Abstract: Fire extinguishing plant for three extinguishing agents, water, powder-mixed water and heavy foam, comprising water supply conduits (4, 5, 6) from a source of pressurized water to a number of spraying nozzles (2, 3), and wherein there to the water supply conduits (4, 5, 6) being provided an inlet (7) for admixing foam agent. Moreover, to each nozzle (2, 3) therein being provided supply conduits (9, 10, 11) for a non-combustible gas, siad conduits having a device (13) for admixing fire extinguishing powder into the gas. The supply conduits for the non-combustible gas have a non-return valve (28) adjacent the outlet; there being provided a bypass conduit (14) in the gas supply conduit past the device (13) for the admixing of powder.An arrangement in spraying nozzles for use in the plant comprises a preferably circular housing (15), on end of which is closed, the other end thereof being open and having a radially extending annular flange (32).