Ogle RA — Dust Explosion Dynamics

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To Donna,
“. . .I love you just the way you are.” —Billy Joel, The Stranger (1977)

List of Figures
Figure 1.1
Figure 1.2
Figure 1.3 Figure 1.4 Figure 1.5 Figure 1.6 Figure 1.7 Figure 1.8 Figure 1.9 Figure 1.10 Figure 2.1 Figure 2.2 Figure 2.3 Figure 2.4 Figure 2.5 Figure 2.6 Figure 2.7

Figure 2.8
Figure 2.9

Figure 3.1
Figure 3.2
Figure 3.3
Figure 3.4
Figure 3.5

Depiction of the structure of a combustion wave.
Combustible dust pentagon.
Schematic of the 20-L sphere explosion testing device.
The smoldering fire hazard of combustible dust.
The flash fire hazard of combustible dust.
The dust explosion hazard scenario.
The secondary explosion hazard scenario.
The confined accelerating flame hazard scenario.
The pressure piling hazard scenario.
Total uncertainty of model predictions as a function of combustion model uncertainty and input data uncertainty.
Equivalent spherical diameters.
Discrete frequency distribution of atomized aluminum particle size measurements by light scattering.
Continuous frequency distribution of atomized aluminum particle size measurements by light scattering.
Cumulative distribution of atomized aluminum particle size measurements by light scattering.
Continuous cumulative distribution of atomized aluminum particle size measurements by light scattering.
Subdivision of sample sizes.
The effect of dust concentration and particle size on the dust explosbility parameters: (A) explosion pressure and (B) maximum rate of pressure rise.
Explosion parameters as a function of polydispersity for aluminum dust: (A) explosion pressure and (B) the deflagration index, Kst.
Ignition properties for Pittsburgh bituminous coal as a function of particle size: (A) minimum ignition temperature and (B) minimum explosible concentration.
Illustration of closed and open thermodynamic systems.
Definition sketch for a multiphase mixture.
Illustration of the macroscale and microscale dimensions for a dust flame burning at constant pressure.
Definition sketch for the adiabatic isobaric flame temperature.
Thermodynamic model for constant volume combustion.

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List of Figures

Figure 3.6

Figure 3.7
Figure 3.8

Figure 3.9
Figure 3.10
Figure 4.1
Figure 4.2

Figure 4.3

Figure 4.4
Figure 4.5
Figure 4.6
Figure 4.7
Figure 4.8 Figure 4.9 Figure 4.10 Figure 4.11

Maximum pressure measurements as a function of dust concentration: (A) cornstarch and (B) aluminum. The solid lines indicate the chemical equilibrium calculation.
Definition sketch for the analysis of a fractional volume deflagration.
Fractional deflagration model for a combustible dust with an isochoric combustion (explosion) pressure of 8 bars at the stoichiometric condition.
Thermodynamic model for the secondary dust explosion pressure.
Thermodynamic model for a secondary dust explosion compared with the fractional deflagration model.
Illustration of one-dimensional rectangular and spherical coordinate systems.
Open tube ignition of premixed flammable gas mixture:
(A) the ignition event and (B) the propagation of the flame into the unburnt mixture with the combustion products flowing out of the tube in the opposite direction.
Closed tube ignition of premixed flammable gas mixture:
(A) the ignition event, (B) the propagation of the flame into the unburnt mixture, (C) the formation of a shock wave ahead of the combustion wave, and (D) the merging of the shock and combustion waves into a detonation wave.
Shock wave properties relative to laboratory and shockfixed coordinate frames of reference.
P 2 diagram showing the Rayleigh line and the Rankine
Hugoniot curve.
Rankine
Hugoniot curve with chemical energy addition (Q . 0).
Rankine
Hugoniot diagram divided into different regimes.
Temperature and fuel mass fraction profiles in a planar premixed gas flame.
Definition sketch for Annamalai and Puri’s energy balance for a premixed flame.
Definition sketch for Spalding analysis of premixed flame propagation.
Premixed flame thickness divided into a preheat zone and a reaction zone.

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List of Figures

Figure 4.12
Figure 4.13
Figure 4.14
Figure 4.15 Figure 4.16

Figure 4.17
Figure 4.18
Figure 4.19
Figure 4.20 Figure 4.21 Figure 4.22 Figure 4.23 Figure 4.24 Figure 4.25 Figure 4.26 Figure 5.1 Figure 5.2 Figure 5.3

Figure 5.4
Figure 5.5
Figure 5.6
Figure 5.7
Figure 5.8 Figure 5.9

Definition sketch for critical radius of ignition.
Definition sketch for flame quenching in a tube.
Isolated liquid fuel droplet surrounded by a flame sheet.
Heat fluxes for a single burning particle.
Sketch showing relationship of species flux directions with respect to the flame sheet (F is fuel, OX is oxidizer, and P is products).
Temperature and mass fraction profiles for a burning liquid droplet.
Diagram of a representative elementary volume for a combustible dust deposit.
Effective thermal conductivity of a porous medium with parallel structure.
Effective thermal conductivity of a porous medium with series structure.
Flow regimes for dispersed multiphase flow.
Control volume sketch for the radiative transfer equation.
Definition of the solid angle ω.
Surface energy balance for thermal radiation on a solid surface.
Spectrum of electromagnetic waves in comparison with the potential particle size range of combustible dusts.
Absorption and scattering of incident thermal radiation by a spherical particle.
Thermal structure of a smolder wave.
Depiction of a self-heating deposit of combustible dust.
Temperature profiles for a self-heating body in subcritical and supercritical states. The critical temperature occurs between the subcritical and supercritical states.
Heat generation and heat loss rate for the Semenov analysis.
Rectangular slab geometry for a self-heating porous medium.
Definition sketch for Williams’s scale analysis of smolder wave propagation.
Reverse smolder wave propagation.
Ohlemiller’s diagram showing the influx of oxygen into a two-dimensional smolder front.
Definition sketch for the diffusion analysis of the vertical profile of the smolder front.

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List of Figures

Figure 5.10
Figure 6.1
Figure 6.2
Figure 6.3
Figure 6.4 Figure 6.5 Figure 6.6

Figure 6.7
Figure 6.8

Figure 6.9

Figure 6.10
Figure 6.11
Figure 6.12
Figure 6.13 Figure 6.14 Figure 6.15

Figure 6.16
Figure 6.17

Figure 6.18

Vertical profile of the smolder wave front.
Sequence of diffusion, adsorption, and chemical reaction steps in a gas
solid combustion process.
The shrinking particle model.
Concentration profile for species A when the gas film resistance is controlling.
Concentration profile of species A when the chemical reaction is the rate-determining step.
The shrinking unreacted core model with constant particle diameter.
Concentration profile for species A for the shrinking unreacted core model when the gas film resistance is controlling.
Concentration profile for species A for the shrinking unreacted core model when the product layer diffusion resistance is controlling.
Concentration profile for species A for the shrinking unreacted core model when the chemical reaction rate is the controlling step.
Relative importance of the rates of gas film diffusion, product layer (ash) diffusion, and chemical reaction on the overall reaction rate as a function of temperature.
The progressive conversion model for a particle of constant diameter.
Photographs of single droplet diffusion flames for four different hydrocarbon liquids.
Silhouette photograph of burning petroleum ether droplet, original diameter 1.5 mm.
Godsave’s plot of droplet diameter-squared versus time for three liquid fuels.
Typical unburnt polymer particles used in a single particle combustion study by Panagiotou and Levendis.
High-speed video frames of a burning polystyrene particle. The time between two consecutive frames is 1 ms (left to right).
Variation in the particle sizes and shapes of a Pittsburgh coal dust sample before and after combustion.
Sections of a 30-mm bituminous particle at various stages of conversion from 0% to 100% (from left to right) in a combustion furnace at 1000 C.
Four examples of biomass material.

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List of Figures

Figure 6.19

Figure 6.20
Figure 6.21
Figure 6.22

Figure 6.23

Figure 6.24
Figure 6.25

Figure 6.26
Figure 6.27

Figure 6.28

Figure 6.29

Figure 6.30
Figure 6.31

Figure 6.32

SEM micrographs of beech wood char particles after fast pyrolysis at a temperature of 950 C: (A) 350 μm, (B) 500 μm, (C) 700 μm, and (D) 800 μm.
Burnout time for volatiles combustion of corncob particles as a function of particle diameter.
Burnout time for char combustion of corncob particles as a function of particle diameter.
Spherical diffusion flame surrounding burning particle at three different oxygen concentrations. Volatile combustion in first three frames followed by char oxidation. Numbers underneath each photograph represents the burning time in milliseconds.
Typical char formation on a flat slab of Douglas fir wood. Top and side views of char fissures and cracks;
box denotes the termination of a fissure. Scale is in inches.
Conceptual model of wood char development.
Char pattern development in 50 mm diameter rosewood spheres with the formation of characteristic cracks and fissures.
Parent pine sawdust particle (A) and charred particles caused by low (B), high (C), and extremely high heating rates (D).
Carbon combustion models: (A) the heterogeneous chemical reactions involved in oxidation, (B) concentration profiles for the one-film model, and (C) concentration profiles for the two-film model.
Surface control volume at the particle surface showing reaction rates for the one-film carbon particle combustion model.
Surface control volumes at the particle surface and the flame sheet showing the reaction rates for the two-film model of carbon combustion.
Aluminum particle diameter-squared versus burnout time.
Luminosity images for four burning aluminum particles (210 μm diameter) in free fall. Scale on the left indicates distance from point of ignition by laser. Images show the full range of combustion behavior.
Shrinking unreacted core model for iron particle combustion.

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List of Figures

Figure 6.33

Figure 7.1
Figure 7.2

Figure 7.3

Figure 7.4
Figure 7.5

Figure 7.6

Figure 7.7
Figure 7.8

Figure 7.9

Figure 7.10

Flame propagation in a cloud of iron dust. Iron dust concentration of 1.05 kg/m3; time is the burning time since ignition.
Schematic of typical dust flame burner.
Homogeneous flame behavior in a dispersed phase fuel cloud. The flame preheats and vaporizes the fuel particles creating a premixed fuel vapor
air mixture.
Heterogeneous flame behavior in a dispersed phase fuel cloud. The individual burning particles preheats and ignites their nearest neighbors with each particle burning essentially independently.
Mallard
Le Chatelier model for a dust flame.
Burning velocity of dust flame for aluminum (left side) and magnesium (right side) as a function of dust concentration. Families of curves represent different mean particle diameters. Symbols are measured velocities and solid lines are the model predictions.
Burning velocity of coal dust flames as a function of equivalence factor (dust concentration). (A) Comparison of Bersham (▲), Beynon (x), and Annesley (’) coals.
Influence of volatile matter (v.m.) and particle size (p.s.) indicated by arrows. (B) Annesley coal: Theory versus experiment. (C) Bersham coal: Theory versus experiment.
Dimensionless flame thickness for different fuels as a function of the equivalence ratio.
Burning velocity versus the Spalding transfer number B.
The types of fuel depicted in this figure range from propane vapor (g.f., gaseous fuel) to iso-octane liquid mist (l.m.), and from volatile solid fuels (s.f.) to nonvolatile solids. Calculations based on the stoichiometric concentration of fuel, a particle diameter of 30 μm, atmospheric pressure, and ambient temperature. Fuel abbreviations: k, kerosene; d.f., diesel fuel; h.f.o., heavy fuel oil; p.f., prevaporized fuel; and f.l., flammability limit.
Laminar burning velocity for iso-octane mist flames at different Sauter mean diameters (SMD) and fuel vapor fractions (Ω) for two different equivalence ratios.
Plot of maximum flame temperature and mean flame speed as a function of dust concentration for three fatty alcohols.

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List of Figures

Figure 7.11

Figure 7.12
Figure 7.13
Figure 7.14
Figure 7.15 Figure 7.16 Figure 7.17 Figure 7.18

Figure 7.19

Figure 7.20
Figure 7.21

Figure 7.22

Figure 7.23

Figure 7.24
Figure 7.25

Images of alcohol mist flames and dust flames using direct photography (left-hand side columns) and UV band filter photography (right-hand side columns).
Particle size distributions of three octadecanol powders with their size parameters indicated.
Photographs of flame propagation for three 1-octadecanol powders.
Laminar burning velocity for lycopodium powder as a function of dust concentration.
The sequence of laminar flame propagation through a lycopodium dust cloud with a concentration of 592 g/m3.
Dust particle motion near the flame front.
Lycopodium particle trajectory diagram.
Detailed conceptual model of lycopodium dust flame propagation: (A) heating and ignition of single particles;
(B) heating and ignition of particle agglomerates; and (C) final stage of pyrolysis and combustion of particles.
Laminar burning velocity of aluminum dust flames at different dust concentrations and with different oxygen concentrations and nitrogen as the carrier gas.
Laminar burning velocity of aluminum in 21% oxygen and two different carrier gases, helium and argon.
Premixed aluminum dust flames stabilized on a Bunsen burner apparatus with different oxidizing mixtures: air (oxygen
nitrogen) and oxygen
helium.
Aluminum dust flame propagation recorded by high-speed photography (dust concentration of 420 g/m3) and Schlieren photography (dust concentration 490 g/m3). Times indicated in images is the elapsed time from ignition and length scale indicated below image.
High-speed photographs of flame propagation in an iron dust cloud with a dust concentration of 1050 g/m3. Time is elapsed time from ignition.
Flame speed for two different iron powders as a function of dust concentration.
Iron dust flame temperature measurements. The figure on the left is the axial temperature profile measurement (solid line) and the corrected temperature measurement (dashed line). The figure on the right is the maximum flame temperature.

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List of Figures

Figure 7.26

Figure 7.27

Figure 7.28
Figure 7.29

Figure 7.30
Figure 7.31
Figure 7.32
Figure 7.33

Figure 7.34
Figure 7.35

Figure 7.36
Figure 8.1
Figure 8.2
Figure 8.3

Figure 8.4

Gas and particle velocity profiles in an iron dust flame (left-hand side) and a premixed gaseous flame (righthand side).
Comparison of the axial profile measurements of the iron particle concentration and particle velocity. The iron dust concentration was 1050 g/m3.
Axial particle velocity measurements for upward flame propagation (left-hand side) and downward flame propagation (right-hand side).
Axial profile of the particle concentration enrichment for upward and downward flame propagations.
Concentrations are normalized by the free stream (unburnt) particle concentration.
Iron dust flames propagating from right to left. Average particle diameter increases from left to right (A , B , C).
Flame speed as a function of particle diameter for different carrier gases.
Constant pressure deflagration model for a combustible dust flash fire.
Time sequence of photographs of constant pressure deflagration of lycopodium dust in a balloon. Dust concentration 285 g/m3.
Plot of balloon radius and flame radius measurements versus time.
Constant pressure deflagration test with aluminum powder at a dust concentration of 500 g/m3: (A) sequence of photographs showing flame growth in the balloon and (B) flame radius as a function of time.
Flame speed measurements and burning velocity calculations for aluminum powder.
Spherical dust flame propagation in a spherical vessel.
Plot of pressure history and flame motion for a carbon monoxide
oxygen mixture in a closed vessel.
Pressure rise history plotted with a timed sequence of photographs showing the growth of an aluminum dust flame in a 10-L test vessel. The dust concentration was 1000 g/m3 and the shape of the vessel was a right circular cylinder. The conversion for the pressure units is 1 kg/cm2 5 0.9807 bar.
Depiction of the Flamm
Mache temperature profile in a spherical vessel.

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List of Figures

Figure 8.5
Figure 8.6

Figure 8.7

Figure 8.8
Figure 8.9

Figure 8.10
Figure 8.11

Figure 8.12
Figure 8.13
Figure 8.14

Figure 8.15
Figure 8.16

Figure 8.17
Figure 8.18
Figure 8.19

Coordinate frame for dust deflagration in a spherical vessel.
Flame propagation model predictions: (A) flame radius and particle path histories and (B) burnt gas temperature profile.
Explosion pressures for methane
air mixtures:
(A) explosion pressure versus equivalence ratio (computer solution compared with isochoric explosion pressure) and (B) pressure history showing performance of numerical solution with approximate solutions and experimental data.
Deflagration pressure histories plotted as dimensionless pressure rise versus time cubed.
Pressure history of stoichiometric methane
air deflagration in a 12-ft-diameter sphere: (A) comparison of computed pressure history and experimental data and (B) cubic pressure rise in early portion.
Drawings of the Siwek 20-L (A) and Fike 1-m3 (B) spherical test vessels.
Comparison of predicted versus measured flame radius histories using the NCV adiabatic and isothermal integral models.
Comparison of predicted versus measured pressure histories using the NCV adiabatic and isothermal integral models.
Temperature profile at distinct times during flame propagation.
Comparison of predicted versus measured pressure histories using the NCV adiabatic and isothermal integral models.
Ignition of a stoichiometric methane
air mixtures with a range of ignition energies.
Variation of ignition delay time for cornstarch dust deflagrations at a fixed dust concentration and igniter energy.
Three different dispersion nozzles designed for the 20-L test vessel.
Space-averaged turbulent intensity in a 20-L sphere using the perforated dispersion ring device.
Turbulent intensity measurements: (A) the 1-m3 vessel and (B) comparison of 20-L sphere measurements from Dahoe.

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Figure 8.20

Figure 8.21
Figure 8.22

Figure 8.23
Figure 8.24
Figure 8.25

Figure 8.26
Figure 8.27
Figure 8.28

Figure 8.29
Figure 8.30
Figure 8.31
Figure 8.32 Figure 8.33 Figure 8.34 Figure 8.35 Figure 8.36 Figure 8.37 Figure 8.38 Figure 8.39

Pressure histories for methane
air deflagrations in a 20-L sphere; the upper graph is for fuel lean concentrations and the lower graph is for fuel rich concentrations.
Deflagration parameters Pmax and KG for methane
air mixtures as a function of the equivalence ratio.
Laminar burning velocities for methane-air mixtures obtained by estimation from a confined deflagration model versus estimates obtained by other investigators.
Comparison of methane deflagration data with two combustible dusts: polyethylene and high volatile bituminous coal.
Deflagration parameters for Prince 1 bituminous coal (Nova Scotia, Canada).
Proximate analysis, ultimate analysis, and the deflagration parameters for various coals measured in a 20-L sphere.
Bureau of Mines 20-L deflagration test vessel.
Coal dust deflagration parameters obtained from the Bureau of Mines 20-L test vessel.
Deflagration parameters for activated carbon measured in a 20-L sphere. The dashed line denotes the stoichiometric concentration of 100 g/m3.
Comparison of the deflagration index for activated carbon and graphite.
Graphite
air deflagration parameters for different particle sizes.
Deflagration parameters for cork dust.
Deflagration parameters obtained from a 1-m3 test vessel.
Deflagration pressure histories for four atomized aluminum powders. The tests were conducted in a 20-L sphere.
Deflagration index for four atomized aluminum powders and four aluminum flake powders.
Time to maximum pressure versus particle diameter for atomized and flake aluminum powders.
Deflagration parameters from Dufaud et al. 20-L test vessel.
Particle size distributions tested and the time to maximum pressure (labeled as the combustion time).
Results of tests in a 36-L vessel according to the ASTM E1226 procedure.
Deflagration data obtained from the Bureau of Mines 20-L test vessel.

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List of Figures

Figure 8.40
Figure 9.1
Figure 9.2

Figure 9.3
Figure 9.4

Figure 9.5
Figure 9.6

Figure 9.7
Figure 9.8

Figure 9.9
Figure 9.10
Figure 9.11
Figure 9.12 Figure 9.13 Figure 9.14

Figure 9.15

Figure 9.16

Generic explosibility diagram for a combustible dust.
Turbulent combustion feedback loop.
Expansion wave caused by withdrawal of piston from a tube: (A) physical situation; (B) axial profile of pressure at different times; and (C) wave diagram showing expansion wave and piston trajectories.
Flame chasing the shock wave.
Formation of a shock wave by the coalescence of acoustic waves: (A) initial condition with piston at rest;
(B) piston in motion generating successive acoustic waves (t4 . t3 . t2 . t1); and (C) shock wave formation.
Shock wave properties relative to laboratory and shock-fixed coordinate frames of reference.
Shock wave properties for a shock reflected from a solid wall in both laboratory coordinates and shock-fixed coordinates.
Spatial profile and control volume for moving pressure disturbance.
Experimental validation of the acoustic approximation for a weak shock wave. Data are from deflagration tests conducted in the Bureau of Mines experimental mine.
Blast wave features.
Modes of particle motion with a dust layer.
Turbulent boundary layer velocity profile for a smooth surface (A) and a rough surface (B).
The logarithmic velocity correlation for turbulent boundary layer flow in a smooth tube.
Turbulent boundary layer structure with a free stream velocity of 30 m/s showing two particle profiles with diameters of 10 and 100 μm.
Photographs of wind tunnel experiment showing two different modes of dust lofting: (A) erosion and (B) denudation. Airflow was approximately 30 m/s from right to left.
Photographs of dust deposit looking downwards. Wind tunnel test for erosion of limestone dust deposit by airflow of approximately 30 m/s. Airflow was from right to left.
The arrow indicates the leading edge of the dust deposit.
Wind tunnel test with limestone powder exhibiting both erosion and denudation processes. Side view with airflow going from right to left.

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Figure 9.17

Figure 9.18
Figure 9.19
Figure 9.20

Figure 9.21
Figure 9.22
Figure 9.23

Figure 9.24

Figure 9.25
Figure 9.26
Figure 10.1
Figure 10.2

Figure 10.3

Wave diagram showing the wave trajectory in the experimental mine and the pressure history at each pressure transducer location. Deflagration was a 7.5% methane
air flame in 4.8 m compartment.
Threshold velocity for wood, sugar, aluminum, and iron particles.
Wave diagram for the propagation of a coal dust flame in the U.S. Bureau of Mines experimental mine.
Comparison of gas and dust flame propagation in tubes with flow obstacles (blockage ratio 40%). Gas mixture is 6.5% methane in air and dust is cornstarch at 500 g/m3.
Spacing between obstacles is 25 mm. Frame rate for Schlieren photography is (A) 640 frames/s and (B) 500 frames/s.
Wave diagram for DDT of cornstarch in a 0.3-mdiameter detonation tube and length of 37 m.
Pressure piling scenario.
Pressure records at three locations in the integrated system: (A) maize starch at 1000 g/m3, 0.04 m2 vent on dust filter, 0.25 m2 vent on process vessel and (b) wheat dust at 650 g/m3, 0.08 m2 vent on dust filter, 0.25 m2 process vessel. Note the difference in scale for the pressure coordinate.
Overpressure versus flame length in the conduit between dust filter and process vessel. Results for all five dusts are shown, but the test with silicon was conducted without the process vessel.
Coal dust explosion for large volume ratio.
Coal dust explosion for small volume ratio.
Annual sales revenue for CFD software.
Finite difference representation of a material body:
(A) the original continuous medium which is a rod with a circular cross-section, (B) the same body now divided into discrete segments, and (C) the discrete pieces collapsed into points on a number line representing the x-coordinate.
Definition sketch for the finite volume technique. The node of interest, designated P, is centered at the midpoint of the control volume. The nodes to the left and right of P are designated W (west) and E (east). The volume of the cell is ΔV ¼ A  Δx.

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Figure 10.4

Figure 10.5
Figure 10.6
Figure 10.7
Figure 10.8 Figure 10.9

Figure 10.10

Figure 10.11
Figure 10.12
Figure 10.13

Figure 10.14

Figure 10.15

Figure 10.16
Figure 10.17
Figure 10.18

Species concentration, temperature, and particle diameter profiles in a coal dust flame, dust concentration 300 g/m3, mean particle diameter 33 μm.
Flame structure for carbon dust
40% O2
60% N2 system.
Flame speed oscillation for carbon dust
oxygen
nitrogen system.
Flame speed of coal dust flame as a function of radial position.
Flame speed as a function of radial position for coal dust flames with different particle diameters.
Simulation results for an aluminum dust deflagration in a 20-L sphere: (A) temperature profiles at two times; (B) mixture velocity at two times; and (C) pressure history and rate of pressure rise history.
Aluminum dust deflagration simulations with a dust concentration of 500 g/m3: (A) flame position at four distinct times and (B) pressure histories for four powders (data from Ogle et al., 1988) and the CFD simulation.
Example of igniter-induced overpressure.
Sequence of events triggered by an igniter in a deflagration test vessel.
Axial velocity profiles at different times as a flame propagates through the 24.4 m3 spherical vessel. The flame trajectory and the first characteristic wave trajectory are shown.
Calculated flame speed and flame position histories in the 24.4 m3 spherical vessel. The acceleration and deceleration from wave interactions are evident. ISS (infinite sound speed) denotes the integral flame propagation model and FSS (finite sound speed).
Schematic diagram of coal dust flame with three zones traveling in a one-dimensional passageway. Zone F denotes the flame region.
Simulation results for the effect of turbulence on the flame propagation by varying the conduit diameter.
Accelerating coal dust flame behavior as a function of particle size.
Comparison of model predictions versus experimental data for the relationship between flame speed and pressure. Experimental data denoted by circles, squares, and triangles. See original reference for data sources.

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Figure 10.19

Figure 10.20

Figure 10.21

Figure 10.22
Figure 10.23

Figure 10.24

Cross-section of the laboratory wind tunnel used for dust lifting experiments. Case A is the base case, Case B includes a gridding refinement at the dust
air interface, Case C is a second gridding refinement, and Case D is a finer resolution of the grid spacing.
Pressure histories for the six primary simulations of the explosion tests conducted in the experimental mine “Barbara.” The measurements correspond to four locations in the tunnel: 20, 40, 60, and 80 m from the closed end of the tunnel with a total length of 100 m.
Flame length predicted by DESC for different cases of fugitive dust deployment and different levels of dust reactivity. The key indicates the reactivity level and the dispersability constant.
Computational domain for the pressure piling problem.
The effect of channel height on the speed of displacement of the unburnt solids in the second vessel.
The solids’ concentration fields in the second vessel are shown at three distinct times (from top to bottom): 7.5, 12.5, and 27.5 milliseconds.
(A) The three-dimensional rendering of the interconnected vessels from DESC. (B) A graphical image of deflagration venting from both vessels.

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List of Tables
Table 1.1
Table 1.2
Table 1.3
Table 1.4 Table 1.5 Table 2.1 Table 2.2 Table 2.3 Table 3.1 Table 3.2 Table 3.3

Table 3.4
Table 3.5
Table 3.6
Table 4.1
Table 4.2 Table 4.3 Table 4.4 Table 4.5 Table 4.6

Test Methods for Dust Explosibility Parameters Test Methods for Ignition Characteristics of Combustible Dust System Safety Hierarchy for Hazard Control Application of Inherently Safer Design Principles to Combustible Dust Hazard Management Combustible Dust Hazard Control Strategies Organized Around the Combustible Dust Pentagon Selected Values of Sieve Sizes Single Particle Properties for Combustible Dust Suggestions for Developing a Combustible Dust Sampling Plan Composition of Air Calculation Procedure for the Adiabatic Flame Temperature Maximum Measured Flame Temperatures for Elemental Dust Flames in Isobaric Combustion. Dust Concentration Corresponds to the Maximum Measured Flame Temperature Maximum Measured Flame Temperatures for Organic Dust Flames in Isobaric Combustion Temperature and Pressure Measurements in Isochoric Combustion Experiments for Elemental Combustible Dusts Temperature and Pressure Measurements in Isochoric Combustion Experiments for Organic Combustible Dusts Detonation Properties for Various Fuel–Oxidizer Mixtures (P1 5 1.01 bars; T 5 298 K) Fractional Arrhenius Rate Coefficient Versus Fractional Temperature Rise for Different Activation Energies Select Values of B for Liquid Fuels Drag Coefficient for Single Spherical Particles Over a Range of Reynolds Numbers Momentum Response Times in Milliseconds as a Function of Particle Diameter and Density Extinction Coefficient and Optical Thickness for Various Particle Diameters

17
18
25
26
27
37
42
47
55
71
76

77
83
84
119
125
144
159
162
172

xxxi

xxxii

List of Tables

Table 4.7

Table 5.1
Table 6.1
Table 6.2
Table 6.3
Table 6.4 Table 6.5 Table 6.6 Table 6.7 Table 6.8 Table 6.9 Table 7.1 Table 7.2 Table 7.3 Table 7.4 Table 7.5 Table 7.6 Table 8.1 Table 8.2 Table 8.3 Table 8.4 Table 8.5

Calculation of the Kolmogorov Length Scale for Different Fluctuating Velocity Measurements During Dispersal in a 20-L sphere Critical Frank–Kamenetskii Parameters for Several SelfHeating Bodies Thermal Conduction Time Scale for Anthracite and Aluminum as a Function of Particle Size Summary of Key Performance Equations for the Shrinking Particle and Shrinking Unreacted Core Models Burning Rate Constants Experimental Values from Single Droplet Combustion Tests Summary Polymer Burning Rate Constants Summary of Burning Rate Constants for Three Polymers Under Various Combustion Conditions Approximate Elemental Composition of Common Organic Solid Fuels in Mass Percent Summary of Burning Rate Constants for Volatiles and Char Derived from 10 Bituminous Coals Comparison of the Proximate and Ultimate Analyses Values for a Woody Biomass and a Herbaceous Biomass Metal Combustion Regimes Typical Values of Interparticle Spacing Ratio at Different Dust Concentrations for Three Combustible Dusts Impact of a Diminishing Oxygen Atmosphere on Diffusion-Controlled and Kinetic-Controlled Combustions of a Dust Cloud with Perfect Mixing Comparison of Lean Limits for Flammable Gases/Vapors and Combustible Dusts Dust Flame Dynamics Based on Time Scales Flame Speeds Measured for Alcohol Mist and Dust Flames Lower and Upper Flammability Limits of Coal Dust Based on a 50% Probability of Ignition Tabulation of Dimensionless Burnt Gas Volume as a Function of Flame Radius for a Spherical Combustion Vessel Dust Hazard Classification Based on the Kst Value Dust Deflagration Parameters for Select Biomass Materials Aluminum Powder Characteristics Limit Flame Temperatures and Minimum Explosible Concentrations

177

193
220
243
248
250
253
255
258
262
285
313
318 325 335 359 362 411 461 472 473 482

List of Tables

Table 9.1
Table 9.2

Table 9.3
Table 9.4
Table 10.1

Comparison of Limiting Property Ratios for Weak and Strong Shocks Tabulation of Weak Shock Overpressure as a Function of Flame Speed Calculated from the Acoustic Approximation for Air at 1.013 bars and 300 K Injury Potential and Structural Damage Criteria from Explosion Overpressures Deflagration Parameters for Dusts Tested CFD Modeling Strategy

507
514

516
554
571

xxxiii

Nomenclature
ROMAN LETTERS
A
Av
ag
aR
B
BM
bFT bOxT bFOx C CD Ci CL Cp Cv c Da d dn dp dp dquench d32 E Ea Eign Ff 20
F dp F=A
F=A st f
f dp G H Hi

Arrhenius pre-exponential factor
Specific surface area Speed of sound in a gas Rosseland mean absorptivity Spalding’s transfer number Bradley
Mitcheson model Shvab
Zeldovich variable based on fuel mass fraction and enthalpy values Shvab
Zeldovich variable based on oxidizer mass fraction and enthalpy values Shvab
Zeldovich variable based on fuel and oxidizer mass fraction values Heat capacity of condensed phase material Drag coefficient Molar concentration of species i Local dust concentration in a flammability tube, mass units Heat capacity at constant pressure Heat capacity at constant volume Speed of light Damkohler number Diameter or distance nth moment of the particle size distribution Particle diameter Mean particle diameter Flame quenching distance Sauter mean diameter Expansion ratio, Mu Tb =Mb Tu Activation energy Ignition energy Radiation view factor from the flame to the ambient environment Cumulative distribution function for a particle size distribution Fuel
air ratio Stoichiometric fuel
air ratio Fraction of fuel mass burnt Frequency distribution function for a particle size distribution Incident radiation on solid surface Height Enthalpy of species i

xxxv

xxxvi

Nomenclature

h
hi
HHV
Iλω
J
k
kc
kg
k0
Kof
Kst
L
Le
LFL
LFLup LFLdown LHV LvE Ma m mi m_ i Mi NCV Nu ni np P Pmax Q Qa Qe Qs qb qbλ 000 qx Pr Re Rg r rc rf ; r flame rs

Convective heat transfer coefficient, Planck’s constant Specific enthalpy of species i Higher heating value Radiation intensity per unit wavelength per unit solid angle Variable for gravitational settling in the transition regime Thermal conductivity, Boltzmann’s constant, kinetic rate constant Kinetic rate constant Film mass transfer coefficient Overall rate coefficient Burn rate coefficient
Dust explosibility parameter, Kst 5 dP=dt max  V 1=3 Characteristic length Lewis number Lower flammable limit, mass concentration Lower flammable limit, upward flame propagation, mass concentration Lower flammable limit, downward flame propagation, mass concentration Lower heating value Lewis
von Elbe model Mach number Total mass, complex index of refraction Mass of species i Mass flow rate of species i Molar mass of species i Nagy
Conn
Verakis model Nusselt number Moles of species i Number concentration of particles Pressure Dust explosibility parameter, maximum explosion pressure Heat interaction; enthalpy of combustion per unit mass of fuel Dimensionless absorption efficiency coefficient Dimensionless extinction efficiency coefficient Dimensionless scattering efficiency coefficient Black body hemispherical emission Black body spectral radiant heat flux Volumetric heat interaction Prandtl number Reynolds number Universal gas constant 5 8314.5 J/(kmol-K) Radial coordinate in cylindrical or spherical geometry Instantaneous radius of particle, radius of dust cloud Radius of flame surrounding a fuel particle Particle surface radius

Nomenclature xxxvii

rw
r0
Sb
Su
s
Sc
Sh
T
t
twave
t1=2
Ui
ui
V
Vb
v vp;TSV vsm vx vx 0 vx W Xi x xB YF;U Yi Ze

Radius of spherical vessel
Initial radius of particle Flame speed of a premixed flame Laminar burning velocity of a premixed flame Path length for radiative intensity Schmidt number Sherwood number Temperature Time Time scale for a deflagration wave Half-life Internal energy of species i Specific internal energy of species i Volume Volume of burnt mixture Velocity Terminal settling velocity for a single particle Smolder wave velocity Velocity component in the x-direction Time averaged velocity component in the x-direction Instantaneous velocity fluctuation in the x-direction Work interaction Mole fraction of species i Spatial coordinate direction, size parameter for Mie scattering theory Fractional conversion of species B Mass fraction of fuel, unburnt condition Mass fraction of species i Zeldovich number

GREEK SYMBOLS
α
αfill
αi
αT
β
β
βλ
γ
δ
δd
δsm

Absorptivity in thermal radiation
Volume fraction of enclosure filled with a combustible dust cloud Volume fraction of phase i Thermal diffusivity Density ratio for gas-solid reaction in Chapter 6 Defined constant in Chapter 9, β 5 ðγ 1 1Þ=ðγ 2 1Þ Extinction coefficient Ratio of heat capacities Premixed flame thickness, Frank
Kamenetskii number Thickness of accumulated dust layer Smolder wave thickness

xxxviii Nomenclature

E0
ε
κ
λ
θ
μ
υi
Πi
ρ
ρ
ρi
ρd
ρmix
ρs
σ
σ
τ
τ cloud τx τ0 Φ φ ϕ ω 0 00 ωi

Turbulent dissipation rate
Emissivity
Flame curvature Wavelength of electromagnetic radiation Dimensionless temperature, flame cone angle on Bunsen burner flame Dynamic viscosity Specific volume of species i Dimensionless ratio of type i Mass density Reflectivity in thermal radiation Mass density of chemical species i Mass concentration of dust
air mixture Mixture density Solid phase density Stefan
Boltzmann constant 5 5.67 3 10-8 W/m2-K4 Standard deviation Optical thickness, transmissivity in thermal radiation, burnout time for a single particle Burnout time for a dust cloud Time scale for process x Shear stress at bounding wall or surface in Chapter 9 Equivalence ratio Velocity potential in acoustics Mass ratio of carbon to oxygen for the stoichiometric condition Solid angle Chemical reaction rate per unit volume for species i

SUPERSCRIPTS
0
g
m
s
0
ðprimeÞ
1

Standard state for energy value
Gas phase
Mixture Solid phase Shock-fixed coordinate system Dimensionless quantity for turbulent boundary layer

SUBSCRIPTS
act
ad
b

Actual value
Adiabatic value at constant pressure Burnt mixture

Nomenclature

CJ
c
d
ex
fg
i
in
mix
of
out
p
ref
s
stoich
tf th u x 0 N

Chapman
Jouget detonation
Combustion
Dust
Explosion, adiabatic value at constant volume Liquid
vapor phase transition Species i Inflow of material Mixture value one-film combustion model Outflow of material particle Reference state Solid Stoichiometric value two-film combustion model Threshold value in Chapter 9 Unburnt mixture Coordinate direction Initial condition Free stream property in Chapter 9

SPECIAL SYMBOLS
A^
A_
A^
Aλω
De
Di
E
F drag
E λω Lflow Lint Lk LM lp Mi

Molar value of quantity A
Flow rate of quantity A Dimensionless value of A Radiative absorption per unit wavelength per unit solid angle Effective diffusivity in a porous medium Diffusivity of species i Oxygen to fuel mass ratio Aerodynamic drag force Radiative emission per unit wavelength per unit solid angle Characteristic length scale of flow Integral microscale Kolmogorov microscale Markstein length Interparticle spacing in dust cloud Molar mass of species i Stoichiometric coefficient, mass of oxidizer per unit mass of fuel

xxxix

Preface
Combustible dust is both an explosion and a fire hazard. Over the last 300 years, coal mines, grain elevators, and numerous manufacturing facilities have experienced catastrophic accidents resulting in thousands of deaths and injuries and destroying hundreds of structures. The investigation and control of combustible dust hazards has been the subject of intense effort between two primary groups:
industrial safety experts and research scientists. The industrial safety experts have concentrated on evaluating the magnitude of the hazard for a given dust and developed various methods for protection. The research scientists have devoted their efforts to understanding the fundamental physical and chemical factors underlying combustible dust behavior. Both groups have produced a large volume of literature that suits the needs of their peers, but there seems to be little interaction or communication between these two groups. I believe that industrial safety experts could benefit greatly from the insights and knowledge produced by combustion scientists. My goal is for this book to help bridge that gap by demonstrating how a deeper understanding of combustible dust hazards can be achieved through combustion science.
Dust explosion dynamics is the investigation of the physical and chemical phenomena that govern dust explosions and related combustible dust hazards.
This text explores the use of fundamental principles of combustion science to evaluate the magnitude of combustible dust hazards in a variety of settings.
Models are developed to describe dust combustion phenomena using the principles of thermodynamics, fluid dynamics, transport phenomena, and chemical kinetics. Simple, tractable models are described and compared with experimental data when possible. The purpose of these simple models is to give the reader insight into the complex phenomena involved in dust explosions. Later, more sophisticated models are introduced to help the reader gain an appreciation for the challenges yet to be tackled.
Some excellent books have been written on dust explosions. But for the most part, books on dust explosions emphasize the industrial safety perspective. The serious student of combustible dust hazards should consult the following texts:
• • • • • • • •

Amyotte, P. An Introduction to Dust Explosions.
Bartknecht, W. Dust Explosions: Course, Prevention, Protection.
Barton, K. Dust Explosion Prevention and Protection.
CCPS/AIChE. Guidelines for Safe Handling of Powders and Bulk Solids.
Cheremisinoff, N.P. Dust Explosion and Fire Prevention Handbook: A Guide to Good Industry Practices.
Eckhoff, R. Dust Explosions in the Process Industries, Third Edition.
Frank, W.L. and S.A. Rodgers. NFPA Guide to Combustible Dusts.
Nagy, J. and Verakis, H.C. Development and Control of Dust Explosions.

xli

xlii

Preface

The texts cited above are largely devoted to the prevention of and protection from dust explosions. Three of these books do take a more fundamental approach.
The book by Dr. Amyotte offers many conceptual insights into the physical and chemical phenomena involved in combustible dust hazards. The book by Dr. Eckhoff is especially noteworthy and in that he has done a masterful job of summarizing both the pragmatic industrial investigations and the scientific research on combustible dust. The book by Mssrs. Nagy and Verakis summarizes the extensive work performed by the U.S. Bureau of Mines and does a particularly good job of describing and deriving integral models for explosion development and venting. But none of these books provides the foundation in combustion science that can assist the reader interested in gaining a deeper understanding of the scientific research on combustible dusts.
This book is different in that it focuses on exploring the combustion science underlying combustible dust hazards. Using simple models and detailed examples, it demonstrates how the fundamental principles of combustion science can be applied to better understand dust explosion phenomena. The intent of the book is to eliminate some of the empiricism used to explain dust explosions and to give the reader insight into the physical and chemical phenomena involved. To accomplish this goal, I will introduce you to just enough combustion science so that you can read, interpret, and use the scientific literature on combustible dusts.
One of the elements of hazard analysis is the evaluation of hazard severity or consequences. This book is about consequence analysis for combustible dusts. Consequence analysis uses mathematical models to make predictions about the severity of hazardous outcomes. There are four primary hazards of combustible dust: smoldering, flash fires, dust explosions, and flame acceleration effects (shock waves or detonations). The consequences of these hazards are addressed in this book through mathematical models based on combustion science. The models developed herein are simplified versions of more reliable, and strongly empirical, methods that are presented in the safety literature.
It is my hope that the insight derived from simple models will give the reader a better appreciation for the strengths and limitations of the more empirical design methods. There are a number of worked examples throughout the text.
These are mostly straightforward calculation exercises designed to give the reader an appreciation for the relative magnitude of physical quantities important to dust explosion dynamics.
The plan of this book reflects my philosophy for mathematical model building: start with a simple model, challenge it with empirical data, and improve the model as guided by the data. Thus, we will begin with models based solely on thermodynamics and neglect finite rate processes. Next finite rate processes are introduced through formulations using a burning velocity for the dust flame.
Models based on computational fluid dynamics (CFD) will complete the presentation. CFD models offer the opportunity to introduce important concepts from multiphase flow, turbulence, thermal radiation, and chemical kinetics.

Preface

There is no question that CFD models are the most powerful and comprehensive formulations, but they are also the most complex to use. CFD models impose a burden on the user to specify a number of model inputs that must either be measured or be estimated. Many CFD codes are proprietary and can be expensive to purchase or lease, and are therefore not always readily available to the analyst.
The emphasis on simpler models offers an opportunity to extract physical insight with less investment of resources. Similarly, in addition to the current literature, the reader will notice many citations to the older technical literature. In many of these older citations, one can find clever conceptual approaches and analytical techniques which offer deep insight into dust explosion phenomena. With the onset of robust numerical methods and fast, yet inexpensive, digital computers, one finds that much of the current combustion literature turns immediately to CFD simulations.
While CFD is a powerful tool, it requires a great deal more effort to develop results and may not be available to all analysts interested in dust fires and explosions.
This book is written at a level suitable for both students and practicing professionals in the engineering and scientific fields. My objective is to introduce the reader to specific concepts from combustion science that will lead to deeper insight into the behavior of combustible dusts. I hope you will not be deterred by the over 600 equations in this book. There is a large number of equations because I have worked out many derivations in detail so that the you, the reader, will not spend endless hours trying to retrace the footsteps of so many combustion scientists before you. I have purposefully omitted many topics from combustion science because they are not germane to my immediate goals. For the reader desiring a broader introduction to combustion phenomena, I recommend the following books:
• • • • • • • •

Glassman, I., Yetter, R.A., and Glumac, N.G. Combustion, Fifth Edition.
Kuo, K. Principles of Combustion, Second Edition.
Law, C.K. Combustion Physics.
Linan, A. and Williams, F.A. Fundamental Aspects of Combustion.
McAllister, S., Chen, J-Y., and Fernandez-Pello, A.C. Fundamentals of Combustion Processes.
Turns, S.R. An Introduction to Combustion, Third Edition.
Williams, F.A. Combustion Theory, Second Edition.
Zeldovich, Ya.B., Barenblatt, G.I., Librovich, V.B., and Makhviladze, G.M.
The Mathematical Theory of Combustion and Explosions.

A brief word about the references cited in this book. I have made no attempt to comprehensively review the scientific literature on combustible dust. I have been selective and have focused mostly on papers, reports, and books which I have found useful in my consulting practice. This is not to say that the omitted works are of an inferior quality, far from it. Eckhoff has presented an excellent survey of the scientific literature in his text on dust explosions. For the interested reader seeking a broader, more balanced introduction to the scientific literature, I strongly recommend his Dust Explosions in the Process Industries, Third Edition.

xliii

xliv

Preface

It is my hope that you will find this book useful in your efforts to manage combustible dust hazards. If you have any comments, criticisms, suggestions, or if you discover any typographical errors, I will be most grateful if you would send me an email at dustexplosiondynamics@gmail.com.

LIABILITY DISCLAIMER
Although the information in this book is believed to be factual and accurate, no warranty or representation, expressed or implied, is made with respect to any or all of the content thereof and no legal responsibility is assumed therefore. The equations, methods, and examples used are for illustrative purposes only and may not be suitable for engineering design. The reader assumes all liability in the application of the material in this book.

Acknowledgments
In some ways, this book has been 30 years in the making. My doctoral research project, published in 1986, was an investigation of aluminum dust explosions with a 20-L sphere. I have been interested in the combustion science of dust explosions ever since. Fiona Geraghty, acquisitions editor at Elsevier, opened the door for me to begin this project. Maria Convey and Laura Jackson at Elsevier have guided me through the writing and production process with both grace and patience. I am grateful to Fiona, Maria, and Laura for all of their efforts.
I would like to thank my attorney, Karen Shatzkin (Shatzkin & Mayer, New York), for her professional guidance. I thank my colleague, Timothy Myers, who voiced his support and encouragement on this book project from its inception. I have benefited greatly from the support of my friends and colleagues at Exponent over the years, and I am especially grateful for the guidance and encouragement I have received from my mentor and supervisor Harri Kytomaa.
I must also acknowledge the technical assistance of Brenton Cox, Sean Dee, and Stephen Garner, my colleagues at Exponent. They checked my mathematical derivations, corrected errors, and suggested a number of lucid edits to the text. With their assistance, I have made every effort to eliminate errors in the text. Any errors that remain are mine alone.
I am grateful to my parents, Jim and Dorothy, for their love and guidance throughout the years. While writing this book my adult children-Laura (and her husband, Scott), Andrew, and Peter-provided some desperately needed distraction and encouragement.
And finally, I thank my wife, Donna, for her love and support. She makes all good things possible.

xlv

CHAPTER

Introduction to combustible
dust hazards

1

Finely divided solid matter plays an irreplaceable role in modern technology. It has been estimated that three-quarters of all raw materials used in the chemical and process industries and half its products, on a weight basis, are particulate solids. At least 1% of the world’s electrical power is consumed in crushing and grinding operations.
Particulate solids are an eminently useful form of solid matter. They are especially well suited for storage, handling, transportation, and processing operations. However, simply converting a bulk solid material into a particulate material introduces new hazards. For example, a large block of quartz is relatively inert. But as a finely divided solid (sand) poured into a silo, the quartz becomes an engulfment hazard to personnel who enter the silo.
Any oxidizable material with a sufficiently small particle size is, under the right circumstances, potentially capable of combustion. In general, the finer the particle size, the faster the rate of combustion and thus the greater the hazard.
Easily oxidized, finely divided material is called combustible dust.1 Combustible dust presents three types of combustion hazards: smoldering fires, flash fires, and dust explosions. A dust explosion is the most severe of these hazards.
A dust explosion begins when a cloud of combustible dust is ignited. The ignition event can be thought of as a ball of flame. The flame creates a high temperature volume of gas which tends to expand into the unburnt portion of the dust cloud. As the surface of the flame expands it consumes fuel creating a larger volume of combustion products. The continued expansion of the burnt gases accelerates the flame causing it to consume fuel faster and faster. If the dust cloud is confined in a vessel or structure, the high temperature of the combustion products leads to a rise in pressure. If the rising pressure exceeds the strength of the confinement, the vessel or structure will rupture allowing the high pressure gas to expand into the surroundings.
Dust explosion dynamics is the study of the physical and chemical phenomena that govern the fire and explosion hazards of combustible dust. This book is written for the student or the expert who is interested in seeing how simple combustion models can yield insight into the physical and chemical phenomena that govern combustible dust hazards. From the perspective of safety risk assessment, these simple models will help the investigator gain a deeper understanding of the consequences of combustible dust hazards. However, this is not a book devoted 1

This definition is very informal and should not be confused with definitions for combustible dust that are based on government regulations, safety standards, or specific industry guidelines.
Dust Explosion Dynamics.
© 2017 Elsevier Inc. All rights reserved.

1

2

CHAPTER 1 Introduction to combustible dust hazards

to the important subjects of explosion protection, safety standards, or risk assessment. These topics are covered in several books cited in the references.
This book assumes the reader has taken undergraduate level courses in thermodynamics, fluid dynamics, heat and mass transfer, and some chemical kinetics. These are the foundation subjects for combustion. I will introduce certain fundamentals and key results from combustion science as needed to develop the elements of dust fire and explosion dynamics. Citations to combustion textbooks and the literature are given for additional reading and investigation. The combustion behavior of flammable gases and vapors tends to occupy the majority of attention in combustion texts. The unique hazards of combustible dusts garner less attention in these books.
To gain an appreciation for the science behind combustible dust hazards, a brief history of dust explosion research will be presented from the perspective of combustion science. Some basic aspects of combustion behavior are introduced and key terms are defined. I then establish seven important differences between combustible dusts and flammable gases. These differences will become the basis for organizing many of the empirical observations and combustion models to be discussed later in this book.
The goal in studying the combustion behavior of combustible dust is to better manage its hazards. Safety management has three basic components: hazard identification, evaluation, and control. The first two components, identification and evaluation, are based on laboratory testing. In a very brief fashion, I next define the common parameters used to evaluate combustible dust hazards and describe the typical test methods for characterizing combustible dusts. The task of hazard control requires some sense of how the hazards of combustible dust can reveal themselves in the real world. I describe some common hazard scenarios to provide a conceptual framework for thinking about these hazards. Finally, some of the basic dust explosion prevention and control strategies are summarized.
These sections are exceptionally brief as there are many good books and review papers available for further study.

1.1 HISTORICAL PERSPECTIVE ON COMBUSTIBLE DUST HAZARDS RESEARCH When speaking of an awareness of combustible dust hazards, there are two groups to consider: the technical community and the industrial community.
Unfortunately, the knowledge of combustible dust hazards has been slow to diffuse beyond specialists