What is the primary purpose of stairwell pressurization during a fire?

• A. To maintain a constant temperature in the stairwell.
• B. To move smoke into the stairwell for ventilation.
• C. To push air out of the building through exterior openings.
• D. To keep stairwells free of smoke by creating a higher pressure inside than outside, aiding safe egress and access.

Answer: (D)

Keeping stairwells free of smoke by creating a higher pressure inside than outside is the main idea. When the stairwell is pressurized, air naturally moves from the high-pressure space to lower-pressure areas, so smoke from the fire floor and adjacent spaces is kept out of the stairwell. This creates a tenable path for occupants to evacuate and for firefighters to gain access without inhaling or navigating through dense smoke. The system typically supplies clean air into the stairwell and exhausts from it to maintain the pressure difference, helping to contain smoke and reduce heat and visibility hazards inside the stair enclosure.

The other options miss the point because they either focus on temperature control, which pressurization doesn’t directly guarantee, or on moving smoke into the stairwell or out through exterior openings, which would defeat the goal of keeping the stairs clear for safe egress and access.