The definition of 'flame spread' is

• A. the propagation of flame over a surface
• B. the rate at which flames spread through a material
• C. the color of flame
• D. the ignition temperature of surfaces

Answer: (A)

Flame spread describes how a flame front moves along the surface of a material. It captures how quickly fire can travel across walls, ceilings, or other finishes, which is crucial for understanding fire growth and safety in buildings. This is about movement along a surface, not through the material itself. The other ideas—color of the flame or the ignition temperature—deal with combustion appearance or when burning starts, not how fast the flame propagates along a surface. The notion of rate at which flames move through a material would be describing flame movement inside the substance, rather than along its exterior. Therefore, the best definition is the propagation of flame over a surface.