Efficient ventilation systems in underground mines are paramount for regulating airflow, the amount and quality of air, as well as returning contaminants (gases, dust and heat) to the surface.
Without proper control, extraction or dilution of contaminants, poor ventilation conditions can jeopardise the occupational health and safety of underground mine workers, resulting in potential fatalities.
Generally made up of two ventilation systems, the primary one controls the total air volume flow through an underground mine, drawn in from the surface, and is also the exhaust circuit for the mine’s ventilation, or return airways (RAW)
The secondary ventilation system refers to the provision of ventilation to development ends, stopes and services facilities which constitute secondary circuits tapped off the primary circuit through secondary ventilation fans.
There are also dedicated fresh airways (FAW) in some mines, that have a secondary pusher fan circuit, that the secondary vent fans tap into, to supply the best ventilation possible for the underground workings.
Both systems work as an integrated whole with an unbalanced combination causing recirculation of air, which is inefficient and potentially hazardous.
The construction and maintenance of mine ventilation systems is a highly-specialised engineering division by itself, with high-capital costs and power, or energy costs likely being the largest operational cost in underground mine ventilation at around half-a-million dollars a year for a Twin stage 180 kw or 220 kw fan.
Ventchoke is a low-cost system that controls secondary ventilation circuits underground by diverting, reducing or stopping airflow completely.
It is quick to install by a service crew and increases production or project capacity almost instantaneously.
With diesel engines prevalent in hardrock underground mining, Ventchoke is able to reduce high concentration of diesel fumes, especially in environments with high humidity, by supplying an increased flow of ventilation to working areas.
The brainchild of UVS chief executive Darren Gilbertson, who has spent more than 30 years working underground in mines in Australia and around the globe, Ventchoke is an innovative system that is designed to be installed within an existing secondary vent ducting circuit.
Developed over four years with 13 months of on-site research and development at a Kalgoorlie underground mine, Ventchoke is a robust, reliable and highly-efficient system that will work continuously without attention for a minimum of 12 months.
There is virtually zero cost on repairs and maintenance, compared to the rope and pulley system, with torn or flapping vent bags from ‘rope choke’ being non-effective and efficient.
Made from hard-wearing PVC material, the Ventchoke sleeve wraps around existing ventilation ducts and it is pneumatically operated with low-pressure compressed air, around 18-20psi, used to inflate the bag in around 30-50 seconds.
Only one person is required for the task of inflating the Ventchoke system, which allows for secondary ventilation circuits (vent ducting) to be shut-off with ventilation redirected to other active headings.
People working underground receive the maximum amount of quality air, while other unmanned areas of the mine do not waste fresh air.
Proudly Australian-owned, it is supplied and manufactured in Australia with on-line product training and installation and additional assistance with product selection, planning and placement.
Mr Gilbertson says Ventchoke makes continual improvements to its design with the latest one consisting of all internal fittings now made entirely of steel.
“The old design had poly nyglass fittings, which is very strong, but we resolved the underlying brittleness in this material by converting all elbow, nipple and internal fittings to steel,” he said.
“All the internal steel fittings, including the air inlet and air exhaust, are CNC-machined and manufactured locally in Perth, as well as fully-enclosed in the Ventchoke sleeve, providing a smooth, clean finish.
“Compressed air systems in underground mines usually run at a maximum of 8-bar or 110psi and these steel fittings would easily handle five times that pressure.”
The Ventchoke design is patented for the standard 22 years in Australia, with further patents pending in Canada and the US.
The standard sleeve length is 1.7m and the standard diameter sizes are 610mm, 720mm, 1067mm, 1220mm and 1400mm.
Each diameter size is colour coded for ease of reference, while Ventchoke also offers custom-made sizes for specialised applications.
A recent order to supply customised Ventchokes to the underground civil construction works at the Melbourne Metro Tunnel Project via word-of-mouth saw Mr Gilberton and his team designing and constructing specialised 1500mm diameter sizing with additional hanging fins.
Extra specifications – such as longer sleeve lengths to cover the 250m vent duct jointing system used and alternative hole reinforcements for the eyelets currently used in standard Ventchokes – were no issues for the team.
Mr Gilbertson is currently conducting research and development on a dedicated Ventchoke for partial closings with trial works being done.
“Instead of operating fully choked Ventchoke, feedback received from clients is that there are requirements for partial choking, which would be at 40-50% choked,” he said.
“You can get some form of partial choking with the current Ventchokes, but it’s really designed for a fully-closed or fully-open system.
“Example scenarios of partial choking are when there aren’t machinery running with exhaustion requirements, and someone is working solo in certain parts of the mine such as with a survey team, or with a geologist, and they may only require a minimum of 0.5 m/s of vent flow, or when you may want air continually flushing the heading, to dilute or vent certain gases that may be emitted from the rock surface.”
Secondary ventilation systems are essential in blasting situations where air needs to be directed to a specific heading.
Without the aid of Ventchokes to control the secondary ventilation circuits, the air will go to the closest headings and the ones furthest away will get less.
The worker who wires in and fires the charges (shot firer) has generally a half-hour window between shift changes to complete his job.
If the old and outdated rope and pulley system is still being used at the mine, the worker may not be able to close or choke off headings that are NOT BEING FIRED in time, due to ropes being cut, torn off, knotted or caught up in a knot in the backs.
Ventchoke is controlled pneumatically from the ground, and is as simple as turning an air header tap on or off, or getting the surface control room to turn them on or off, via Ventilation-on-Demand (VOD) that can easily be adapted to each mine’s system, if the necessary wiring infrastructure is already in place.
“Charge-up personnel also have greater potential risks, as they are operating diesel-powered machinery, which is set at full throttle to move them around in the basket, while they dispense the explosives into the face holes or stope holes,” Mr Gilbertson said.
“Some of these headings maybe also be applied with shotcrete, and if there has not been a long enough time frame from shotcrete application to charge up phase, there is a potential of ammonia fumes being released when in contact with ANFO (ammonium nitrate and fuel oil).
“This deadly gas mixture rises to the backs of the drive, where the charge-up personnel are working, and is not a good combination.
“Should oxygen run low in the tunnel when he arrives in the drive, the worker needs to attempt to divert the ventilation to that heading.
“If the old rope and pulley system is used to choke off the vent bag – but the worker notices the ropes are tangled, will not tighten or the bags are torn and flapping – he has to make a decision between expediency and safety.
“Time is of the essence and with schedules and production deadlines, the worker must decide between completing the job without adequate ventilation or waiting for the busy service crew to deal with tangled ropes and torn vent bags.”
Mr Gilbertson said that if the Ventchoke system is already in place, the worker simply checks that the other headings are free and unmanned, then activates the Ventchoke by turning the air header tap to choke off these unmanned headings, and increase oxygen and ventilation flow, in the drive they will be working in.
In under a minute, all available fresh air is flowing into the specific heading and the charge up crew can complete the job in a fully ventilated environment.
With hardly any loss in production time, there is continued productivity and increased crew efficiency.
Benefits to Mines
The simplicity of Ventchoke’s design and the ease and speed of installation increases the efficiency of the project or production as soon as it is up and running.
There is a total of only 10 steps to installing, inflating, operating and deflating the Ventchoke, with just one person required for the task at the designated area with the aid of an integrated tool carrier and operator.
For a low cost of $2000, the mine can install one part of the Ventchoke system that comes with a full year’s warranty, with no moving parts, no electronics and no maintenance hours.
Ventchoke can be installed into any underground ventilation system without additional computer cables or electronic parts that are prone to corrosion in the hot salty tunnel environment.
VOD or VCS systems can also benefit from the installation of Ventchoke to enable a faster re-entry after blasting by diverting the maximum amount of available secondary ventilation to all active headings after firing has taken place, and can be activated from the mine’s control room or pit ram system.
The secondary ventilation circuit can be used to its maximum potential, reducing expensive repairs and reworks to existing ventilation circuits.
“Just imagine driving into an underground heading that is Ventchoked off. Call up pit ram or your mine’s control room and ask for heading “xyz” to have the secondary vent opened,” Mr Gilbertson said.
“Within one minute, ventilation is re-supplied and work continues in that area. The operator or mine worker leaves the active heading onem, two or three hours later and calls up the mine’s control room, and states, all work completed, please close off ventilation to heading “xyz”.
“This is true total control of your mine’s secondary ventilation circuit, and if used and set up correctly, will aid to the health and safety of all underground employees, and assist in making sure your mines production targets are met. This is a win-win for the mechanised mining companies of our time.”
Ventchoke is an easy-to-operate system which can be removed and reinstalled in various sections of the underground mine.
It may also prolong the requirement to introduce additional secondary ventilation fans into the mine.
Ventchoke is hard and durable with a solid three layers covering the bladder.
Constructed from heavy duty PVC and joined with high frequency welding for the ultimate in a robust structure, 12Kw and 8Kw high frequency welding machines are used at the manufacturing facility. Radio waves are used to activate the PVC molecules.
A pneumatic press then moulds the crossed layers of PVC together, creating the incredibly strong vent duct structure as it cools.
The Ventchoke design has a large air flow but low pressure.
The device is filled with 18psi but holds at 5-6psi internally to maintain inflation.
Despite the low pressure, when fully inflated it is as solid as concrete.
The 18psi pressure required is easily sourced from any mining compressed air line available.
A small amount of leakage, around 2-4cfm, is built in, to prevent over inflation.
A spring mechanism with the springs, customised and manufactured by Boynes Springs in Perth, WA, controls the Ventchoke’s dump valve rate.
To prevent wear from trucks loaders and Jumbos etc, for tight drives, the Ventchoke has a heavy ripstop layer on the base circle.
The tough material contributes toward the longevity of the system.
Where it works
When the current ventilation system needs to be upgraded or replaced, underground firing is about to take place, increased distance from secondary vent fans or work is required on the backs such as running HV electrical cables, Ventchoke provides an efficient use, not just to increase ventilation in active headings, but as an addition to the mining toolbox.
It is easily installed at the join between vent bags, by sliding over the join and held in place by eyelets and clipped onto a catenary wire.
The bag is joined back together and the Ventchoke is connected by air hose to one of the air headers in the tunnel.
How It Works
When low pressure air at 18-20psi fills the tube, it applies an inward force on ventilation ducting, achieved by a set air pressure regulator built into the Ventchoke.
The constriction in the vent ducting, caused by the pressure in the Ventchoke, stops airflow through the ventilation.
Quick to install, it takes about 30-50 seconds to inflate and runs with the same ease and efficiency when deflating with the inbuilt auto dump value on the Ventchoke.
Air consumption is 2-4cfm and Ventchoke relies on the use of compressed air inflating a sealed tube annular restrictor to apply inward force on the ventilation ducting.
An inbuilt air pressure regulator that is set and locked allows the system to work at low pressure.
Exciting times lie ahead for Ventchoke as news of its underground secondary ventilation system has spread far and wide, reaching as far as North America.
Mr Gilbertson has signed an agreement with Schauenburg Industries in Canada, a manufacturer or underground ventilation ducting and systems, to add Ventchoke to its product range.
Schauenburg Industries is now the sole distributor of Ventchoke to the North American hard rock mining industry.
Closer to home, Ventchoke has been picked up by third-party suppliers for immediate distribution to OZ Minerals’ Carapateena copper and gold mine in South Australia, Newmont’s Tanami gold mine in the Northern Territory and also via AC Industries, a supplier of low leakage mine ventilation ducting systems.
Ventchoke has been supplying its system and products to multiple underground mines since it began more than five years ago, including Silver Lake Resources and other mines around Kalgoorlie, WA, for specialised applications including airleg mining and narrow reef mining.
**Ventchoke will be available for viewing at the Underground Operators Conference at the Perth Convention and Exhibition Centre between March 15-17. Darren Gilbertson and his team from Underground Ventilation System will be at Booth # 17 to answer queries and provide more information.
P: +61 408 034 786
Facebook: Underground Ventilation@Ventchoke