Abstract: A fire damper for impeding the spread of fire from the burning of plastic pipes inside a wall or floor structure. The fire damper is installed adjacent to only one side of an opening where the pipe penetrates the structure so that the damper can be added as a retrofit without disturbing the pipe. The damper comprises a base which can be easily mounted on a two by four or similar structural member, a disk-like gate, and a torsion spring. The gate is slightly larger in area than the opening for the pipe. The coil of the spring acts as a hinge connection between the gate and the base. One arm of the spring is fixed to the gate. The free end of the torsion spring is activated by rotating the gate toward the base and then pressing the base against the plastic pipe before securing the base permanently in place.