What does it indicate when smoke still fills a door but appears to thin upon opening?

When smoke still fills a door but appears to thin upon opening, it indicates that the fire is likely below the level of that door. This scenario typically suggests that the heat and smoke have risen, but there may not be enough intensity or fuel at the door level to sustain a full blaze. As the door is opened, cooler, less dense air enters through the opening, causing the smoke to appear thinner. This difference in air pressure and temperature creates a visual effect where the smoke may seem to disperse.

In contrast, if the fire were extinguished, there would be significantly less smoke present; hence it would not fill the door at all. If the fire were at the same level as the door, you would likely see more consistent density and darkness of smoke rather than a thinning effect. If there were no smoke present, one wouldn’t observe any smoke filling the area around the door at all.

Understanding the dynamics of smoke behavior is essential for firefighters as it helps in assessing the fire's location and intensity, aiding in the decision-making process during fire response.