What is the purpose of a pressurized stairwell in high-rise design?

• A. To exhaust air from stairwells during routine ventilation.
• B. To supply fresh air to occupancies on upper floors during normal operations.
• C. To allow easy access for maintenance staff during fires.
• D. To prevent smoke intrusion into stairs, preserving tenable escape routes for occupants.

Answer: (D)

Keeping stairwells at a higher air pressure than surrounding spaces ensures smoke is kept out of the egress path during a fire. By creating a positive pressure inside the stairwell, air naturally pushes outward through any openings rather than allowing smoke and hot gases to seep in. This preserves a tenable escape route for occupants, giving them breathable air, better visibility, and lower heat exposure while they evacuate, and it also provides a safer corridor for firefighters to operate within. This system is designed for fire conditions, using dedicated fans and dampers to maintain the pressure difference. It isn’t about routine ventilation or supplying upper floors during normal operations, and it isn’t intended to improve maintenance access during fires.