Containers that have been involved in a fire shall be permanently removed from service if they are which of the following materials?

Containers that have been involved in a fire must be permanently removed from service if they are made of aluminum or composite materials due to the risks associated with their structural integrity after exposure to high temperatures. When subjected to fire, aluminum can lose its strength significantly, making it unsafe for continued use. This material can soften or warp at temperatures that might not affect steel as severely, leading to potential failures if the container is reused. Composites, which often contain a mix of resin and reinforcing fibers, can also degrade and lose their mechanical properties when exposed to heat, posing additional safety hazards.

In contrast, while steel can be affected by fire, it can often retain its structural integrity up to a certain temperature, allowing for a more thorough examination and potential reuse after being properly evaluated. Similarly, plastic containers typically have a lower thermal tolerance and can deform, yet their removal criteria may differ based on specific types and standards. Copper does not have the same risks associated with structural compromise after a fire and has different uses that typically don't involve container storage under high-pressure conditions, thus not having the same critical concern as aluminum or composite containers.