The stairway that is enclosed by fire-resistive rated walls and self-closing rated doors is a:

• A. Continuous exit enclosure
• B. Smoke-proof enclosure
• C. Rated exit door enclosure
• D. Horizontal exit enclosure

Answer: (B)

The key idea is providing a protected vertical path for people to use during a fire that stays free from smoke. When a stairway is enclosed by fire-resistive walls and has self-closing rated doors, that stairwell is designed to resist smoke ingress and heat, keeping the environment tenable for occupants as they evacuate. This combination of barriers and automatic door closure is precisely what a smoke-proof enclosure describes.

So, the stairway remains accessible and safer for occupants during a fire, which is the defining feature of a smoke-proof enclosure. Other terms either refer to protected routes in a more general sense or describe different concepts (like a horizontal exit that connects two areas at the same or different levels, not specifically a stairwell as a sealed, smoke-resistant path), so they don’t capture the same specific purpose and construction as this option.