ALFABS Hunter Valley | Wollongong | Mackay Engineering | Protective Coatings | Mining | Equipment Hire | Rail 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.