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

There’s probably lots of ways, but the way I know is that they try to figure out what was burning the longest. The stuff that looks the most burnt, melted, and crispy had to have been burning for longer than the stuff that just has a little layer of ash on it. And then they can assume that whatever started burning first must have been burning the longest, so the fire must have started where the most crispy stuff is.