Handbook for Methane Control in Mining - AMMSA

materials oxidize. In mines that liberate small amounts of methane, low airflows could result inoxygen deficiency before elevated methane levels occur.The information collected at the examination locations and recorded in mine records should beused in evaluating the effectiveness of the bleeder system. Trends can be monitored. However,a thorough understanding of the system is needed to fully assess bleeder system performance. Incomplex systems or those with which there are concerns over limited capacity or effectiveness,there may be times when an investigation beyond the regular examination locations, such as intothe primary internal airflow paths, may be appropriate if an investigation can be conductedsafely. Confirmation of the internal airflow patterns and assessment of the dilution of contaminantsmay be appropriate to ensure that the examination locations provide the necessary informationand can also provide a better understanding of what the trends at specific measurement pointlocations reflect about the internal workings of the bleeder system.Situational indicators. As bleeder systems change, some conditions can develop as a result of,or in response to, declining system performance. These circumstances often warrant closer scrutinyto determine the impact of the condition on bleeder system effectiveness. The location andnumber of the present measurement point locations should be reassessed as to the adequacy forproviding sufficient information for evaluation. Routine changes in the bleeder system can alsocause problems. Situations such as the following should raise the level of interest and caution ofpersons evaluating bleeder system effectiveness.• Separate mine fans. Directing airflow from the pillared area to separate mine fans maydiminish the pressure differential established across segments of the pillared area, sometimesresulting in poorly ventilated areas, unventilated areas, or complication of theevaluation of the bleeder system effectiveness. Similar problems can result when theairflow ventilating the face area is directed to a mine fan separate from the mine fan ventilatingthe pillared area. Some of the airflow ventilating the active face should always bedirected into the pillared area to prevent unventilated areas of the pillared area close tothe active working section. Depending on the configuration of the system and the controlof the airflow in the system, similar problems can occur even when a single mine fan isventilating the face area and the mined-out area.• Splits of air directed into the pillared area (other than the split ventilating the activeworking section). Although other splits are often necessary and important to maintainventilation of the pillared area, understanding the impact of introducing other splits on thebleeder system is important. Splits of air directed into the pillared area (other than thesplit ventilating the face(s) from the active working section) can decrease ventilatingpressure across the pillared area and adversely affect airflow away from the active workingsection. Depending on ventilating pressure differentials, poorly ventilated areas maydevelop within the pillared area. Extreme conditions would be stagnation of the airflowentering the pillared area from the face area or the airflow from the mined-out area movingto or toward the active working section. The proposed introduction of other splits ofair into the pillared area should be evaluated to predict what overall effect the change willhave on the system. Following implementation of changes, the bleeder system should beevaluated through in-mine examinations to determine if the changes produced theexpected results.73