The hot water was stopped and cold water added back. Nitrogen was then used to gently raise the cylinder's pressure to continue. The cylinder was then filled with water, flushed and filled again to prevent any pyrophoric polymer from igniting. With the main hazard gone, removing the polymer would be saved for the next day. Polymer destruction was also done remotely since peroxides could be entrained in it.
Popcorn polymer is insoluble and difficult to remove from surfaces.
We chose to destroy it by a controlled burn of the cylinder's interior. This was done by drilling a two inch hole and lowering a flare inside. The water level was slowly dropped so that the popcorn polymer's burn would be controlled. After interior was fully exposed to flame, the cylinder was finally safe. It was removed from the vessel and the interior steamed.