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Are you sure your air purifier kills coronavirus? Ask these questions before choosing a virus attenuation device

Dilip PatilEver since the CDC confirmed that Covid-19 is an airborne infection and can be transmitted through the air even beyond a two-metre distance, the FM market as well as the mainstream media have been flooded with air purifiers that claim to kill the coronavirus in the air itself.
While some of these devices are research-backed, the science behind some of the others at least needs to be questioned, if they aren’t already downright questionable. Since virus attenuation is a relatively new demand, decision-makers may not be familiar with how to inspect, assess and analyse a product before making an informed purchase.
Dilip Patil is a biomedical (electronics) engineer, has completed a course on Airborne Infection Control from Harvard Medical School Founder and is Managing Partner, Trivector Biomed LLP. He deconstructs the decision-making process of purchasing an air purification device that claims to kill the coronavirus.

What questions should one ask while considering a virus attenuation device?

  • What type/family of coronavirus (or any microbe) was the device tested on?
  • Was it an actual clinical isolate (aerosolized) of SARS, SARS-CoV-2, Delta variant virus or a surrogate marker (e.g. MS2 Bacteriophage etc.)?
  • Was it tested in a controlled environment in a lab in a bio-safety cabinet or in a big simulated chamber or real-life clinical setting? What was the size of the test chamber?
  • Was the actual device tested or was only the prototype or assembled components of the device used for the test?
  • Was an active air-sampling or a passive air-sampling method employed to collect the air samples?
  • Was the test process approved by the Ethical Advisory Committee? How were the tests conducted, the time intervals, duration of tests, repeat cycles, locations, number of occupants in the room etc.? What measuring devices were used?
  • What was the ‘Kill Log Rate’? How much time did it take to achieve this kill rate? It is important to know the ‘Kill log rate’ i.e. one decimal point (10-fold) reduction in the number of live microorganisms Colony Forming Units by using the device for a specified time. For example, assuming 10,000,000 microbes in air at a given time, a 1-log kill reduces the colony to 1,000,000 bacteria after a 90% reduction; a 2-log kill reduces the colony to 100,000 bacteria after a 99% reduction and so on.

What is the significance of tests and certifications advertised by the manufacturer?

Any device which is being used in the vicinity of human-beings should undergo electrical, electromagnetic interference, mechanical and bio-safety tests.

  • CE marking is a test for checking electrical and electromagnetic safety. Many manufacturers who claim to have Class-1 devices would have actually done self-declaration for the CE mark, and not been certified by a third party.
  • UL867 standard is for evaluating the amount of ozone generated by portable air-purifiers. It should be below specified limits set by EPA/UL/OSHA etc.
  • EPA (Environmental Protection Agency) compliance
  • OSHA (Occupational Safety & Health Administration) Standards/Guidelines
  • US-FDA (510K) Approval: It is not the same as FDA’s temporary Emergency Use Authorization (EUA) for COVID-19 purpose, which many Air Cleaners claim to have.
  • For India it is NABH accreditation or testing/validation done at ICMR affiliated labs, even though US-FDA’s (510k) approval shall suffice.

Is it possible to have an air purifier that is effective against multiple categories of pathogens (viruses/bacteria/fungi)?

An ideal air-purifier, irrespective of the technology used, in principle is supposed to reduce all sort of airborne impurities without any discrimination towards any micro-organism. However, the by-products of discharge released in the room by most air-purifiers to neutralise the microbes would also attack good microbes and human cells.

Many air-purification technologies or combinations of multiple methods can reduce/eliminate bacteria, viruses, fungi, molds, VOCs and odours. There are technologies like plasma, which totally eliminate all types of pathogens on contact inside a device within nano-seconds, not allowing microbes to replicate or mutate, and release only disinfected air in the room.

Certain devices which claim to neutralise only a particular pathogen or limited family of it, will have limited utility in controlling other airborne infections and may not be viable in the long-run (e.g. when the Covid-19 pandemic subsides).

How is such a device tested to calculate the maximum area in which it is effective?

HygieneTo say that a certain device is effective up to a certain area/ volume of the room is not an accurate statement, as the effective coverage of an air-purifier depends on many factors.

The performance or coverage of any air purifier is measured normally by the air flow volume (in cubic feet per minute – CFM) of the fan motor used by the device at different speeds. Many air-purifier companies also label it as Clean Air Delivery Rate, measured only for dust, smoke and pollen at full fan speed as recommended by American Association of Home Appliances.

For example, if the device has an air-flow rate of 100 CFM, that means hundred cubic feet of air volume in the room would be processed by the device in one minute. i.e. A device with 100 CFM rating can process all the air in a closed room of 1,000 cubic feet in 10 minutes.

The actual calculations are very complex and depend on multiple factors including the bio-burden, type of microbes, aerodynamics of the room, height of the room, number of people, number of openings/closings of the room, natural/mechanical ventilation available in the room etc.

Air Changes per Hours (ACH) is another term which is used frequently, pertaining to AHUs and HVAC systems. It indicates how many times the entire air of the room is replaced with (presumably) fresh outside air or decontaminated air in an hour. There are recommended numbers of ACH for each area in the healthcare setting.

For in-room portable air sterilisers, it is a measure of reduction in bio-burden (dilution of impurities in the air) which is equivalent to replacement of room-air in an hour. It is known as eACH (equivalent Air Changes per Hour delivered by the air-purifier) which adds to the ACH provided by the HVAC system or other ventilation methods.

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