ABSTRACT
At present, hybrid injection nitrogen is widely adopted to extinguish the fire in sealed goaf. The theory of hybrid injection nitrogen is to dilute the oxygen concentration in goaf. Nitrogen is injected to the sealed goaf with buried pipes and mixed turbulently with original air. Therefore, inert gas concentration is increased in goaf, and oxygen content is reduced less than 5% (critical concentration) relatively. Thus the targets of stifling fire source and inhibiting the development of spontaneous combustion are achieved. This technique requires the goaf be sealed strictly and air leakage never happen.
