Infection Control is About Reduction of Risk

Understandably, we are getting asked by a lot of people some variant of “Can you catch/kill corona virus?!?!?” 

The situation went from fake news to “Holy Cow!” in about 3.5 days, and people are looking for solutions.

I don’t want to re-hash the solid information that is already out there from the CDC, ASHRAE, the WHO, and others.  (Some of which are attached.)  This is an evolving situation and we continue to learn.

But I think it is important to emphasize certain things.

  • COVID-19 is dangerous because it spreads readily, and humans have no immunity to it. That is what makes it special/unique/unprecedented: its interaction with people.  In terms of its interaction with the external world and things like filters, UVC, and disinfectants, it is totally run of the mill.  So given the chance, MERV 13+ filtration will catch it; 254nm UVC, bleach, alcohol, etc. will inactivate it, and it will die by itself on a surface over time.  And, like other viruses, there are multiple paths to infection.
  • From the CDC: “The virus is thought to spread mainly from person-to-person. Between people who are in close contact with one another (within about 6 feet).  Through respiratory droplets produced when an infected person coughs or sneezes.  These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs.”
  • The virus itself is relatively small, ~0.15micron range. But it is coughed, sneezed, exhaled as part of a larger 0.6 to 10+ micron droplet nuclei.  The larger of these will fall quickly and that is why the focus on 6 feet of separation.  However, the smaller can remain suspended and be entrained into HVAC systems.
  • Infection control is about reduction of risk, not elimination of possibility. It is not one thing, but rather must be a systems approach with a lot of elements and purposeful redundancy. It is belts and suspenders.  Despite what some seem to be claiming, there is no magic bullet here.  There are just the regular bullets that have been employed in infection and contaminant control for decades:
  • MERV 13+ air filtration and UVC to capture and inactivate pathogens that are entrained into the HVAC system and prevent it from being a means of distribution/infection
  • Localized supplemental air cleaning systems.
  • High ventilation rates and airflow patterns that draw contaminants out of the breathing zone.
  • Isolation and negative pressurization of the areas where the sick are cared for.
  • Personal protection of face, eyes, nose and mouth.
  • Personal hygiene and frequent handwashing.
  • Frequent sanitation of all surfaces.
  • Social distancing.

This is not a complete or prioritized list. Each is a link in a chain, but not one of them is foolproof or 100% effective.

For example, having HEPA filters in the AHU doesn’t matter if someone coughs in your face.

Two important points on the above:

1.) Doing them well is critical, e.g. high-efficiency filters with gaps are not high-efficiency filters.

2.) since the effectiveness will be in the doing and real life is not a lab test, lab tests are useful for comparing products, but cannot be extrapolated easily to end results.

For example, a sufficient dose of UVC will kill essentially all viruses.   UV dosage is based on dwell time, proximity, and light intensity.  Supplying a lethal dose instantly as droplet nuclei are expelled is not possible and supplying the necessary dose in the fast-moving airstream of a duct is difficult and has many variables.

Therefore, while duct-mounted UVGI can be quite effective at significant inactivation and lowering of contaminant levels, it does not mean that all viruses in a space will be instantly killed.

Focusing on filtration and UVGI, from page 10 of the attached ASHRAE Position Document:

“The addition of highly efficient particle filtration to the central ventilation systems is likely to reduce the airborne load of infectious particles. This control strategy can reduce the transport of infectious agents within individual areas and from one area to another when these areas share the same central ventilation system….

…Local, efficient filtration units reduce local airborne loads and may serve purposes in specific areas such as health-care facilities or high traffic public occupancies…

… UVGI strategies for general application: (1) installation into air handlers and/ or ventilating ducts…

…In both duct-mounted and unoccupied in-room UVGI, the amount of radiation applied can be much higher compared to what can be used for upper-zone UVGI, resulting in higher aerosol exposure and quicker inactivation. Duct-mounted UVGI can be compared to filtration in the central ventilation system, because it inactivates the potentially infectious organisms while filtration removes them. UVGI does not impose a pressure drop burden on the ventilation system.”

Lastly, how can we help?

Dynamic has been designing and manufacturing air cleaning systems for over 35 years. We make high-efficiency filtration systems with low pressure drop—allowing for retrofit into air handlers that might not have the fan horsepower for high-efficiency passive filters.

We also make germicidal UVC systems, that irradiate both the airstream and a translucent capture media.  Both systems have been used for decades in high-impact medical, laboratory, and pharmaceutical applications, as well as situations like the anthrax clean-ups.  We are committed to doing everything we can to help fight this pandemic.

That said, our products fit into only one of at least six other things people should be doing.

Please make sure you do the other six as well.

From: The President of Dynamic Air Quality Solutions