After many years working in mines and studying mine disasters I’ve decided to add some science to all the media hype that we’ve been hearing. Some communities like Wiimali have suffered mining disasters. The causes are many – sometimes it’s a collapse from rock fall and at other times it’s an explosion from high levels of methane gas. Whilst open cut mining simply takes the top off the land to access the underlying coal, underground mining accesses the coal seams by incisions burrowed deep underground. Recently there have been explosions at underground mines, such as Pike River in New Zealand. Twenty-nine people died, many of them local community members. In the Pike River mine methane gas levels apparently built up without detection, creating pockets of highly explosive gas that ignited and exploded.
The presence of naturally occurring methane gas is one of the main reasons mining companies, like the one in Wiimali, place emphasis on how their mining sites monitor for gases and are ventilated. Often coal seams that have high levels of methane are called ‘gassy coal’ and need extra management to ensure the mine is safe for the employees. Methane monitors are usually connected to the electrical system and automatically shut down everything when they detect dangerous gas levels.
Once a major explosion occurs in an underground mine it can be difficult to re-enter the shafts. After the explosion the rescue teams try to get into the mine to help those trapped and investigate. They can however only enter when it is safe. Sometime inert gas (e.g. nitrogen or carbon dioxide) is pumped into the mine to displace the explosive and toxic gases. When this strategy is used it threatens the life of any workers left trapped in the shaft, and rescuers need to wear fully self-contained breathing apparatus. Rescue operations are in themselves risky business.
Open cut mines have fewer problems with methane gas levels. They do however create high levels of dust and substantially change the landscape. In addition they potentially impact local water supplies through contaminated run off and changes to the water table. Having a mine near your community is not without its problems. You have to wonder whether the benefits really do outweigh the costs?
Story by Joseph Lewis