1、Designation: E2021 15Standard Test Method forHot-Surface Ignition Temperature of Dust Layers1This standard is issued under the fixed designation E2021; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A nu
2、mber 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 covers a laboratory procedure todetermine the hot-surface ignition temperature of dust layers,that is, measuring the min
3、imum temperature at which a dustlayer will self-heat. The test consists of a dust layer heated ona hot plate.2,31.2 Data obtained from this test method provide a relativemeasure of the hot-surface ignition temperature of a dust layer.1.3 This test method should be used to measure and describethe pro
4、perties of materials in response to heat and flame undercontrolled laboratory conditions and should not be used todescribe or appraise the fire hazard or fire hazard risk ofmaterials, products, or assemblies under actual fire conditions.However, results of this test method may be used as elementsof
5、a fire risk assessment that takes into account all of the factorsthat are pertinent to an assessment of the fire hazard risk of aparticular end use product.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 do
6、es 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. Specific precau-tionary statements
7、 are given in Section 8.2. Referenced Documents2.1 ASTM Standards:4E771 Test Method for Spontaneous Heating Tendency ofMaterials (Withdrawn 2001)5E1445 Terminology Relating to Hazard Potential of Chemi-calsE1491 Test Method for Minimum Autoignition Temperatureof Dust Clouds2.2 IEC Standard:6IEC 1241
8、-2-1 Electrical Apparatus for Use in the Presenceof Combustible Dust; Part 2: Test MethodsSection 1:Methods for Determining the Minimum Ignition Tempera-tures of Dusts, Method A3. Terminology3.1 DefinitionsFor definitions of other terms used in thisstandard, see Terminology E1445.3.2 Definitions of
9、Terms Specific to This Standard:3.2.1 hot-surface ignition temperature of a dust layer,nlowest set temperature of the hot plate that causes ignitionof the dust layer.3.2.2 ignition of a dust layer, ninitiation of self-heating orcombustion in a material under test.3.2.3 ignition time, ntime between t
10、he start of heating andthe point at which the maximum temperature or flamingcombustion is reached.3.2.4 temperature rise, T, nthe difference between Tmaxand the initial set temperature of the hot plate.3.2.5 Tmax,nmaximum temperature measured during test.4. Summary of Test Method4.1 The test materia
11、l is placed within a metal ring on top ofa hot plate, that is at a preset constant temperature.4.2 The sample temperature is monitored to determinetemperature rise due to oxidative reactions or decompositionreactions, or both.4.3 Ignition is considered to have taken place when either ofthe following
12、 occurs:1This test method is under the jurisdiction of ASTM Committee E27 on HazardPotential of Chemicals and is the direct responsibility of Subcommittee E27.04 onthe Flammability and Ignitability of Chemicals.Current edition approved July 1, 2015. Published July 2015. Originally approvedin 1999. L
13、ast previous edition approved in 2013 as E2021 09 (2013). DOI:10.1520/E2021-15.2This test method is based on recommendations of the National MaterialsAdvisory Board of the National Academy of Sciences (1).33The boldface numbers in parentheses refer to the list of references at the end ofthis standar
14、d.4For 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.5The last approved version of this historical standard is r
15、eferenced onwww.astm.org.6Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.3.1 Temperature in the dust laye
16、r at position of thermo-couple rises at least 50C above the hot plate temperature, or4.3.2 Visible evidence of combustion is apparent, such asred glow or flame.4.4 Hot plate surface temperature is varied from test to test,as necessary, until the hot-surface ignition temperature isdetermined.5. Signi
17、ficance and Use5.1 This test method is applicable to dusts and powders, andprovides a procedure for performing laboratory tests to evalu-ate hot-surface ignition temperatures of dust layers.5.2 The test data can be of value in determining safeoperating conditions in industrial plants, mines, manufac
18、turingprocesses, and locations of material usage and storage.5.3 Due to variation of ignition temperature with layerthickness, the test data at one thickness may not be applicableto all industrial situations (see Appendix X1). Tests at variouslayer thicknesses may provide a means for extrapolation t
19、othicker layers, as listed in the following for pulverized Pitts-burgh bituminous coal dust (2). Mathematical modeling oflayer ignition at various layer thicknesses is described in Ref.(3).Layer Thickness, mm Hot-Surface Ignition Temperature, C6.4 3009.4 26012.7 24025.4 2105.4 This hot plate test me
20、thod allows for loss of heat fromthe top surface of the dust layer, and therefore generally givesa higher ignition temperature for a material than Test MethodE771, which is a more adiabatic system.5.5 This test method for dust layers generally will give alower ignition temperature than Test Method E
21、1491, which isfor dust clouds. The layer ignition temperature is determinedwhile monitoring for periods of minutes to hours, while thedust cloud is only exposed to the furnace for a period ofseconds.NOTE 1Much of the literature data for layer ignition is actually froma basket in a heated furnace (4)
22、, known as the modified Godbert-Greenwald furnace test. Other data are from nonstandardized hot plates(5-9).5.6 Additional information on the significance and use ofthis test method may be found in Ref. (10).6. Limitations and Interferences6.1 This test method should not be used with materialshaving
23、 explosive or highly reactive properties.6.2 If the metal (for example, aluminum) plate or ring reactswith the test material, choose another type of metal that doesnot react.7. Apparatus7.1 The complete apparatus, shown in Fig. 1, consists of acircular metal (for example, aluminum) plate centrally p
24、osi-tioned on top of a hot plate. The dust layer is confined withina metal ring on top of the metal plate. An example of anapparatus that has been found suitable is given in AppendixX2.7.1.1 Heated Surface, consisting of a metal plate of approxi-mately 200-mm diameter and at least 20-mm thick. This
25、plateis centrally placed on top of a commercial hotplate. A thermo-couple is mounted radially in the metal plate, with its junctionin contact with the plate within 1.0 6 0.5 mm of the uppersurface. This thermocouple is connected to a temperaturecontroller. The plate and its thermocouple-controller a
26、ssembly,in conjunction with the commercial hotplate, should satisfy thefollowing requirements:7.1.1.1 The plate should be capable of attaining a maximumtemperature of 450C without a dust layer in position,7.1.1.2 The temperature controller must be capable of main-taining the temperature of the plate
27、 constant to within 65Cthroughout the time period of the test,7.1.1.3 When the temperature of the plate has reached aconstant value, the temperature across the plate should beuniform to within 65C, as shown in Fig. 2,7.1.1.4 The temperature control should be such that therecorded plate temperature w
28、ill not change by more than 65C during the placing of the dust layer and will be restored towithin 2C of the previous value within 5 min of placing thedust layer, and7.1.1.5 The thermocouple in the plate and its readout deviceshould be calibrated and should be accurate to within 63C.FIG. 1 Schematic
29、 of Hotplate Layer Ignition ApparatusE2021 1527.1.2 Metal Ring, to be placed on the heated metal plate, forcontaining the dust layer. Stainless steel is suitable for mostdusts. The standard ring is 12.7 mm (12 in.) in depth andapproximately 100 mm (4 in.) in diameter. Rings may be ofother depths.7.1
30、.3 Dust Layer ThermocoupleSlots on opposite sides ofthe perimeter of the ring accommodate the positioning of a typeK bare thermocouple (0.20 to 0.25 mm or 10 mil in diameter)through the dust sample. This bare thermocouple is positionedparallel to the surface of the metal plate with its junction at t
31、hegeometric center of the dust layer. This thermocouple shouldbe connected to a digital thermometer for observing thetemperature of a dust layer during a test. Temperature mea-surements with the thermocouple should be made eitherrelative to a fixed reference junction temperature or withautomatic col
32、d junction compensation. Most digital thermom-eters have built-in compensation. The thermocouple in the dustlayer and its readout device should be calibrated and should beaccurate to within 63C.7.2 Ambient Temperature Thermometer, placed in a conve-nient position within1mofthehotplate but shielded f
33、rom heatconvection and radiation from the hot plate. The ambienttemperature should be within the range of 15 to 30C.8. Hazards8.1 The user should consider the toxicity of the sample dustand possible combustion products.8.2 This test method should not be used with materialshaving explosive or highly
34、reactive properties.8.3 Metal dusts can ignite and burn with high temperatures.If a flame is observed, the dust layer should be covered with aflat metal sheet to exclude the air and extinguish the flame.8.4 The user should use due caution around the hot surfacespresent on the test apparatus.8.5 Test
35、s should be conducted in a ventilated hood or otherarea having adequate ventilation to remove any smoke orfumes.9. Sampling and Test Specimens9.1 It is not practical to specify a single method of samplingdust for test purposes because the character of the material andits available form affect select
36、ion of the sampling procedure.Generally accepted sampling procedures should be used. SeeMNL 32 Manual on Test Sieving Methods.9.2 Tests may be run on an as-received sample. However,since finer dusts have lower hot-surface ignition temperatures(2) and due to the possible accumulation of fines at some
37、locations in a processing system, it is recommended that thetest sample be at least 95 % minus 200 mesh (75 m). Toachieve this particle fineness, grind, pulverize, or sieve thesample.NOTE 2The operator should consider the thermal stability and thefriction and impact sensitivity of the dust during an
38、y 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 3It may be desirable in some cases to conduct dust layerignition tests on a material as sampled from a process because (a) duststr
39、eams may contain a wide range of particle sizes or have a well-definedspecific moisture content, (b) materials consisting of a mixture ofchemicals may be selectively separated on sieves, and (c) certain fibrousmaterials may not pass through a relatively coarse screen. When a materialis tested in the
40、 as-received state, it should be recognized that the testresults may not represent the lowest dust layer ignition temperaturepossible. Any process change resulting in a higher fraction of fines thannormal or drier product than normal may decrease the ignition tempera-ture.10. Calibration and Standar
41、dization10.1 The calibration of the dust sample thermocouple andthe thermocouple embedded in the circular metal plate must bechecked using appropriate standards.10.2 The temperature across the metal plate should beuniform to within 65C when measured across two diametersat right angles, as shown in F
42、ig. 2. This requirement must besatisfied at two plate temperatures, one in the range of between200 and 250C and the second in the range of between 300 and350C, measured at the center of the plate.10.3 Verify the performance of the apparatus using at leasttwo dust layers having different hot-surface
43、ignition tempera-tures. Representative data including both published and unpub-lished values (2)7for 12.7-mm thick layers of three dusts are:Brass 155-160CPittsburgh coal dust 230-240CLycopodium spores 240-250CThe brass was a very fine flake (100 % minus 325 mesh)with a small amount (1.7 %) of stear
44、ic acid coating. Thelycopodium is a natural plant spore having a narrow sizedistribution with 100 % minus 200 mesh and mass mediandiameter of ;28 m. This is the reticulate form Lycopodiumclavatum. The Pittsburgh seam bituminous coal has ;80 %7Some data are from unpublished work of the Fenwal (Marlbo
45、rough, MA) andFike (Blue Springs, MO) companies.FIG. 2 Uniformity of Aluminum Plate Temperature at Set Tempera-ture of 250CE2021 153minus 200 mesh, a mass median diameter of ;45 m, and36 % volatility. Additional data that can be used for calibrationare those listed in 5.3 for different layer thickne
46、sses of this coaldust.11. Procedure11.1 General Set-UpSet up the apparatus in a position freefrom drafts while exhausting smoke and fumes. Ensure that theair flow in the hood is sufficient for removing smoke andfumes, but low enough so as not to disturb the layer or affectthe test results. This can
47、be achieved by adjusting the baffles inthe back of the hood. If desired, an angled mirror can beprovided above the test sample for visual observation.11.2 Procedure for Individual Test:11.2.1 Centrally place a ring of the required height on theclean surface of the heated metal plate. Make adjustment
48、s tothe thermocouple position. Set the desired test temperature onthe temperature controller and heat the hot plate.11.2.2 When hot plate temperature is steady within therequired limit, fill the ring with the test dust, and level thesurface of the layer within a period of 2 min. Do not compressthe d
49、ust layer. Put the dust into the ring with a spatula anddistribute with mainly sideways movements of the spatula untilthe ring is slightly over-filled; then, level the layer by drawinga straight edge across the top of the ring. Remove the excessdust that spills on the metal plate. The amount of dust that willjust fill the ring can be predetermined so as to minimizespillage. Also to minimize spillage, it is convenient to use ascoop with a concave edge, as shown in Fig. 3, and to draw thestraight edge towards the scoop.NOTE 4The bulk density of ea
