HEPA Filter Placement: Is Central Filtration a Design Risk?

Series Introduction
Welcome to the sixth article in our series tailored for hospital architects and technical consultants. Each post addresses a common misconception about Temperature-controlled Airflow (TcAF) systems and compares their real-world performance to traditional Unidirectional Airflow (UDAF). Drawing on engineering principles and empirical data, this series aims to support evidence-based decisions in operating room design.

Claim: “TcAF is a risk design because it uses centrally placed HEPA filters instead of terminal HEPA filters as advocated by some standards.”

Reality: Centrally located HEPA filters in TcAF systems are effective, reliable, and offer several advantages in both performance and maintenance.

Context and Analysis
Many ventilation standards emphasize the use of terminal HEPA filters, largely to ensure air cleanliness close to the point of delivery. However, this approach introduces practical complications, particularly in operating rooms.

Terminal HEPA filters require in-room access, increasing exposure to surgical aerosols and fluids. They also add complexity during maintenance, often requiring operating room shutdowns for testing or replacement. Additionally, each filter introduces a potential leakage point through its seal.

TcAF systems use centrally placed HEPA filters located in the air handling unit or upstream ductwork. This design lowers cost by opening up for standard filters, minimizes contamination risks, simplifies filter testing, and reduces operational disruptions. High-integrity ducting ensures that ultra-clean air is delivered from the filter to the room without compromising air quality.

By concentrating the filtration process in a protected and easily accessible location, TcAF improves system resilience while maintaining ultra-clean air conditions throughout the operating room.

Should a terminal filter placement be required, the HEPA filter box can be located immediately next to the central diffusor plenum, which together should be considered as one terminal assembly complying with the terminal requirement.

Conclusion
Central HEPA filters in TcAF are not a compromise. They are a controlled, reliable design choice. They reduce contamination risk, simplify maintenance, and ensure uninterrupted ultra-clean air delivery.

This blog post is part of our ongoing series on TcAF-related claims. The next article addresses the broader question of whether directional airflow should be abandoned altogether considering challenges with traditional UDAF systems.