What key change occurs to combustible materials in the free-burning phase?

During the free-burning phase of a fire, combustion is at its most intense, and temperatures can rise significantly. As the fire progresses and heat is generated, combustible materials are subjected to these elevated temperatures, which can lead to their ignition. This phase is characterized by an increase in energy release, causing surrounding materials to reach their ignition temperature more quickly. Therefore, combustible materials become more likely to ignite due to the increased thermal energy surrounding them, leading to a rapid spread of the fire. This understanding is crucial for fire safety and prevention strategies, as it underscores the importance of managing heat sources and combustible materials in environments where fires can occur.