Horizontal fire separation is defined as:

• A. A rated barrier within a floor that constrains fire spread across the plane of the floor
• B. A vertical barrier between floors
• C. An opening in the floor
• D. An exterior thermal barrier

Answer: (A)

Horizontal fire separation refers to a rated barrier within a floor that confines fire and smoke from moving across the plane of that floor. It is achieved with a fire-resistance–rated floor/ceiling assembly (or a rated partition that spans the floor) to slow or stop horizontal spread between areas on the same level. This is different from a vertical fire separation, which protects between floors, and it’s not about openings in the floor or about the exterior building envelope.