Sanitising options compared
What can you use to sanitise a room with people in it?
Seven things are in common use: Far-UVC at 222nm, ordinary UV at 254nm in empty rooms or sealed ducts, upper-room UV, HEPA filters, ionisers, chemical fogging, and ventilation. They differ in whether they treat the air, the surfaces or both, whether they can run with the room occupied, what they use up, and how good the evidence is. Far-UVC is the only one that treats both air and surfaces, continuously, in the part of the room where people are breathing, without moving air, spraying chemicals or changing filters.
| Treats | Works with people in the room? | Evidence | Issues | |
|---|---|---|---|---|
| Far-UVC 222nm (the ProTech 2) | Air and surfaces, whole room | Yes, inside the exposure limits | Chamber, occupied-room and clinical studies | |
| 254nm UV, mobile towers and fixed lamps | Air and surfaces in line of sight | No, the room must be empty | Long established | Room must be empty - contaminated when people enter |
| 254nm UV in the duct | Only the air passing through the duct | Yes, it is sealed away | Established for ducts and coils | Only sanitises air that has been extracted |
| Upper-room UV, 254nm | The air in the top of the room, relying on mixing | Yes, with louvred fittings and a high ceiling | Strong, from TB control | Limited efficacy for where people actually are |
| HEPA filter units | The air drawn through the filter | Yes | Strong for removing particles | Only sanitises air that has been extracted |
| Bipolar ionisation | Air, according to the makers | Yes | Weak and contested; not recommended by ASHRAE for pathogens | Poor efficacy |
| Chemical Fogging | Surfaces and air | No, empty the room and air it afterwards | Established for surfaces | Room must be empty - contaminated when people enter |
| Chemical cleaning | Surfaces (not air) | Yes | Established | Requires significant manpower, chemicals may cause issues for people |
| Ventilation | Air, by dilution | Yes | Strong | Either a strong breeze through room or low efficacy |
Why the differences matter
Illness spreads through the air people breathe and the surfaces they touch, at the height people are. Anything that only treats the duct or the top of the room depends on how well the air mixes before someone inhales it. Far-UVC treats the breathing zone directly.
254nm UV and fogging work well but need the room empty, so they can only reset a room between uses. The first person back in starts the contamination again. Things that run with people present, Far-UVC, HEPA and ventilation, keep the load down all day.
HEPA and ventilation do nothing for surfaces. Fogging does nothing for the air once the spray has settled. Far-UVC does both.
Fogging and chemical cleaning puts chemicals into the room and, on a ship, eventually over the side. HEPA units need filters and make noise. Far-UVC uses 20W and a lamp every couple of years.
Ventilation, HEPA and upper-room UV have decades of evidence behind them. Far-UVC now has peer reviewed studies in occupied rooms and clinics; see the studies. Ionisers have repeatedly failed to match their makers' claims in independent tests and can produce ozone; the professional bodies advise against relying on them.