Natural gas is a kind of clean energy. under the industrial policy suppor of two-pronged for gas and oil, natural gas will be more and more important in our country's Energy structure. However, Natural gas has inflammable, explosive, toxic and other dangerous characteristics almost simultaneously. City gas pipeline as the conveying medium are the key link of the safe using natural gas. As a result, it has double important meaning of theory and practice for the urban security to study the gas accident releas...