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Venting on the issue: Underground mine ventilation

Editorial
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Ventilation has always been a difficult issue on site. 

Getting enough air underground efficiently without endangering the structure of the mine is something that many countries approach differently. 

What goes in China is definitely not the norm for Australia. 

But countries can get in a rut technology wise, using the same old solutions because it simply is what has always been used, so getting an outside opinion is always a 'breath of fresh air' and in the end can help to maintain safer underground operations. 

Gary Thorinson, of Canadian firm ABC Ventilation System, recently visited Australian mines. 

He noted that overall Australian mines, compared to other nations, tend to have good primary ventilation, which takes the pressure off of secondary ventilation. 

Thorinson added that these primary systems at the surface are key to maintaining good ventilation. 

However he said that Australia does have one unusual and potential habit - its high use of poly ducting, which in a number of mining countries is considered unsafe due to variable burning characteristics in flame testing. 

"We find that some poly ducts are flame resistant to code in some tests and then in a later batch of tests will fail - some of the problem has to do with the thickness of the poly. 

"Australian mines tend to have good management and that extends to ventilation. I see more standardisation in sizes of ducting and fans here than any other place, with standardisation you have a better chance of succeeding in getting the right things in the right places," Thorinson said. 

However in maintaining a healthy airflow secondary systems should not be forgotten, especially during expansion work, when more air is needed underground. 

"When we get too far from the areas where air is coming in or those sources are insufficient to feed the stopes we need to look at a raise bore to allow better airflow - the fan in the mine has to be large enough to deliver the air a certain distance to the miner," he said. 

In designing secondary system fan motor sizes need to be chosen based on expected leakages and the resistance of the system.
 
"Often the fans are large enough to deliver the air but we have problems with greater than expected leakages along the ducting and sometimes increased resistance in the system due to installation errors." 

Leakage comes from the coupling design and from tears or holes in the ducting caused by blasting and equipment contact. 

Having a leakfree coupling such as a Zipper or Velcro coupling is a good start. 

By using these zipper couplings it makes the joint between the duct sections invisible. 

"Couplings are a source of potential leakage and as such the fewer the better. We need short 10 metre sections for advance after blasting but if mines can replace a group of ducts with a 50 metre section this will give less leakage and perhaps less resistance. 

"In Australia the grommet and 'Minsup' clip style coupling, or 'Aussie' Coupling is prevalent on site but it is a higher leakage coupling." 

Thorinson went on to say while PVC ducting has the advantage of being more easily repairable but does come at a higher cost than the less durable poly ducting. 

In the end, while repair is key to good ventilation a good installation with holes in it will not deliver the air required to give the miner a safe and healthy working environment. 

"The installation errors we often see is that of people trying to bend the straight ducting around corners - you need smooth transitions to get low resistance and good air." 

Small installation issues aside, ventilation has improved in the current 'safety first' environment. 

However it is "not as fast as we would like to see it," Thorinson said.
 
"Mining is still the industry will the largest number of cases of respiratory and hearing problems, and while there is a greater awareness of the importance of protective equipment nonetheless we continue to see miners with respiratory problems that are a reflection that we are not able to keep the air as clean as we want," he said. 

"We need to work hard on training and maintenance of the equipment that we have in the mine."

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