COVID-19 and the Air Inside

Decades of research have clearly demonstrated the impact of Indoor Air Quality (IAQ) on building occupants. The health and well-being of building users are linked to the atmosphere around them, from inadequate ventilation to material off-gassing. In this age of virus hyper-awareness, the role of IAQ mitigation of airborne bioaerosols, like COVID-19, has yet to be explored.

IAQ is often boiled down to preventing sick building syndrome (SBS,) a complex process of poor ventilation compounded by environmental factors like outside contamination, building materials and inadequate ventilation. The latter is generally considered the primary reason for SBS complaints including cough, headaches, nasal irritation, etc. According to the National Institute of Occupational Safety and Health, bioaerosols  are connected to approximately five percent of IAQ issues. Bioaerosols are airborne particles of microbial, animal or plant origin, and include viable or inert viruses, fungi and allergens.

Inhalation of biological agents – whether transmission person to person or transfer from contaminated objects – remains a consistent public health issue in the workplace and in close quarters. Traditionally, as Dr. Brian Crook wrote in 2007, bioaerosol high-risk locations/professions have been understood as medical environments. Within the healthcare setting, airborne contaminates are plentiful, and not just biological agents. Potentially recirculating contaminated air through mechanical ventilation systems, heating, ventilation, and air conditioning (HVAC ) pushes risks further into the facility beyond the point of exposure when handling diagnostic chemicals, medical waste, aerosolized bodily fluids, etc. Evidence of COVID spread in the hospital setting was studied in China, where the virus was detected on surfaces and in the air. Importantly, this early survey in a hospital setting focused on parts of the air exchange system, with 66.7% of ICU air vent swabs showing the presence of the virus (although it is unclear if it was viable or inert).

A variety of indoor locations may be susceptible to bioaerosol contamination as well, like meat and agricultural processing plants, which are also found to have risks of COVID exposure. The IAQ of processing plants, with their prevalence of hard surfaces, colder air temperatures, and the creation of aerosols along with close proximity of employees, raises the chances of contracting an airborne virus. Workplace exposure to bioaerosols requires not just human-based interventions – handwashing or masks – but long-term technical solutions such as air filtration and, if possible, future technological advances in real-time monitoring.

With COVID altering lives – professionally and personally – groups like the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recently concluded, “that airborne exposure to the virus should be controlled. Changes to building operations, including the operation of heating, ventilating, and air-conditioning systems, can reduce airborne exposures.” The practice of reducing indoor exposures of dander, allergens and bioaerosols is a well-established cornerstone of IAQ mitigation techniques. The two main strategies to controlling and improving IAQ remain consistent – mechanical or natural methods – with the two sometimes combined as mixed-mode ventilation. Mechanical systems are traditional HVAC, while natural methods include windows or other systems designed to bring in outside air without mechanical assistance, known broadly as stack systems. An essential piece of the mechanical IAQ system remains the air filter.

High-efficiency particulate air filters (HEPA) are filtration systems rated by the size of the contaminant caught in its filtration matrix, with the higher MERV or minimum efficiency reporting value, the more restriction of airborne particulates. It is well understood the COVID-19 size is 0.12 microns, and MERV filters rated 13-16 are considered optimal for capturing airborne viruses. HEPA filters are found primarily in commercial construction, yet some of the best data on the performance of HEPA-type filters in confined space comes from the airline industry. “No evidence has been found that microbial contamination of cabin air entails a greater risk of disease transmission aboard a commercial aircraft,” wrote WHO authors in a 2008 study of aircraft cabin air. The International Air Transport Associate writes that there is, “15 to 20 cubic feet of total air supply per minute per person … [t]he total air supply is essentially sterile and particle-free.” Modern airliners possess redundant air filtration systems that constantly circulate and completely refresh air 20 to 30 times an hour. While this level of technical intervention is not proposed for buildings, it does demonstrate the quality of air achievable through thorough mechanical ventilation.

Based on the current understanding of COVID, ASHRAE recommends specific interventions to deal with the virus: increase outdoor ventilation (which increases dilution of individual ventilation), improve central air filters to a MERV 13 standard, and reduce air recirculation within the system. Air quality engineers at ASHRAE also suggest the use of portable HEPA air filters and consider ultraviolet germicidal irradiation (UVGI) for particular spaces. IEEE member Anderson Maciel notes IAQ’s best action, “seems to be the use of filters. Several ultraviolet light or ozone-based filters that kill viruses and bacteria have existed for years.” Even with the on-hand filters, UV irradiators, increase of natural airflow rates options, no one solution has been identified as we still learn about the novel virus.

And, without consensus as to how long COVID stays viable in the air or on surfaces, the distances it may typically travel, and whether speech is as distributive as a cough, IAQ elements and techniques may add to the non-pharmaceutical interventions recommended by health official`s around the world until a vaccine becomes available.


Image courtesy of Flickr. Originally published by S&S on July 23, 2020.


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