ASTM E2021-00
(Test Method)Standard Test Method for Hot-Surface Ignition Temperature of Dust Layers
Standard Test Method for Hot-Surface Ignition Temperature of Dust Layers
SCOPE
1.1 This test method covers a laboratory procedure to determine the hot-surface ignition temperature of dust layers, that is, measuring the minimum temperature at which a dust layer will self-heat. The test consists of a dust layer heated on a hot plate.
1.2 Data obtained from this test method provide a relative measure of the hot-surface ignition temperature of a dust layer.
1.3 This test method should be used to measure and describe the properties of materials in response to heat and flame under controlled laboratory conditions and should not be used to describe or appraise the fire hazard or fire hazard 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 that takes into account all of the factors that are pertinent to an assessment of the fire hazard risk of a particular end use product.
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. Specific precautionary statements are given in Section 8.
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Designation: E 2021 – 00
Standard Test Method for
Hot-Surface Ignition Temperature of Dust Layers
This standard is issued under the fixed designation E 2021; 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.
1. Scope Methods for Determining the Minimum Ignition Tempera-
tures of Dusts, Method A
1.1 This test method covers a laboratory procedure to
determine the hot-surface ignition temperature of dust layers,
3. Terminology
that is, measuring the minimum temperature at which a dust
3.1 Definitions of Terms Specific to This Standard:
layer will self-heat. The test consists of a dust layer heated on
,
2 3 3.1.1 hot-surface ignition temperature of a dust layer,
a hot plate.
n—lowest set temperature of the hot plate that causes ignition
1.2 Data obtained from this test method provide a relative
of the dust layer.
measure of the hot-surface ignition temperature of a dust layer.
3.1.2 ignition of a dust layer, n—initiation of self-heating or
1.3 This test method should be used to measure and describe
combustion in a material under test.
the properties of materials in response to heat and flame under
3.1.3 ignition time, n—time between the start of heating and
controlled laboratory conditions and should not be used to
the point at which the maximum temperature or flaming
describe or appraise the fire hazard or fire hazard risk of
combustion is reached.
materials, products, or assemblies under actual fire conditions.
3.1.4 temperature rise, DT, n—the difference between T
max
However, results of this test method may be used as elements
and the initial set temperature of the hot plate.
of a fire risk assessment that takes into account all of the factors
3.1.5 T , n—maximum temperature measured during test.
max
that are pertinent to an assessment of the fire hazard risk of a
particular end use product.
4. Summary of Test Method
1.4 This standard does not purport to address all of the
4.1 The test material is placed within a metal ring on top of
safety concerns, if any, associated with its use. It is the
a hot plate, that is at a preset constant temperature.
responsibility of the user of this standard to establish appro-
4.2 The sample temperature is monitored to determine
priate safety and health practices and determine the applica-
temperature rise due to oxidative reactions or decomposition
bility of regulatory limitations prior to use. Specific precau-
reactions, or both.
tionary statements are given in Section 8.
4.3 Ignition is considered to have taken place when either of
the following occurs:
2. Referenced Documents
4.3.1 Temperature in the dust layer at position of thermo-
2.1 ASTM Standards:
couple rises at least 50°C above the hot plate temperature, or
D 3175 Test Method for Volatile Matter in the Analysis
4 4.3.2 Visible evidence of combustion is apparent, such as
Sample of Coal and Coke
red glow or flame.
E 771 Test Method for Spontaneous Heating Tendency of
5 4.4 Hot plate surface temperature is varied from test to test,
Materials
as necessary, until the hot-surface ignition temperature is
E 1491 Test Method for Minimum Autoignition Tempera-
5 determined.
ture of Dust Clouds
2.2 IEC Standard:
5. Significance and Use
IEC 1241-2-1 Electrical Apparatus for Use in the Presence
5.1 This test method is applicable to dusts and powders, and
of Combustible Dust; Part 2: Test Methods—Section 1:
provides a procedure for performing laboratory tests to evalu-
ate hot-surface ignition temperatures of dust layers.
This test method is under the jurisdiction of ASTM Committee E-27 on Hazard 5.2 The test data can be of value in determining safe
Potential of Chemicals and is the direct responsibility of Subcommittee E27.04 on
operating conditions in industrial plants, mines, manufacturing
the Flammability and Ignitability of Chemicals.
processes, and locations of material usage and storage.
Current edition approved March 10, 2000. Published June 2000.
5.3 Due to variation of ignition temperature with layer
This test method is based on recommendations of the National Materials
Advisory Board of the National Academy of Sciences (1).
thickness, the test data at one thickness may not be applicable
The boldface numbers in parentheses refer to the list of references at the end of
to all industrial situations (see Appendix X1). Tests at various
this standard.
4 layer thicknesses may provide a means for extrapolation to
Annual Book of ASTM Standards, Vol 05.05.
Annual Book of ASTM Standards, Vol 14.02.
Available from ANSI, 11 W. 42nd Street, New York, NY,10036.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 2021
thicker layers, as listed in the following for pulverized Pitts- in contact with the plate within 1.0 6 0.5 mm of the upper
burgh bituminous coal dust (2). Mathematical modeling of surface. This thermocouple is connected to a temperature
layer ignition at various layer thicknesses is described in Ref. controller. The plate and its thermocouple-controller assembly,
(3). in conjunction with the commercial hotplate, should satisfy the
following requirements:
Layer Thickness, mm Hot-Surface Ignition Temperature, °C
6.4 300
7.1.1.1 The plate should be capable of attaining a maximum
9.4 260
temperature of 400°C without a dust layer in position,
12.7 240
25.4 210
7.1.1.2 The temperature controller must be capable of main-
taining the temperature of the plate constant to within 6 5°C
5.4 This hot plate test method allows for loss of heat from
throughout the time period of the test,
the top surface of the dust layer, and therefore generally gives
7.1.1.3 When the temperature of the plate has reached a
a higher ignition temperature for a material than Test Method
constant value, the temperature across the plate should be
E 771, which is a more adiabatic system.
uniform to within6 5°C, as shown in Fig. 2,
5.5 This test method for dust layers generally will give a
lower ignition temperature than Test Method E 1491, which is 7.1.1.4 The temperature control should be such that the
for dust clouds. The layer ignition temperature is determined recorded plate temperature will not change by more than 6 5°
while monitoring for periods of minutes to hours, while the C during the placing of the dust layer and will be restored to
dust cloud is only exposed to the furnace for a period of within 2°C of the previous value within 5 min of placing the
seconds. dust layer, and
7.1.1.5 The thermocouple in the plate and its readout device
NOTE 1—Much of the literature data for layer ignition is actually from
should be calibrated and should be accurate to within 6 3°C.
a basket in a heated furnace (4), known as the modified Godbert-
Greenwald furnace test. Other data are from nonstandardized hot plates
7.1.2 Metal Ring, to be placed on the heated metal plate, for
(5-9).
containing the dust layer. Stainless steel is suitable for most
dusts. The standard ring is 12.7 mm ( ⁄2 in.) in depth and
5.6 Additional information on the significance and use of
approximately 100 mm (4 in.) in diameter. Rings may be of
this test method may be found in Ref. (10).
other depths.
6. Limitations and Interferences
7.1.3 Dust Layer Thermocouple—Slots on opposite sides of
the perimeter of the ring accommodate the positioning of a type
6.1 This test method should not be used with materials
having explosive or highly reactive properties. K bare thermocouple (0.20 to 0.25 mm or 10 mil in diameter)
through the dust sample. This bare thermocouple is positioned
6.2 If the metal (for example, aluminum) plate or ring reacts
with the test material, choose another type of metal that does parallel to the surface of the metal plate with its junction at the
geometric center of the dust layer. This thermocouple should
not react.
be connected to a digital thermometer for observing the
7. Apparatus
temperature of a dust layer during a test. Temperature mea-
surements with the thermocouple should be made either
7.1 The complete apparatus, shown in Fig. 1, consists of a
relative to a fixed reference junction temperature or with
circular metal (for example, aluminum) plate centrally posi-
automatic cold junction compensation. Most digital thermom-
tioned on top of a hot plate. The dust layer is confined within
eters have built-in compensation. The thermocouple in the dust
a metal ring on top of the metal plate. An example of an
layer and its readout device should be calibrated and should be
apparatus that has been found suitable is given in Appendix
accurate to within6 3°C.
X2.
7.1.1 Heated Surface, consisting of a metal plate of approxi- 7.2 Ambient Temperature Thermometer, placed in a conve-
mately 200-mm diameter and at least 20-mm thick. This plate nient position within1mofthehot plate but shielded from heat
is centrally placed on top of a commercial hotplate. A thermo- convection and radiation from the hot plate. The ambient
couple is mounted radially in the metal plate, with its junction temperature should be within the range of 15 to 30°C.
FIG. 1 Schematic of Hotplate Layer Ignition Apparatus
E 2021
is tested in the as-received state, it should be recognized that the test
results may not represent the lowest dust layer ignition temperature
possible. Any process change resulting in a higher fraction of fines than
normal or drier product than normal may decrease the ignition tempera-
ture.
10. Calibration and Standardization
10.1 The calibration of the dust sample thermocouple and
the thermocouple embedded in the circular metal plate must be
checked using appropriate standards (for example, ice/water
for 0°C and boiling water for 100°C). Boiling diphenylamine
(302°C) can be used to check the calibration at a higher
temperature.
10.2 The temperature across the metal plate should be
uniform to within 6 5°C when measured across two diameters
at right angles, as shown in Fig. 2. This requirement must be
satisfied at two plate temperatures, one in the range of between
200 and 250°C and the second in the range of between 300 and
350°C, measured at the center of the plate.
10.3 Verify the performance of the apparatus using at least
FIG. 2 Uniformity of Aluminum Plate Temperature at Set two dust layers having different hot-surface ignition tempera-
Temperature of 250°C
tures. Representative data (2) for 12.7-mm thick layers of
three dusts are:
Brass 155-160°C
8. Hazards
Pittsburgh coal dust 230-240°C
8.1 The user should consider the toxicity of the sample dust
Lycopodium spores 240-250°C
and possible combustion products.
The brass was a very fine flake (100 % minus 325 mesh)
8.2 This test method should not be used with materials
with a small amount (<1.7 %) of stearic acid coating. The
having explosive or highly reactive properties.
lycopodium is a natural plant spore having a narrow size
8.3 Metal dusts can ignite and burn with high temperatures.
distribution with 100 % minus 200 mesh and mass median
If a flame is observed, the dust layer should be covered with a
diameter of ;28 μm. This is the reticulate form Lycopodium
flat metal sheet to exclude the air and extinguish the flame.
clavatum. The Pittsburgh seam bituminous coal has ;80 %
8.4 The user should use due caution around the hot surfaces
minus 200 mesh, a mass median diameter of ;45 μm, and
present on the test apparatus.
36 % volatility. Additional data that can be used for calibration
8.5 Tests should be conducted in a ventilated hood or other
are those listed in 5.3 for different layer thicknesses of this coal
area having adequate ventilation to remove any smoke or
dust.
fumes.
11. Procedure
9. Sampling and Test Specimens
11.1 General Set-Up—Set up the apparatus in a position
9.1 It is not practical to specify a single method of sampling
free from drafts and under a hood capable of exhausting smoke
dust for test purposes because the character of the material and
and fumes. Ensure that the air flow in the hood is sufficient for
its available form affect selection of the sampling procedure.
removing smoke and fumes, but low enough so as not to
Generally accepted sampling procedures should be used .
disturb the layer or affect the test results. This can be achieved
9.2 Tests may be run on an as-received sample. However,
by adjusting the baffles in the back of the hood. If desired, an
since finer dusts have lower hot-surface ignition temperatures
angled mirror can be provided above the test sample for visual
(2) and due to the possible accumulation of fines at some
observation.
locations in a processing system, it is recommended that the
11.2 Procedure for Individual Test:
test sample be at least 95 % minus 200 mesh (75 μm). To
11.2.1 Centrally place a ring of the required height on the
achieve this particle fineness, grind, pulverize, or sieve the
clean surface of the heated metal plate. Make adjustments to
sample.
the thermocouple position. Set the desired test temperature on
NOTE 2—The operator should consider the thermal stability and the
the temperature controller and heat the hot plate.
friction and impact sensitivity of the dust during any grinding or
11.2.2 When hot plate temperature is steady within the
pulverizing. In sieving the material, the operator must verify that there is
required limit, fill the ring with the test dust, and level the
no selective separation of components in a dust that is not a pure
surface of the layer within a period of 2 min. Do not compress
substance.
the dust layer unduly. Put the dust into the ring with a spatula
NOTE 3—It may be desirable in some cases to conduct dust layer
and distribute with mainly sideways movements of the spatula
ignition tests on a material as sampled from a process because (a) dust
streams may contain a wide range of particle sizes or have a well-defined until the ring is slightly over-filled; then, level the layer by
specific moisture content, (b) materials consisting of a mixture of
chemicals may be selectively separated on sieves, and (c) certain fibrous
materials may not pass through a relatively coarse screen. When a material Some data are from unpublished work of the Fike Co., Blue Springs, MO.
E 2021
necessary to be certain that failure to ignite at a given temperature is not
drawing a straight edge across the top of the ring. Remove the
merely a result of premature termination of a test. Thus, the temperatures
excess dust that spills on the metal plate. The amount of dust
at which ignition fails to occur must be confirmed by continuing a test
that will
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