HomeMy WebLinkAboutFAI-2018-0752 Dust Explosibility report for Southeast Building Solutions
Proprietary Property of Fauske & Associates, LLC
July 31, 2018
Gary Mayfield Report No.: FAI18-0752
Southeast Building Solutions Project No.: DST 6789
104 Meco Lane
Oak Ridge, TN 37830
Tel: (865) 298-0194
E-mail: gmayfield@sbsmechanical.com
Subject: Dust Explosibility Testing
Dear Gary,
In response to your request, Fauske and Associates, LLC (FAI) conducted an Explosion Severity
Test per ASTM E1226, a Minimum Explosible Concentration test per ASTM E1515, a
Minimum Ignition Energy test per ASTM E2019, a Minimum Autoignition Temperature (MAIT
or commonly MIT) test per ASTM E1491, and a Total Combustible Content Test by DSC/TGA.
These tests were conducted on the following sample labeled:
1. Maverick Boats.
**Sample was received on June 21, 2018.**
The material properties and explosion hazard results are summarized in Tables 1 and 2,
respectively.
Table 1: Material Properties
Material Moisture Content
(wt.%)
Mean Particle Size
(µm)
Maverick Boats 1.3
52
79% < 75 µm
100% < 500 µm
Table 2: Explosion Hazard Results
Material Pmax
(bar)
KSt
(bar-m/s)
MEC
(g/m³)
MIE
(with inductance)
(mJ)
Maverick Boats
7.5 ± 10% 201 ± 10% 50 < MEC < 60
MECestimate = 59
1 < MIE < 3
Es = 2.1
MIT Cloud
(°C)
Combustible
Content
(wt.%)
460 ~64
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
The calculated Explosion Severity (ES) and Ignition Sensitivity (IS) numbers for the sample
tested are listed in Table 3 based on Pittsburgh Pulverized Coal (Lot#1157) dust (Pmax = 7.1 bar,
(dP/dt)max= 530 bar/s, MIE (w/ inductance) = 140 mJ, MEC = 43 g/m³, MIT = 580°C, Particle
Size Distribution = 97% < 75µm [January 2012]). The ES and IS values were calculated using
the following equations:
ܧܵ ൌ
ሺܲ ൈ ܴሻ௦
ሺܲ ൈ ܴሻ௧௧௦௨
Where: P = Maximum explosion overpressure, (Pmax)
R = Maximum rate of pressure rise, (dP/dtmax)
ܫܵ ൌ
ሺܶ ൈ ܧ ൈ ܥሻ௧௧௦௨
ሺܶ ൈ ܧ ൈ ܥሻ௦
Where: T = Minimum Auto-Ignition Temperature, (MIT)
E = Minimum Ignition Energy, (MIE)
C = Minimum Explosion Concentration, (MEC)
Table 3: ES and IS Numbers
Material ES IS
Maverick Boats 1.5 61.3
NFPA 499-2008 recognizes a Class II dust as having an IS greater than or equal to 0.2 or ES
greater than or equal to 0.5 to be appreciable explosion hazards requiring electrical equipment
suitable for Class II locations. However, please note that current NFPA 499-2017 recognizes a
Class II dust as having an overpressure greater than, or equal to, 1 bar in the 20-L screening test.
Based on the both NFPA criterions, this sample is classified as a Class II dust for National
Electrical Code purposes.
Please refer to Appendix E in OSHA Directive Number CPL-03-00-008 and NFPA 499-2008 for
further discussion of the ES and IS numbers.
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
The following paragraphs describe the methods, procedures, and detailed results for the tests
conducted at Fauske and Associates, LLC.
Material Preparation
Per ASTM recommendation, the moisture content of the test sample should not exceed 5 wt.%.
The sample was tested “as received” per the client’s request. The moisture content of the sample
was analyzed using a Mettler Toledo HR83 Halogen Moisture Analyzer and was determined to
be 1.3 wt.%.
Per ASTM recommendation, the materials for dust explosibility testing should have a particle
size distribution that is at least 95% less than 200-mesh (75 µm). The sample was tested “as
received” per the client’s request. The particle size distribution of the sample was measured
using a Malvern MS 3000 Particle Analyzer and was determined to be 79% less than 75 µm (see
Appendix A for detailed results). Please note that finer dust under actual process conditions may
produce higher risk explosibility parameters. Coarser dust may produce lower risk explosibility
parameters.
Explosion Severity (Pmax, KSt) Tests
The test was conducted in accordance with ASTM E1226, “Standard Test Method for
Explosibility of Dust Clouds”. A 20-L Siwek chamber manufactured by Kühner A.G. of Basel
Switzerland was used for the test.
Scope
This test method is used to determine the deflagration parameters of a combustible dust-air
mixture. The parameters measured are the maximum pressure and the maximum rate of pressure
rise. Data obtained from this test method provides a relative measure of deflagration
characteristics and is also used for the design of protection systems, such as deflagration venting.
Terminology
The Pmax is the average maximum pressure (above pressure in the vessel at the time of ignition)
reached during the course of a deflagration for the optimum concentration of the dust tested. Pmax
is determined by a series of tests over a large range of concentrations.
The (dP/dt)max is the average maximum value for the rate of pressure increase per unit time
reached during the course of a deflagration for the optimum concentration of dust tested. It is
determined by a series of tests over a large range of concentrations.
The Deflagration Index, KSt is the average maximum dP/dt normalized to a 1.0-m³ volume. It is
measured at the optimum dust concentration. KSt is defined in accordance with the following
cubic relationship:
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
ܭௌ௧ ൌ ൬݀ܲ
݀ݐ ൰
௫
ൈ ܸଵ
ଷ
where:
P = pressure, bar
t = time, sec
V = test chamber volume, m³
KSt = Deflagration Index, bar-m/s
Test Setup
The 20-liter chamber, as depicted in Figure 1, was equipped with an air nozzle to disperse the
material dust, and two electrodes for connecting two (2) squib (Sobbe) igniters (2 × 5 kJ = 10 kJ
of ignition energy) to a voltage source. The chamber was equipped with two pressure transducers
to measure the pressure output of an explosion. The pressure-time data was collected by a high-
speed data acquisition system. The test was automated and computer controlled. A more detailed
description of the apparatus is available from the manufacturer.
Figure 1: 20-L Siwek Chamber Test Setup
Calibration
Per ASTM E1226, “Standard Test Method for Explosibility of Dust Clouds,” §10, “Calibration
and Standardization” p.p. 10.2, the test vessel to be used for routine work must be standardized
using dust samples whose KSt and Pmax parameters are known in the 1-m³ chamber. The Pmax
value for each dust must agree to within ± 10% with the 1-m³ value and the KSt value must agree
to within ± 20%.
The Kühner 20-L Siwek chamber test equipment used for testing was calibrated by carrying out
the calibrating tests on Niacin USP Special (Nicotinic Acid ~28 µm mean diameter) provided by
the test equipment manufacturer as part of a bi-annual round robin inter-lab calibration exercise.
The dust deflagration data measured in the FAI 20-L chamber, shown in Table 4, is compared
with the data reported by the manufacturer for other 20-L and 1-m³ chamber data. The FAI test
equipment and methodology compare very well to the accepted explosion severity values.
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Table 4: Dust Deflagration Calibration Data
FAI Results (20-L) Kühner CaRo 17 Results
Chamber # Pmax
(bar)
KSt
(bar-m/s)
Pmax
(bar)
KSt
(bar-m/s)
1 8.1 ± 10% 256 ± 10%
8.2 ± 10% 243 ± 10%
2 8.2 ± 10% 254 ± 10%
3 8.4 ± 10% 252 ± 10%
4 8.2 ± 10% 252 ± 10%
FAI Results (1-m³)
Dispersion System Pmax
(bar)
KSt
(bar-m/s)
Single 7.8 ± 10% 248 ± 10%
Dual 7.9 ± 10% 246 ± 10%
Procedure
For each test, a known amount of material was weighed and then placed in the dust dispersion
chamber or on top of the rebound nozzle if there was too much dust to fit in the dispersion
chamber.
The ignition source (igniters) was placed in the center of the chamber. The chamber was sealed
and all valves were closed. Then the chamber was partially evacuated so after addition of
dispersing air, the desired nominal pressure in the chamber of one bar absolute was reached prior
to initiation of the deflagration test. Then the automated test sequence was initiated using the
computer control software provided by the manufacturer. The dust dispersion chamber was
pressurized to 21 bar(a). The dispersion solenoid valve was opened releasing the dust into the 20-
L chamber and raising the chamber pressure to 1 bar(a).
After a computer controlled delay time of 60 ± 5 ms the chemical squib igniters were initiated.
The resulting pressure rise was measured by two piezoelectric pressure transducers. The
pressure-time history data was then reviewed and the maximum explosion pressure and rate of
pressure rise was determined. The manufacturer supplied computer program used to review the
pressure-time data applies a correction factor to the maximum measured explosion overpressure
to account for the energy of the ignition source and the quenching effect of the vessel walls.
To determine the maximum explosion pressure and pressure rise rate, successive tests were run
at increasing dust concentrations while using the same strength ignition source (10 kJ).
Material Tested Moisture Content
(wt. %)
Mean Particle Size
(µm)
Niacin USP Special
(Nicotinic Acid )
~0.12
(as received)
~28 µm
(as received)
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
The peak pressure was determined by analyzing the pressure-time curve. The peak pressure rise
rate was determined by measuring the slope of the pressure-time curve (dP/dt).
An initial concentration of 125 g/m³ was tested. Then the dust concentration was systematically
increased until curves were obtained for both (dP/dt)max and Pmax that indicated an optimum value
had been reached. If it was indicated that the optimum concentration for (dP/dt)max or Pmax was
less than 125 g/m³, the tested concentration was halved; (60, 30 g/m³) until the optimum value
was obtained. At least two (2) additional test series were run at the concentrations where the
maximums were found and at one (1) concentration on each side of the maximums.
Explosion Severity (Pmax, KSt) Results
The explosion severity test results for the sample tested are summarized in Table 5. Figures 2
and 3 depict the explosion overpressure and rate of pressure rise as a function of dust
concentration for the dust sample tested. The detailed explosibility data are also presented in
Table 6.
The sample tested was found to be highly explosible producing a KSt value of 201 bar-m/sec,
thus, classifying it as an St2 class dust since the KSt value was between 200 bar-m/sec and 300
bar-m/sec. Mitigation strategies will be required when handling this powder in order to
minimize the risk of an explosion. Please consult NFPA 652, 654, 68, and 69 for guidance on
explosion mitigation.
Please note that finer dust under actual process conditions may produce higher risk explosibility
parameters.
Table 5: Explosion Severity Test Results
Material Tested
Moisture
Content
(wt.%)
Mean Particle
Size (µm)
Pmax
(bar)
(dP/dt)max
(bar/s)
KSt
(bar-m/s)
Maverick Boats 1.3
52
79% < 75 µm
100% < 500 µm
7.5 ± 10% 739 ± 10% 201 ± 10%
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
Table 6: Detailed Explosion Severity Test Results
Sample: Maverick Boats
Room Temperature: 16°C Barometric Pressure: 997 mbar
Relative Humidity: 64% Date of test: July 25, 2018
Run
125 g/m³ 250 g/m³ 500 g/m³ 750 g/m³ 1000 g/m³ 1250 g/m³
Pm
[barg]
dP/dt
[bar/s]
Pm
[barg]
dP/dt
[bar/s]
Pm
[barg]
dP/dt
[bar/s]
Pm
[barg]
dP/dt
[bar/s]
Pm
[barg]
dP/dt
[bar/s]
Pm
[barg]
dP/dt
[bar/s]
1 3.9 106 6.5 236 7.5 483 7.4 613 7.1 764 6.8 676
2 - - 6.2 300 7.4 391 7.3 568 7.0 712 6.6 604
3 - - 6.3 314 7.7 681 7.4 669 7.1 740 6.7 528
Run
1500 g/m³
Pm
[barg]
dP/dt
[bar/s]
1 6.6 545
2 - -
3 - -
Figure 2: Explosion overpressure as a function of dust concentration in a 20-L chamber
for Maverick Boats
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Figure 3: Rate of pressure rise as a function of dust concentration in the 20-L chamber
for Maverick Boats
Minimum Explosible Concentration (MEC) Tests
The test was performed per ASTM E1515, “Standard Test Method for Minimum Explosible
Concentration of Combustible Dusts”. A 20-L Siwek chamber, manufactured by Kühner A.G. of
Basel Switzerland, was used for the test.
Scope
Minimum Explosible Concentration is the minimum concentration of a combustible dust that is
capable of propagating a deflagration through a uniform mixture of the dust in air, under the
specified conditions of the test. The MEC data obtained from this test method can provide a
relative measure of the concentration of a dust in the form of a uniform cloud necessary for an
explosion.
The values obtained by this test method are specific to the sample tested (particularly the particle
size distribution) and the method used and is not to be considered intrinsic material constants.
Test Setup
The 20-liter Siwek chamber, as depicted in Figure 1, was equipped with an air nozzle to disperse
the material dust, and two electrodes for connecting one squib (Sobbe) igniter (5 kJ stored
energy) to a voltage source. The chamber was equipped with two pressure transducers to
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
measure the pressure output of an explosion. The pressure-time data was collected by a high-
speed data acquisition system. The test was automated and computer controlled. A more detailed
description of the apparatus is available from the manufacturer.
Procedure
For each test, a known amount of material was weighed and then placed in the dust dispersion
chamber or on top of the rebound nozzle if there was too much dust to fit in the dispersion
chamber.
The ignition source (igniter) was placed in the center of the chamber. The chamber was sealed
and all valves were closed. Then the chamber was partially evacuated so after addition of
dispersing air, the desired normal pressure in the chamber of one bar absolute was reached prior
to initiation of the deflagration test. Then the automated test sequence was initiated using the
computer control software provided by the manufacturer. The dust dispersion chamber was
pressurized to 21 bar(a). The dispersion solenoid valve was opened releasing the dust into the 20-
L chamber and raising the chamber pressure to 1 bar(a).
After a computer controlled delay time of 60 ± 5 ms the chemical squib igniter was initiated. The
resulting pressure rise was measured by two piezoelectric pressure transducers. The pressure-
time history data were then reviewed and the maximum explosion pressure was determined. The
manufacturer supplied computer program used to review the pressure-time data applies a
correction factor to the maximum measured explosion over pressure to account for the energy of
the ignition source and the quenching effect of the vessel walls.
To determine the minimum explosible concentration, successive tests were run at decreasing dust
concentrations while using the same strength ignition source (5 kJ). An explosion can be
differentiated from a “NO GO” by evaluating the increase in pressure (due to air-dust mixture
explosion) above that of the igniter. If peak pressure was 1 (one) bar more than the igniter
pressure, the explosion was considered a “GO”. The rate of pressure rise (dP/dt) is not
considered for MEC calculations. The MEC is interpolated between the “Go” and “No Go”
concentrations.
An initial concentration (usually 100 g/m³) was tested. The dust concentration was then
incrementally increased or decreased until “GO” and “NO GO” were established. Then the dust
concentration was systematically modified by 10 g/m³ when the concentration is 100 g/m³ or
less, or ≤ 25% if greater than 100 g/m³ until the MEC of the sample was determined.
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Minimum Explosible Concentration Test Results
The MEC test results for the sample are summarized in Table 7, the MEC being the interpolated
concentration for a 1 bar explosion pressure. The calculation is made using the lowest
concentration for which an ignition has been observed and the highest concentration tested at
which 3 subsequent no ignitions have been observed. The detailed explosibility data is also
presented in Table 8.
The MEC value for the sample was determined to be between 50 g/m³ and 60 g/m³ with an
interpolated value of 59 g/m³. It is important to keep dust concentrations below the MEC in order
to minimize the risk of a dust explosion. As an illustration, consider a scenario where the sample
is deposited as a thin and even layer in an empty room with dimensions of 12m × 12m × 3m.
Assuming an approximate bulk density of 0.3 g/ml, a dust layer that is 0.6 mm thick is sufficient,
when uniformly dispersed, to create an explosible dust cloud. Please refer to NFPA 652 and 654
for guidance and instructions.
Table 7: MEC Test Results
Material Tested Moisture Content
(wt. %)
Mean Particle Size
(µm)
Minimum Explosible
Concentration
(g/m³)
MECest
(g/m³)
Maverick Boats 1.3
52
79% < 75 µm
100% < 500 µm
50 < MEC < 60 59
Table 8: Detailed MEC Test Results
Room Temperature: 15°C Barometric Pressure: 997 mbar
Relative Humidity: 59% Date of Test: July 25, 2018
50 g/m³ 60 g/m³ 70 g/m³ 80 g/m³ 90 g/m³ 100 g/m³
Pm
[barg]
Pm
[barg]
Pm
[barg]
Pm
[barg]
Pm
[barg]
Pm
[barg]
Run 1 0.0 0.1 0.6 0.8 2.9 2.9
Run 2 0.0 1.1 1.1 0.0 - -
Run 3 0.0 - - 1.6 - -
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
Minimum Ignition Energy (MIE) of a Dust Cloud in Air Tests
The test was performed per ASTM E2019, “Standard Test Method for Minimum Ignition Energy
of a Dust Cloud in Air” using a Mike 3 MIE test apparatus manufactured by Kühner A.G. of
Basel Switzerland.
Scope
This test method covers the determination of the minimum ignition energy of a dust cloud in air
by a high voltage spark. Data obtained from this test method provides relative data of ignition
sensitivity of a dust cloud.
The values obtained are specific to the sample tested, the method used and the test equipment
used. The values are not to be considered intrinsic material constants. Any change in particle
size, shape, volatility or moisture will change results.
The Test Equipment Calibration
The test equipment used for testing was calibrated by carrying out the calibrating tests on Niacin
USP Special (Nicotinic Acid ~30 µm mean diameter) provided by the Mike 3 test equipment
manufacturer as part of a bi-annual round robin inter-lab calibration exercise. As a reference,
Minimum Ignition Energy (MIE) values and ranges for the equipment manufacturer’s reference
dust, and MIE value determined for the same reference dust by the FAI test equipment used are
shown in Table 9.
Table 9: Minimum Ignition Energy Test Results on Reference Dust
Material: Niacin USP Special (Nicotinic Acid “as received”)
Moisture
Content
(wt. %)
Mean
Particle
Size
(µm)
Kühner CaRo 17
Results
(mJ)
FAI MIE Results
(mJ)
MIKE3 #1 MIKE3 #2 MIKE3 #3 CTL
MIE 1
CTL
MIE 2
~0.15 ~30 µm 0.5 < MIE < 4.7
Es = 1.6
1 < MIE < 3
Es = 1.4
1 < MIE < 3
Es = 1.4
1 < MIE < 3
Es = 2.5 2.1 to 3.0 2.7 to 3.0
Test Setup
The Mike 3 apparatus, as depicted in Figure 4, is equipped with a dust dispersion cup, a
dispersion nozzle (mounted at the center of the dispersion cup), a compressed air source (7 bar)
and a pair of electrodes mounted on the clear glass cylinder wall (one a fixed high voltage
electrode, the other a moving ground electrode). The discharge circuit consists of a high voltage
supply (15 kV or 11 kV), interchangeable capacitors, and inductance source (1 mH). A more
detailed description of the apparatus is available from the manufacturer.
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Figure 4: MIKE 3 Minimum Ignition Energy (MIE) test setup
Procedure
The Mike 3 apparatus was powered up and allowed to stabilize for thirty minutes before testing.
The compressed air supply was turned on and adjusted to 7 bar(g). Then using the control/data
acquisition software supplied with the apparatus, the energy levels for the various discharge
levels were tested for operability (1000, 300, 100, 30, 10, 3, and 1 mJ). Once successfully
completed the apparatus was deemed ready for dust tests.
For each test, a desired amount of dust material was placed in the cup around the dispersion
nozzle. The electrode gap was set at 6 mm.
Using the computer control/data acquisition software the desired energy level was selected, and
the program initiated. The dust was then dispersed as a dust cloud inside the chamber. After a set
delay time the computer controlled spark would discharge and observations would be made for
flame ignition/propagation.
The difference between an ignition, “Go” and a non-ignition, “No Go” was evidenced by the
appearance of a fireball in the chamber. Once “Go/No Go” spark energy was found for a
particular concentration, the procedure was repeated for higher and lower dust concentrations.
The spark energy was reduced in steps at the given dust concentration until the dust cloud no
longer ignited in any of ten (10) tests at a given energy. The procedure was repeated at different
dust concentrations, and ignition delay times, until the lowest (minimum) ignition energy value
was found. To calculate the capacitor stored ignition energy (stored in the capacitor by an
applied voltage) the following equation was utilized:
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ܹௌ௧ௗ ൌ 1
2 ܥሺܸଵଶ െܸଶଶ ሻ
Where: WSTORED = capacitor stored ignition energy, Joules
C = capacitance of the discharge circuit capacitor, Farads
V1 = voltage to which the capacitor is charged, Volts
V2 = voltage on the capacitor after discharge, Volts
The MIE is then reported as being greater than the highest energy that was not able to ignite the
dust cloud and lower than the lowest energy that was able to ignite the dust cloud (Energy for
Non-Ignition < MIE < Energy for Ignition). In situations where the lowest energy the tester is
capable of producing (1 mJ) ignites the dust being tested, no additional testing is required and the
MIE is reported as being <1 mJ.
For the purpose of comparison between different apparatus, one statistical MIE value (Es)
instead of the energy range (E1, E2) may be used. This single statistically interpolated value (Es)
can be estimated by the use of the probability of ignition as follows:
ܧ௦ ൌ10ቆாమ ି൬ூሾாమሿሺாమିாభ ሻ
ሺேூାூሻሾாమሿାଵ ൰ቇ
Where: I[E2] = number of tests with ignition at the energy E2.
(NI+I)[E2] = total number of tests at the energy E2.
Below is an example calculation:
Ignition
Energy
(mJ)
Dust Loading in 1.2-L chamber
(mg) Probability
300 600 900 1200 1500
30 NI I I I NI 3 of 5
10 NI NI NI 0 of 3
ܧ௦ ൌ10ቆଷି൬ଷሺଷିଵሻ
ହାଵ ൰ቇ ൌ 17 ݉ܬ
Where: I = ignition of dust
NI = no ignition of dust in 10 trials
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
Minimum Ignition Energy (MIE) Test Results
The MIE test results for the material tested are summarized in Table 10. The data is represented
graphically in Figure 5. The open circles in the figure are dust concentrations that did not ignite
at a given ignition energy. The solid squares (if present) represent concentrations that ignited.
The vertical bar above the solid square (if present) is proportional to the number of experiments
conducted before the test material ignited. The blue mark ([]) represents data from tests
conducted with an ignition time delay of 120 ms between dust dispersion and spark discharge;
while the red mark ([]) represents data from tests with an ignition time delay of 90 ms.
Tests with inductance better simulate spark discharges from electrical/electronic sources,
whereas tests without inductance simulate sparks from pure/ideal electrostatic sources. Please
note that tests conducted with inductance in the circuit produce sparks that are more incendive
than circuits without inductance – thereby generating a conservative MIE level.
The results indicate that the sample tested has a very low MIE value between 1 mJ and 3 mJ with
an interpolated value of 2.1 mJ. Most electrostatic ignition sources have energies less than 1000
mJ. Common electrostatic ignition sources are typically less than 30 mJ (people, small isolated
components, etc.). Figure 6 is an illustration comparing various electrostatic discharge energies
to the ignitability level of various fuels Grounding and bonding of process equipment should be
implemented. Please see NFPA 654, 652, 77, 68, and 69 for guidance and instructions.
Table 10: Minimum Ignition Energy Test Results [with inductance]
Room Temperature: 17°C Barometric Pressure: 995 mbar
Relative Humidity: 54% Date of Test: July 23, 2018
Material Tested Moisture Content
(wt.%)
Mean Particle Size
(µm)
MIE
(mJ)
Interpolated MIE, Es
(mJ)
Maverick Boats 1.3
52
79% < 75 µm
100% < 500 µm
1 < MIE < 3 2.1
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
Figure 5: Ignition Energy as a function of dust concentration in the Mike 3 MIE [with
inductance] apparatus for Maverick Boats
Figure 6: An illustration of typical discharge energies compared to ignition energies of
various fuel types
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
Minimum Autoignition Temperature (MIT) of a Dust Cloud Tests
The test was conducted per ASTM E1491, "Standard Test Method for Minimum Autoignition
Temperature of Dust Clouds". The apparatus used was the BAM Oven manufactured by Kühner
A.G. of Basel Switzerland.
Scope
The test method covers the determination of the minimum temperature at which a given dust
cloud will auto ignite when exposed to air heated in a furnace at local atmospheric pressure. The
data obtained from this test method can provide a relative measure of dust-cloud autoignition
temperature.
Significance and Use
The test data developed from this test method can be used to limit the temperature to which a
dust cloud is exposed, thereby mitigating ignition of the cloud. Because of the short duration of
the test the data obtained are most applicable to industrial equipment where dust is present as
cloud for a short time.
The Test Equipment Calibration
The test equipment used for testing was calibrated by carrying out the calibrating tests on
Pittsburgh Bituminous Coal, and the calibration results are presented in Table 11.
Table 11: Minimum Autoignition Temperature MIT-Dust Cloud Test Results
Material Tested Mean Particle Size
(µm)
Moisture Content
(wt.%)
Literature Data FAI Result
MITdust cloud
(°C)
MITdust cloud
(°C)
Pittsburgh Bituminous Coal
(Standard Reference Material)
<75µm
(as received)
<5
(as received) 570 580
Procedure
The minimum autoignition temperature (MITdust cloud) of the material was determined using a
BAM Oven designed at the Bundesanstalt für Materialforschung und prüfung in Berlin,
Germany and manufactured by Kühner A.G. of Basel Switzerland. The BAM Oven apparatus is
shown in Figure 7.
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FAI18-0752 Proprietary Property of Fauske & Associates, LLC July 31, 2018
Figure 7: BAM Oven apparatus
An initial estimate of the MIT was made by heating the oven to a predetermined temperature
(maximum of 600°C) and then switching off the power and allowing the temperature to fall. At
intervals of 50°C, as the temperature falls, premeasured dust (1 ml) was dispersed into the
furnace with a blast of air. Observations for the presence, or absence, of flame exiting the rear of
the oven were made. After obtaining an estimate of the MIT, the exact value was determined by
a series of tests at various dust concentrations and at temperatures near the estimate. The selected
starting temperature was the lowest temperature for which flame was observed. The ignition tests
were continued by decreasing the test temperature in 10°C increments until flame is no longer
observed (within 5 seconds). For this series, the oven was stabilized at the set temperature
before each test.
For each test, the oven was set to the predetermined test temperature. The premeasured dust was
placed in the dust sample tube. The initial test concentration was a measured volume of 1 ml.
The dust sample tube was then inserted into the furnace and the dust dispersed with a blast of air.
Ignition of the dust was defined as the observation of flame exiting the flap at the rear of the
oven. At the highest temperature for which no flame was observed, at least three dust
concentrations were tested (volumes of 0.5, 1, and 2 ml). The test report lists the MIT as the
lowest temperature at which any positive result (flame) was observed over a series of
concentrations.
Minimum Autoignition Temperature (MIT) of a Dust Cloud Test Results
The Minimum Autoignition Temperature (MITdust cloud) results for the sample tested are
summarized in Table 12. Figure 8 graphically contains the tabulated test data for the material
tested. The MITdust cloud for this sample was determined to be at 460°C. This ignition risk should
be evaluated in light of the process environment. Please consult NFPA 652, 654, and 70 for
guidance and instructions.
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Table 12: Minimum Autoignition Temperature MIT-Dust Cloud Test Results
Material Tested Moisture Content
(wt.%)
Mean Particle Size
(µm)
MITdust cloud
(°C)
Maverick Boats 1.3
52
79% < 75 µm
100% < 500 µm
460
Room Temperature: 18°C Barometric Pressure: 998 mbar
Relative Humidity: 50% Date of Test: July 2, 2018
Figure 8: MIT Results for Maverick Boats
0.0
0.5
1.0
1.5
2.0
2.5
250 300 350 400 450 500 550 600 650Volume (ml)Temperature (°C)
Go No Go
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Total Combustible Content Determination
The test was conducted by Thermogravimetric Analysis / Differential Scanning Calorimeter
Analysis (TGA/DSC) using a TA Instruments SDT 650 apparatus. The test was conducted per
the manufacturer’s accepted method.
Scope
The test method covers a laboratory procedure to assess the presence of enthalpic (exothermic
reactions and endothermic reactions) and mass changes using milligram sample sizes, and
approximates the temperatures at which these enthalpic changes occur.
Setup
The TGA/DSC measures mass loss/gain and heat flow at various temperatures. A TA
Instruments SDT 650 Thermogravimetric Analyzer / Differential Scanning Calorimeter (TA
Instrument Corporation, New Castle, DE) with a standard configuration (temperature range of
room temperature to 1000°C) was utilized for this test to determine the endothermic (i.e.
melting) and exothermic (i.e. ignition) temperatures of the material in addition to mass loss or
gain. The TGA/DSC cell was confined in a ceramic heating cylinder, which was purged with a
desired flow rate of purge gas.
Procedure
In the TA Instruments SDT 650 TGA/DSC, a reference and the sample were heated under a
specific temperature program rate of 20°C/min. A computer-based thermal analysis/controller
unit controls the temperature program.
The TGA/DSC thermograph, as a function of time/temperature, was stored and monitored in the
computer. Each thermograph was then analyzed to determine endothermic and exothermic peak
temperatures and mass loss or gain.
In the TGA/DSC, each sample was placed in a 90 µl alumina pan. A lid was not used during this
analysis. The pan and an empty reference pan were placed onto the TGA/DSC balance arm in the
cell and heated at a preset rate while the heat flow and mass changes, as a function of
temperature, of the sample pan and reference pan were recorded. In this way, the differential heat
flow and mass change between the sample and the reference pan was measured.
When the test material released thermal energy, a positive heat flow (exothermic release of
energy) was recorded. The opposite occurred for absorption of energy, loss of thermal energy
(melting). Sample mass loss was recorded directly.
From this information, the onset temperature (when the differential heat flow starts to occur) and
peak temperature (when no more heat is liberated or released) can be determined.
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These reactions, in which the material absorbs or generates heat, are phase changes that equate to
complete or partial melting/vaporization (endothermic) or reaction (exothermic). Reactions are
considered complete when the peak exothermic temperature is reached.
The TGA/DSC tests were conducted under an air environment.
Results from TGA/DSC Analysis
The results of the TGA/DSC testing are presented in Figure 9. The results are discussed further
in the figure caption.
Figure 9: TGA/DSC thermograph for the “Maverick Boats” sample. The Total
Combustible Content of this sample was estimated to be around 64 wt.%
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CONCLUSIONS
Dust Explosibility results indicate that the sample tested had a KSt value of 201 bar-m/s;
therefore, this dust is classified as an St2 class dust. This material will present an explosion and
deflagration hazard risk when dispersed and ignited in air. Secondary explosions may also pose a
risk once an initial explosion occurs with the presence of a combustible dust or powder in the
area. The KSt and Pmax values are used in designing plant explosion relief and suppression/
containment systems (see NFPA 68 and 69). Additionally, please consult NFPA 652 and 654 for
explosion mitigation guidance and instructions.
The MEC value for the sample tested was estimated to be 59 g/m³. It is important to keep dust
concentrations below the MEC in order to minimize the risk of a dust explosion. Higher MEC
levels reduce the risk of fugitive dust explosions and explosions in dilute phase pneumatic
transport. Materials which require low concentrations of dust dispersed in air to create a
combustible mixture present a greater explosion hazard. Fugitive dust may also pose a risk once
an initial explosion occurs. The presence of combustible dust, or powder, in an area acts as an
additional fuel for the explosion. It is recommended that concentrations be kept at a minimum
(i.e. remove fugitive dust), otherwise explosion venting and inerting or nitrogen suppression may
be employed. Please consult NFPA 652 and 654 for guidance and instructions.
The results indicate that the sample had an MIE value that is between 1 mJ and 3 mJ with an
interpolated value of 2.1 mJ. Most electrostatic ignition sources have energies less than 1000
mJ. Common electrostatic ignition sources are typically less than 30 mJ (people, small isolated
components, etc.). Grounding and bonding of process equipment should be implemented. The
client may also wish to consider inerting the process environment to mitigate an explosion
hazard. Please see NFPA 652, 654, 77, 68, and 69 for guidance and instructions.
The MITdust cloud result for the sample tested was at 460°C. High temperature process
environments should be avoided to minimize the risk of a dust cloud explosion. Please consult
NFPA 652, 654, and 70 for guidance and instructions.
The TGA/DSC method demonstrated that the Total Combustible Content of the sample tested
was found to be ~ 64 wt.%.
Please note that finer dust under actual process conditions may produce higher risk explosibility
parameters.
Results from the experimental tests determined that the sample is deemed to be Class II dust for
National Electrical Code (NFPA 70) purposes. Please refer to NFPA 499-2017 for further
discussion of classification of combustible dusts and hazardous locations for electrical
installations in chemical process areas.
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FAI can assist in interpreting these tests and results and can also facilitate developing explosion
mitigation/protection strategies.
If you have any further questions regarding the content of this report, please feel free to contact
us.
Respectfully submitted,
Fauske and Associates, LLC.
Prepared by:
Rachelle Andreasen
Dust Projects Manager
Reviewed and Approved by:
Ashok Ghose Dastidar, PhD MBA
Vice President, Dust & Flammability
Testing and Consulting Services
Note that the conclusions and recommendations in this report are based on the specific considerations stated
and laboratory test methodologies used. These considerations include (but are not limited to) exact sample materials
tested [including particle size distribution, particle morphology, moisture content and level of oxidation];
formulae/composition tested, conditions of the test, and assumed plant physical parameters. The conclusions and
recommendations may not be applicable for conditions not identical to those considered. Consult local building and
fire codes, in addition to NFPA 652, 70, 1, 101 and other relevant NFPA codes, for instructions and guidance.
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Appendix A:
Figure A1: Maverick Boats particle size distribution
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Figure A2: Maverick Boats particle image [portion of the batch – non statistical representation]