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VENTILATION TRADITIONAL APPROACH CLEAN AIR FLOW PATH E


LOW LEVEL EXTRACT EITHER SIDE OF PATIENT HEAD TO ENSURE MAXIMUM CAPTURE OF CONTAMINANTS.


S


GRILLE/DIFFUSER POSITION NOT DEFINED.


SUPPLY AT FOOT OF BED TO ENSURE OPTIMUM AIR FLUSHING OVER PATIENT.


E A BEDROOM A A BEDROOM E


LOW LEVEL EXTRACT EITHER SIDE OF PATIENT HEAD TO ENSURE MAXIMUM CAPTURE OF CONTAMINANTS.


A S


E


E


En-Suite PLAN VIEW


En-Suite PLAN VIEW


HIGH LEVEL MECHANICAL VENTILATION EXTRACT


HIGH LEVEL MECHANICAL VENTILATION SUPPLY


ES


HIGH LEVEL MECHANICAL VENTILATION SUPPLY


S


LOW LEVEL EXTRACT. CAPTURE HEIGHT TO BE UP TO PATIENT HEAD.


E


CROSS SECTION A-A VIEW KEY


ROOM CONTAMINATION ONLY REDUCED BY DILUTION THROUGH AIR CHANGES (SPREAD OF CONTAMINATION UN-CONTROLLED


AIR FLOW PATH. KEY DIRECTION OF CONTAMINANTS. AIR FLOW PATH.


CROSS SECTION A-A VIEW


Figure 1: Traditional patient bedroom ventilation strategy: With a typical patient bedroom ventilation strategy, there is no defined methodology for the positioning of the supply diffusers and extract grilles, and it is largely down to the interpretation of the designer to promote good air distribution. A high-level air distribution strategy is commonplace in most standard patient bedrooms and multi-bed ward environments. This relies on the air moving/mixing within the space, and being delivered/extracted at a rate to meet the required air change rates. As the air distribution is largely uncontrolled, the removal of contaminants is reliant on dilution through the replenishment of the room air with fresh air via the ventilation system.


Highest risks in indoor settings In her IHEEM Digital Week 2020 presentation, Prof. Noakes acknowledged that there is little data from real-world medical settings about COVID-19 transmission, but explained that evidence from community settings indicates that the highest risk is probably within indoor environments, and over short ranges. In addition to droplets settling on surfaces, and the virus transmitting directly between people during physical contact, there is also evidence of airborne transmission of COVID-19, particularly in poorly ventilated spaces, placing added onus on ensuring effective and appropriate ventilation of spaces housing patients. Prof. Noakes pointed out that 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. This is where clean-air ventilation can have a


46 Health Estate Journal February 2021


Figure 2: Clean air flow path ventilation strategy: Good ventilation in healthcare settings is becoming increasingly important, and the current pandemic is changing the requirements for ward environments to be flexible in their use. Creating a clean air flow path via appropriate positioning of the supply diffusers and extract grilles focuses the air flows, reduces the reliance on contaminant dilution, and promotes source extract. While traditionally utilised for scenarios when anaesthetic gases were used, the benefits of clean air flows in the reduction of patient-to-patient cross-contamination are well documented.


significant impact. “If a space is well ventilated you can’t completely contain the virus, but the ventilation will dilute the virus and the risks are technically lower,” reasoned Professor Noakes. This view is reflected in the Federation of European Heating, Ventilation and Air Conditioning Association’s recently-updated REHVA COVID-19 Guidance, which cites ventilation as the principal engineering control to help control infection, thus giving further weight to the vital role that ventilation plays in the COVID-19 response effort. The guidance document states that in hospitals with an optimal 12 air changes/hour (ACH) ventilation rate, aerosol transmission is mostly eliminated, but in poorly-ventilated spaces, it may be dominant.


Considering smaller, ‘more relaxed’ environments Professor Noakes suggests that in a hospital context it is not the obvious patient wards that will be most affected, as these tend to be better ventilated.


Instead, estates and facilities managers and IPC teams need to also consider smaller, more ‘relaxed’ environments such as staff restrooms, waiting areas, corridors and treatment rooms. ‘Hospitals need to consider where they are ventilating and what impact this has on a particular space’, Professor Noakes said. However, mechanical ventilation is not provided in the standard specification of modular buildings, and compliance with HTM 03-01 simply means that the supplier has met the most basic standard stipulated. In addition, as with any natural ventilation method, the air flow and air change rates cannot be guaranteed, as they are subject to external factors such as wind speed and direction.


The HTM 03-01 standard dates back to 2007, and therefore does not take into account the latest thinking on the need for clean-air design within the types of modular buildings increasingly used by hospitals for patient accommodation. When it was produced in 2007, the use of modular buildings was very limited, but


©David Guilfoyle, DSSR


©David Guilfoyle, DSSR


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