What is the primary purpose of stair pressurization in tall buildings?

• A. It creates a negative pressure to pull smoke away from the stairs
• B. It maintains a clean, smoke-free stairway by applying a slight positive pressure
• C. It enhances stairwell acoustics
• D. It improves energy efficiency of building systems

Answer: (B)

Stair pressurization works by keeping the stairwell air slightly more pressurized than surrounding spaces. That gentle positive pressure pushes air out of the stairwell whenever a door is opened, which helps prevent smoke from seeping in and contaminating the route used for evacuation. In tall buildings, maintaining a clean, smoke-free stairway is essential for safe egress during a fire, giving occupants a tenable path to evacuate and allowing responders to access the stairs more safely. So the goal is a slight positive pressure to keep the stairs smoke-free. Creating negative pressure would pull smoke into the stairs, and improving acoustics or energy efficiency are not the aims of this system.