A firefighting nozzle is provided with a relief valve assembly that opens to discharge a fine spray or “curtain” of liquid extending 360° around the nozzle, thus cooling off the nozzle operator and the surrounding area, while at the same preventing dangerous pressure build-up in the nozzle. In a preferred embodiment, the relief valve assembly comprises a housing having a substantially cylindrical side wall defining a bore. A tubular sleeve divides the bore into two parts: a cylindrical inner passage defining the primary flow path for liquid traveling through the nozzle; and an annular space defining a valve chamber. A plurality of relief ports is formed in a 360° degree pattern around the side wall of housing, each relief port defining a secondary flow path extending substantially perpendicularly to the primary flow path. An annular plug is mounted for sliding movement on the inner sleeve, from a first position blocking the relief ports to a second position allowing flow therethrough. A compression spring or other biasing element is provided for normally urging the plug toward the first position. When liquid entering the nozzle exerts enough pressure on the inlet end of the annular plug to overcome the force of the biasing element, the annular plug moves away from the relief plugs, thereby allowing liquid to escape through the relief ports, simultaneously reducing the pressure inside the nozzle as well as the air temperature outside the nozzle.