The Certification Study Guide (6th edition) explains that during construction, renovation, or maintenance activities in healthcare facilities, negative (reduced) air pressure within the contained work area is a critical engineering control to prevent the spread of dust and potentially infectious microorganisms. When the pressure inside the containment is lower than in adjacent occupied areas, air naturally flows from areas of higher pressure to areas of lower pressure.

As a result, airflow moves from the clean adjacent space into the contained work space, rather than allowing contaminated air to escape outward. Once inside the containment, the air is then exhausted directly to the outside of the building or through appropriate filtration systems. This airflow pattern protects patients, visitors, and healthcare personnel in occupied areas by preventing construction-related contaminants—such as fungal spores (e.g., Aspergillus)—from spreading into patient care environments.

The study guide emphasizes that this principle is foundational to Infection Control Risk Assessments (ICRAs) and construction containment planning. Improper airflow direction can result in airborne contamination and has been associated with outbreaks, particularly among immunocompromised patients.

The incorrect options either reverse the airflow direction or allow contaminated air to re-enter the building, both of which violate infection prevention standards. Understanding airflow dynamics and pressure differentials is a frequently tested concept on the CIC exam and is essential for ensuring safe construction practices in healthcare facilities.