ASTM E1491-06(2012)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: E1491 − 06 (Reapproved 2012)
Standard Test Method for
Minimum Autoignition Temperature of Dust Clouds
This standard is issued under the fixed designation E1491; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method covers the determination of the minimum temperature at which a dust cloud will
autoignite.The dust cloud is exposed to air heated to various temperatures in a furnace. Ignition of the
cloud is indicated by visual observation of the flame. The chemical nature of the dust as well as its
concentration, particle size, moisture, and surface area affects the results.
1. Scope 2. Referenced Documents
1.1 This test method covers the minimum temperature at 2.1 ASTM Standards:
which a given dust cloud will autoignite when exposed to air D3173 Test Method for Moisture in the Analysis Sample of
heated in a furnace at local atmospheric pressure. Coal and Coke
D3175 Test Method for Volatile Matter in the Analysis
1.2 Data obtained from this test method provide a relative
Sample of Coal and Coke
measure of dust cloud autoignition temperatures.
E659 Test Method for Autoignition Temperature of Chemi-
1.3 Thistestmethodshouldbeusedtomeasureanddescribe
cals
the properties of materials, products, or assemblies in response
E1226 Test Method for Explosibility of Dust Clouds
to heat and flame under controlled laboratory conditions and
shouldnotbeusedtodescribeorappraisethefirehazardorfire
3. Terminology
risk of materials, products, or assemblies under actual fire
3.1 Definitions of Terms Specific to This Standard:
conditions.However,resultsofthistestmethodmaybeusedas
3.1.1 dust concentration—the mass of dust divided by the
elements of a fire risk assessment which takes into account all
internal volume of the test chamber.
of the factors which are pertinent to an assessment of the fire
3.1.2 minimum autoignition temperature (MAIT)—the mini-
hazard of a particular end use.
mum temperature at which a dust cloud will self ignite under
1.4 The values stated in SI units are to be regarded as
the specified conditions of test.
standard. No other units of measurement are included in this
standard.
4. Summary of Test Method
1.5 This standard does not purport to address all of the
4.1 The temperature of the furnace or oven is set at a
safety concerns, if any, associated with its use. It is the
predetermined value.
responsibility of the user of this standard to establish appro-
4.2 Dust is blown into the heated furnace, which is at
priate safety, health, and environmental practices and deter-
ambient pressure.
mine the applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accor-
4.3 Ignitionisdeterminedbyvisualobservationoftheflame
dance with internationally recognized principles on standard-
exiting the furnace.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
5. Significance and Use
mendations issued by the World Trade Organization Technical
5.1 This test method provides a procedure for performing
Barriers to Trade (TBT) Committee.
laboratory tests to determine the minimum autoignition tem-
perature (MAIT) of a dust cloud.
This test method is under the jurisdiction ofASTM Committee E27 on Hazard
Potential of Chemicals and is the direct responsibility of Subcommittee E27.05 on
Explosibility and Ignitability of Dust Clouds. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Dec. 1, 2012. Published December 2012. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1991. Last previous edition approved in 2006 as E1491 – 06. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E1491-06R12. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1491 − 06 (2012)
5.2 The test data developed from this test method can be 8. Hazards
used to limit the temperature to which a dust cloud is exposed
8.1 Safety Precautions:
so as to prevent ignition of the cloud. Because of the short
8.1.1 Prior to handling a dust, its toxicity and the toxicity of
duration of the test, the data obtained are most applicable to
its combustion products must be considered. This information
industrialequipmentwheredustispresentasacloudforashort
can usually be obtained from the manufacturer. Consideration
time. Because of the small scale of the test and the possible
will have to be given to ventilation, use of hoods, personal
variation of the MAIT value with scale, the data obtained by
protective gear, and procedures.
this test method may not be directly applicable to all industrial
8.1.2 Explosive, highly reactive, or easily decomposed ma-
conditions.
terials should not be tested unless they have been characterized
5.3 The MAIT data can also be used in conjunction with by prior testing. Procedures such as the use of barricades,
minimum spark ignition data to evaluate the hazards of hoods, and personal protective equipment should be used as
grinding and impact sparks in the presence of dust clouds (1 judgment indicates.
and 2). 8.1.3 Electrical systems must be grounded.
5.4 The test values obtained are specific to the sample
9. Sampling
tested, the method used, and the test equipment utilized. The
9.1 It is not practical to specify a single method of sampling
test values are not to be considered intrinsic material constants,
dust for test purposes because the character of the material and
but may be used as a relative measure of the temperature at
its available form affect selection of the sampling procedure.
which a dust cloud self ignites.
Generally accepted sampling procedures should be used as
5.5 The test data are for cloud ignition. Dust in the form of
described in STP 447A.
a layer may ignite at significantly lower temperatures than the
9.2 Tests may be run on an as-received sample. However,
same dust in the form of a cloud (3). For liquid chemicals, see
due to the possible accumulation of fines at some location in a
Test Method E659.
processingsystem,itisrecommendedthatthetestsamplebeat
6. Interferences
least 95 % minus 200 mesh (75 µm).
6.1 Unburneddustfromaprevioustestmayaffectresults.If
9.3 To achieve this particle fineness (95 % minus 200
there is a question, the furnace should be heated to its
mesh), grind, pulverize, or sieve the sample.
maximum temperature to clean it before future tests are made.
NOTE 1—The operator should consider the thermal stability and the
6.2 The material of construction of this test method may
friction and impact sensitivity of the dust during any grinding or
pulverizing. In sieving the material, the operator must verify that there is
have catalytic effects on the ignition and should be considered
no selective separation of components in a dust that is not a pure
during testing.
substance.
NOTE 2—It may be desirable in some cases to conduct dust autoignition
7. Apparatus
tests on a material as sampled from a process because dust streams may
7.1 Theequipmentconsistsofaheatedchamberclosedwith
contain a wide range of particle sizes or have a well-defined specific
moisture content, materials consisting of a mixture of chemicals may be
a frangible diaphragm, or flap vent, or a hole open to the
selectively separated on sieves, and certain fibrous materials may not pass
atmosphere.
through a relatively coarse screen. When a material is tested in the
7.2 The chamber is insulated and provided with a thermo- as-received state, it should be recognized that the test results may not
represent the lowest cloud autoignition temperature possible.Any process
statically controlled electric heater. A thermocouple measures
change resulting in a higher fraction of fines than normal or drier product
the set temperature of the chamber.
than normal may decrease the autoignition temperature.
7.3 Adust dispersion system generates a fairly uniform dust
9.4 The moisture content of the test sample should not
cloud within the chamber. There should be a minimal amount
exceed 10 % in order to avoid noticeable influence on test
of dust remaining in the disperser after the test.
results of a given dust.
7.4 Athermocouple(1milor25µm)andarecordingsystem
NOTE 3—There is no single method for determining the moisture
having a fast enough response may be used to measure the
content or for drying a sample. ASTM lists many methods for moisture
temperature rise during ignition of the dust cloud in the
determination in the Annual Book of ASTM Standards. Sample drying is
equally complex due to the presence of volatiles, lack of or varying
chamber.
porosity (see Test Methods D3173 and D3175), and sensitivity of the
7.5 Examplesofchambersandspecificproceduresthathave
sample to heat. Therefore, each must be dried in a manner that will not
been found suitable are listed in chronological order in
modify or destroy the integrity of the sample. Hygroscopic materials must
be desiccated.
Appendix X1 – Appendix X4.
10. Calibration and Standardization
10.1 Any new test vessel design other than those listed in
the appendixes must be standardized using dust samples whose
MAIT values are known. A minimum of three dust samples
The boldface numbers in parentheses refer to the list of references at the end of
this test method. STP 447A is available from ASTM Headquarters.
E1491 − 06 (2012)
over a wide range of MAIT values is required. For tempera- 11.4 Place a weighed amount of dust in the disperser. The
tures below 600°C, the MAIT value for each dust measured in recommended initial test concentration for most dusts is from
a furnace must agree to within 660°C of the average MAIT 300 to 1000 g/m . If data from Test Method E1226 exist for
value for that dust as measured in the four furnaces in the dust, the initial test could be made at the concentration at
Appendix X1 – Appendix X4. which the maximum pressure, P , and the maximum
max
normalized rate of pressure increase, K , were found.
st
10.2 Representative MAIT data for six dusts are listed in
degrees Celsius in Table 1. These data are only intended to 11.5 Disperse the dust and observe whether or not flame
indicatethevariabilityamongfurnaces.Theanthracitecoalhas exits the furnace.
;85 % minus 200 mesh and a mass median diameter of ;40
NOTE 5—It is useful to darken the room to make it easier to observe the
µm. The anthraquinone (C H O ) has ;73 % minus 200
14 8 2
flame. Some flames, such as the blue flame of sulfur, are difficult to see.
mesh and a mass median diameter of ;56 µm.The Pocahontas
11.6 If no ignition occurs, increase the temperature 50 to
(Poc.) seam bituminous coal has ;70 % minus 200 mesh, a
100°C and test the dust again at the same concentration.
mass median diameter of ;56 µm, and 18 % volatility. The
11.7 After ignition has been achieved, lower the test tem-
Pittsburgh (Pgh.) seam bituminous coal has ;80 % minus 200
perature in 25°C increments to determine the lowest tempera-
mesh, a mass median diameter of ;45 µm, and 36 % volatility.
ture at which ignition occurs and the highest temperature at
The lycopodium is the reticulate form, Lycopodium clavatum.
which ignition does not occur for this dust concentration.
Itisanaturalplantsporehavinganarrowsizedistributionwith
Ignition is defined as flame exiting from the chamber.
100 % minus 200 mesh and mass median diameter of ;28 µm.
The sulfur has ;81 % minus 200 mesh and a mass median
11.8 At the highest temperature at which ignition is not
diameter of ;38 µm.
observed, vary the dust concentration. If the dust ignites at any
10.2.1 These data are from the four furnaces listed in the
concentration at this temperature, lower the test temperature
appendixes—the 0.27-L Godbert-Greenwald (G-G) Furnace,
and continue the testing. At least five tests over a range of
the 0.35-L BAM Oven, the 1.2-L Bureau of Mines Furnace,
concentrations must be run at the highest temperature at which
and the 6.8-L Bureau of Mines Furnace. The BAM oven is
ignition is not observed.
limited to a maximum test temperature of 600°C. The G-G
11.9 At the temperature at which ignition is observed, vary
Furnace generally yields somewhat higher MAIT data than the
the dust concentration to determine the range over which
other three. The greatest deviation in MAIT values occurs at
ignition occurs. In order to assure the repeatability of the data,
the highest temperatures, as shown by the anthracite coal data
observe at least three ignitions over a range of concentrations
in the table. However, the lower MAIT values (where agree-
at the lowest temperature at which ignition occurs.
ment is better) are of greater practical importance.
11.10 The reason for varying the concentration in 11.8 and
10.3 In addition to the initial calibration of a furnace, retest
11.9 is to ensure that the autoignition temperature is measured
at least one standard dust periodically to verify that the furnace
at the most easily ignited concentration. However, the autoi-
test conditions have not changed.
gnition temperature is usually relatively independent of
concentration, as shown in Fig. 1 and Fig. 2.
11. Procedure
11.11 ThefinaldeterminationoftheMAITmustbemadeby
11.1 These general procedures are applicable for all suitable
varying the temperature in increments of 25°C or smaller.
furnaces. The detailed procedures specific to each furnace are
11.12 Fig. 1 is an example of a typical test pattern of
listed in the corresponding appendix.
temperatures and concentrations. Fig. 2 is a more detailed
11.2 Inspect equipment to be sure it is thoroughly clean and
series of tests to show the reproducibility of the data and the
in good operational condition.
range of concentrations over which ignition occurs.
11.3 Set the temperature of the furnace or oven at the
predetermined value.
NOTE 4—For most furnaces, it is generally desirable to approach the
MAIT from below to avoid a violent dust explosion in the chamber.
However, the recommended procedure for the BAM oven is to approach
the MAIT from above (see Appendix X2).
TABLE 1 Examples of MAIT Data, °C
G-G BAM 1.2-L 6.8-L
Furnace Oven Furnace Furnace
Anthracite coal >900 >600 740 730
Anthraquinone 670 >600 620 680
Pocahontas (Poc) bituminous coal 640 580 610 600
Pittsburgh (Pgh) bituminous coal 600 570 540 530
Lycopodium 460 410 440 380
Sulfur 260 240 290 260 FIG. 1 Typical Data for the Measurement of the Minimum Autoi-
gnition Tempe
...