What characteristic makes listed fire stopping materials effective when heated?

• A. are physically stable
• B. expand and adhere
• C. melt and seal
• D. become brittle

Answer: (A)

The main idea here is that fire stopping materials must stay in one piece when exposed to heat. If the material remains physically stable, it won’t sag, melt, crack, or fall away, so the seal around the opening stays intact as temperatures rise. That stability keeps the barrier effective long enough to stop flames and smoke from passing through the penetration. While some products rely on expansion to seal gaps, this only works if the material doesn’t lose its form or detach; otherwise gaps can form and the firestop fails. Melting, becoming brittle, or drifting away would defeat the purpose, making physical stability the most important trait.