What is the vertical spread of fire on the exterior of a multistory building from one floor to the floors above called?

The vertical spread of fire on the exterior of a multistory building from one floor to the floors above is known as autoexposure. This term refers to the phenomenon where flames can ignite materials located vertically above the fire source, often facilitated by factors such as wind, thermal radiation, or the presence of combustible materials on balconies or facade surfaces. Autoexposure becomes a significant concern in fire scenarios within multistory buildings, as it can rapidly lead to larger areas being involved in the fire due to the transmission of heat and flames upward through openings, exterior surfaces, and adjacent spaces.

While flame propagation typically describes how flames move through an area or object, and heat transfer focuses on how heat moves from one material to another, these concepts do not specifically address the upward movement of fire in the context of multistory structures. Vertical ignition refers generally to the process where flames or heat ignite materials above the fire source but does not encompass the broader mechanism of autoexposure as it pertains to a building's facade. Therefore, autoexposure is the most accurate term for describing this particular phenomenon in fire behavior.