What term refers to the exchange of air measured in cubic feet per hour?

• A. Air Changes Per Hour (ACH)
• B. Air Pressure Differential
• C. Vector
• D. Walk-off mats

Answer: (A)

Air changes per hour describes how many times the air in a space is replaced in one hour, providing a direct measure of ventilation effectiveness and dilution of airborne contaminants. In infection control, ACH helps ensure spaces meet isolation and contamination-control requirements by tying airflow to room size. While airflow can be described in cubic feet per hour, ACH standardizes that by room volume to express replacements per hour. The other terms don’t describe the rate at which the room’s air is exchanged: air pressure differential is about pressure differences between spaces; a vector is a directional quantity; walk-off mats relate to physical contamination control rather than ventilation.