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Water-jet-assisted cutting involves the use of a mechanical cutting bit in combination with a high-pressure water jet directed just in front of the bit tip. Such a jet can offer benefits in terms of improved cutting, reduced dust and fines, and improved bit wear. The USBM, through a contract with the British NCB, has researched the use of water-jet-assisted cutting on roadheaders. After several engineering design problems were overcome, this programme led to the successful underground testing of these roadheaders. Today, more than 60 water-jet-assisted roadheaders are in operation around the world and numerous others are on order. This paper details the evolution of these machines and the benefits to be gained by their use., Water-jet-assisted cutting involves the use of a mechanical cutting bit in combination with a high-pressure water jet directed just in front of the bit tip. Such a jet can offer benefits in terms of improved cutting, reduced dust and fines, and improved bit wear. The USBM, through a contract with the British NCB, has researched the use of water-jet-assisted cutting on roadheaders. After several engineering design problems were overcome, this programme led to the successful underground testing of these roadheaders. Today, more than 60 water-jet-assisted roadheaders are in operation around the world and numerous others are on order. This paper details the evolution of these machines and the benefits to be gained by their use.

The cyclone classifies respirable size dust particles, and is used for both stationary and personal sampling. Investigations using photometric mass sensing measurements have shown that if the cyclone is sampling in a high wind it will oversample relative to ore sampling in a low wind. Orientation of the sampler introduced measurable differences in sampling efficiency at higher wind velocities. A shield placed around the cyclone diminisihes the effects of wind velocity and sampler orientation on sampler performance., The cyclone classifies respirable size dust particles, and is used for both stationary and personal sampling. Investigations using photometric mass sensing measurements have shown that if the cyclone is sampling in a high wind it will oversample relative to ore sampling in a low wind. Orientation of the sampler introduced measurable differences in sampling efficiency at higher wind velocities. A shield placed around the cyclone diminisihes the effects of wind velocity and sampler orientation on sampler performance.

Various stopping construction techniques have been evaluated on the basis that airtightness can be enhanced by brushing rather than troweling on mortar sealant and that modified mortars (containing glass fibre and other additives for increased strength and adhesion) should improve sealing performance. Air leakage tests comparing conventional with modified stoppings, were done when the stoppings were built, after 6 months, after 1 year and following simple maintenance. Results indicated that building and maintenance of stoppings can be improved if: the area where a stopping is to be built is properly prepared; stoppings are periodically examined for leaks; and stoppings found to be leaking, especially at the perimeters are resealed., Various stopping construction techniques have been evaluated on the basis that airtightness can be enhanced by brushing rather than troweling on mortar sealant and that modified mortars (containing glass fibre and other additives for increased strength and adhesion) should improve sealing performance. Air leakage tests comparing conventional with modified stoppings, were done when the stoppings were built, after 6 months, after 1 year and following simple maintenance. Results indicated that building and maintenance of stoppings can be improved if: the area where a stopping is to be built is properly prepared; stoppings are periodically examined for leaks; and stoppings found to be leaking, especially at the perimeters are resealed.

A test system was developed for measuring airflow in the NIOSH ventilation gallery using a three-axis ultrasonic anemometer. The gallery was used to simulate face airflow conditions in underground mines with a blowing curtain. Airflow data collected at multiple sampling locations were used to draw airflow profiles for different curtain setback distances, intake flow quantities and entry widths. Methane was released at the face and measured to generate methane distribution profiles in the area between the curtain and the face. Entry geometry had a significant effect on airflow patterns, and they in turn affected the distribution of methane in the entry. Flow measures at and parallel to the face was a good predictor of methane dilution and removal within two feet of the face., A test system was developed for measuring airflow in the NIOSH ventilation gallery using a three-axis ultrasonic anemometer. The gallery was used to simulate face airflow conditions in underground mines with a blowing curtain. Airflow data collected at multiple sampling locations were used to draw airflow profiles for different curtain setback distances, intake flow quantities and entry widths. Methane was released at the face and measured to generate methane distribution profiles in the area between the curtain and the face. Entry geometry had a significant effect on airflow patterns, and they in turn affected the distribution of methane in the entry. Flow measures at and parallel to the face was a good predictor of methane dilution and removal within two feet of the face.

The delivery and distribution of intake air at the face is critical for effective face ventilation. Improved techniques for monitoring the movement of intake air to the face are needed. A test system was developed and a computer program written for using a three-axis ultrasonic anemometer to measure air flow in a simulated mine entry. Results of tests conducted in the entry showed that the anemometer is a valuable tool for measuring mine air-flow conditions near the face., The delivery and distribution of intake air at the face is critical for effective face ventilation. Improved techniques for monitoring the movement of intake air to the face are needed. A test system was developed and a computer program written for using a three-axis ultrasonic anemometer to measure air flow in a simulated mine entry. Results of tests conducted in the entry showed that the anemometer is a valuable tool for measuring mine air-flow conditions near the face.

A controlled recirculation system was evaluated at the Texas Gulf trona mine in Granger, Wyoming. A 1.52 m diameter, 37.3 kW vane axial fan was installed in a crosscut between the intake and return airways and recirculated approximately 31.4 m3/s of air back into the intake. This amounted to a recirculation factor of approximately 20% of the return air which was part of the primary ventilation to three different continuous miner sections. The results of this study showed only small increases in dust, while all other mine contaminants (methane and carbon monoxide) remained at such low levels that it was impossible to determine any relative changes from the recirculation system. A brief SF6 tracer gas analysis study was undertaken to more precisely determine an increase in mine contaminants as compared to gas chromatography., A controlled recirculation system was evaluated at the Texas Gulf trona mine in Granger, Wyoming. A 1.52 m diameter, 37.3 kW vane axial fan was installed in a crosscut between the intake and return airways and recirculated approximately 31.4 m3/s of air back into the intake. This amounted to a recirculation factor of approximately 20% of the return air which was part of the primary ventilation to three different continuous miner sections. The results of this study showed only small increases in dust, while all other mine contaminants (methane and carbon monoxide) remained at such low levels that it was impossible to determine any relative changes from the recirculation system. A brief SF6 tracer gas analysis study was undertaken to more precisely determine an increase in mine contaminants as compared to gas chromatography.

Strata convergence will cause cracks and joint openings in masonry stoppings, resulting in significant air leakage losses. Where the problem is severe complete structural failure of the stopping can ultimately occur. Ideally, a stopping should maintain high resistance to air flow, while yielding to strata convergence. By incorporating a polyisocyanurate rigid foam material within the masonry block structure, stopping service life can be increased in mines experiencing strata convergence problems such as floor heave, roof loading, and lateral rib movement., Strata convergence will cause cracks and joint openings in masonry stoppings, resulting in significant air leakage losses. Where the problem is severe complete structural failure of the stopping can ultimately occur. Ideally, a stopping should maintain high resistance to air flow, while yielding to strata convergence. By incorporating a polyisocyanurate rigid foam material within the masonry block structure, stopping service life can be increased in mines experiencing strata convergence problems such as floor heave, roof loading, and lateral rib movement.

A review is presented of gas sampling equipment, methods for taking samples and the nature of various gases and gas-related equations that should be analysed and related to changes over time to assist in determining if a heating event is taking place. Atmospheric status equations are tools to help personnel determine the condition of underground atmospheres. Some equations provide realistic analyses of atmospheric conditions as the mine or section continues to be ventilated and others are used once the mine or section has been sealed. Prior to re-entering a sealed area, equations exist that can enable personnel to determine if the fire will rekindle once fresh air is reintroduced. An equation is also available that can be used to determine if the atmosphere could become explosive when reintroducing fresh air., A review is presented of gas sampling equipment, methods for taking samples and the nature of various gases and gas-related equations that should be analysed and related to changes over time to assist in determining if a heating event is taking place. Atmospheric status equations are tools to help personnel determine the condition of underground atmospheres. Some equations provide realistic analyses of atmospheric conditions as the mine or section continues to be ventilated and others are used once the mine or section has been sealed. Prior to re-entering a sealed area, equations exist that can enable personnel to determine if the fire will rekindle once fresh air is reintroduced. An equation is also available that can be used to determine if the atmosphere could become explosive when reintroducing fresh air.

This US Bureau of Mines study is based on a review of US mine fire accidents that occurred from 1970 to 1989. The study found that the most prolific source of haulage entry fires was the inadvertent grounding of trolley wires. 15 out of 40 trolley wire fires resulted from not maintaining adequate clearance between the vehicle and the trolley wire. Several novel fire prevention and control ideas proposed include: discriminating power isolation devices, wire cutting devices, more accessible fire extinguishers, vehicle overcurrent protection, and vehicle fire supression., This US Bureau of Mines study is based on a review of US mine fire accidents that occurred from 1970 to 1989. The study found that the most prolific source of haulage entry fires was the inadvertent grounding of trolley wires. 15 out of 40 trolley wire fires resulted from not maintaining adequate clearance between the vehicle and the trolley wire. Several novel fire prevention and control ideas proposed include: discriminating power isolation devices, wire cutting devices, more accessible fire extinguishers, vehicle overcurrent protection, and vehicle fire supression.

Reducing time delays is the most important factor in saving lives. Each event during a fire was measured in terms of its duration and the effectiveness of any action taken to improve survival was measured in terms of the time it saves. By ranking actions according to time saved it was found that a combination of actions was most effective. This combination was: installing lifelines; moderately decreasing air leakage; and decreasing the fire growth rate., Reducing time delays is the most important factor in saving lives. Each event during a fire was measured in terms of its duration and the effectiveness of any action taken to improve survival was measured in terms of the time it saves. By ranking actions according to time saved it was found that a combination of actions was most effective. This combination was: installing lifelines; moderately decreasing air leakage; and decreasing the fire growth rate.

In early June 1986, an underground fire of unknown origin erupted in one of several entries of the Orchard Valley coal mine in Colorado. Control of the fire was unsuccessful and to prevent further damage and reduce the possibility of an explosion, all portals and shafts to the mine were sealed. Samples of mine fire gases were taken from sampling ports that were placed through the mine seals and boreholes that were drilled after the fire. The activities that took place within the first two years of the mine being sealed are recounted. Descriptions of the gases that were analysed and the mine atmosphere status equations generated from the analysed gases are presented. The gases were analysed by chromatography and included standard atmospheric gases as well as higher hydrocarbons that are found in postfire atmospheres. Nine equations were used to evaluate what was occurring within the sealed mine. Following a description of the rationale behind each equation, the 2-year trend is briefly analysed., In early June 1986, an underground fire of unknown origin erupted in one of several entries of the Orchard Valley coal mine in Colorado. Control of the fire was unsuccessful and to prevent further damage and reduce the possibility of an explosion, all portals and shafts to the mine were sealed. Samples of mine fire gases were taken from sampling ports that were placed through the mine seals and boreholes that were drilled after the fire. The activities that took place within the first two years of the mine being sealed are recounted. Descriptions of the gases that were analysed and the mine atmosphere status equations generated from the analysed gases are presented. The gases were analysed by chromatography and included standard atmospheric gases as well as higher hydrocarbons that are found in postfire atmospheres. Nine equations were used to evaluate what was occurring within the sealed mine. Following a description of the rationale behind each equation, the 2-year trend is briefly analysed.

Water-jet-assisted cutting was found to decrease average resultant conical and radial longwall bit cutting forces 6.4 and 8.4% in coalcrete, 5.5 and 1.4% in Berea sandstone, and 2.0 and 5.5% in Indiana limestone. Slight reductions of power requirements resulting from water-jet assist were ascertained during these experiments., Water-jet-assisted cutting was found to decrease average resultant conical and radial longwall bit cutting forces 6.4 and 8.4% in coalcrete, 5.5 and 1.4% in Berea sandstone, and 2.0 and 5.5% in Indiana limestone. Slight reductions of power requirements resulting from water-jet assist were ascertained during these experiments.

Damage-resistant brattice (DRB) stoppings developed by the USBM have been tested during blasting in a Colorado oil shale mine with openings some 17 m wide and 9 m high. The results proved the ability of the design to reduce air leakage and minimise blast damage to stoppings in mines with entries of large cross-section, while minimising contruction costs., Damage-resistant brattice (DRB) stoppings developed by the USBM have been tested during blasting in a Colorado oil shale mine with openings some 17 m wide and 9 m high. The results proved the ability of the design to reduce air leakage and minimise blast damage to stoppings in mines with entries of large cross-section, while minimising contruction costs.

SF6 tracer gas was used to evaluate the effectiveness of gob ventilation and/or sealing practices at three coal mines, in order to understand better whether current techniques employed for ventilation or sealing are successful at minimising the potential for gob fires and explosions., SF6 tracer gas was used to evaluate the effectiveness of gob ventilation and/or sealing practices at three coal mines, in order to understand better whether current techniques employed for ventilation or sealing are successful at minimising the potential for gob fires and explosions.

Water-jet assisted cutting involves the use of a mechanical cutting bit in combination with a high-pressure water jet directed just in front of the bit tip. The evolution of these machines and the benefits to be gained by their use are detailed., Water-jet assisted cutting involves the use of a mechanical cutting bit in combination with a high-pressure water jet directed just in front of the bit tip. The evolution of these machines and the benefits to be gained by their use are detailed.

Metal, wood, a wood-polyisocyanurate hybrid, and small and large expanded polystyrene (EPS) blocks were tested in underground trona mines, with overburdens in excess of 1000 ft. This overburden depth, in conjunction with the relatively soft floor in trona mines has commonly created excessive floor heave throughout mined out entries. Testing was done in both elliptical and rectangular openings, and both rigid urethane foam (RUF) and a mortar-based sealant were used in different tests, for sealing either the perimeter and joints or the entire stopping face. Results showed that the EPS stoppings sealed with RUF were superior in prevention of air leakage in the mine openings evaluated. EPS has the advantage of being capable of cutting to any size and shape required. The mortar-based sealant was susceptible to degradation, especially around perimeter interfaces with the mineral surface, because of the hygroscopic nature of trona., Metal, wood, a wood-polyisocyanurate hybrid, and small and large expanded polystyrene (EPS) blocks were tested in underground trona mines, with overburdens in excess of 1000 ft. This overburden depth, in conjunction with the relatively soft floor in trona mines has commonly created excessive floor heave throughout mined out entries. Testing was done in both elliptical and rectangular openings, and both rigid urethane foam (RUF) and a mortar-based sealant were used in different tests, for sealing either the perimeter and joints or the entire stopping face. Results showed that the EPS stoppings sealed with RUF were superior in prevention of air leakage in the mine openings evaluated. EPS has the advantage of being capable of cutting to any size and shape required. The mortar-based sealant was susceptible to degradation, especially around perimeter interfaces with the mineral surface, because of the hygroscopic nature of trona.