When does a chemical chain reaction occur in relation to fire?

A chemical chain reaction in the context of fire refers to the process that continues to fuel the combustion once it has been initiated. This occurs after a fire starts, as the heat, fuel, and oxygen present interact in a way that releases energy, leading to the production of more heat and gases that further sustain the fire.

When a fire ignites, the initial reaction begins, but it's during the ongoing combustion that this chain reaction becomes crucial. It allows the fire to continue burning and spreading as long as the essential elements—heat, fuel, and oxygen—are available. Therefore, recognizing that the chemical chain reaction is an ongoing process that takes place after ignition is key to understanding fire dynamics and effective firefighting strategies.