Every underground coal mine should undertake a hazard analysis of ventilation hazards which should encompass the following: historical records of the mine’s ventilation systems, including gas trends; existing primary and auxiliary ventilation systems and its adequacy as the mine expands; changes in mining conditions or mine design which may lead to hazards such as spontaneous combustion or outbursts having a greater influence; coal seam and adjacent strata properties; methods of mining.
Poor ventilation plans can result in problems with gas, dust and diesel particulate, spontaneous combustion; frictional ignition; windblast, heat, poor / inadequate ventilation, and poor ventilation management.
The hazards related to gas include inrush, outburst, ignition, explosion and asphyxiation. Controlling these risks includes:
1. Regular Inspections to ensure compliance with legislative standards.
2. Well maintained and calibrated gas detection equipment. (Both hand-held, still includes the locked oil flame safety lamp, and telemetric instruments)
3. Sufficient air quantities for dilution.
4. Gas drainage (where applicable – large gas reservoirs)
5. Gas régime reservoir modeling
6. Have systems in place that can deal with large quantities of gas if required.
7. Management Plan – with triggers and response action plans.
Dangers from dust and diesel emission and particulate relate primarily to respirable health issues. Issues to consider regarding dust include:
1. Airborne and respirable dust can be well controlled via dust extraction units and new technology is now available.
2. It is easier to keep dust from becoming suspended then it is to eliminate or control once in suspension.
3. Sprays – machine mounted and fixed systems – are effective.
4. Wet drilling
5. Too much air velocity can create dust issues.
6. Pre-drained coal may require water injection to assist with dust suppression.
7. An array of ‘wetting’ agents are available to assist with dust suppression.
8. Limit employee exposure to dust.
Improving the management of diesel emissions could include:
1. Wet or dry filtration systems
2. Catalytic converters, ceramic filters.
3. Air quantities sufficient to dilute emissions.
4. Well maintained diesel fleet with regular testing of exhaust systems
5. Ventilate “dead ends” and “blind stubs” if personnel are working in these places with diesel powered machines.
6. Clean fuel technology is now more readily available. (The current technology has improved to a point where excessive engine wear or damage due to fuel additives is not an issue).
7. Consider decreasing the diesel fleet and increasing battery powered fleet.
Spontaneous combustion can cause heating, fire and explosion. Management techniques include:
1. Regular inspections using both handheld detection equipment and body senses.
2. Mine design/ventilation layout must take Spontaneous Combustion into consideration.
3. Long term air stream analysis trending.
4. Tube bundle gas detection systems may be worth considering.
5. Ventilation pressures need to be watched carefully. High differential pressures across pillars and slack coal will cause issues.
6. Ventilation appliances need to be well maintained.
7. The Management Plan must include triggers and response action plans.
Frictional ignition can cause fire, gas or dust explosions. Its management should include:
1. Sharp Cutting Picks
2. Good sprays
3. Air velocities capable of eliminating accumulations of gas
4. Operators must trained and be vigilant. Regular revision of training for operators will assist in maintaining knowledge base.
5. Try not to cut roof / floor stone
6. Minimise depth of cut in high flammable gas zones
7. Ready access to fire fighting equipment in working order.
8. Management Plan.
The risk of windblast can cause damage to ventilation appliances and mine equipment as well as injury to workers.
1. High standard of ventilation appliances required.
2. Mine plan needs to focus on minimising the windblast effect by having multiple entries/exits for air to travel.
3. Consider pressure relief doors in appliances that are adjacent to Windblast zone areas.
4. Operators need to be vigilant.
5. The Management Plan must include triggers and response action plans.
Risks from heat include dehydration, exhaustion and injury.
1. Maintain reasonable air velocities for cooling effect.
2. Minimise radiated heat, especially in single entries.
3. Operators must be educated in hydration principles.
4. Regular humidity checks and monitoring.
5. Consider installation of hydraulically driven fans for roof bolting machines to create cooling velocities for operators.
6. Management must understand the physiological issued that are created when heat is an issue.
7. Consider air refrigeration.
Poor or inadequate ventilation can cause frictional ignition, spontaneous combustion, heat, dust and particulate contamination, gas issues. Adequate ventilation controls include:
1. Auxiliary fans
2. Dust extractors
5. Permanent and temporary stoppings.
8. Booster fans
Ventilation structure integrity is a critical area and includes:
1. Seals, permanent and temporary stoppings and overcasts.
2. Structure integrity is critical for operations that mine seams with large gas reservoirs or have a propensity for Spontaneous Combustion.
3. Consider ‘keying’ into ribs to ensure minimal leakage past structures.
4. Consider grouting or P.U.R. injection of coal pillars to assist with structure integrity, especially in areas of high differential pressure.
Some useful resources for developing a systematic approach to ventilation risk control include (for NSW): 1999 –Mines Department Guideline 1023 “Ventilation Control System Guideline” prepared by Dr. Roy Moreby – Associate Professor UNSW, MDG 1003 – Windblast Code of Practice and MDG 1006 – Spontaneous Combustion Management Code. For Queensland Ventilation Appliance Standards is available from the Mines Department.