Factory-built fireplace hearth extensions must be readily distinguishable from what?

Factory-built fireplace hearth extensions must be readily distinguishable from the surrounding floor area to ensure safety and visibility. This distinction is critical because the hearth extension is designed to absorb heat and protect combustible surfaces from the intense heat produced by the fireplace. By making the hearth extension visibly different from the surrounding floor area, it helps prevent accidental contact and ensures that individuals using the fireplace clearly recognize the boundary of the safe area. This visual differentiation contributes to overall fire safety by minimizing the risk of igniting nearby combustibles and maintaining proper spacing around the fireplace. The other options, while they may relate to safety in different contexts, do not address the specific need for clear differentiation from the floor where the fireplace is situated.