Materiały konferencyjne SEP 1992

374 Underground Explołtation School * 92 1. Introductlon Outbursts of coal and gases have been registered łn the western part of Ostrava-Karvina Coalfield sińce 1894. Outburst prone part is formed by the so called Ostravian beds characterł- zed by rather thin coal seams (0,4 - 1,5 m) and very complex tectonical structure Including intensive folding. Outbursts of methane type are prevai1ing. Outbursts of carbon dioxide type represent about one third pEirt of total nuraber. Typical outburst phenomena could be deser ibed by several main features: - pneumatic transport of flne-grained coal with remarkable amount of very fIne coal powder which could be transported even very far from a face» - extremely great amount of released gas, - circular gas chSLnnels łn bursted coal, - a cavity with typical "pear" shape is formed as a conseąuence of the outburst, - the role of rock stress is not very visible. The state of the outburst prone is monitored by routine measure- ments consisting usually of the parameters: - gas pressvire index {3 m borehole) - desorption ratio. Gas content in the seam and strength of coal are determined by special tests. The main principle of outburst prevention is based on decreasing of the gas pressure in the seam. There are three main routine measures: - distress blasting - large diameter boreholes - water injection. Apart from it there are some phenomena which decline from above ment ioned features. In such cases the reiiability of the routine monitoring and effectiveness of usual distressing measures are lower. Then the phenomena could occur suddenly and unexpectedly and become more dangerous for people working there.