
46、3Chamber at Blue Springs, MO. See Cashdollar, K. L. and Chatrathi, K.,“Minimum Explosible Concentrations in 20-L and 1-m3Chambers,” Combust. Sci.Tech., Vol. 87, 1993, pp. 157171.The Pocahontas seam bituminous coal has ;75 % minus200 mesh, a mass median diameter of ;52 m, and 17 %volatility. The Pitt
47、sburgh seam bituminous coal has ;80 %minus 200 mesh, a mass median diameter of ;48 m, and36 % volatility. The lycopodium is a natural plant spore havinga narrow size distribution with 100 % minus 200 mesh and amass median diameter of ;28 m. The gilsonite has ;91 %minus 200 mesh, a mass median diamet
48、er of ;28 m, and84 % volatility. The polyethylene has ;98 % minus 200 mesh,a mass median diameter of ;29 m, and 100 % volatility.10.3 In addition to the initial calibration and standardizationprocedure, at least one reference dust sample should be retestedperiodically to verify that the dispersion a
49、nd other character-istics of the chamber have not changed.11. Procedure11.1 These general procedures are applicable for all suitablechambers. The detailed procedures specific to each chamberare listed in Appendix X1.11.2 Inspect equipment to be sure it is thoroughly clean andin good operational condition.NOTE 6A high frequency of tests could increase the operatingtemperature in some chambers. Tests should not be run at chambertemperatures more than 20C above ambient as this may affect themeasured MEC value.11.3 Ensure that the oxygen content of the dispersio
