On 26 April, the world will mark the 81st anniversary of what many believe to be the worst mining disaster in history: the Benixhu colliery gas explosion. An explosion at the mine in Liaoning Province – which was, at the time, under the control of invading Japanese forces during the Second World War – killed more than 1,500 people.
However, those killed in the accident are also thought to have helped prevent the fire’s spread by shutting off ventilation to deprive the flames of oxygen. The role oxygen plays in feeding fire is indisputable; yet as critical as it is to a fire’s spread, it is also essential to sustain human life. A 2011 bulletin note by the US Mine Safety and Health Administration (MSHA) warned of the risks to human health of declining oxygen levels, which can be the result of oxidation of coal, wood or other organic materials, as well as the contaminant gases liberated from the coal strata.
MSHA notes that a lack of oxygen can begin to have an impact when oxygen levels drop below 19.5% of their typical value. It added that at 15% hearing can be affected, and by 9% people are at serious risk of unconsciousness and death.
So balancing the supply of oxygen with the risks it poses to safety has long been a difficult tightrope to negotiate. Reducing the use of oxygen is something an Australia-based manufacturer of advanced gas separation systems has said mines should consider. Oxair Gas Systems has called on the sector to look to the latest on-site gas generating technologies, particularly nitrogen, to usher in a new age of technological advances that would increase safety, enhance cost efficiency and ultimately improve sustainability.
Both oxygen and nitrogen play key roles in helping extract or process raw materials at mining sites. Each has a different application, according to Oxair’s chief engineer David Cheeseman, either playing a role in safety, for example at a coal face to control methane or production, such as their role in leaching during gold mining.
However, bringing the raw materials, oxygen and nitrogen, over large distances to site can be “expensive and environmentally unsound,” says Cheeseman. “The best method, where possible, is to generate the raw material on-site where it is needed.” It’s something the sector is beginning to take note of, he believes, saying underground nitrogen generation at the coal face is a growing trend as it gives the user the ability to move the generator with the rest of the auxiliary equipment and reduce the number of down holes needed to run pipelines underground.
“The production on-site reduces transport costs and risks and gives the client control over usage,” Cheeseman continues. “Moving any item around the country is expensive, and any effort to reduce this will also cut the drain on the environment. To be able to self-generate some of your raw materials within your own facility will reduce the footprint.” He acknowledges there will be a capital cost to introduce the infrastructure; but, he adds, the timetable for a return “can be as low as within a year”.
Nitrogen tyres: improving tyre safety
Until recently, securing a stable supply of nitrogen has been a challenge for those needing to buy it in. It’s also a logistical nightmare thanks to the considerable distances involved in this transportation and the unwieldly containers the gas is supplied in. Together, these elements conspire against businesses’s increasingly apparent desires to protect the environments they operate in, and wider climate health.
Investing in an on-site nitrogen supply could open the door to another realm that Cheeseman and Oxair are particularly passionate about too: improved tyre safety. Guidance released by the Government of Western Australia’s Department for Mines and Petroleum in 2015 spoke of the risks associated with gigantic mining vehicles and their tyres.
It said: “Working with off-the-road tyres for earth-moving machinery is potentially dangerous because of their large size and mass, magnitude of air or gas pressures and presence of combustible materials.”
This isn’t the only concern; an academic study by Dr Rickard Hansen of the University of Queensland’s Sustainable Minerals Institute last year concluded that tyre fires and their flames behave differently underground and, more importantly, between different mining vehicles. The study concluded that increased knowledge of the tyre fire risk on mining vehicles and mitigating measures would improve the fire safety in underground mines.
One option to reduce that risk would be to eradicate the existence of oxygen in the tyre as much as possible.
Responding to pressure
In recent years a move towards nitrogen-filled tyres has gathered pace across the world’s mines. “The use of nitrogen helps to reduce the risk of truck tyre fires and explosion,” according to Cheeseman. “This has an effect on human life and machinery should the tyre explode. Some of the tyres used on the larger trucks can hold up to 10 cubic meters of air.”
He says that although much is known about tyre pressures, and there are tools at the disposal of today’s mining professionals to monitor them, part of the safety pyramid is “to engineer the risk out”. Globally, hot tyre stoppages are an ongoing burden, sometimes leading to significant downtime. Air is known to compromise their safety and stability, according to Sullair, a member of the Hitachi group.
In press releases, the company has noted that vehicles such as haul trucks, for example, have huge tyres inflated using air drawn from the atmosphere, delivered into the chamber of the tyre at high pressure via an air compressor. The air, continued the company, comprises around 78% nitrogen, 21% oxygen and some water vapour, which comes with “inherent risks”.
For climates like that of Australia, cutting the risk of tyre fires is critical, but Australia isn’t unique. “We have higher temperatures than most countries so we will be operating at a higher risk,” Cheeseman says. “However, tyre overheating can happen very easily as you are carrying heavy loads over rough ground in dry conditions with extreme climates. If you place your hand on your normal car tyres after a regular journey you will feel the effect of friction and road surface contact.”
It seems that whilst not new, the allure of nitrogen, produced on site, is fast becoming too much for Australia’s mining community to ignore. It’s a shift, however, Cheeseman is happy to see. “Like any development, services grow with the demand for improvement and flexibility, the drive to make machines more usable and efficient is always a top priority, both internally within our company and externally for the client,” he concludes.