By Jon A. Barrett

Indoor air quality (IAQ) is extremely important for productivity and occupant health in any industrial, commercial, or residential property, and it has become even more important in the era of SARS-CoV-2 (the virus that causes COVID-19). HVAC air conveyance systems, with associated ductwork and ductless mini-split systems, provide acceptable indoor air quality atmospheres, but to operate effectively they must be inspected, maintained, and cleaned on a routine schedule, including replacing filters and cleaning ductwork interiors. HVAC system maintenance also helps the system to run more efficiently, therefore saving operating costs.

Air conveyance systems filter out dust, particulates, volatile organic compounds (VOCs), mold spores, bacteria, and viruses, as well as lower humidity levels by removing moisture. Unfortunately, dust, particulates, VOCs, mold spores, bacteria, and viruses—including SARS-CoV-2—can accumulate on the interior surfaces of HVAC systems and ductwork. Without proper system maintenance, this accumulated mass of debris can then become aerosolized and transmitted through air currents, worsening IAQ.

SARS-CoV-2 and airflow research

Regarding the SARS-CoV-2 virus, a study has shown that a human sneeze or cough can disperse smaller droplet nuclei into air currents up to 12 feet away and linger in the air for more than one minute.1 Another study confirmed that a burst from a person’s mouth at nearly a hundred miles an hour can travel as far as 27 feet.2 The airborne virus droplets can then make their way into a building’s HVAC system, where they will continue to circulate.

A ducted HVAC system creates air currents, which can likely carry smaller viral particles even farther. According to Chinese health officials, when the COVID-19 pandemic first started, 10 people from three families eating in a Guangzhou, China, restaurant became infected. Aerosolized droplet transmission was prompted by air-conditioned ventilation. Researchers reviewed a video from the restaurant and saw many of these patrons were more than six feet apart from one another, suggesting that the virus followed the airflow, traveling through the air.3

An ongoing study of environmental contamination obtained surface and air samples in two Nebraska Biocontainment Units (NBUs) and nine residential isolation rooms housing individuals who tested positive for COVID-19. The room surfaces that were tested included ventilation grates, tabletops, and window ledges. Virus samples with the highest concentration were recovered from an air handling grate in the NBU, suggesting that airborne droplets were drawn into the HVAC system.

A recent study of SARS-CoV-2 stability indicates that infectious aerosol may persist for several hours and on surfaces for as long as two days. The most prolonged viability of viruses was on stainless steel and plastic. The estimated median half-life of SARS-CoV-2 was approximately 5.6 hours on stainless steel and 6.8 hours on plastic.5 In conjunction, influenza viruses can spread through the air on dust, fibers, and other microscopic particles, according to new research from the University of California, Davis, and the Icahn School of Medicine at Mt. Sinai.6

Contaminant buildup

Although ductwork interiors can be made of smooth metal, fine dust can collect on air duct surfaces, vents, motors, and coils. Flakes of dead skin, hair, and pet dander catch onto the dust, and before long, this process creates a dense, mat-like environment where viruses, bacteria, mold, dust mites, and allergens can flourish.

hvac filter

HVAC filter with particulate. Image courtesy of Jon A. Barrett.

Dust adheres to surfaces and attracts other contaminants due to the force generated by static electricity, which is known as “Coulomb force.”7 For instance, when dust is carried on air currents created by air conditioning and similar devices, the dust takes on a positive or negative static electric charge due to contact with various objects. Additionally, when sources of dust (mainly people and clothing) are electrically charged, the dust that is generated from these sources is electrically charged as well.

Dust with a positive electric charge will be attracted to objects with a negative electric charge and vice versa. The more dust is in the air, the more considerable the amount of dust that clings to objects within the room, including air vents. Also, ductwork return airstreams contain levels of humidity and moisture that adhere to the ductwork interior and capture dust particulate.

HVAC air filters might help in capturing some viral particles and dust particulates. A high-efficiency particulate air (HEPA) filter effectively removes small particles—99.7 percent of particles as small as 0.3 microns. A minimum efficiency reporting value (MERV) filter removes larger particles, 0.3 microns to 10 microns. A MERV filter rated 17 or higher is considered HEPA-like in efficiency; however, most commercial buildings have MERV filters rated 12 or lower. Unfortunately, a coronavirus particle is about 0.1 microns and cannot be viewed with human eyesight, so there’s no guarantee that a HEPA filter would stop viral particles and dust particulates from traveling through the HVAC system.

Current standard air handling units in HVAC systems circulate up to 80-90% of the air in regular systems during peak-load conditions, such as winter and summer, when outdoor ventilation airflow is set at the minimum percentage to save energy. Standard filtration units in HVAC systems cannot remove the virus within an airstream effectively. Thus, the HVAC system has become a central point of contact to spread the virus by recirculating contaminated air into indoor spaces.

Based on the studies and information, proper HVAC system maintenance, including inspection; testing; surface and air sampling; cleaning; and disinfecting air conveyance systems and ductwork, can help prevent the transmission of COVID-19.

Course of action

The following is a list of HVAC system maintenance and disinfecting best practices that are especially important during the current pandemic:

  1. Review HVAC air conveyance systems and associated ductwork drawings and diagrams.
  2. While donning proper PPE, perform a visual inspection of the exterior and interior of the HVAC air conveyance systems and associated ductwork, registers/vents, motors, coils, and filters. Use a video borescope camera if necessary and take digital pictures. Document and log any observations, even if the ductwork “looks clean.”
  3. Test and inspect for any air leakage, VOCs, particulates, and duct metal seam issues.
  4. Perform pre- and post-surface swab sampling of the HVAC air conveyance systems and associated ductwork, registers/vents, motors, coils, and filters. The pre-surface swab sampling may identify any hazardous substances and hazardous particulates.
  5. Perform pre- and post-air sampling of the project area. Performing these samplings will help identify and isolate specific systems and affected areas, along with identifying any hazardous substances and/or particulates.
  6. Use environmental controls and infection control risk assessment protocols to contain and isolate the cleaning and disinfecting project. This includes setting up HEPA air scrubbers, negative air machines, and containment barriers while using a particulate counter and air pressure monitor.
  7. Ultra-low volume fogging using a non-acidic, non-chlorine-based Environmental Protection Agency (EPA)-registered virucide, biocide, and fungicide disinfectant can be implemented outside and inside ductwork, on registers/vents, motors, coils, and the entire project area to inactivate any viral aerosols. For efficacy, allow a minimum of a 10-minute dwell time or the dwell time per the virucide label.
  8. Clean the interior ductwork surfaces from larger dust and particulates using HEPA vacuuming, rotobrushing, air whipping, and mechanical cleaning. Interior fiberglass-lined ductwork requires specialized attention and cleaning to prevent fiber damage and release. Visually inspect to prevent recontamination.
  9. On metal interior ductwork, registers/vents, motors, and coils, clean and disinfect using a non-acidic, non-chlorine-based, EPA-registered virucide, biocide, and fungicide disinfectant. For efficacy, allow a minimum of a 10-minute dwell time or the dwell time per the virucide label.
  10. Replace and install new HEPA filters. Ductless mini-split systems may have a washable filter. It is best to HEPA vacuum the air conveyance unit and disinfect the washable filter often with an EPA registered virucide, biocide, and fungicide disinfectant. For efficacy, allow a minimum of a 10-minute dwell time or the dwell time per the virucide label.

As mentioned, it’s important for an HVAC system to be inspected, maintained, and cleaned on a routine schedule. If thorough HVAC system maintenance is performed, an air conveyance system will operate more efficiently, provide a healthier indoor air environment, and save costs over time.

Resources:

1 fau.edu/newsdesk/articles/mechanical-cough-coronavirus.php 

2 nationalgeographic.com/science/2020/04/coronavirus-covid-sneeze-fluid-dynamics-in-photos 

3 doi.org/10.3201/eid2607.200764

4 nature.com/articles/s41598-020-69286-3

5 nejm.org/doi/10.1056/NEJMc2004973

6 sciencedaily.com/releases/2020/08/200818094026.htm

7 keyence.com/ss/products/static/resource/solution/


Jon A. Barrett is the marketing manager of SERVPRO of Blackwood and Gloucester Township, NJ. He has more than 30 years of remediation and restoration cleaning experience across multiple sectors. Barrett has certifications from OSHA, EPA, IICRC, and ABRA, among others.