Fire may spread vertically in taxpayers through all of the following EXCEPT?

Vertical fire spread in structures, such as taxpayers, occurs primarily through processes that allow heat and flames to move upward.

Conduction happens when heat is transferred through materials, such as walls or ceilings, allowing fire to spread to upper levels directly through contact with hot surfaces. Convection involves the movement of hot air and smoke, which can rise and carry flames to upper areas of a building. Radiation refers to the transfer of heat energy through electromagnetic waves, which can cause ignition of materials located above the fire as they absorb this heat.

The concept of "mushrooming at upper levels" refers to a phenomenon where smoke and hot gases collect at the upper levels of a space, creating a "mushroom" shape as they spread out before venting. While mushrooming is significant in smoke behavior and can impede visibility and air quality for those trapped in a fire, it is not a direct means through which fire itself spreads vertically. It describes the behavior of smoke and gas, not the actual fire spreading through convection, conduction, or radiation.

Thus, the option related to mushrooming is the one that does not contribute to vertical fire spread in taxpayers.