Reassessing Segregation Testing: Is It Relevant for TcAF?

Series Introduction
This is the third installment in our blog series aimed at technical consultants and architects working with hospital operating rooms. Each post addresses a specific claim or misconception about Temperature-controlled Airflow (TcAF), comparing it to traditional Unidirectional Airflow (UDAF) systems. Our goal is to help project stakeholders evaluate ventilation strategies based on sound engineering principles, scientific evidence, and real-world results.

Claim: “UDAF has a strong protective barrier, while TcAF fails segregation tests.”

Reality: Segregation tests are based on assumptions that do not apply to TcAF’s design principles.

Context and Analysis
Segregation tests assess whether a physical velocity air barrier separates clean from less clean zones. These tests were developed with UDAF systems in mind, which rely on high-speed vertical airflow to define the boundary between sterile and contaminated areas. However, applying the same method to TcAF overlooks how its design works.

TcAF does not depend on a single-direction barrier. Instead, it supplies ultra-clean, HEPA-filtered air across the entire operating room, including the periphery. The room is not divided into clean and unclean zones in the traditional sense, because the entire space remains within the ultra-clean threshold of <10 CFU/m³.

Edge turbulence and lateral entrainment, which are common problems in high-flow UDAF systems, are actively mitigated in TcAF by a more gentle downflow in the center and supporting peripheral diffusers. These diffusers reinforce a downward displacement and help stabilize air movement throughout the space. As a result, TcAF minimizes cross-contamination without relying on rigid airflow boundaries.

An alternative test used in the Netherlands, a particle recovery time test, requires a 1,000-fold particle reduction within 10 minutes in the periphery. TcAF passes this test, demonstrating effective contaminant removal in all room zones, not just the center.

Conclusion
Segregation testing assumes a need to protect the clean zone from a contaminated periphery, an assumption that doesn’t apply when the entire room is maintained as ultra-clean. TcAF’s approach is based on full-room contamination control through stable, distributed airflow, rendering traditional segregation tests an unsuitable measure of its effectiveness.

This article is part of our series examining common claims about TcAF. Next, we’ll address concerns regarding surgical smoke removal and airflow velocity.