Have you ever watched a campfire burn? Every fire needs three things to keep going. Scientists call this the fire triangle. The first side is fuel, which is anything that burns, like wood or paper. The second side is oxygen from the air. The third side is heat. Remove any one of these three things, and the fire goes out. On October 8, 1871, all three sides came together in a devastating way. A fire broke out on the southwest side of Chicago. The summer had been unusually dry. Wooden buildings, wooden sidewalks, and even wooden streets provided endless fuel. Strong winds from the southwest pushed the flames north and east. The intense heat from burning buildings set nearby buildings on fire before the flames even reached them. This process is called radiant heat transfer. The fire burned for over thirty hours and destroyed about 17,500 buildings. Afterward, Chicago passed strict building codes. New buildings had to use fireproof materials like brick and stone. The disaster led to major improvements in fire science and city planning.