Which phenomenon describes gases forming into layers according to temperature?

Which phenomenon describes gases forming into layers according to temperature?

• A. Smoke inversion.
• B. Ventilation.
• C. Thermal layering.
• D. Flashover.

Answer: (C)

Gases forming into layers by temperature happens because temperature changes change gas density. Hotter gas is lighter and tends to rise, while cooler gas is heavier and stays lower. In an enclosed space, this creates horizontal strata: a warm, lighter layer near the ceiling and cooler, denser air nearer the floor.

This separation is described as thermal layering, and it’s a common way to understand how smoke and heat behave in a fire. It matters for safety and ventilation because the hot layer carries most of the heat and toxic products, and moving or ventilating can disturb the layers, affecting visibility and fire behavior.

The other terms describe different ideas: ventilation is about moving air through or within a space, not about temperature-based layering; flashover refers to a rapid transition to nearly simultaneous ignition of all combustibles in a room, not a stable layered structure; and “smoke inversion” isn’t a standard term for this specific layering phenomenon.