Coal produced in underground coal mines is transported to the earth by means of belt conveyors throughout long roadways. The combustion of belts in underground mining operations causes large number of employees to face great risks. Underground collieries have a different feature compared to other underground mines and structures. The main reason for this difference is that the transported material carries high-carbon containing coal. The most important cause of belt fires occurring in this type of underground mines is the hidden burning feature of coal. The combustion process that starts with oxidation also enables the belt conveyor to burn over time. In 2014, there was an accident in an underground coal mine in Manisa Soma. In this accident, 301 employees died. It has been studied on this subject for about 3 years. The most important of these researches are; the tests carried out in the research gallery, comparison of the test results with the documents obtained from the mine officially after the accident and CFD analysis.The authors believe that the cause of death is a very large amount of toxic gas, which occurs after belt conveyor fire.