Grain dust

1. CHARACTERISTIC OF DUST AND
PREVENTION OF DUST EXPLOSION
SUBMITTED BY
K.Y.RAJALAKSHMI

2. GRAIN DUST
• Manipulation of grain, handling, storage,
processing any operation - produces dust
• Consists of outer parts mixed with crushed
and brokens
• Production of grain dust is 100000 metric
tonnes
• Maize processing – more dust

3. Composition
moisture content - 5-11%
carbohydrates - 30-70%
Proteins - 6-20%
Lipids - 1- 4 %
Ashes - 3-40%
Fiber - 7- 15%

4. Characteristic of dust
• Average size of particles- 15-120 µm
• Particles greater than 400 µm- risk of human
and not increase the primary explosion
• Smaller particles less than µ orless
• Total external surface area 0.6- 2 m2/g
(soyabean – smallest, sorghum – largest)
• Velocity ( large one – 3m/s, smaller – 0.4 m/s)

5. • Specific density 1.4- 1.7 per unit volume
• Bulk density depends on nature of material
• 200-300 kg/m3 for wheat
• 250 – 300 kg/m3 for soybean
• 100-300 kg/m3 for sorghum
• Dust particles are not compressed – weight
can vary(150 – 350 kg/m3)
• Heat of combustion – 4030 cal/g(presence of
organic material)

6. • Soybean – low heat of combustion and rice
have high
• Concentration of dust inhaled by workmen
sample should taken 1.5 m above ground
ILL EFFECTS
• Maximum concentration upto 15 mg/m3
• Particle inhaled by men cause allergic and
lung diseases
• Skin irritation due to clipper barley dust –
clipper scabies

7. Difference between grain and dust
Dust
• Arsenic (2-50 ppm)
• Lead – 10 ppm
• Iron content 20- 40 times
greater
• Equal amount of copper
• Less phosporus
Grain
• Less than 1 ppm
• Less than 1 ppm
• Iron content is low
• Equal amount of copper
• More amount of phosporus

8. FACTORS CAUSING EXPLOSION
Factors to produce explosion are
• Minimum energy required for ignition of grain dust (
flame at 10 cm long)
• Minimum explosive concentration
• Characteristic of dust includes – moisture content,
diameter of particles
• Ignition temperatures ( cloud of air and dust/ layer of
air and dust)
• Pressure permitting the explosion
• Speed at which pressure increases
• Limiting concentration of oxygen

10. RISK OF EXPLOSION
• Foreign material mixed with dust cause
explosion
• Gas and vapour have a synergistic effect in
dust explosion
• First explosion in 1784 – flour mill at turin-

12. DUST EXPLOSION PHASES
• Primary and secondary explosions.
• Primary and secondary explosions often are
so close together (a split second apart) that
they may be heard as one explosion or a
series of explosions, like rolling thunder.
• The primary explosion is caused by
confinement of airborne dust in contact with a
heat source that ignites the dust.

13. • pressures of 2 pounds per square inch during
primary explosions, with secondary explosion
pressures greater than 80 pounds per square
inch.
• if a dust explosion is limited to a primary
explosion because of good housekeeping and
sanitation, far less damage is done than if
secondary explosions occur

14. Various cause triggering explosion
• Metal work done at high temperature
• Hot surfaces
• Defective electrical equipment
• Heating from friction during transport
• Fire
• Flammable liquids
• Sparks cause by various factors

15. FACTORSEXPLOSION
• Reducing the formation of dust
• Control of insects that generate dust
• Equipment for the control of dust
• Improving the equipment for collection of
dust
• Improving the quality of air in grain storage
facilities
• Transport and stocking of silos