What is a typical minimum rate of air exchanges described for laboratory ventilation?

• A. 2 exchanges per hour
• B. 6 exchanges per hour
• C. 24 exchanges per 24 hours
• D. 60 exchanges per hour

Answer: (C)

Ventilation effectiveness is described by how many times the air in a space is replaced each hour, known as air changes per hour (ACH). The idea is to keep contaminants diluted and remove stale air.

The option stating 24 exchanges per 24 hours is equivalent to one air change per hour (24 per day ÷ 24 hours = 1 ACH). This phrasing—expressing the rate as daily exchanges—reflects a common way some laboratory ventilation guidelines describe a minimal baseline. So, it captures a basic minimum level of ventilation: enough to ensure dilution without being excessive.

The other numbers correspond to different ACH values (2 per hour = 2 ACH, 6 per hour = 6 ACH, 60 per hour = 60 ACH). These represent higher or more specific requirements, but the daily rate wording aligns with a minimal, broadly described baseline, making the 24 exchanges per 24 hours the best fit.