Before considering which method of purification to use, consumers must first understand exactly how each technology works because this impacts how practical and effective they are.
For example, there are many passive technologies being sold as solutions for viral transmission prevention but one must remember a passive system can only perform its task if the following conditions are met:
– the pathogen or pollutant or particulate must first be drawn into the unit
– the pathogen or pollutant or particulate must be stationary and/or have passed very close to direct UV-C source and/or through an ionisation field.
– the pathogen or pollutant or particulate must not be smaller than the filter grading which excludes all viruses
If one considers it can take hours/days/never and lots of energy for these conditions to be met for airborne particles and never for surface contamination it is undeniable that the risk of viral transmission remains high with passive systems so they should not be used for this purpose especially if more effective alternatives exist.
There are other drawbacks with passive systems. Filters collect dust and quickly become clogged up which affects performance. They also become breeding grounds and harbours for viruses and bacteria which creates a health risk when filters are changed and allows pathogens to fall off and get passed back into the room. Also filters, UV-C and PCO technologies do not guarantee to remove or destroy all pathogens as they pass through the unit. For example, HEPA’s smallest grade is 0.3 microns yet all viruses are smaller than this so will pass straight through and back into the room. Also, UV-C and PCO are subject to the Inverse Square law and require “dwell time” to deactivate viruses, bacteria and odours meaning their effectiveness drops off considerably the further away the particle is (at 4 inches distant UV strength is reduced by 93.75%) and they have no effect on particles in a moving airstream. Ionisation only technologies cause particles to drop out of the air or collect on plates and viruses, bacteria or odours remain infectious and a health risk for hours before they are deactivated. Similarly, PCO and ionisation technologies are known to produce dangerous and even carcinogenic by-products including ozone and Formaldehyde.