In pre-flashover conditions, what is the primary heat transfer mechanism for fire spread?

In pre-flashover conditions, convection is the primary heat transfer mechanism for fire spread. During this phase, heat is transferred from the fire source to the surrounding combustible materials primarily through the movement of air and gases.

As the fire grows, hot gases rise and carry heat with them, heating nearby objects and surfaces. This action can ignite fuel sources that are in proximity to the flames, thus spreading the fire.

While conduction and radiation also play a role in heat transfer, they are not as significant in this phase as convection. Conduction involves heat transfer through direct contact, which is generally slower and less effective in spreading fire in early stages compared to the rapid movement of heated gases. Radiation does contribute to heat transfer as well, but in the context of pre-flashover conditions, convection's effectiveness in moving hot air to new fuel sources is the dominant mechanism driving the spread of the fire.

Therefore, understanding the role of convection in the dynamics of fire spread is crucial for recognizing how fire behavior can evolve in these early stages.