What is thermal layering?

• A. The phenomenon of gases mixing evenly throughout the air.
• B. A process where smoke becomes more concentrated near the ceiling.
• C. The gradual cooling of a heated surface.
• D. The phenomenon of gases forming into layers according to temperature.

Answer: (D)

Thermal layering happens because temperature affects air density. Hot, lighter gases rise and form a layer near the ceiling, while cooler, denser air stays lower down. This creates distinct temperature-based layers rather than a uniform mix. In a room fire, you’ll commonly have a cooler lower layer and a hotter upper layer, with the boundary between them shifting as heat and ventilation change. Understanding this helps you predict how heat, smoke, and toxic gases will move, which is crucial for safe entry and effective ventilation strategies. The idea is simply that gases separate into layers according to temperature, making that description the most accurate.