Donbass was dominated by heavy industry, such as coal mining and metallurgy. While annual extraction of coal had reduced since the 1970s, Donbass remained an important supplier. Coal mining in Donbass is conducted at very deep depths. Lignite mining takes place at around 600 metres below the surface, whilst mining for more valuable anthracite and bituminous coal takes place at depths of around 1,800 metres. Ukrainian coal miners have to risk their lives every time they go to work because their job is extremely dangerous. The coal mines of Donbass are among the most hazardous in the world due to enormous working depths as a result of natural depletion, as well as high levels of methane explosion, coal dust explosion and rock burst dangers. Since 1991, up to 300 miners have died at work every year. In the early 21st century, country's coal reserves were estimated more than 10 billion tonnes. According to the Ukrainian mining trade union, coal was 95% of Ukraine's domestic energy resources and before the start of the region's war in April 2014, Donetsk and Luhansk oblasts produced together about 30% of Ukraine's exports. In July 2014 several mines were closed because of fighting in Ukraine. According to the Ukrainian Energy and Coal Industry Ministry, raw coal production in Ukraine dropped to 64.976 million tonnes (-22,4%) and the country has begun importing power-generating coal from South Africa and Russia.