Mining has been a central part of human civilisation for millennia. The Romans mined, the Egyptians mined, the Aztecs mined – and we still mine. It’s only recently however, that this ancient practice has taken on the enormous proportions that we see today. Both open cut and underground mines are far larger than they’ve ever been. Carving out the earth in the form of an open cut mine is impressive enough, but when things head underground a host of extra problems are presented.
If all we did was dig and nothing else, we’d soon find out just how unforgiving being underground can be. Mining into the earth requires precautions and technological marvels. So how have we managed to mine so deep? Let’s explore some of the ways.
Air has a lot of trouble circulating far underground. Even if it weren’t for the equipment spurting out various pollutants, some sort of ventilation would be necessary just to keep the miners breathing.
In the past, ventilation in underground mines was a serious problem. Coal miners during the early 20th century were susceptible to carbon monoxide poisoning and other hazards while performing their job. There were many searches for out-of-the box ways to make the job safer, which led to the famous trope of ‘the canary in the coal mine”. The birds, with their high metabolism and accelerated breathing, were more susceptible to the gas than the miners and their unfortunate deaths would give time to don gas masks or escape to safety.
Fortunately in this day and age we don’t need to sacrifice any more avids to the cause of keeping our miners alive. Ventilation systems today are extremely complex and have to work extremely hard. The electricity needed to run just the fans of a typical underground mine’s ventilation system can account for over 30% of the mine’s total electricity costs.
For such an expensive operation, the fundamental idea behind ventilation is surprisingly simple. The concept is known as “flow through” ventilation: air is sucked into a shaft underground by fans on the surface, while extractors at the top of the mine drag the air back out. As it passes through the various passageways of the mine it brings with it the fresh supply of oxygen.
Underground ventilation is far more advanced today than a century ago, but the technology is always improving. Advances in electric engines and battery technology for example could soon reduce the need for internal combustion engines underground. This would make ventilation much easier as the harmful carcinogens produced by these engines would no longer need to be scrubbed from the air.
Hand-in-hand with ventilation systems are dust monitors. Because chronic exposure to respirable coal mine dust causes lung diseases that can lead to permanent disability and death, the U.S. Mine Safety and Health Administration (MSHA) considers respirable coal dust to be one of the most serious occupational hazards in the mining industry and issued a dust rule. (Read more about the dust rule and what it means, in our previous articleThe MSHA Dust Rule and How Mines Can Comply.)
In a nutshell, the rule provides for single shift compliance sampling by MSHA inspectors, establishes sampling requirements for mine operators’ use of Personal Dust Monitors, requires operator corrective action on a single, full-shift operator sample, changes the averaging method to determine compliance on operator samples, and expands requirements for medical surveillance of coal miners.
A personal dust monitor protects miners’ health by tracking the shift-average respirable dust exposure as it approaches regulatory limits. Providing mine workers and management with the tools to personally monitor and reduce their exposure, the monitor is the first line of defense in preventing long-term health effects. (Read more about helping to protect miner health with dust monitors.)
We previously published a three-part series on pneumoconiosis, more commonly known as Black Lung Disease – a devastating illness that can afflict anyone exposed to coal and crystalline silica dust. This includes not only coal miners or workers who load coal for storage; workers in graphite mines or mills, and in carbon electrodes and carbon black manufacturing operations are at risk due to coal dust inhalation. Explore the series to learn about the risk of coal dust inhalation, a historical look at legislation, and a mine safety and health facts review.
As most people know, the inside of the earth is a giant ball of molten rock. On the surface this doesn’t pose much of an issue apart from the odd volcano or two, but once you start digging a long way down, residual heat from the earth’s core can start to become a serious problem. In most underground mines, this sort of heat isn’t really much of a problem, since the digging doesn’t extend deep enough to feel the effects of getting closer to the earth’s core. However, some super deep mines in the world, such as the gold mines of North Eastern South Africa, reach so deep underground that the rocks the miners are drilling into can reach a staggering 66 degrees Celsius (over 150 degrees Fahrenheit). In normal circumstances, working in such conditions would be impossible.
Which is where technology comes in. Super deep mines such as Mponeng Gold Mine, which extends 4km underground, use a variety of techniques to keep things workable. The first and most significant is the constant circulation of slurry ice. This special ice isn’t the sort you grab from the supermarket on your way to a barbeque, it’s rather more advanced than simple frozen water. Slurry ice is specially formulated to cool longer and more efficiently than other forms, and helps to keep working temperatures in the lower reaches of the mine at a far more bearable 28 degrees.
Apart from literally pumping the place full of ice, mines such as Mponeng invest hugely in insulating techniques to keep temperatures in check. Excavated rock goes someway towards this. Rather than being entirely removed, some of the rock is mixed with concrete and water and packed into areas requiring insulation. This recycling of material helps to keep material and labour costs down as well as the temperature.
The deeper a mine gets the more pressure it’s put under. Endless tons of earth and rock put mines under an enormous amount of stress, which is why cave ins and mine collapses can be such a huge risk in underground mining.
Keeping those tons of earth suspended above the holes we dig in the earth is no trifling matter. Mines go to great lengths to ensure that everything stays in place no matter how deep they delve.
The types of reinforcement techniques have come a very long way since the early days of underground mining, where the most workers could hope for were timber supports. Today, specially designed rock bolts, shotcrete, steel mesh and pillars are used, amongst other things, to shore up the rock in underground mines.
The type of reinforcement encountered in each mine, and indeed in different sections of each mine, vary quite widely. This is all due to the type of rock the miners encounter as they dig. Loose shale, fractured rock or mines in unstable areas are going to require very different forms of reinforcement than stable mines with smooth, solid rock walls.
Underground mining isn’t a matter of grabbing a shovel and digging. Well, maybe in it’s most basic form it is, but in the modern world underground mines are feats of engineering that are up there with some of the most remarkable devised by man. It may seem like a simple proposition to drill deep underground in pursuit of the minerals the earth offers, but doing so safely and productively is a whole different story. Enormous advances in ventilation, heat mitigation and reinforcement techniques have taken underground mining away from its traditional status as an extremely hazardous job, into the realms of modern efficiency. Where next?
For more information about our being a partner in the mine against black lung, go to: www.thermoscientific.com/endblacklung (and order a free hardhat sticker!).
Editor’s Note: This article was written in association with Tuff Stuff Australia Earth moving parts, leaders in mining equipment and parts.