The Times has an interesting article on underground coal fires in China, with one effort to extinguish a fire succeeding after 3 years of effort. These aren't just a Chinese problem - they occur around the world - the oldest known example being Burning Mountain in Australia.
After a three-year effort and untold quantities of water, Chinese firefighters have extinguished a fire that had been burning underground in a coalmine for more than 50 years.
Firefighters finally beat the fire by boring into the coal seam and flooding it with water and slurry. They then capped the mine shafts to starve the flames of oxygen. As well as staving off further environmental damage, they have saved more than 651 million tonnes of coal, which will be mined to fuel the Chinese economic and industrial juggernaut.
Miao Pu, head of the firefighting team at the Terak mine in Xinjiang, a sparsely populated, mainly Muslim region in northwestern China that is rich in resources, said: “First, we drilled into the burning coal bed and then poured water and slurry into it to lower the temperature. After the temperature dropped we covered the surface to starve the fire of oxygen.” Officials plan to monitor the coal seam for several years in case the fire reignites.
The smouldering furnace 100 metres (330ft) underground at the second-largest coalfield in Xinjiang had released more than 70,000 tonnes of toxic gases annually since the 1950s. Two years ago firefighters in the area put out a similar fire that had been burning for more than 50 years, but there is much more to do.
Thousands of underground coalmine fires are believed to cover an area of 720sq km (280sq miles) in China. They consume as much as 20 million tonnes of high-quality coal and another 200 million tonnes of coal storage each year. ... The fires, often smouldering in coal seams on or just below the surface, have shaped the landscape of coal-rich regions in China for millenniums. The layers of coal can go on for miles underground, with fuel to burn for decades or centuries.
The smoke darkens already polluted skies. The fires emit poisonous gases and can even make the earth cave in — swallowing roads, homes, animals and humans — when weak ash replaces firm coal underground. The are also wasting resources in a rapidly developing country that relies on coal for about three quarters of its energy requirements, and the Government wants them extinguished.
The fires can start spontaneously. The oldest is believed to be at Baijigou, northwest China, and has been burning since the Qing Dynasty, a century before the mine opened in 1965.