Eli5: How can they tell where a fire starts and how it grew after the building has already been burned down?

Question

Eli5: How can they tell where a fire starts and how it grew after the building has already been burned down?

In: 6

Answer 1

The way the burns are within the structure and the evidence left behind can be pieced together to get an understanding of what caused it or where it started.

Typically, the area that received the most damage and where the fire burned hottest, will be where the fire started. Things like the materials that burned or how badly burned was it will give them these clues. Metals, for example, have different melting points that can help indicate temperature.

Residue left behind can also give an indication if an accelerate was used, like lighter fluid or kerosene.

TLDR: a lot of science, math and experiential history comes into play.