When triggered, inert gas fire extinguishing systems rapidly displace approximately 50% of the air in the protected space by inert gas, so extinguishing the fire. The inert gas must be introduced in a controlled manner so as not to generate excessive pressures in the room, and traditionally this is done using an orifice plate in the pipeline. This has the characteristics of a high initial flow rate, decaying with time. An alternative system is described which uses a discharge valve to regulate the gas flow rate. This gives a more constant gas discharge, reduces the cost of the delivery piping, enables longer pipe runs, and requires a smaller vent to control the room pressure during discharge.