No PPV fans should be used in which type of construction during the fire attack?

The use of positive pressure ventilation (PPV) fans can significantly affect fire dynamics and conditions within a structure. In balloon-frame construction, the vertical spaces within the walls create a direct channel between floors. This means that air can travel quickly up and down within these cavities, potentially allowing fire and smoke to spread rapidly to upper levels.

Using PPV fans in such structures can inadvertently push air and smoke into these concealed spaces, exacerbating the fire’s spread rather than controlling it. The risk of backdrafts and other dangerous conditions increases with the use of fans, as they can introduce air into areas that already have high heat and smoke accumulation.

Building types such as cinder-block, steel-frame, and reinforced concrete have more fire-resistant walls and fewer hidden spaces for fire to spread uncontrollably, making them less susceptible to the risks associated with using PPV fans during fire attacks. Hence, the correct response identifies balloon-frame construction as the type where PPV fans should be avoided due to the specific fire spread dynamics associated with it.