As a structure fire becomes ventilation limited it can often hide the fires location from the exterior. Height of Neutral Plane As the fire develops, the neutral plane (the boundary between the heated smoke and the cooler air) will lower, and the thickness of the smoke gases will increase. The neutral plane marks the level in a structure fire where below it …
While level or thickness of the hot gas layer is categorized as a smoke indicator, the neutral plane relates to movement of smoke and air and would be categorized as an air track indicator. Therefore, Understanding the concept of a neutral plane can aid in determining the floor the fire is located on. At a doorway, the existence of a mid-level neutral plane with air being drawn into the structure at a considerable velocity is a strong indicator that the fire is in need of more air to burn optimally and is ventilation-limited. On the other hand, if the fire is above the opening (i.e., opening is below the neutral plane for the structure), there will likely be very little, if any, flow of smoke from the vent. The term "neutral plane" is often used by firefighters to describe both the neutral plane … Neutral Plane vs. Interface Height.