Which condition is most likely to cause smoke to stratify in a large building?

The correct choice is temperature inversion. In fire behavior, stratification of smoke occurs when warmer, lighter smoke rises and becomes trapped under a layer of cooler air. This phenomenon is significantly impacted by temperature inversion, which can create a stable atmospheric condition where the temperature increases with altitude rather than decreases. This stability prevents the smoke from dispersing and allows it to accumulate at lower levels, making it more dangerous for both occupants and firefighters.

Other factors such as high humidity or sprinkler system activation may influence fire dynamics but do not play as critical a role in the stratification of smoke in large buildings. High humidity can affect visibility but is not as prevalent in causing smoke to layer. Sprinkler system activation works to suppress fires and actively helps in reducing smoke production, thereby preventing stratification rather than causing it. Ventilation failure can lead to smoke accumulation, but the specific layering effect associated with temperature inversion is more significant in this context. Therefore, temperature inversion is the condition most likely to directly cause smoke stratification.