According to Eximo , mining is constantly under close scrutiny from all angles over occupational health and safety matters. Mine ventilation calls for a number of work practices and technologies to be developed so as to assure the safety of all mining employees.
Eximo, which supply ducting technologies that form an integral part of a ventilation and/or filtration system for mine ventilation, have worked with their technical partners to make sure such installations and identified key objectives are implemented.
Eximo observe that when designing a mine auxiliary ventilation system, the basic objectives are the sufficient provision of clean air for individuals and equipment and adequate ventilation for the removal or dilution of hazardous gasses or dust.
The quantity of air required and physical restraints present must be considered and taken into account. Air quantity must be considered in terms of both velocity and volume. The air velocity in the entry or tunnel, the volume of air required for workers, the operation of diesel equipment, the dilution or removal of gasses and dust must be considered.
Following are the physical constraints, which require consideration:
- head room over haulage
- material transport equipment
- length of duct
- associated handling and hanging problems
- potential for damage from blasting and other activities
- the correct sizing of duct and fans to ensure that the fans are not working in a stall, i.e. attempting to move a volume of air greater than the duct’s capacity
A larger duct allows for a more efficient and lower horsepower system. Other considerations include:
- the legal and contractual requirements for fans and ducts
- the preferred directional airflow: suction, or blowing
- the acceptable levels of leakage for the determination of duct length. With most leakage occurring at the joints, longer length has less leakage
When evaluating the different types of duct, there are four broad categories to consider such as steel, fibreglass, flexible suction and lay-flat. For suction ducting, steel requires low initial investment. The steel is non-flammable, holds high positive and negative pressure, allows medium leakage, is low friction, and is suited for moderate length ventilation runs (less than 1000m), such as drill and shoot operations and single use applications.
Fibreglass, the most durable of suction ducting materials, is flame resistant, holds up well to abuse, is light-weight, gives high positive and negative pressure, has a low friction factor, and is suited for short-length ventilation runs (less than 500m), multiple reuse operations, drill and shoot operations and mine development.
Eximo point out that flexible suction has the advantage of being both expandable and contractible in length, it can be stored in small areas and its weight is dependent on the negative pressure rating. Flexible suction is also flame-resistant and suitable for starter tunnels, short ventilation runs, and flexible connections with other types of duct.
Lay-flat has a pressure rating dependent on material and construction. It has a medium friction factor, low leakage in long length and requires an additional fan for reversing airflow on OSHA jobs.
This technology requires special expertise in applications for booster fans. Lay-flat is flame resistant, available in many grades, and is suited for short ventilation runs using low cost duct, long ventilation runs using long-length ducts and TBM tunnels.When calculating ducting air pressure losses, losses can be categorised as either dynamic or friction induced. With dynamic losses, the pressure loss in each fitting, inlet and outlet must be calculated separately and is based on the velocity pressure of air at that point in the system, while with friction losses, friction loss curves and formula are used to give the pressure loss caused by friction in the duct.