Many years ago when they converted 39A and B from Apollo to the Space Shuttle, they had to rework the launch pads. One thing they needed was an emergency door through the wall of the flame pit into a room near the bottom of the pad. I think it was for an escape hatch? Anyway, it was 36" of concrete and rebar. They used rods (pipe actually) filled with magnesium that were lit off with pure oxygen flowing through them. They were so hot they'd melt the concrete, rebar, everything. My job was to keep the oxygen flowing.

Anyway, they would poke these into the concrete and melt a several-inch, round hole through the entire 36 inches. When they burned up one pipe, they simply screwed anpother piece of pipe on and kept going. What seemed like a gazillion holes later, they had the shape of a doorway.

It was very hot on a Florida beach in July, and the job was obviously hot by nature. They rotated the burners in and out, but I stayed down there. Liters of water? I drank GALLONS. But what a thrill.