the.com/fire triangle

means A model used in fire safety that shows the three elements — heat, fuel, and oxygen — that must combine for combustion to occur, and that removing any one of them extinguishes a fire.

from Not an ancient word but a 20th-century teaching device from fire science and firefighting training, built on the long-understood chemistry of combustion. The 'triangle' shape was chosen simply because three sides make the logic visible at a glance: pull away any one side — smother the oxygen, cut the fuel, or cool the heat — and the whole figure, like the fire itself, falls apart. Some modern safety courses expand it into a 'fire tetrahedron' by adding the chemical chain reaction as a fourth side, but the original triangle remains the classic shorthand.