【正文】 ous events. Since the famous mining catastrophe with over 1000 fatalities in Courri232?！癛esearch of Prevention of Gas Outbursts”, 2003, by the Department of Safety of Hunosa。a (Mieres) and Montsacro, in Riosa. This research study has taken place in both mines and has an unquestionable importance in orderto fulfill some gaps: to quantify some unknown parameters of the 8th Coalbed very related to mining hazards(such as gas pressure), to improve the mining sequence in the sublevel method (a factor very related, after Thielemann et al., 2001, with the risk of sudden outbursts), to establish the accuracy of some of the prevention measurements applied or to delimit the hazardous areas.2. Description of the Asturian Central basin and ofthe 8th Coalbed The 8th Coalbed of the Riosa–Olloniego unit, located in the Southwest of the Asturian Central Coal Basin (the largest coal basin in the Cantabrian Mountains, IGME, 1985), has CBM potential of about Gm3. This is around % of the estimated resources of the Asturian Central Basin and % of the total assessed CBM resources in Spain (Zapatero et al., 2004). Gm3 of the CBM potential of the 8th Coalbed belongs to San Nicol225。nez, 2004). The Riosa–Olloniego geological unit consists of three seams series: Esperanza, with a total thickness of 350 m, contains 3–6 coalbeds with a cumulative coal thickness of to m。s et al., 2004). Fig. 1 shows the geological map of the two coal mines, whereas Fig. 2represents a front view of both mines and the location of the instrumented areas. In this particular study, the 8th Coalbed is situated at a depth of between 993 and 1017 m, in an area of low seismi intensity. Instantaneous outbursts pose a hazard to safe, productive extraction of coal in both mines. The mechanisms of gas outbursts are still unresolved but include the effect of stress, gas content and properties of the coal. Other factors such as geological features, mining methods, bord and pillar workings or increase in rate of advance may bine to exacerbate the problem (Beamish and Crosdale, 1998). Some of the main properties of the 8th Coalbed favoring gas outbursts (Creedy and Garner, 2001。lez Nicieza / International Journal of Coal Geology 69 (2007) 253–266 255Fig. 1. Geological map.as well as in the different research studies cited in Section 1: the geological structure of the basin, the stress state of the coalbed and its surrounding wall rock and some properties of both coalbearing strata and the coalbed itself. The next paragraphs summarize the state of the research when this project started. Many researchers have studied relationships between coal outbursts and geological factors. Cao et al. (2001), found that, in the four mining districts analyzed, outbursts occurred within tectonically altered zones surrounding reverse faults。35 s) at 2 m depth, cm3 / (10 gndez, 1998). Particularly, in the Riosa–Olloniego unit, the gas content varies from to m3/t of coal (Pend225。35 s). Due to incidents detected during this research study, the limit value was reduced to cm3 / (10 gs (where 480 kPa were reached in the gas pressure measurements at the greatest depth). These parameters, together with the systematic measurement of concentration and desorption rate that were already being carried out by the mine staff, require monitoring and control. A gasmeasurementtube set was designed, for measuring gas pressure and its variations as well as the influence of nearby workings to determine outburstprone areas. The efficacy of injection as a preventative measure was shown by means of these measurement tubes. Injection decreases the gas pressure in the coalbed, although the test must be conducted maximizing all the precautionary measures, because gas outbursts may occur during the process itself. The instrumentation results indicated the convenienceof mining the 7th Coalbed at least one sublevel ahead of the 8th Coalbed. This means having pleted longwall caving of the corresponding sublevel both eastward and westward, and having allowed the necessary time to elapse for distention to take effect. This distention time was estimated between two and three months. The constructed instrumentation likewise allowed the effect of overlapping of workings to be measured: as the longwall caving of the coalbed situated to the roof of the instrumented coalbed approaches the area of advance of the 8th Coalbed, an increase in the pressure of the gas is produced in the 8th Coalbed. This may even triplicate the pressure of the gas and is more pronounced as the longwall caving approaches the position of the measuring equipment. A spatial range of the influence of longwall caving of some 55–60 m was estimated and a time duration of 2–3 months. The main contribution of this article resides in theproposal of measures of control and risk of gas outbursts that plement the systematic measurements in the mine itself, with the aim of improving safety in mining work. This proposal, apart from certain practical improvements in mining work, above all regarding the exploitation sequence, would involve the installation of gas measurement tubes before initiating the advance or at the overlap of workings. It would consist intemporarily detaining the advance in the 8th Coalbed when an overlap of workings may occur