If a fire's flame begins bright and then dulls, what likely causes this change?

The scenario of a fire's flame starting bright and then dulling is primarily indicative of insufficient oxygen supply. When a fire initially burns brightly, it is often consuming available fuel and oxygen effectively, leading to a vibrant flame. However, as the supply of oxygen diminishes, the combustion process becomes less efficient, resulting in a duller flame.

Insufficient oxygen can be caused by various factors such as enclosing the fire in a confined space, or the fire consuming all of the available oxygen, leading to incomplete combustion. In contrast, while increased temperatures with proper oxygen levels would maintain a bright flame, in this scenario, the dulling indicates a restriction in oxygen rather than an increase in temperature.

Understanding the dynamics of fire behavior is crucial for effective firefighting strategies, which often involve ensuring that there is a sufficient oxygen supply for sustained combustion.