Abstract: An inert gas for fighting a fire occurring in an enclosed space is produced by the reaction of ammonia with atmospheric air to produce nitrogen mixed with water vapor which is introduced into the fire in the enclosed space. This fire fighting gas mixture is produced in a small gas turbine having a combustion chamber into which ammonia, preferably liquid ammonia, is sprayed. Additionally, water may be sprayed into the combustion chamber to cool the combustion gas to a desired temperature and supplied to the turbine which feeds its exhaust gas to a mixing chamber where a further temperature control may be performed by spraying water into the mixing chamber. The gas output of the mixing chamber is used for the fire fighting.