What type of firestop is typically used to resist fire and smoke in walls and floors?

The correct choice is intumescent firestop because it is specifically designed to expand when exposed to heat, forming an insulating barrier that can resist the passage of fire and smoke through walls and floors. This property is essential in preventing flames and toxic gases from spreading to adjacent areas during a fire, thereby providing critical time for occupants to evacuate and for fire services to respond.

Intumescent firestops are commonly used in joints and penetrations that may occur in fire-rated walls and floors, ensuring the integrity of fire-resistant barriers is maintained even in the event of a fire. Their unique ability to swell and seal off openings effectively makes them a crucial component in firestop systems.

In contrast, sealants can provide a level of resistance but may not expand like intumescent materials when exposed to high temperatures. Fire-resistant boards are used for different structural and insulation purposes and aren't typically a material that can be applied to penetrations or joints in the same way. Backup material, while sometimes used in conjunction with other firestop materials, does not serve the primary function of stopping fire and smoke on its own.