VENTILATION Main Airways

As mines become larger and production rates increase the quantity of air flowing in the main intakes becomes large and ventilation effectiveness and cost is usually the main factor deciding the number of main airways required. For other purposes it would often be the case that only two intakes, one each for coal haulage and personnel/materials transport, and one return are necessary. Additional headings are to reduce the resistance to air flow and /or to reduce air velocities. For ventilation, the more airways the better, but after a point the incremental benefit is small; for development costs, the fewer the better – the best compromise is required.
Air velocity also has to be considered where air flows are large relative to:

• Safety and comfort of personnel working in windy locations or walking against high flows
  
• Raising of dust and its ability to settle, mostly in conveyor and transport roads
  

The requirement for high air flows and, increasingly, high pressures dictates a high standard of ventilation control devices. Where access doors are required for personnel or machinery at least double doors forming air locks are required with pneumatically or hydraulically operated doors becoming more common.
Minimising leakage through stoppings, doors, etc is important, but mostly from an efficiency point of view. Removing leakage actually removes parallel air paths and thereby increases overall mine resistance and the result may be that minimal additional air is generated at the face areas within the mine.
Main airways should be mined as straight as possible and kept as free of obstructions as possible, a factor often overlooked when siting major items of equipment. At least the presence of such equipment should be taken into account when ventilation planning is carried out.
A further issue to be considered in mine design and ventilation planning is the siting of large motors (e.g. maingate conveyor drives) and other heat generating sources (including high powered diesel equipment) particularly in mines in Central Queensland that experience both a high geothermal gradient and high ambient temperatures (and humidity levels) through summer months. The application of air cooling systems is being increasingly favoured in such environments.