Dust is a common in process industries that manufacture, store and handle particulate material. More than 70% of dusts processed in industries are combustible. Dust explosion regularly occur in process industries, cause serious damage and live loss. Dust explosion was found in literature since 1785 and the records are available from the 20th century. Lot of experiments were done to control explosions occurring in coal mines and other processing industries, but stills explosions are occurring in different countries due to different dusts, these accidents disclose that there are still some technical problems unsolved. Industrial technology in India is similar to develop countries but information relevant to dust explosion occurring in India is almost negligible because in most accidents that occur in India the broad term explosion is used and recorded while the type of explosion goes unpublicized. It is impossible to eliminate dust explosion but it can be reduced by using different methods.

1. IJSRD - International Journal for Scientific Research & Development| Vol. 2, Issue 09, 2014 | ISSN (online): 2321-0613
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A Review: Dust Explosion of Bulk Solids
Harpreet Singh1
1,2
Department of Mechanical Engineering
1
Marwadi Education Group of Institutions, Rajkot, India
Abstract— Dust is a common in process industries that
manufacture, store and handle particulate material. More
than 70% of dusts processed in industries are combustible.
Dust explosion regularly occur in process industries, cause
serious damage and live loss. Dust explosion was found in
literature since 1785 and the records are available from the
20th century. Lot of experiments were done to control
explosions occurring in coal mines and other processing
industries, but stills explosions are occurring in different
countries due to different dusts, these accidents disclose that
there are still some technical problems unsolved. Industrial
technology in India is similar to develop countries but
information relevant to dust explosion occurring in India is
almost negligible because in most accidents that occur in
India the broad term explosion is used and recorded while
the type of explosion goes unpublicized. It is impossible to
eliminate dust explosion but it can be reduced by using
different methods.
Key words: Dust explosion is one of the serious problems in
industrial. It is impossible to eliminate dust explosion
problem, but prevent it by using different method like by
using vent holes, Flameless vents etc.
I. INTRODUCTION
Dust explosions were found in literature in 1785[1]. In
Europe coal mining was an important industry and
explosions due to coal dust were recognized earlier but in
starting scientists did not accept this. It was found in 1803
that coal dust in passageways had burned and cause flame as
well as violence of coal mine. In 1800s many more
statements shows explosions because of coal even thought
there was no fire damp. A dust explosion crops up by rapid
combustion of fine combustible particles in air. Due to this
there is libration of gaseous products with huge pressure
rise; this pressure rise will destruct plant, property and lives
of people. Smaller will be the particle size, more fast and
explosive burning will takes place, till a stage is reached
when particles are too much fine and they join to form
nugget. The ignited combustible dust cloud would only
cause a flash fire if dust cloud is unconfined, but if the
ignited dust cloud is confined the gases released by
combustion of cloud may result in rapid development of
pressure and results to explosion. Explosion violence not
only depends upon degree of subdivisions, it also depends
upon energy released per unit confinement area. In some
situations the destructive explosion also occurs even when
cloud is not confined. Conditions required for a dust
explosion to occur are presence of oxidant, combustible dust
cloud, presence of oxygen, confinement area and an ignition
source to trigger dust cloud. The flame or spark that trigged
a dust explosion can be produced by blowtorch, static
electricity, electric spark, friction or any open flame. More
than 70% of dusts processed in industries are combustible
[1]. Dust composed of sugar, cotton, coal, flour, starch,
grain, combustible metallic dust or other organic materials,
which are highly explosive. Certain metallic dusts like
magnesium, aluminum are also explosive. Grain elevators,
size reducer, packing dust conveying- manual or mechanical
cyclones, electrostatic precipitator, settling chambers,
classifying operations mixing and blending operation
storage ,filter scrubbers, bag unloading stations, unloaders
are mainly subject to dust explosion (where there is a
change of dust collection there will be a chance of dust
explosion). Dust explosion is effected by particle size (Finer
the particle size more chances of explosion), dust
concentration (between LEL and MEL), oxidant
concentration (more percentage of oxidant or gases more
will be possibility of explosion), ignition temperature,
turbulence of dust cloud, admixed inert dust concentration.
II. DUST EXPLOSION
When a very fine dust gets suspended in air and is ignited by
heating element or sparked, it will cause dust explosion. A
dust explosion will cause a very rapid burning and due to
this rapid burning there is release of gases with a huge
pressure rise of explosive force that will cause, damage
property, plant, and people lives. Initially one particle of
dust will ignite and after that chain will start that will ignite
the whole cloud. Dust cloud will be ignited by heating
element such as spark, electric motor, heating operations etc.
Sometimes dust clouds will also be ignited by electrostatic
charge that is produced by friction between the particles.
Fig 1.1: Burnout sugar after explosion [2]
A. Mechanism of Dust Explosion
Surface area of dust is very large as compared to their mass.
Burning will occur on the surface of dust where it reacts
with oxygen. For 1.0 kg of a material of spherical shape
with density and surface area of 1.0 g/cm3
, 0.3
m2
respectively, if this material is crushed into spheres of 50
micrometer diameter then surface area is increased to 60m2
.
This large amount of increased surface area of dust allows
the material to burn much faster. Finer will be the particle
size; more rapid and explosive burning will occur, till a
limiting stage is reached when particles are too much fine in
size. At this stage cohesive force of particles increase and
they tend to form nugget.
B. Conditions for Dust Explosion [3]
For dust explosion to occur certain conditions are required
to fulfill; without fulfillment of these conditions there is no
chance of dust explosion to occur:

2. A Review: Dust Explosion of Bulk Solids
(IJSRD/Vol. 2/Issue 09/2014/043)
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 The dust which will form cloud must be
combustible.
 Supply of oxygen must be there.
 Finer the dust will be, more will be the chance of
dust explosion.
 Dust per unit volume must be in explosive.
 Without Ignition source explosion will not occur.
Fig. 1.2: Explosion Pentagon [1]
C. Dust Cloud Formation in Environment [3]
 Interparticle forces (cohesion) between dust
particles.
 Entrainment of particles when shock wave passing
across deposit surface.
 Transport of dust particles in turbulent gas flows.
D. Areas of Dust Explosion [1, 4, 5]
Areas where dust explosion mainly occurs are
 Filters
 Tray drier
 Cyclones
 Electrostatic precipitator
 Scrubbers
 Driers
 Unloaders
 Storage
 Mixing
 Bag unloading stations
 Fluidizing bed drier
 Packing
 Pneumatic driers
 Screening and classifying operation
 Conveying – manual or mechanical
 Pulverizers
Fig 1.3: Explosions occurred in Germany [1]
E. Factors Influence Explosion [1, 6, 7, 8, 9]
 Dust Particle size
 Dust concentration
 Oxidant concentration
 Dust cloud Ignition temperature
 Turbulence of dust cloud
 Maximum rate of pressure rise
 Admixed inert dust concentration
 Presence of flammable gases
F. Types of Dust Explosions [10,11]
There are two types of dust explosions
 Primary explosion
 secondary explosion
1) Primary explosion
The combustible dust will form cloud in equipment’s such
as mills, mixers, screen, dryers, cyclone separators, hoppers,
bucket elevators, silos, aspiration ducts, and pneumatic
transport system and when this cloud got ignited this will
cause increase in pressure and destruction occurs. This
explosion occurred in equipment’s called primary explosion.
2) Secondary explosion
Fig 1.4: Secondary dust explosion [12]
Secondary dust explosion occurred when a dust
layer is disturbed by primary explosion and form a second
dust cloud which will be again ignited. Small amount of
dust layer occupies a very little space but when it disturbed
once then it will form dangerous cloud.
G. Flame Propagation Process in Dust Clouds [3]
 Laminar and turbulent flames propagation in dust
clouds.
 Mechanism of heat transfer through three modes;
conduction, convection and radiation.
 A blast wave property is a function of properties of
burning dust clouds.
 Effects of blast wave on human lives as well as
structures.
 Ability of blast wave from dust explosion to
transfer dust layer into explosive dust clouds.
H. Cause Which Trigger Dust Cloud [1, 13]
 Hot work
 Flames and direct heat
 Shock waves
 Electrostatic sparks
 Friction sparks
 Electrostatic sparks
 Impact sparks
0
5
10
15
20
25
30
35
40 wood and wood
products
Total
Coal Dust

3. A Review: Dust Explosion of Bulk Solids
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All rights reserved by www.ijsrd.com 196
 Self-heating
 Static electricity
 Lightning
 Heating surface
I. Prevention from Dust Explosions [14]
There are certain methods to prevent dust explosions and
their effect these are:
 Elimination of ignition sources
 By using pressure relief vent holes
 By inerting the dust
 By static electrification of powder during
 Pneumatic transport
 By magnetize surfactants
 Flameless venting
1) Elimination of ignition sources
It is essential that all sources of ignition are eliminated from
hazardous area like naked flames, lights, smoking, electrical,
gas cutting or welding equipment.
Other precautions
 Earthing and bonding of all equipment to prevent
an accumulation of static electrical charges.
 Use of magnetic separator to prevent the intake of
ferrous materials into dust producing grinding
mills.
 Use of nonferrous blades in fan through which dust
passes.
 Using non sparking tools.
 Avoiding the use of high speed shaft and belts
 Eliminating friction sparks
 Eliminating hot surfaces, so that ignition of dust
deposits
2) Relief of explosion pressure [16]
If ignition of combustible dust cloud takes place in an
enclosed area then there will be a rapid rise of pressure
which damages the plant and building. There must be vent
holes, explosion vents are provided for releasing of this
excess pressure so that damage of plant will be minimized.
The vents that we are providing must be able to respond
instaneously. There must be some safety factor between the
operation of the vent and brusting the pressure of the plant.
The products of dust explosion are discharged by using vent
hence keeps the explosion pressure lower than that of design
strength and protect the vessel from effects of explosion.
Explosion must be vented to the safe place in the open air.
3) Safe venting [16]
The most effective way of obtaining safe venting is to locate
the plant in the open air so that the flames, hot gases are
vented away. If this is not possible then the explosion relief
vents, inside the workroom must be linked to the outside,
using duct. This ducting must be strong enough to withstand
high pressure and should be as short and straight as much as
possible. Longer the duct will be, less effective it is.
Increasing the diameter of the duct as the duct length
increases is essential to overcome this problem. A distance
of six meter is the usual maximum length for an explosion
relief vent duct. At six meter length the cross section of the
duct must be twice the area of the vent itself or the vessel
must be capable of withstanding twice the pressure required
for that vent area.
4) Inerting of dust [6, 17]
When the dust is collected in an enclosure, the explosion is
prevented by inerting the dust. Due to inert gas oxygen
content in the atmosphere is reduced to that level where
combustion will not occur. The reactivity of dust, strength
and duration of ignition source must be taken into
consideration when choosing an inerting gas as the oxygen
level required for an inert atmosphere. CO2 is more effective
than nitrogen as an inert gas for dust clouds of most
carbonaceous materials. Nitrogen is more suitable for higher
temperatures.
5) By magnetize surfactants [8]
Attraction of a Solid surface towards the water is measured
by contact angle. It is an important parameter for liquid’s
wettability of dust. The smaller will be the contact angle, the
better the solution’s wettability of dust will be. The
available researches suggested that magnetization of water
can reduce the surface tension. So water droplets divide into
large number of small drops which will decrease angle of
contact and results in the better wettability of water dust.
6) Flameless venting [15]
Fig 1.5: Explosion, without and with Flameless venting
A flameless Venting device is used to keep gases
safely out of the confined area after explosion. It is made up
of layers of metal mash, which does not permit fire to go
out. This not only stops fire, also stop dust particles after
explosion. Some are designed to suit particular storage and
process equipment such as dust collectors, bins, hoppers,
dryers, silos, cyclones also transport equipment such as
screw conveyor, belt conveyor and bucket elevator.
Fig 1.6: Flameless vents type and their use [15]
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