AIR SAFETY
Above: The risks of airborne contamination in clinical environments highlights the importance of effective ventilation and monitoring. Above right: There is evidence linking airborne contamination to surgical site infections.
well-protected, others not. Even where standards exist, they are enforced intermittently rather than continuously. Ventilation is not just a clinical issue but a financial one.
Andrew Carnegie
Andrew Carnegie is Managing director at Air Sentry Limited. He trained in electrical engineering and audiology before being recruited into the Royal Army Medical Corps where he served for five years. He founded Capital Diagnostics PLC in 1988, the model for which is now being emulated across community diagnostic centres. He later worked in life-support roles with PPG Hellige and Dräger Medical. He established Kreuzer UK, reshaping ICU design across about half the country’s units and a third of operating theatres before its sale to Trumpf. Andrew identified an issue with ventilation design and founded what has become Air Sentry 25 years ago. He has been a contributor to various NHS England documents over the years, including most recently the HTM 03.01 Technical update ‘Application of HEPA filter devices for air cleaning in healthcare spaces’.
Operating theatres provide a clear example. When a theatre’s ventilation fails, operations are cancelled. Staff time is lost. Patients wait longer. Trusts incur costs that are rarely budgeted for. Studies and estates reports often cite £20,000–£30,000 per day as the cost of a single theatre being out of action. That figure includes lost tariff income, wasted resource, and patient harm through delay. In large Trusts, failures can snowball into millions of pounds. The economic case for monitoring is straightforward. The cost of installing closed-loop monitoring with redundancy is modest – often equivalent to a single day’s cancelled operating list. Running costs are negligible. Energy savings from trusted AHU setback or shutdown, once real-time monitoring is in place, can deliver up to 40 per cent reduction in annual ventilation energy spend. In an NHS under constant financial strain, the argument writes itself. One day saved covers the investment. Every day after that is pure return.
From lag to lead: Practical solutions
Redundancy through air purification It is entirely feasible to design low-cost redundancy into clinical ventilation systems. Supplementary air purification can remove particulates and volatile organic compounds, while fresh or conditioned air manages CO₂ dilution. If the primary plant fails, a secondary system can activate automatically, keeping the environment safe. With an audit trail and continuous monitoring, estates teams can prove compliance and restore confidence. The shift from lag to lead transforms resilience.
Energy and Net Zero HTM 03.01 already encourages AHU setback and shutdown strategies, but uptake is limited. Why? Because in an open-loop system, staff cannot be confident the environment remains safe during reduced operation. With closed-loop monitoring, reassurance is built in.
Staff see that air quality remains within safe limits. Estates can allow automatic secondary systems to respond if thresholds are breached. The result? Significant energy savings and reduced carbon footprint, aligning directly with NHS Net Zero commitments.
56 Health Estate Journal November 2025
Patient safety: Surgical site infections The evidence linking airborne contamination to surgical site infections is longstanding. Monitoring airborne particulates and microbes is the first step. Automating responses through supplementary filtration or directional airflow is the second. Together, these interventions reduce infection risk, shorten stays, and improve outcomes.
Staff wellbeing During the COVID-19 pandemic, infection among healthcare staff was a major problem. In one clinical area we assessed, the airflow patterns caused contaminated air to be drawn across the nursing station – the very hub where staff congregated. PPE was in place, but PPE is the last line of defence and often fails in practice. By installing supplementary purification, particulate
levels dropped, and staff infection rates followed. Yet this was a reactive intervention – a lagging response. If monitoring had been in place, the issue could have been identified and mitigated proactively.
Case study: Lessons from the pandemic Consider a real example from the pandemic. A department reported unusually high staff infections. Commissioning surveys confirmed that air change rates were technically within design requirements, yet the layout had evolved over decades. Supply air crossed the ceiling and was drawn directly towards the nursing station. The result: concentrated exposure for staff. Retrospective action improved the situation, but dozens of staff had already fallen ill.
Had real-time monitoring been in place, early warning
would have been possible. Estates teams could have acted before the infection curve rose. Supplementary engineering controls could have been triggered automatically. This single example illustrates the cost of lag. Monitoring
transforms response from retrospective to proactive, from lagging to leading.
Future design principles
Vector flows and low-level extract Low-level extract behind patient beds, with supply air at the foot of the bed, ensures airflow crosses the patient and removes contaminants efficiently. This is particularly effective for heavier-than-air gases and airborne pathogens. Designers often prioritise ceiling supply for thermal reasons, but hybrid approaches are
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