Ultra-clean ventilation (UCV) systems are used in operating theatres to reduce airborne contamination associated with surgical site infection risk by supplying downward unidirectional airflow over the surgical zone. In the UK, UCV commissioning is assessed against Health Technical Memorandum (HTM) 03-01 Part A (2021), with acceptance criteria defined for airflow velocity and particle entrainment. However, these tests rely on discrete probe locations and limited sampling heights, providing limited insight into the three-dimensional flow structures that govern velocity distribution and particle transport beneath UCV canopies. This study combines full-scale HTM-compliant measurements with computational fluid dynamics (CFD) to examine the relationship between HTM acceptance criteria and underlying airflow behaviour. Experimental testing was conducted beneath a Howorth UCV canopy in a UK operating theatre, including velocity mapping at 1 m and 2 m above floor level and particle entrainment testing using 0.3 µm aerosols released at prescribed HTM challenge positions. A CFD model was developed to reproduce the same commissioning conditions and simulate three-dimensional airflow and Lagrangian particle transport. The model showed close agreement with measured velocity data and consistently reproduced particle penetration trends across the HTM challenge positions within experimental uncertainty. The UCV system satisfied all HTM acceptance criteria. This study demonstrates how validated CFD can reveal flow mechanisms underpinning commissioning metrics and provides a reproducible HTM-aligned benchmark dataset for future UCV model development and performance assessment.
