"That is no longer a good idea. Cans now have a plastic
liner (BPA) and putting them over a fire is not a good
idea."

I understand. However, I'm talking about using cans to do such tasks as heating water in a short-term situation. Canned food has to go through a process with a heat that I doubt is duplicated if I boil water. Without pressure, food won't get hotter than liquid allows. OK, it will be something above 212 F unless I'm boiling plain water, but not as hot as a dry-baked food or burning the can dry.