How did E2 realize that the fire was active even without visible smoke coming from the sliding door?

The realization that a fire is active without visible smoke can be attributed to the intense heat felt inside the structure. Fire produces significant amounts of heat, and firefighters are trained to recognize that heat can be an early indicator of a fire's presence. This understanding is vital in fire response situations where visual cues like smoke may not be immediately apparent.

When firefighters enter a premises where a fire is suspected, they often rely on their ability to gauge the temperature as an indicator of fire activity. Even if the traditional signs such as smoke are absent, the presence of high heat levels can be a strong indicator that fire is indeed active within the structure. In this case, the significant heat felt inside serves as a critical warning that the fire is ongoing and possibly expanding, necessitating immediate action from the firefighters to ensure their safety and the safety of others. This awareness allows for a quicker and safer firefighting response, emphasizing the importance of heat detection in fire behavior assessment.