In operating rooms, a minimum of 15 air changes per hour (ACH) is required, with at least 3 of those ACH being from fresh or outdoor air. This requirement helps reduce microbial contamination and provides a clean surgical environment.

According to the APIC Text:

"In each, air should flow out of the room and the minimum ACH should be 15, with three of these ACH being fresh or outdoor air."

This aligns with design specifications outlined in the 2006 Guidelines for design and construction of health care facilities.