HEALTHCARE FACILITY AIR QUALITY
Protection in larger spaces When we look at larger spaces, we have more options. Our starting points continue to be the NHS Health Building Notes (HBNs), and Health Technical Memoranda (HTMs), especially HTM 03- 01, Specialised ventilation for healthcare premises. Readers of this journal will be well-acquainted with their advice, requirements, and regulations, with particular relevance to ventilation and litres per second of air change. In the September 2021 issue of HEJ, Steve Tomkins of BESA covered this important aspect of ventilation, and also the importance of controlled relative humidity. Bacteria like high humidity for reproduction, so a high relative humidity is to be avoided (also for human comfort levels), but lower the relative humidity too far (below 40%), and viruses in the air start to become preserved.
We have been advised that ‘good’ (and ideally ‘natural’) ventilation is important to disperse airborne aerosols, and thereby reduce the risk of catching a COVID-19 infection. It is also preferable to follow processes of infection prevention by destroying the sources of infection as early in the process as possible. The means to remove and destroy microbes can also be effective in destroying other pollutants such as allergens and odours at the same time. The HBNs and HTMs do not always cover in detail the pros and cons of different technologies. There are systems which are systematically purifying the air while a room is occupied, and there are more aggressive approaches that can, and must, only be used on spaces which can be vacated while the disinfection process is carried out.
Ongoing protection
As I have already explained, air filtration is a sound basis to remove particles from the air, but it does not destroy them. As a means of ongoing disinfection, ultraviolet light in the UVC wavebands is good at killing microbes, but is also dangerous to human skin and eyes. Research has been taking place at the University of St Andrews, and with the University of Leeds and Dundee’s Ninewells Hospital, to explore the use of Far-UVC, which is less dangerous to humans, and has potential in the future, but in the meantime the risks
UV BULB
PHOTOCATALYST (TiO2
) OH OH OH OH OH
Photocatalyst absorbs UV light
Strong oxidising hydroxyl radicals (–OH) are formed
OH OH OH Cells of
microorganisms are destroyed
Bacteria, pollutants and allergens decompose
Figure 3: A graphic showing the kinds of processes possible in a more sophisticated UVC system. 90 Health Estate Journal September 2021 OH
BACTERIA & POLLUTANT
Figure 2: A UVC air decontamination unit.
of UVC mean that the light source has to be contained out of sight. Air therefore needs to be pumped to and through the UV units to eradicate the microbes; thus the effectiveness of the units depends on the ability to get the air circulated around a room at a rate that is proportional to the air space being treated.
Not all UV units are the same, and some are more effective than others. The wavelength of UV emitted is critical to ensure that microbes will be killed. The quality of the quartz in the UV bulb will affect the quality of the UV emitted. Argon filling and leakage prevention are critical elements of a long-life effective unit. In addition, greater efficacy can be achieved by combining technologies: for example, one system employs titanium dioxide in the UV unit, which utilises the UV light to activate the TiO2
into a
photocatalyst, which creates strongly oxidising hydroxyl radicals from the water molecules in the air. Not only do these radicals help to break down macromolecules such as volatile organic compounds (VOCs), carbohydrates, proteins, lipids, etc. in the pollutants in the air, but these radicals are also released to circulate in the outer air and kill bacteria around the room and away from the UV unit, without harming the room’s occupants.
Again, among the more sophisticated systems, specialist prefiltration units make use of a series of filters that are first bactericidal, virucidal, and acaricidal, followed by medical grade HEPA H13 filters, and then Very High Density
OH OH CO2 OH H2 OH O H2 O
Harmless water and carbon dioxide are formed
H2 O H2 O CO2
Activated Carbon filters. Localised production of ozone can then kill remaining microbes as they pass through the unit. There are models from NatéoSanté that not only do this, but also have air quality indicators monitoring VOCs and particulate counts, and a data log of how these have changed over time. The company’s EOLIS Air Manager Active Oxygen system also can be switched to an ozone room decontamination mode, as discussed below.
Room decontamination Just as there are times when a ‘deep clean’ of a room is called for, there are also times for a ‘deep disinfect’. For this the room needs to be vacated, the disinfection process carried out (without leakage of the disinfectant elsewhere), and then any residual disinfectant removed from the air before the room is reoccupied. For this kind of process to take place, the room needs to be airtight, and ventilation systems switched off, so that the disinfecting chemical does not leak out of the room. There is technology available to confirm how airtight a room is, such as the Portascanner AIRTIGHT 520, or Portascanner COVID-19, both from Coltraco.
For room decontamination there are disinfectant systems that can be applied locally from devices with hand-held spray nozzles, and these are valuable for disinfecting smaller areas, and for items that cannot be removed into washer- disinfector equipment. This approach is particularly useful for textile/upholstered
CO2
©Airdri
©Airdri
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