I also have been inside one. Spooky feeling. News photog wanted "that" shot and I had to escort him in for it. Inside, he made some smart-ass comment about his camera making a spark, and I reminded him that his cajones were inches from a million-plus pounds of rocket fuel.
When they are firing, they burn over five TONS of fuel per second, and all that fire goes out through a hole just about a yard in diameter. It holds right at 2,000 psi the whole time. The flame is 6000 degrees and it exits at about five times the speed of sound.
