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Bat Bags
Stone Dust Explosion Barrier
1. What is a Coal Dust explosion
2. How does an Explosion Barrier
work
3. What is a “Bat Bag”
4. How does the Alfabs “Bat Bag”
Stone Dust Explosion Barrier work
5. Conclusion
A coal dust explosion demonstration – Experimental mine in the USA.
What is a Coal Dust explosion
Possible ignition sources of Coal Dust explosions
• Spontaneous combustion
• Friction ignition of explosive concentration of methane
• High voltage cable arcing
• Lightning
What is a Coal Dust explosion
Description of a Coal Dust Explosions
• Ahead of the blast the air is still.
• As the explosion develops the front of the blast becomes a “shock
wave” that travels faster than sound and it is impossible to hear it
coming.
• The speed of the shockwave is between 1300km/h and 2500km/h. Even
faster for very strong explosions.
What is a Coal Dust explosion
Description of a Coal Dust Explosions
• The region behind the shockwave, ahead of the flame, experiences a
cyclonic force wind. The air is thick with dust scoured from every
surface in the roadway.
• Wind speeds range from 108km/h to 1600km/h for weak to fairly strong
explosions. Heavy equipment is over turned and anything loose
becomes a missile.
• The distance between the shockwave and the flame front increases as
the explosion travels further as the shock wave is considerably faster
than the flame.
What is a Coal Dust explosion
Description of a Coal Dust Explosions
• The flame travels at speeds slightly greater than the wind, but slower
than the shockwave. This means that it travels in the dust laden air
rather than its own combustion products.
• Speeds are between 120km/h to 1900km/h for weak to fairly strong
explosions.
• Behind the flame the air is still but still very hot. Soon it will cool and
contract drawing gas back towards the point of ignition.
What is a Coal Dust explosion
Description of a Coal Dust Explosions
• By comparison to a methane or gas explosion that will burn relatively
clean, a coal dust explosion will likely be fuel rich. This will generate
extremely high levels Carbon Monoxide (CO) in the mine atmosphere.
• With damage to the mines ventilation system likely, these high levels
of Carbon Monoxide often prove fatal to any miners who may have
survived the initial explosion.
How does an Explosion Barrier work
How do Explosion Barriers Work?
• Any passive explosion barrier relies on the fact that the wind blast or
shock wave from an explosion travels ahead of the flame.
• The energy in the wind blast is used to disperse the suppressant into
the the path of the oncoming flame so that the flame will be
extinguished.
• Once the flame is extinguished propagation ceases and the energy
behind the wind blast will disperse as it travels though the mine and
intersects other roadways.
• The problem faced by anyone who must design an explosion barrier is
that there is no way to know how strong any particular explosion may
be.
How does an Explosion Barrier work
Why use explosion barriers?
• An explosion should always be contained close to the point of ignition
when it is likely to be relatively weak.
• Protection of an entire mine against a very strong well developed coal
dust explosion would require very high levels of incombustible dust
content in every mine roadway – this is considered impractical and
difficult to achieve.
• Explosion barriers provide additional protection to roadways where
high levels of coal float dust are likely to accumulate and high levels of
incombustible dust are difficult to maintain.
• Explosion barriers protect the rest of the mine from high explosion risk
areas.
How does an Explosion Barrier work
History of Stone Dust used as an Explosion
Suppressant
• Professor Cybulski of Poland originally started experimenting with the
use of Stone Dust as an explosion suppressant in the 1920’s.
• As head of GIG in Poland, Professor Cybulski continued his research on
the use of stone dust as an explosion suppressant which led to the
publication of his book in the 1970’s called “Investigations on stopping
coal dust explosions by stone dust barriers.”
• Professor Cybulski’s research and book have led to and formed the
basis of many stone dusting practices around the world including
underground coal mining industries in Australia, South Africa, North
America and Europe.
How does an Explosion Barrier work
History of Stone Dust used as an Explosion
Suppressant
• In the 1990’s, carrying on from Cybulski’s research the method of using
Stone Dust in “Bat Bags” to form an explosion barrier was developed
and testing began.
• Physical testing was carried out in South Africa, Germany, Australia
and the experimental mine Lake Lynn in the USA.
• The use of “Bat Bags” as an explosion barrier is now considered Best
Practice is countries such as Australia and South Africa.
What is a “Bat Bag”
What is a “Bat Bag”?
A “Bat Bag” is a specially designed, tested
and certified Bag, Hook and Collar that
holds 6kg of stone dust.
The “Bat Bags” are hung in groups from the
roof of the coal mine and individually they
form part of a passive stone dust explosion
barrier.
Like the animals Bats, our bags hang from
the roof in groups in the dark, hence why
we call them “Bat Bags”.
How does the Alfabs Bat Bags
Stone Dust Explosion Barrier work
The Alfabs Stone Dust
Explosion Barrier
How does the Alfabs Bat Bags
Stone Dust Explosion Barrier work
• “Bat Bags” are hung in groups from the roof of the coal mine to form
an “Explosion Barrier”.
• The size of the barrier and the amount of “Bat Bags” in the barrier are
calculated by a formula using the size of the roadway.
• A certain level of redundancy has been built into the barrier design so
that even if individual bags are damaged or missing, the barrier will
still be compliant.
How does the Alfabs Bat Bags
Stone Dust Explosion Barrier work
• In the case of an explosion underground, the shockwave from the
explosion ruptures the individual “Bat Bags”.
• The wind blast following the shockwave disperses the previously
contained stone dust into the atmosphere.
• The stone dust then forms a curtain of suppressant that suppresses
the flame from the explosion.
• Once this has occurred, propagation of the coal dust explosion ceases.
The energy from the shockwave begins to dissipate as explosion
travels outbye.
How does the Alfabs Bat Bags
Stone Dust Explosion Barrier work
Testing Certification and Compliance
• The individual components of the Alfabs “Bat Bag” have all been
destructively tested by SIMTARS. SIMTARS are a mine safety technology
service and testing organisation run by the QLD state government in
Australia.
• Testing was carried out according to Australian Standard - AS1199-2003
and to satisfy the requirements of the Australian state of NSW specific
underground coal mining legislation ( MDG3006 MRT5 ).
How does the Alfabs Bat Bags
Stone Dust Explosion Barrier work
Testing Certification and Compliance
• The testing found that the components of the “Bat Bags” operated at a
dynamic pressure ranges as low as 4.65kPa to 8.37kPa.
• These results and methods have been published in test report number
R 1250664 2004/2005.
• A random sample of “Bat Bags” from each and every batch is tested on
behalf of Alfabs by SIMTARS, SIMTARS provide Alfabs with a third party
testing and quality control capability and produce test results for every
batch of “Bat Bags” before they are sent to our customers.
How does the Alfabs Bat Bags
Stone Dust Explosion Barrier work
Benefits of the Alfabs “Bat Bag” Stone Dust Explosion
Barrier
• Individual bags are light weight (6kg) and easy to handle for installation.
• Stone Dust is sealed inside each bag, thus protected from the wet and
humid mining environment.
• The bags are easy to see and inspect, each bag is conveniently marked
with a fill line so during installation and inspection the end user can
easily identify that the bag is filled with the correct amount of stone
dust to ensure the barrier remains intact and compliant.
How does the Alfabs Bat Bags
Stone Dust Explosion Barrier work
Benefits of the Alfabs “Bat Bag” Stone Dust Explosion
Barrier
• Each bag is fitted with a tested and proven hook and collar design that
allows easy installation of the bag from the roof of the mine and
underneath roadway obstructions.
• The “Bat Bag” explosion barrier can be installed during mine roadway
development and be left in place without the need for ongoing
maintenance.
Conclusion
• Coal Dust Explosions are a principal hazard risk in all underground coal
mining operations in that they have the potential to result in multiple
fatalities and the total loss of the mining operation.
• Without the use of an explosion barrier, any mine operator is increasing
their exposure to a catastrophic explosion.
• Bat Bag Explosion Barriers have been tried and tested around the world
and in many regions are now considered as Best Practice.