What’s the Current Challenge with Contagious Disease & Indoor Air Quality?
Research has shown that certain environmental conditions will contribute to the transmission of infectious diseases requiring multiple key steps to reverse that transmission. Ventilation supplemented by proven air purification technology has accomplished this. The new variant strain of SARS CoV-2 Omicron is continuing it’s march into the world’s indoor air environments and there will be more strains of covid and other infectious diseases to follow. The good news is that this pandemic will eventually end. The bad news is that influenza and the COVID variants will be with us for years. The current low rates of influenza and common colds have shown us that we can effectively reduce these contagious diseases by effectively cleaning the air we share with others. The focus needs to be on the areas where person to person transmission is occurring.
It is clear now that the vast majority of the spread from person to person is the result of inhaled aerosol, with a lesser amount of transmission attributed to droplet contact. Indoor aerosols linger longer inside that outdoors and in a stale air environment may pose a transmission threat for up to 72 hours under the right environmental conditions. Also, certain environmental factors such as relative humidity and carbon dioxide levels and other common airborne components can actually increase the overall transmission.
What Are the Real Variables?
Single step actions to clean and disinfect the indoor air will not be effective in a real-world setting.
Marketing rhetoric claiming a 99.9% reduction in particles, microbials or viruses are primarily generated in closed testing chamber settings. The varied circumstances found in a real-world setting where transmission can occur by several potential routes and where frequently found conditions actually promote the spread are everchanging and problematic. Providing the best overall indoor air quality is a necessary component to success.
What Are the Choices?
Ventilation, natural and mechanical, is the first and primary choice to reduce the risk of airborne infections.
The US CDC recommends 6 to 12 room air changes per hour (ACH) with infection free fresh air. Studies have shown that one air change removes approximately 63% of room air contaminants, the second air change, another 63% etc. The greater the source of infection, the higher rate of infection free air is needed. For Omicron, 6 -12 ACH of infection free ventilation may not be enough. Achieving that high rate of ventilation is beyond typical building and HVAC design parameters. Adding HRV and ERV devices can assist in boosting that number of turns but risk the advent of recirculating air containing airborne contaminants throughout the building. Mechanical alterations are also costly and may not be possible in some building designs or in settings that are required to support the buildings usage or function. To battle the viral pathogens that are emerging, equivalent ventilation producing high levels of supplemental air disinfection will be needed.
The Importance of High Efficiency Air Filtration
The use of MERV 14 to 20 high efficiency HEPA filters that remove up to 99.9% of respirable particles can convert recirculated air into an equivalent of infection free air. This will require the use of these filters in duct systems within central forced air systems as well as in portable in room units. There is little confirmed evidence that this virus is successfully transmitted through duct systems but it is theoretically possible. This strategy supports the practical action of decontaminating the air within the room where the person-to-person transmission is occurring.
Portable in room units depend on two key factors to evaluate their efficacy.
1. The CADR (clean air delivery rate) relative to the space being treated.
2. The flow patterns of the treated air within the space.
When this supplement action can produce at least 6 ACH throughout the entire space, these in room units can provide an effective intervention to reduce in- room transmission of airborne pathogens and viruses.
Germicidal UV (GUV) Technology
UV-C refers to ultraviolet light with wavelengths between 200 – 280 nanometers(nm). UV-C destroys the RNA/DNA of microbials, infectious diseases and viruses, rendering them unable to replicate. UVGI (Ultraviolet Germicidal Irradiance) effectiveness depends primarily on the UV dosage delivered to the microorganisms and the necessary dwell time being achieved to produce the desired inactivation level of > 99%. PCO (photocatalytic) and PHI ( photo hydro ionization units) emit an output of ionized hydro peroxide plasma using a metal oxide semiconductor that produces a faster inactivation rate in the air and on surfaces.
This technology is used in upper room germicidal UV (GUV) fixtures, in duct probe units, engineered systems inside Ahu (air handler units) and portable in room devices. The air mixing produced by upper room units results in high rates of air disinfection in the lower occupied spaces sometimes referred to as the “breathing zone.” More efficient LED light sources are being developed for more versatility and may become the predominant technology for upper room use. The use of this technology is done in sealed applications or units where the UV light will not damage the outermost layers of skin and penetrate the liquid layer covering the surface of the eye. Portable in room air purification devices should be sized properly to produce an equivalent of 6 ACH and be placed in a strategic location in relationship to established air flow patterns.
Far UV refers to 222 nm UV that has the ability to be an even more effective use of GUV against airborne viruses and bacteria. Far UV appears to be much safer yet with little potential for even mild eye or skin irritation when used within the exposure guidelines and use of effective filters. GUV is much more cost effective and can be very effective in inactivating airborne pathogens and viruses. GUV devices such as handheld wands to deliver effective dosages of irradiance to surfaces are unreliable in delivering the sanitizing results needed based on the variability of application, dwell times needed on different surfaces and the lower dosage needed to avoid accidental over exposure to eyes and skin.
A variety of ionizers, (bipolar, unipolar and cold plasma) generate positive and negative ions, directed into occupied rooms and forced air filtered systems. Raising the indoor level of positive ions to > 500 ions per cubic centimeter is required to become effective. This causes infectious particles to be attracted to filters of stick to each other and settle out of the air and onto surfaces where they can no longer be inhaled. The overall effectiveness against airborne pathogens and viruses in a real-world setting is still being studied. This technology is inherently safe and will freshen the air. This can result in particles clinging to walls and surfaces that became ionized and the generation of ozone and interaction with other room contaminants to produce potentially other harmful compounds.
The Hybrid- Combined Technologies
The combining of these technologies into an active and passive synergistic application has emerged. This entails the combined use of HEPA air filtration, BPI and UVC in portable units designed for placement on walls, counters and floors. In duct HVAC applications utilizing UVC PCO and BPI are also available. Prefilters and HEPA filter are being coated with a proprietary coating that traps and destroys odors and VOC’s (volatile organic compounds) and increases the overall effectiveness of purifying air and sanitizing surfaces within the delivery area. This promotes a continuous air / surface cleaning and sanitation process.
Real World testing being performed on this hybrid delivery system has shown significant and sustained efficacy in reducing airborne VOC’s, allergens, pathogens and disease. This is utilizing existing proven technologies into a synergistic delivery system that is both cost effective and extremely versatile in application to achieve the best and sustained results.
It is clear that for indoor spaces, air disinfection is a safe and efficient way to reduce transmission. The continued practice of real-world on-site testing on the delivery devices designed to deliver these technologies is most critical. Technology is most effective when properly utilized and uniformly delivered to the target spaces. Implementation of effective air disinfection devices should find its way into building codes and practices so that we can be best prepared to mitigate ongoing epidemics and the next pandemic.
Edward A. Nardell, Feb 1st, 2022 – If we are going to Live with COVID-19, Its time to clean our air properly.
ASHRAE Position Document on Airborne Infectious Disease
ASHARAE Position Document on Filtration and Air Cleaning