INF ECTION P R EVENTION
ventilation engineering level of control. “That means that we have to try and improve the amount of clean-air in the environment compared to the amount of contaminated air. The research has shown that there are certain types of ventilation – beyond just different speed and volume of ventilation – that can benefit healthcare workers better without being detrimental to the patient. “And this report has tried to highlight
those particular designs to show that if you are going to build a new hospital with new isolation rooms, these sorts of design are what you might want to follow.” The IOSH report focuses particularly on treating patients in isolation rooms, which are typically provided with a minimum of 10 air changes per hour of mechanical ventilation. It underlines the importance of mechanical ventilation in reducing airborne aerosol infection.
At MTX Contracts, we recognise the
importance of engineering air movement and clean-air flow pathways within modular buildings – particularly those housing patients. Those factors are a vital consideration for our engineers when assessing the performance of the buildings we provide for health Trusts and hospitals. Optimum airflow is accepted as an
important factor in the health, wellbeing and comfort of patients and staff. It is much more difficult and expensive to retrofit air handling systems to modular units, which is why it is so important to give it full consideration at the design and build stages. David Guilfoyle is a director at consulting mechanical and electrical engineers DSSR which works with MTX. DSSR has been involved as a technical expert in updating the HTM 03-01 memorandum to make it fit-for-purpose in modern healthcare. The new version is currently being ratified for publication later this year. He explains: “Ventilation has become much more of an issue with the emergence of COVID-19, and it has reshaped the priorities for ventilation requirements. We work with MTX to ensure that the air handling provision is effective, bringing maximum benefit and enhancing the safety of patients and staff.” DSSR designs central air handling for each modular unit according to how it will be used, the patient group and the internal configuration.
David argues: “You have to walk in the shoes of the people who will be working in that building. If you simply follow the basic HTM guidance you are not walking in their shoes. HTM is a baseline, not a target. “Without talking to the clinicians and the infection control team you cannot possibly design an air handling system that is fit-for- purpose. You must know the configuration of the beds and know how they are to be used.
Airborne aerosol particles need drag force to keep them up and gravity to bring them down. But air velocity in a room is known to impact on this and various-sized particles can remain in the air for a significant amount of time, often travelling quite far from their original source – particularly when driven by patient coughing typical in someone suffering from COVID-19. That is where clean-air ventilation can have a significant impact.
Then you can design the system around the clinical requirements, not simply pump air into the room. The configuration, positions of walls and corridors all influence the effectiveness of the air handling system. “For example, people talk about 6 or 12 air changes per hour (ACH) ventilation rate in terms of volume, but that rate depends on the configuration. Previously one of the priorities for air exchange was mitigating the effects of medical gases that could affect staff. Now it is more about infection control – a priority that has gained momentum over the last year.
“Six ACH may be quite appropriate for one layout, but a different layout occupying the same floor space may require 12. It should a bespoke solution every time to provide the benefit of flexible M&E design by experts in their field who understand the needs of staff and patients.” David adds: “We must also take into account air dilution rates – which reduce the particulate content of the air – a vital tool in reducing airborne infection of a virus like COVID-19. In addition, clean-air pathways can be custom-designed according to the configuration of each individual modular building. If you want to capture the ‘bad air’ and vent it – then it all comes down to the pathways you create through the design of the system. Interestingly, the study published in February once again brings into question how areas such as corridors and communal spaces are ventilated, due to the coughing issue which could be anyone in the facility. These types of areas generally get forgotten about.” Factory-built units are too often simply mass-produced shells; they are not engineered for a specific purpose which may vary from one hospital site to the next. It is not one-size fits all. For example, people who deliver a building in just a few short weeks may be working hard to fulfil a need – but the building they produce may be a basic shell which could as easily be a schoolroom or an office. Modular buildings
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used for patient care should be specifically designed and engineered for healthcare use. Taking into account the threat from COVID-19 it is apparent that more attention needs to be paid to ensuring mechanical ventilation is considered in every case when designing and creating modular buildings. CSJ
Reference 1 Dodd JW, et al, Aerosol emission from the respiratory tract: an analysis of relative risks from oxygen delivery systems, February 2021. medRxiv preprint doi:
https://doi.org/10.1101/2021.01.29.21250552.
About the author
David Hartley is managing director of MTX, a specialist healthcare construction company providing design, construction, funding and aftercare services for MMC (Modern Methods of Construction) healthcare projects throughout the UK. He has worked serving the NHS and private healthcare sectors for 27 years and, during this time, has supported MTX in becoming a ‘leader in the provision of innovative, compliant, healthcare buildings’.
APRIL 2021
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