COVID-19 Manual Case Studies: One Birdcage Walk


The IMechE building in London, One Birdcage Walk, has sample units installed to demonstrate how UV units can be used to clean air in meeting rooms.

Figure 1, shows such a mobile unit, supplied by Midtherm UV, installed at One Birdcage Walk reception area as a demonstration unit, where it cleans and sterilises re-circulated air. The unit is capable of treating up to 250m3/h and can be wall or ceiling mounted.


This particular unit has been tested by the NHS at the Freeman Hospital in Newcastle, by the NHS Northern Medical Physics department, to verify that it is safe to be used in public areas. The internal irradiance was also measured by them; this measurement when used with the dwell time the air spends within the reactor zone confirms that the UVC dose administered is more than twice the LD90 figure (3.3 mJ/cm2) for influenza type viruses, at 6.98 mJ/cm2. This means that each time the air is re-circulated through the sanitiser there will be a 99% reduction in the virus concentration of the  air being treated.

Figure 1

  Figure 1: Midtherm UV air cleaner on show in entrance area of One Birdcage Walk

An alternative room unit is available as a recessed ceiling unit to go into a false ceiling grid and supply cleaned air via jet nozzles. A demonstrator is installed into a lower ground meeting room.

It is recommended that before installing any UV units, or any similar, verification checks should be undertaken. Manufacturers should have completed investigations using a UK laboratory to establish the viability of the equipment, availability of spare parts (particularly lamps) and terms of the Warranty. Each of the units on display ay HQ have been through testing procedures at NHS and/or PHE and the manufacturers can provide copies of results if requested.

UV light is hazardous to humans and should be obscured. With any UV air cleaner, the UV lamps must be hidden from view whenever operating.

The type of units used as demonstrators at HQ have the UV lamps hidden within and use a fan to draw air across the lamp. This ensures the lamps are not visible to humans and that the lamps have close contact with the air borne particles and sufficient dwell time to ‘kill’ the virus.

COVID-19 Task Force


Francis Mills


COVID-19 Task Force

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