A suppression unit comprising: a nozzle having an exterior surface, an interior bore extending along a longitudinal axis, and a plurality of discharge orifices passing from the interior bore to the exterior surface; an actuator piston including an interior channel in fluid communication with the interior bore; a casing, the actuator piston and the nozzle disposed within the casing; and a biasing device compressible between the actuator piston and the casing; wherein the discharge orifices are protected by the casing in a biased passive condition of the nozzle, and the discharge orifices are moved longitudinally out of the casing in an active condition of the nozzle; wherein the discharge orifices are located in a discharge area of the nozzle and the discharge area is slidable within a protection portion of the casing, the discharge area having approximately same outer dimensions as inner dimensions of the protection portion; and wherein the exterior surface in the discharge area has a constant outer diameter along the longitudinal axis, characterized in that: the nozzle is separably attached to the actuator piston; the nozzle includes a filter having inlets to fluidically communicate the interior channel of the actuator piston to the interior bore of the nozzle, and the interior channel includes an annular space between the filter and an interior surface of the actuator piston; and the casing comprises a flange to secure the suppression unit to a surface separating a protected area and an unprotected area, such that the interior bore of the nozzle passes through the surface and the protection portion extends into the protected area. a nozzle having an exterior surface, an interior bore extending along a longitudinal axis, and a plurality of discharge orifices passing from the interior bore to the exterior surface; an actuator piston including an interior channel in fluid communication with the interior bore; a casing, the actuator piston and the nozzle disposed within the casing; and a biasing device compressible between the actuator piston and the casing; wherein the discharge orifices are protected by the casing in a biased passive condition of the nozzle, and the discharge orifices are moved longitudinally out of the casing in an active condition of the nozzle; wherein the discharge orifices are located in a discharge area of the nozzle and the discharge area is slidable within a protection portion of the casing, the discharge area having approximately same outer dimensions as inner dimensions of the protection portion; and wherein the exterior surface in the discharge area has a constant outer diameter along the longitudinal axis, characterized in that: the nozzle is separably attached to the actuator piston; the nozzle includes a filter having inlets to fluidically communicate the interior channel of the actuator piston to the interior bore of the nozzle, and the interior channel includes an annular space between the filter and an interior surface of the actuator piston; and the casing comprises a flange to secure the suppression unit to a surface separating a protected area and an unprotected area, such that the interior bore of the nozzle passes through the surface and the protection portion extends into the protected area. the nozzle is separably attached to the actuator piston; the nozzle includes a filter having inlets to fluidically communicate the interior channel of the actuator piston to the interior bore of the nozzle, and the interior channel includes an annular space between the filter and an interior surface of the actuator piston; and the casing comprises a flange to secure the suppression unit to a surface separating a protected area and an unprotected area, such that the interior bore of the nozzle passes through the surface and the protection portion extends into the protected area.