1、Designation: E2021 09Standard 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.2,1.2 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 prop
4、erties 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 a
5、 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 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of
6、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 ASTM Standards:3E771 Test Method for Spontaneous Heating Tendency ofMateri
7、als4E1445 Terminology Relating to Hazard Potential of Chemi-calsE1491 Test Method for Minimum Autoignition Tempera-ture of Dust Clouds2.2 IEC Standard:5IEC 1241-2-1 Electrical Apparatus for Use in the Presenceof Combustible Dust; Part 2: Test MethodsSection 1:Methods for Determining the Minimum Igni
8、tion Tempera-tures of Dusts, Method A3. Terminology3.1 Definitions: For definitions of other terms used in thisstandard see Terminology E1445.3.2 Definitions of 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
9、 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 the start of heating andthe point at which the maximum temperature or flamingcombustion is reached.3.2.4 temperature rise, DT, nthe differen
10、ce 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 material 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
11、 determinetemperature rise due to oxidative reactions or decompositionreactions, or both.4.3 Ignition is considered to have taken place when either ofthe following occurs:4.3.1 Temperature in the dust layer at position of thermo-couple rises at least 50C above the hot plate temperature, or4.3.2 Visi
12、ble evidence of combustion is apparent, such asred glow or flame.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 Dec. 1,
13、 2009. Published February 2010 Originallyapproved in 1999. Last previous edition approved in 2006 as E202106 DOI:10.1520/E2021-09.2This test method is based on recommendations of the National MaterialsAdvisory Board of the National Academy of Sciences (1).3The boldface numbers in parentheses refer t
14、o the list of references at the end ofthis standard.3For 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.4Withdraw
15、n. The last approved version of this historical standard is referencedon www.astm.org.5Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, P
16、A 19428-2959, United States.4.4 Hot plate surface temperature is varied from test to test,as necessary, until the hot-surface ignition temperature isdetermined.5. Significance and Use5.1 This test method is applicable to dusts and powders, andprovides a procedure for performing laboratory tests to e
17、valu-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, manufacturingprocesses, and locations of material usage and storage.5.3 Due to variation of ignition temperature with layerthickness, the t
18、est data at one thickness may not be applicableto all industrial situations (see Appendix X1). Tests at variouslayer thicknesses may provide a means for extrapolation tothicker layers, as listed in the following for pulverized Pitts-burgh bituminous coal dust (2). Mathematical modeling oflayer ignit
19、ion 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 method allows for loss of heat fromthe top surface of the dust layer, and therefore generally givesa higher ignition temperature for a
20、 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 E1491, which isfor dust clouds. The layer ignition temperature is determinedwhile monitoring for periods of minutes to hours, while t
21、hedust 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), known as the modified Godbert-Greenwald furnace test. Other data are from nonstandardized hot plates(5-9).5.6 Additional informati
22、on 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 explosive or highly reactive properties.6.2 If the metal (for example, aluminum) plate or ring reactswith the test material, choose
23、 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 posi-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
24、 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 plateis centrally placed on top of a commercial hotplate. A thermo-couple is mounted radially in the metal plate, with its junctioni
25、n 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 assembly,in conjunction with the commercial hotplate, should satisfy thefollowing requirements:7.1.1.1 The plate should be capable of
26、 attaining a maximumtemperature of 400C without a dust layer in position,7.1.1.2 The temperature controller must be capable of main-taining the temperature of the plate constant to within 6 5Cthroughout the time period of the test,7.1.1.3 When the temperature of the plate has reached aconstant value
27、, the temperature across the plate should beuniform to within6 5C, as shown in Fig. 2,7.1.1.4 The temperature control should be such that therecorded plate temperature will not change by more than 6 5C during the placing of the dust layer and will be restored towithin 2C of the previous value within
28、 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 6 3C.7.1.2 Metal Ring, to be placed on the heated metal plate, forcontaining the dust layer. Stainless steel is suitable for mostdusts. The standard r
29、ing is 12.7 mm (12 in.) in depth andapproximately 100 mm (4 in.) in diameter. Rings may be ofother depths.7.1.3 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
30、sample. This bare thermocouple is positionedFIG. 1 Schematic of Hotplate Layer Ignition ApparatusE2021 092parallel to the surface of the metal plate with its junction at thegeometric center of the dust layer. This thermocouple shouldbe connected to a digital thermometer for observing thetemperature
31、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 cold junction compensation. Most digital thermom-eters have built-in compensation. The thermocouple in the dustlayer and its readout
32、 device should be calibrated and should beaccurate to within6 3C.7.2 Ambient Temperature Thermometer, placed in a conve-nient position within1mofthehotplate but shielded from heatconvection and radiation from the hot plate. The ambienttemperature should be within the range of 15 to 30C.8. Hazards8.1
33、 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 reactive properties.8.3 Metal dusts can ignite and burn with high temperatures.If a flame is observed, the dust layer should be c
34、overed 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 Tests should be conducted in a ventilated hood or otherarea having adequate ventilation to remove any smoke orfumes.9. Sampling and T
35、est 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 selection of the sampling procedure.Generally accepted sampling procedures should be used .SeeMNL 32 Manual on Test Sieving Methods.9.2
36、 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 somelocations in a processing system, it is recommended that thetest sample be at least 95 % minus 200 mesh (75 m). Toachieve this pa
37、rticle fineness, grind, pulverize, or sieve thesample.NOTE 2The operator should consider the thermal 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
38、 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) duststreams may contain a wide range of particle sizes or have a well-definedspecific moisture content, (b) materials consisting of a mi
39、xture 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 as-received state, it should be recognized that the testresults may not represent the lowest dust layer ignition temperatureposs
40、ible. 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 Standardization10.1 The calibration of the dust sample thermocouple andthe thermocouple embedded in the circular metal plate must bechec
41、ked using appropriate standards.10.2 The temperature across the metal plate should beuniform to within 6 5C when measured across two diametersat right angles, as shown in Fig. 2. This requirement must besatisfied at two plate temperatures, one in the range of between200 and 250C and the second in th
42、e 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 ignition tempera-tures. Representative data including both published and unpub-lished values (2)6for 12.7-mm thick layers of thr
43、ee 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 stearic acid coating. Thelycopodium is a natural plant spore having a narrow sizedistribution with 100 % minus 200 mesh and mass medi
44、andiameter of ;28 m. This is the reticulate form Lycopodiumclavatum. The Pittsburgh seam bituminous coal has ;80 %minus 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 thicknesses of this coald
45、ust.11. Procedure11.1 General Set-UpSet up the apparatus in a positionfree from drafts while exhausting smoke and fumes. Ensurethat the air flow in the hood is sufficient for removing smokeand fumes, but low enough so as not to disturb the layer or6Some data are from unpublished work of the Fenwal (
46、Marlborough, MA) andFike (Blue Springs, MO) companies.FIG. 2 Uniformity of Aluminum Plate Temperature at SetTemperature of 250CE2021 093affect the test results. This can be achieved by adjusting thebaffles in the back of the hood. If desired, an angled mirror canbe provided above the test sample for
47、 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 adjustments tothe thermocouple position. Set the desired test temperature onthe temperature controller and heat the hot plate.11.2.2 When ho
48、t 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 dust layer. Put the dust into the ring with a spatula anddistribute with mainly sideways movements of the spatula untilthe ring is
49、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 each dust should be determined toprovide a reference should data on a similar material yield significantlydifferent results in later te
