Containers (other than aluminum) shall be ________ when they have been involved in a fire and show no distortion before being used or reinstalled.

The correct answer is that containers (other than aluminum) shall be requalified when they have been involved in a fire and show no distortion before being used or reinstalled. Requalification is a critical process that ensures the safety and integrity of pressure vessels and containers that may have been exposed to high temperatures or structural stress during a fire. It involves a thorough inspection and testing to ascertain that the container still meets the necessary safety standards and specifications to safely hold propane or other gases.

This process is essential because fire can compromise the materials and construction of a container, even if it appears undamaged. Requalification typically includes testing for pressure retention, checking for structural integrity, and verifying that they meet current codes and regulations.

Other options like repair, discard, and repaint do not fully address the safety protocols required for utilizing containers that were previously exposed to fire. Repairing might not ensure that the container retains its intended strength and functionality. Discarding would not be necessary if the container passes the requalification test, and repainting does not contribute to ensuring the container's safety or compliance with regulatory standards. Hence, requalification is the most appropriate and safest step to take.