An underground fire that has consumed more than 12.43 million tons of coal in northwest China has finally been extinguished after more than 50 years.

The Coalfield Fire Fighting Project Office of Xinjiang Uygur Autonomous Region announced the fire in the Terak field was finally out, saving an estimated 651 million tons of coal from burning.

Officials and engineers will closely monitor the coal seam for several years and submit a final report in 2009 to regional and national authorities, said Cai Zhongyong, deputy head of the office.

The fire, covering 923,500 square meters, was fueled by coal more than 100 meters underground. It released more than 70,000 tons of toxic gas, including sulfur dioxide and carbon monoxide each year since it started in the early 1950s, Cai said.

An similar attempt to extinguish this fire was unsuccessful in Aug 2000

Coal fires are also common in underground mines in the US ,  and are difficult to extinguish. The term coal fire refers to a burning or smoldering coal seam, coal storage pile or coal waste pile. The adsorption of oxygen at the outer and inner surface of coal and resulting oxidation is an exothermic reaction. This leads to an increase in temperature within the coal accumulation. If the temperature exceeds approximately 80°C the coal can ignite and start to burn. This process, referred to as “spontaneous combustion”, is the most common cause for coal fires of large extent.