Farenheit 451 is a reference to the autoignition temperature of paper. It’s a flameless ignition. Fire isn’t necessary, just really good at concentrating very high temperature gases into the thing you want to burn. Another good visualization of the fire triangle is burning wood in a campfire vs in a kiln to make coal. By keeping away most fresh air in a kiln, the wood burns differently - higher temps, less material consumption, and the flames only appear at the openings. That’s useful for metal melting