The term associated with the air and gas flow in a compartment fire is

The term associated with the air and gas flow in a compartment fire is

• A. Neutral Plane
• B. Smoke Layer
• C. Ventilation Zone
• D. Gas Boundary

Answer: (A)

In a compartment fire, hot combustion products are buoyant and rise to form a smoky layer near the ceiling, while cooler fresh air is drawn in from below through openings. The boundary that separates these two streams is the neutral plane. It’s the height inside the doorway or opening where the internal flow of air in equals the outward flow of hot gases, so there is little or no net movement across that plane. Below the neutral plane, air enters to feed the fire; above it, smoke and hot gases exit. This concept is essential for understanding how ventilation and fire behavior interact in a confined space. The term smoke layer describes the upper hot gas layer itself, not the interface between inflow and outflow, and other terms like gas boundary or ventilation zone aren’t the standard way to describe this specific two-layer flow.

In a compartment fire, hot combustion products are buoyant and rise to form a smoky layer near the ceiling, while cooler fresh air is drawn in from below through openings. The boundary that separates these two streams is the neutral plane. It’s the height inside the doorway or opening where the internal flow of air in equals the outward flow of hot gases, so there is little or no net movement across that plane. Below the neutral plane, air enters to feed the fire; above it, smoke and hot gases exit. This concept is essential for understanding how ventilation and fire behavior interact in a confined space. The term smoke layer describes the upper hot gas layer itself, not the interface between inflow and outflow, and other terms like gas boundary or ventilation zone aren’t the standard way to describe this specific two-layer flow.