For smoke proof stairways that are pressurized in a building equipped with an automatic sprinkler system, the vestibule is not required if each interior exit stairway or ramp is pressurized not more than what inches of water?

• A. 0.20
• B. 0.25
• C. 0.30
• D. 0.35

Answer: (D)

The correct answer is based on specific requirements set forth in the North Carolina Building Code regarding the pressurization levels of smokeproof stairways in conjunction with automatic sprinkler systems. The code allows for a pressurization level measured in inches of water that determines whether a vestibule is necessary.

In this case, when the pressurization of each interior exit stairway or ramp does not exceed 0.35 inches of water, the code stipulates that a vestibule may not be required. This criterion is designed to ensure that smoke is effectively managed and that the integrity of the stairways as fire escapes is maintained.

If the pressurization were to exceed this level, the presence of a vestibule would be mandated to prevent smoke infiltration into the stairway, improving the safety and accessibility for evacuation during a fire emergency. The choice of 0.35 inches reflects a balance between safety outcomes and practical construction requirements, providing clarity for building designers.