Understanding fire behavior during critical stages such as flashover and fully developed fire is crucial for firefighter training and safety. This empirical research investigates the influence of fuel–air ratio variations on the occurrence of flashover, the forma- tion of fully developed fire stages, and the temperature dynamics of the upper gas layer. Wooden pallets are utilized as the fuel source in experiments conducted under controlled ventilation conditions. Five different fuel–air ratios ranging from 0.2 to 1.2 are examined, revealing significant insights. The findings of this study highlight the importance of fuel–air ratio adjustments in shaping fire behavior within controlled environments, such as firefighter training compartments. As a result, increasing the fuel-air ratio substantially extends the fully developed fire stage\\\\\\\'s duration. Moreover, the experimental findings indicate that a minimum fuel-to-air ratio of 0.545 is necessary to initiate a flashover, and fuel-air ratio escalation accelerates the flashover onset. Fuel–air ratios of 0.73 and higher caused the upper layer of gas in the chamber to reach a temperature exceeding 800°C for more than 180 s. These insights are instrumental in enhancing our understanding of fire dynamics and devising more effective firefighting strategies and safety protocols.

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