Define 'air changes per hour' (ACPH) and its relevance in ICRA.

Define 'air changes per hour' (ACPH) and its relevance in ICRA.

• A. ACPH is the number of times the air within a space is replaced in an hour; higher ACPH in containment zones helps dilute contaminants and supports effective negative pressure and filtration.
• B. ACPH is the ratio of air pressure to humidity.
• C. ACPH is the annual protective heart rate.
• D. ACPH is the cost per room per hour.

Answer: (B)

ACPH measures how many times the air inside a room is replaced in one hour. In infection control risk assessment, this ventilation rate is used to judge how effectively airborne contaminants are diluted and removed, which helps reduce exposure to infectious particles and supports proper containment strategies and filtration. Higher ACPH speeds up dilution and removal, improves the performance of filtration systems, and helps maintain appropriate pressure relationships between spaces, though it also increases energy use and may be limited by building design. You can estimate ACPH from room volume and airflow: ACPH = (airflow rate in CFM × 60) / room volume in cubic feet; for example, a 600 ft³ room with 100 CFM yields about 10 ACPH. The option defining ACPH as the ratio of air pressure to humidity is not correct because ACPH is about how often air is renewed, not about pressure or humidity.

ACPH measures how many times the air inside a room is replaced in one hour. In infection control risk assessment, this ventilation rate is used to judge how effectively airborne contaminants are diluted and removed, which helps reduce exposure to infectious particles and supports proper containment strategies and filtration. Higher ACPH speeds up dilution and removal, improves the performance of filtration systems, and helps maintain appropriate pressure relationships between spaces, though it also increases energy use and may be limited by building design. You can estimate ACPH from room volume and airflow: ACPH = (airflow rate in CFM × 60) / room volume in cubic feet; for example, a 600 ft³ room with 100 CFM yields about 10 ACPH. The option defining ACPH as the ratio of air pressure to humidity is not correct because ACPH is about how often air is renewed, not about pressure or humidity.