1、Designation: E 1491 06Standard Test Method forMinimum Autoignition Temperature of Dust Clouds1This standard is issued under the fixed designation E 1491; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A
2、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 covers the determination of the minimum temperature at which a dust cloud willautoignite. The dust cloud is exposed t
3、o air heated to various temperatures in a furnace. Ignition of thecloud is indicated by visual observation of the flame. The chemical nature of the dust as well as itsconcentration, particle size, moisture, and surface area affects the results.1. Scope1.1 This test method covers the minimum temperat
4、ure atwhich a given dust cloud will autoignite when exposed to airheated in a furnace at local atmospheric pressure.1.2 Data obtained from this test method provide a relativemeasure of dust cloud autoignition temperatures.1.3 This test method should be used to measure and describethe properties of m
5、aterials, products, or assemblies in responseto heat and flame under controlled laboratory conditions andshould not be used to describe or appraise the fire hazard or firerisk of materials, products, or assemblies under actual fireconditions. However, results of this test method may be used aselemen
6、ts of a fire risk assessment which takes into account allof the factors which are pertinent to an assessment of the firehazard of a particular end use.1.4 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
7、 standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 3173 Test Method for Moisture in theAnalysis Sample ofCoal and CokeD 3175 Test Method for Volatile Matter in the Analys
8、isSample of Coal and CokeE 659 Test Method for Autoignition Temperature of LiquidChemicalsE 1226 Test Method for Pressure and Rate of Pressure Risefor Combustible Dusts3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 dust concentrationthe mass of dust divided by theinternal vol
9、ume of the test chamber.3.1.2 minimum autoignition temperature (MAIT)the mini-mum temperature at which a dust cloud will self ignite underthe specified conditions of test.4. Summary of Test Method4.1 The temperature of the furnace or oven is set at apredetermined value.4.2 Dust is blown into the hea
10、ted furnace, which is atambient pressure.4.3 Ignition is determined by visual observation of the flameexiting the furnace.5. Significance and Use5.1 This test method provides a procedure for performinglaboratory tests to determine the minimum autoignition tem-perature (MAIT) of a dust cloud.5.2 The
11、test data developed from this test method can beused to limit the temperature to which a dust cloud is exposedso as to prevent ignition of the cloud. Because of the shortduration of the test, the data obtained are most applicable to1This test method is under the jurisdiction of ASTM Committee E27 on
12、 HazardPotential of Chemicals and is the direct responsibility of Subcommittee E27.05 onExplosibility and Ignitability of Dust Clouds.Current edition approved Oct. 1, 2006. Published November 2006. Originallyapproved in 1991. Last previous edition approved in 2002 as E 1491 97(2002).2For referenced
13、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, PO Box C700, West Consh
14、ohocken, PA 19428-2959, United States.industrial equipment where dust is present as a cloud for a shorttime. Because of the small scale of the test and the possiblevariation of the MAIT value with scale, the data obtained bythis test method may not be directly applicable to all industrialconditions.
15、5.3 The MAIT data can also be used in conjunction withminimum spark ignition data to evaluate the hazards ofgrinding and impact sparks in the presence of dust clouds (1and 2).35.4 The test values obtained are specific to the sampletested, the method used, and the test equipment utilized. Thetest val
16、ues are not to be considered intrinsic material constants,but may be used as a relative measure of the temperature atwhich a dust cloud self ignites.5.5 The test data are for cloud ignition. Dust in the form ofa layer may ignite at significantly lower temperatures than thesame dust in the form of a
17、cloud (3). For liquid chemicals, seeTest Method E 659.6. Interferences6.1 Unburned dust from a previous test may affect results. Ifthere is a question, the furnace should be heated to itsmaximum temperature to clean it before future tests are made.6.2 The material of construction of this test method
18、 mayhave catalytic effects on the ignition and should be consideredduring testing.7. Apparatus7.1 The equipment consists of a heated chamber closed witha frangible diaphragm, or flap vent, or a hole open to theatmosphere.7.2 The chamber is insulated and provided with a thermo-statically controlled e
19、lectric heater. A thermocouple measuresthe set temperature of the chamber.7.3 A dust dispersion system generates a fairly uniform dustcloud within the chamber. There should be a minimal amountof dust remaining in the disperser after the test.7.4 Athermocouple (1 mil or 25 m) and a recording systemha
20、ving a fast enough response may be used to measure thetemperature rise during ignition of the dust cloud in thechamber.7.5 Examples of chambers and specific procedures that havebeen found suitable are listed in chronological order inAppendix X1-Appendix X4.8. Hazards8.1 Safety Precautions:8.1.1 Prio
21、r to handling a dust, its toxicity and the toxicity ofits combustion products must be considered. This informationcan usually be obtained from the manufacturer. Considerationwill have to be given to ventilation, use of hoods, personalprotective gear, and procedures.8.1.2 Explosive, highly reactive,
22、or easily decomposed ma-terials 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.8.1.3 Electrical systems must be grounded.9. Sampling9.1 It is not practical
23、 to specify a single method of 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 STP 447A.49.2 Tests may be run on an as-received sample. However,d
24、ue to the 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), grind, pulverize, or sieve the sample.NOTE 1The operator should consider the therm
25、al stability 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.NOTE 2It may be desirable in some cases to conduct dust autoig
26、nitiontests on a material as sampled from a process because dust streams maycontain 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 may not passthrough
27、a relatively coarse screen. When a material is tested in theas-received state, it should be recognized that the test results may notrepresent the lowest cloud autoignition temperature possible. Any processchange resulting in a higher fraction of fines than normal or drier productthan normal may decr
28、ease the autoignition temperature.9.4 The moisture content of the test sample should notexceed 10 % in order to avoid noticeable influence on testresults of a given dust.NOTE 3There is no single method for determining the moisturecontent or for drying a sample. ASTM lists many methods for moisturede
29、termination 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 thesample to heat. Therefore, each must be dried in a manner that will notmodify or destroy the inte
30、grity of the sample. Hygroscopic materials mustbe desiccated.10. Calibration and Standardization10.1 Any new test vessel design other than those listed inthe appendixes must be standardized using dust samples whoseMAIT values are known. A minimum of three dust samplesover a wide range of MAIT values
31、 is required. For tempera-tures below 600C, the MAIT value for each dust measured ina furnace must agree to within 660C of the average MAITvalue for that dust as measured in the four furnaces inAppendix X1-Appendix X4.10.2 Representative MAIT data for six dusts are listed indegrees Celsius in Table
32、1. These data are only intended toindicate the variability among furnaces. The anthracite coal has;85 % minus 200 mesh and a mass median diameter of ;403The boldface numbers in parentheses refer to the list of references at the end ofthis test method.4STP 447A is available from ASTM Headquarters.E14
33、91062m. The anthraquinone (C14H8O2) has ;73 % minus 200mesh and a mass median diameter of ;56 m. The Pocahontas(Poc.) seam bituminous coal has ;70 % minus 200 mesh, amass median diameter of ;56 m, and 18 % volatility. ThePittsburgh (Pgh.) seam bituminous coal has ;80 % minus 200mesh, a mass median d
34、iameter of ;45 m, and 36 % volatility.The lycopodium is the reticulate form, Lycopodium clavatum.It is a natural plant spore having a narrow size distribution with100 % minus 200 mesh and mass median diameter of ;28 m.The sulfur has ;81 % minus 200 mesh and a mass mediandiameter of ;38 m.10.2.1 Thes
35、e data are from the four furnaces listed in theappendixesthe 0.27-L Godbert-Greenwald (G-G) Furnace,the 0.35-L BAM Oven, the 1.2-L Bureau of Mines Furnace,and the 6.8-L Bureau of Mines Furnace. The BAM oven islimited to a maximum test temperature of 600C. The G-GFurnace generally yields somewhat hig
36、her MAIT data than theother three. The greatest deviation in MAIT values occurs atthe highest temperatures, as shown by the anthracite coal datain the table. However, the lower MAIT values (where agree-ment is better) are of greater practical importance.10.3 In addition to the initial calibration of
37、 a furnace, retestat least one standard dust periodically to verify that the furnacetest conditions have not changed.11. Procedure11.1 These general procedures are applicable for all suitablefurnaces. The detailed procedures specific to each furnace arelisted in the corresponding appendix.11.2 Inspe
38、ct equipment to be sure it is thoroughly clean andin good operational condition.11.3 Set the temperature of the furnace or oven at thepredetermined value.NOTE 4For most furnaces, it is generally desirable to approach theMAIT from below to avoid a violent dust explosion in the chamber.However, the re
39、commended procedure for the BAM oven is to approachthe MAIT from above (see Appendix X2).11.4 Place a weighed amount of dust in the disperser. Therecommended initial test concentration for most dusts is from300 to 1000 g/m3. If data from Test Method E 1226 exist forthe dust, the initial test could b
40、e made at the concentration atwhich the maximum pressure, Pmax, and the maximum nor-malized rate of pressure increase, Kst, were found.11.5 Disperse the dust and observe whether or not flameexits the furnace.NOTE 5It is useful to darken the room to make it easier to observe theflame. Some flames, su
41、ch as the blue flame of sulfur, are difficult to see.11.6 If no ignition occurs, increase the temperature 50 to100C and test the dust again at the same concentration.11.7 After ignition has been achieved, lower the test tem-perature in 25C increments to determine the lowest tempera-ture at which ign
42、ition occurs and the highest temperature atwhich ignition does not occur for this dust concentration.Ignition is defined as flame exiting from the chamber.11.8 At the highest temperature at which ignition is notobserved, vary the dust concentration. If the dust ignites at anyconcentration at this te
43、mperature, lower the test temperatureand continue the testing. At least five tests over a range ofconcentrations must be run at the highest temperature at whichignition is not observed.11.9 At the temperature at which ignition is observed, varythe dust concentration to determine the range over which
44、ignition occurs. In order to assure the repeatability of the data,observe at least three ignitions over a range of concentrationsat the lowest temperature at which ignition occurs.11.10 The reason for varying the concentration in 11.8 and11.9 is to ensure that the autoignition temperature is measure
45、dat the most easily ignited concentration. However, the autoi-gnition temperature is usually relatively independent of con-centration, as shown in Fig. 1 and Fig. 2.11.11 The final determination of the MAIT must be made byvarying the temperature in increments of 25C or smaller.11.12 Fig. 1 is an exa
46、mple of a typical test pattern oftemperatures and concentrations. Fig. 2 is a more detailedseries of tests to show the reproducibility of the data and therange of concentrations over which ignition occurs.12. Calculation12.1 The minimum autoignition temperature (MAIT) of thedust cloud is the average
47、 of the lowest temperature at whichignition was reproducibly observed and the highest tempera-ture at which ignition was not observed at any concentration. Ifthere is an intermediate temperature at which ignition isobserved for about half the tests, report this as the MAIT.Round the reported MAIT va
48、lue to the nearest 10C. As anexample, the MAIT for polyethylene dust in Fig. 1 would be375C, or rounded to 370C for the report. For the coal dustdata in Fig. 2, the MAIT would be 540C.13. Report13.1 Report the following information:13.1.1 Complete identification of the material tested; in-cluding ty
49、pe of dust, source, code numbers, forms, andprevious history,TABLE 1 Examples of MAIT Data, CG-GFurnaceBAMOven1.2-LFurnace6.8-LFurnaceAnthracite coal 900 600 740 730Anthraquinone 670 600 620 680Pocahontas (Poc) bituminous coal 640 580 610 600Pittsburgh (Pgh) bituminous coal 600 570 540 530Lycopodium 460 410 440 380Sulfur 260 240 290 260FIG. 1 Typical Data for the Measurement of the MinimumAutoignition Temperature of a Polyethylene DustE149106313.1.2 Particle size distribution of the sample as receivedand as tested,13.1.3 Moisture or volatile content, or bot
