What is the characteristic of the opposing stack effect?

The characteristic of the opposing stack effect is accurately represented by the choice that states the interior is colder than the exterior, which pushes smoke downwards. This phenomenon occurs when the temperature inside a building is lower than that outside. The disparity creates a pressure difference that influences air movement, causing cooler air from inside to rush out while drawing warmer air downwards.

In this scenario, the cooler interior air can lead to smoke becoming denser and effectively pushed downwards. This can occur especially in high-rise buildings where temperature differences can create significant stack effects. By understanding this principle, firefighters can better predict how smoke and heat will behave in a structure, which is crucial for effective fire suppression and ensuring the safety of both occupants and responders.