Without the plug, plastic pipes soften at about 75°C, and ignite at 140°C, which could allow fire to spread through the opening. The two-part plug is slotted over a pipe at the point where it passes through a wall or ceiling. When exposed to flames or temperatures above 200°C, the rubber expands to more than 10 times its original volume. The maker claims that the expanding plug can even crush aluminium pipes.
When the Crusher Plug is used with PVC or high-density polyethylene pipes that ignite extremely rapidly, the manufacturer recommends that the opening be filled with additional fire-resistant rubber strips wrapped around the pipe to close the opening as soon as possible.