What does "drop down" refer to in the context of fire spread?

In the context of fire spread, "drop down" specifically refers to the phenomenon where burning materials fall or drop from an elevated position, which can lead to the ignition of combustible materials below and result in the spread of fire to new areas. This can occur when embers, sparks, or burning debris from a fire fall downwards, potentially igniting other flammable substances on the ground or in a lower story of a building.

Understanding the mechanics of fire spread, including the role of "drop down," is crucial for fire investigators as it helps them determine the fire's origin and the path it took during its progression. This knowledge assists in developing strategies for fire prevention and fire response procedures by identifying risks associated with falling burning materials in both structural and wildland fire scenarios.