Mine explosions
Introduction
Worst explosions
Year
loss of lives
Place
1962
299
Germany
1963
457
Japan
1965
331
Japan
1965
306
India
1965
144
Yugoslavia
1968
78
USA
1970
51
Yugoslavia
Mine explosions
Requirement of an explosions
Explosive substance:
Methane
Coal dust
Water gas
Fuel oil vapours
Hydrogen
Mine explosions
Methane:
Accumulation
large airways
Goaf
Drainage
Coal dust
Chief factor in causing intensive explosions
Mine explosions
Factors causing coal dust explosions
Fineness
Incombustible content
Volatile content
Moisture content
Age of coal
Occluded flammable gas
Mine explosions
Sources of ignition:
Frictional sparking
Explosives
Open lights
Electricity
Electrostatic sparking
Fires
Mine explosions
Electrostatic charge
Static electricity is caused by the movement of
electrons when dissimilar substances in contact with
each other are separated.
Examples:
1. Moving conveyor belt
2. Non-conducting fluids flowing through hoses.
3. Gas issuing from a nozzle under high speed
4. Human body:
• Contact of shoes with floor
• Working close to a machine generating static
electricity
Mine explosions
Characteristics of an explosion:
1. When flammable mixture of methane is ignited, temp.
rises to 2000 degrees Celsius.
2. A shock wave is produced that moves ahead of the
flame front and raises the dust cloud.
3. The most violent explosions occurs when mixture
contains 9.8% methane. Flame speed in this case may
go up to twice the speed of sound.
4. Speed of the flame front increases when it consumes
layers of coal dust and it may reach to 1100 m/sec.
5. The air in front of the pressure wave is compressed
adiabatically causing spontaneous ignition of dust
particles.
Mine explosions
6. Spontaneous ignition is known as detonation and
flame and shock wave travel at the same speed (2000
m/sec).
Relationship between flame Velocity and shock wave
Flame velocity (m/sec)
Shock wave velocity (m/Sec)
50
375
260
500
400
600
650
800
1000
1100
Mine explosions
Control of explosions:
1. Control over ignition sources
2. Control over flammable material
Stone dusting
Inert dust has the effect of slowing down the flame by absorbing
heat.
Difficulties:
1. Coal dust is more dispersible than stone dust
2. Intimate mixing of stone and coal dust is difficult.
Mine explosions
Barriers
1.Stone dust barriers
2.Water barriers
Stone dust barriers:
 Blast travels ahead of the flame. Barriers are designed
to be operated by the blast thus creating a dust cloud
before the flame of explosion arrives
 To ensure the dispersal of dust, the shelves are made
collapsible.
Mine explosions
 Shelves should collapse at the right time, too early or
too late collapse may severely reduce the effect of
stone dust
 The maximum spacing between two rows of shelves
is equal to number of kilogrammes of stone dust on
one shelf of the barrier.
 The recommended amount of stone dust is 30 kg/m
length of shelves for light barriers and 60 kg/m for
heavy barriers.
 Stone dust barriers may fail to arrest the flame if
methane is present in the form of roof layer.
Mine explosions
Factors to be considered in designing of barriers:
1.Total quantity of dust required
2.The stability of the shelves
3.The placement of the shelves
4.Position of the barrier
Storied barriers:
• Consist of two or more superimposed shelves.
These barriers are more effective than single-layer
shelf barrier
Mine explosions
Water barriers:
1. Water filled troughs operated on the same principle
as stone dust barriers.
2. The water is dispersed throughout the general body
of the area
3. Cooling effect is obtained by reducing heat.
4. Water troughs are made of pvc and of about 90 liter
capacity
5. Water barriers are designed to shatter and to give an
adequate dispersion of water.