During which stage does flashover occur in a fire?

Flashover is a critical and dangerous phenomenon in the progression of a fire, defined as the rapid transition where all combustible materials in a space ignite almost simultaneously due to extreme heat and sufficient oxygen. This event typically occurs in the fully developed stage of a fire. At this point, the fire has reached its peak intensity, and the temperature often exceeds 1,000 degrees Fahrenheit (or about 540 degrees Celsius).

During this stage, various factors align to favor flashover, such as the accumulation of heat in the room and available fuel sources that have reached their ignition points. The presence of adequate ventilation can also influence how quickly flashover occurs, as increased oxygen availability can intensify the fire behavior.

In contrast, during the ignition and initial growth stages, the fire is still developing and may not have sufficient energy or uniform conditions necessary for flashover to happen. The ventilation-limited stage typically involves a decrease in fire intensity due to insufficient oxygen, which makes it less conducive to flashover compared to the fully developed stage.

Thus, understanding the fully developed stage as the point at which flashover occurs is fundamental for fire behavior analysis and safe firefighting operations.