ASTM E1491-97(2002)
(Test Method)Standard Test Method for Minimum Autoignition Temperature of Dust Clouds
Standard Test Method for Minimum Autoignition Temperature of Dust Clouds
SCOPE
1.1 This test method determines the minimum temperature at which a given dust cloud will autoignite when exposed to air heated in a furnace at local atmospheric pressure.
1.2 Data obtained from this test method provide a relative measure of dust cloud autoignition temperatures.
1.3 This test method should be used to measure and describe the properties of materials, products, or assemblies in response to heat and flame under controlled laboratory conditions and should not be used to describe or appraise the fire hazard or fire risk of materials, products, or assemblies under actual fire conditions. However, results of this test method may be used as elements of a fire risk assessment which takes into account all of the factors which are pertinent to an assessment of the fire hazard of a particular end use.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 1491 – 97 (Reapproved 2002)
Standard Test Method for
Minimum Autoignition Temperature of Dust Clouds
This standard is issued under the fixed designation E 1491; 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 (e) 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 E 659 Test Method for Autoignition Temperature of Liquid
Chemicals
1.1 This test method covers the minimum temperature at
E 1226 Test Method for Pressure and Rate of Pressure Rise
which a given dust cloud will autoignite when exposed to air
for Combustible Dusts
heated in a furnace at local atmospheric pressure.
1.2 Data obtained from this test method provide a relative
3. Terminology
measure of dust cloud autoignition temperatures.
3.1 Definitions of Terms Specific to This Standard:
1.3 Thistestmethodshouldbeusedtomeasureanddescribe
3.1.1 dust concentration—the mass of dust divided by the
the properties of materials, products, or assemblies in response
internal volume of the test chamber.
to heat and flame under controlled laboratory conditions and
3.1.2 minimum autoignition temperature (MAIT)—themini-
shouldnotbeusedtodescribeorappraisethefirehazardorfire
mum temperature at which a dust cloud will self ignite under
risk of materials, products, or assemblies under actual fire
the specified conditions of test.
conditions.However,resultsofthistestmethodmaybeusedas
elements of a fire risk assessment which takes into account all
4. Summary of Test Method
of the factors which are pertinent to an assessment of the fire
4.1 The temperature of the furnace or oven is set at a
hazard of a particular end use.
predetermined value.
1.4 This standard does not purport to address all of the
4.2 Dust is blown into the heated furnace, which is at
safety concerns, if any, associated with its use. It is the
ambient pressure.
responsibility of the user of this standard to establish appro-
4.3 Ignitionisdeterminedbyvisualobservationoftheflame
priate safety and health practices and determine the applica-
exiting the furnace.
bility of regulatory limitations prior to use.
5. Significance and Use
2. Referenced Documents
5.1 This test method provides a procedure for performing
2.1 ASTM Standards:
laboratory tests to determine the minimum autoignition tem-
D 3173 Test Method for Moisture in theAnalysis Sample of
perature (MAIT) of a dust cloud.
Coal and Coke
5.2 The test data developed from this test method can be
D 3175 Test Method for Volatile Matter in the Analysis
used to limit the temperature to which a dust cloud is exposed
Sample of Coal and Coke
so as to prevent ignition of the cloud. Because of the short
duration of the test, the data obtained are most applicable to
This test method is under the jurisdiction ofASTM Committee E27 on Hazard industrialequipmentwheredustispresentasacloudforashort
Potential of Chemicalsand is the direct responsibility of Subcommittee E27.05on
time. Because of the small scale of the test and the possible
Explosibility and Ignitability of Dust Clouds.
Current edition approved Sept. 10, 1997. Published November 1997. Originally
published as E 1491 – 91. Last previous editiion E 1491 – 92.
2 3
Annual Book of ASTM Standards, Vol 05.05. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 1491 – 97 (2002)
variation of the MAIT value with scale, the data obtained by 9. Sampling
this test method may not be directly applicable to all industrial
9.1 It is not practical to specify a single method of sampling
conditions.
dust for test purposes because the character of the material and
5.3 The MAIT data can also be used in conjunction with
its available form affect selection of the sampling procedure.
minimum spark ignition data to evaluate the hazards of
Generally accepted sampling procedures should be used as
grinding and impact sparks in the presence of dust clouds (1
described in STP 447A.
and 2).
9.2 Tests may be run on an as-received sample. However,
5.4 The test values obtained are specific to the sample
due to the possible accumulation of fines at some location in a
tested, the method used, and the test equipment utilized. The
processing system, it is recommended that the test sample be at
test values are not to be considered intrinsic material constants,
least 95 % minus 200 mesh (75 µm).
but may be used as a relative measure of the temperature at
9.3 To achieve this particle fineness (95 % minus 200
which a dust cloud self ignites.
mesh), grind, pulverize, or sieve the sample.
5.5 The test data are for cloud ignition. Dust in the form of
NOTE 1—The operator should consider the thermal stability and the
a layer may ignite at significantly lower temperatures than the
friction and impact sensitivity of the dust during any grinding or
same dust in the form of a cloud (3).
pulverizing. In sieving the material, the operator must verify that there is
no selective separation of components in a dust that is not a pure
6. Interferences
substance.
6.1 Unburned dust from a previous test may affect results. If NOTE 2—Itmaybedesirableinsomecasestoconductdustautoignition
tests on a material as sampled from a process because dust streams may
there is a question, the furnace should be heated to its
contain a wide range of particle sizes or have a well-defined specific
maximum temperature to clean it before future tests are made.
moisture content, materials consisting of a mixture of chemicals may be
6.2 The material of construction of this test method may
selectively separated on sieves, and certain fibrous materials may not pass
have catalytic effects on the ignition and should be considered
through a relatively coarse screen. When a material is tested in the
during testing.
as-received state, it should be recognized that the test results may not
represent the lowest cloud autoignition temperature possible.Any process
7. Apparatus
change resulting in a higher fraction of fines than normal or drier product
than normal may decrease the autoignition temperature.
7.1 Theequipmentconsistsofaheatedchamberclosedwith
a frangible diaphragm, or flap vent, or a hole open to the
9.4 The moisture content of the test sample should not
atmosphere.
exceed 10 % in order to avoid noticeable influence on test
7.2 The chamber is insulated and provided with a thermo-
results of a given dust.
statically controlled electric heater. A thermocouple measures
NOTE 3—There is no single method for determining the moisture
the set temperature of the chamber.
content or for drying a sample. ASTM lists many methods for moisture
7.3 Adust dispersion system generates a fairly uniform dust
determination in the Annual Book of ASTM Standards. Sample drying is
cloud within the chamber. There should be a minimal amount
equally complex due to the presence of volatiles, lack of or varying
of dust remaining in the disperser after the test. porosity (see Test Methods D 3173 and D 3175), and sensitivity of the
sample to heat. Therefore, each must be dried in a manner that will not
7.4 Athermocouple(1milor25µm)andarecordingsystem
modify or destroy the integrity of the sample. Hygroscopic materials must
having a fast enough response may be used to measure the
be desiccated.
temperature rise during ignition of the dust cloud in the
chamber.
10. Calibration and Standardization
7.5 Examplesofchambersandspecificproceduresthathave
10.1 Any new test vessel design other than those listed in
been found suitable are listed in chronological order in
the appendixes must be standardized using dust samples whose
Appendix X1-Appendix X4.
MAIT values are known. A minimum of three dust samples
over a wide range of MAIT values is required. For tempera-
8. Hazards
tures below 600°C, the MAIT value for each dust measured in
8.1 Safety Precautions:
a furnace must agree to within 660°C of the average MAIT
8.1.1 Prior to handling a dust, its toxicity and the toxicity of
value for that dust as measured in the four furnaces in
its combustion products must be considered. This information
Appendix X1-Appendix X4.
can usually be obtained from the manufacturer. Consideration
10.2 Representative MAIT data for six dusts are listed in
will have to be given to ventilation, use of hoods, personal
degrees Celsius in Table 1. These data are only intended to
protective gear, and procedures.
indicatethevariabilityamongfurnaces.Theanthracitecoalhas
8.1.2 Explosive, highly reactive, or easily decomposed ma-
;85 % minus 200 mesh and a mass median diameter of ;40
terials should not be tested unless they have been characterized
µm. The anthraquinone (C H O ) has ;73 % minus 200
14 8 2
by prior testing. Procedures such as the use of barricades,
mesh and a mass median diameter of ;56 µm.The Pocahontas
hoods, and personal protective equipment should be used as
(Poc.) seam bituminous coal has ;70 % minus 200 mesh, a
judgment indicates.
mass median diameter of ;56 µm, and 18 % volatility. The
8.1.3 Electrical systems must be grounded.
4 5
The boldface numbers in parentheses refer to the list of references at the end of STP 447Ais available fromASTM Headquarters, 1916 Race St., Philadelphia,
this test method. PA 19103.
E 1491 – 97 (2002)
TABLE 1 Examples of MAIT Data, °C
which ignition does not occur for this dust concentration.
G-G BAM 1.2-L 6.8-L Ignition is defined as flame exiting from the chamber.
Furnace Oven Furnace Furnace
11.8 At the highest temperature at which ignition is not
Anthracite coal >900 >600 740 730
observed, vary the dust concentration. If the dust ignites at any
Anthraquinone 670 >600 620 680
concentration at this temperature, lower the test temperature
Pocahontas (Poc) bituminous coal 640 580 610 600
and continue the testing. At least five tests over a range of
Pittsburgh (Pgh) bituminous coal 600 570 540 530
Lycopodium 460 410 440 380
concentrations must be run at the highest temperature at which
Sulfur 260 240 290 260
ignition is not observed.
11.9 At the temperature at which ignition is observed, vary
the dust concentration to determine the range over which
Pittsburgh (Pgh.) seam bituminous coal has ;80 % minus 200
ignition occurs. In order to assure the repeatability of the data,
mesh, a mass median diameter of ;45 µm, and 36 % volatility.
observe at least three ignitions over a range of concentrations
The lycopodium is the reticulate form, Lycopodium clavatum.
at the lowest temperature at which ignition occurs.
Itisanaturalplantsporehavinganarrowsizedistributionwith
11.10 The reason for varying the concentration in 11.8 and
100 % minus 200 mesh and mass median diameter of ;28 µm.
11.9 is to ensure that the autoignition temperature is measured
The sulfur has ;81 % minus 200 mesh and a mass median
at the most easily ignited concentration. However, the autoi-
diameter of ;38 µm.
gnition temperature is usually relatively independent of con-
10.2.1 These data are from the four furnaces listed in the
centration, as shown in Fig. 1 and Fig. 2.
appendixes—the 0.27-L Godbert-Greenwald (G-G) Furnace,
11.11 ThefinaldeterminationoftheMAITmustbemadeby
the 0.35-L BAM Oven, the 1.2-L Bureau of Mines Furnace,
varying the temperature in increments of 25°C or smaller.
and the 6.8-L Bureau of Mines Furnace. The BAM oven is
11.12 Fig. 1 is an example of a typical test pattern of
limited to a maximum test temperature of 600°C. The G-G
temperatures and concentrations. Fig. 2 is a more detailed
Furnace generally yields somewhat higher MAIT data than the
series of tests to show the reproducibility of the data and the
other three. The greatest deviation in MAIT values occurs at
range of concentrations over which ignition occurs.
the highest temperatures, as shown by the anthracite coal data
in the table. However, the lower MAIT values (where agree- 12. Calculation
ment is better) are of greater practical importance.
12.1 The minimum autoignition temperature (MAIT) of the
10.3 In addition to the initial calibration of a furnace, retest
dust cloud is the average of the lowest temperature at which
at least one standard dust periodically to verify that the furnace
ignition was reproducibly observed and the highest tempera-
test conditions have not changed.
ture at which ignition was not observed at any concentration. If
there is an intermediate temperature at which ignition is
11. Procedure
observed for about half the tests, report this as the MAIT.
11.1 These general procedures are applicable for all suitable
Round the reported MAIT value to the nearest 10°C. As an
furnaces. The detailed procedures specific to each furnace are
example, the MAIT for polyethylene dust in Fig. 1 would be
listed in the corresponding appendix.
375°C, or rounded to 370°C for the report. For the coal dust
11.2 Inspect equipment to be sure it is thoroughly clean and
data in Fig. 2, the MAIT would be 540°C.
in good operational condition.
13. Report
11.3 Set the temperature of the furnace or oven at the
predetermined value.
13.1 Report the following information:
13.1.1 Complete identification of the material tested; in-
NOTE 4—For most furnaces, it is generally desirable to approach the
cluding type of dust, source, code numbers, forms, and
MAIT from below to avoid a violent dust explosion in the chamber.
previous history,
However, the recommended procedure for the BAM oven is to approach
the MAIT from above (see Appendix X2).
13.1.2 Particle size distribution of the sample as received
and as tested,
11.4 Place a weighed amount of dust in the disperser. The
recommended initial test concentration for most dusts is from
300 to 1000 g/m . If data from Test Method E 1226 exist for
the dust, the initial test could be made at the concentration at
which the maximum pressure, P , and the maximum nor-
max
malized rate of pressure increase, K , were found.
st
11.5 Disperse the dust and observe whether or not flame
exits the furnace.
NOTE 5—It is useful to darken the room to make it easier to observe the
flame. Some flames, such as the blue flame of sulfur, are difficult to see.
11.6 If no ignition occurs, increase the temperature 50 to
100°C and test the dust again at the same concentration.
11.7 After ignition h
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