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Indoor Air Quality: Mitigate Risk Of Aerosol Spread

Last updated: 12-22-2020

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Indoor Air Quality: Mitigate Risk Of Aerosol Spread

Even before the COVID-19 pandemic, the impact of indoor air quality on the health and wellness of occupants was becoming increasingly important. Issues such as mold spores or Legionella, organic gasses, particulate matter, radon, and other contaminants have traditionally been concerns for building occupants and facility management. In 2020, indoor air quality became front and center for buildings as CDC and ASHRAE stated that COVID-19 viral particles are likely spread not only through droplets but also via aerosols. Reducing exposure risks to building occupants cannot be accomplished solely through the strategic placement of plexiglass barriers and surface sanitation; it requires ventilation system optimization, verification by testing, and management.

According to ASHRAE in 2020, “the transmission of SARS-CoV-2 through the air is sufficiently likely that airborne exposure to the virus should be controlled. Changes in building operations, including the operation of heating, ventilation, and air-conditioning systems, can reduce airborne exposures.”

Before installing enhanced filtration or advanced air treatment technology, it is important to assess current building ventilation conditions as an initial step. A ventilation health check will assess the system and identify corrections needed for proper functioning, as well as identify maintenance needs and potential occupant health hazards. An assessment should look for biological growth on coils, damper/actuator function, filter condition, and drain pan function. The assessment should verify the controls system is properly functioning so that adequate outside air is entering the building, and confirm preventative maintenance is being performed correctly. This information can be documented in a database to provide verification of building conditions and identify and track corrections.

Assessing and optimizing a building’s current system is an important first step before investing in enhanced filtration or additional technologies. In a recent facility health check of more than 850 units, we at NV5 found 800 of these had issues that required resolution—with 600 potentially creating occupant health hazards (see Chart 1). The inspection check found that 600 units were wasting energy and fixing those problems would result in cost savings over time. These cost savings can offset costs of implementing mitigation measures.

With a firm understanding of your existing system documented, the next step is to identify the mitigation measures that will help prevent potential infectious aerosol spread through the building. ASHRAE guidance for 2020 identifies that the management of indoor air to control the distribution of aerosol movement is critical.

There is technology that uses completely safe DNA particles that are the same size as the SARS-CoV-2 (i.e., COVID-19) viral particles to approximate viral movement and measure load to assess the system for potential risks. It can also compare different mitigation technologies to determine what will work best for the space. This technology can also test room dynamics, and answer key questions such as how long will it take a viral load from an infected individual to disperse in an enclosed space, such as a conference room to a non-infectious level. Testing using this technology can provide data to determine the most effective mitigation combinations of different technologies, increased airflow, enhanced filtration, plexiglass barrier placement, and other mitigation measures.

The technology involves the release of droplets and aerosols from an aqueous solution containing a calibrated concentration of particles to simulate a sneeze or cough of an infectious individual. Air sampling devices are set up in different areas of the building and simulate inhalation. These sampling devices capture particles and are measured in a laboratory. This tracer diagnostic can provide a quantitative assessment of various mitigation measures. This diagnostic tool provides data for the analysis of the impacts of different technologies, changes in airflow, increases in outside, air, space utilization, among other decisions to keep people in buildings safe.

Following efforts to improve a facility for COVID-19 readiness, it is important to continue to operate according to the mitigation measures put in place for the health and wellness of occupants, as well as to optimize for energy savings (potentially offsetting costs of upgrades). Monitoring-based commissioning (MBCx) uses continuous sensor data to give the building owner, engineers, and operators a continual stream of information that helps identify operational issues as these occur, thereby minimizing health risks, saving time, money, and energy consumption over the lifetime of a building (see Chart 2).

MBCx uses sensor technology to continuously collect data, anchors on the continuous flow of big data, leverages the power of IoT (the Internet of Things), data transmission and storage, and applies engineering intelligence on top of analytics to continuously identify building issues that are often overlooked or invisible during manually driven operations and commissioning. After investing in the optimization of building operations as recommended by ASHRAE and using diagnostic tools to make the best choices of mitigation strategies to improve building health, it is important that those measures be maintained. Ensuring that the building continues to function under the proper settings and indoor air quality is critical. MBCx ensures those settings are maintained and provides assurance of building system optimization for its occupants. MBCx provides continuous building oversight, and an ongoing basis, indoor air quality levels and ventilation levels can be tracked by air quality sensors as conditions can change with seasonality and weather. Temperature, humidity, particulate matter counters, VOC sensors, and carbon-monoxide (CO) sensors can be used to provide real-time and historical data to model indoor air quality within a given space as an additional level of assurance and remotely inform of air quality issues in real time.

ASHRAE makes specific recommendations around increased outside airflow, control of humidity, and filtration enhancement to reduce the potential for aerosol spread of SARS-CoV-2 in facilities.

The key steps to ensure building occupants have a healthy building space are:

Coupled together, these approaches provide occupants with the safe indoor air quality and provide ongoing data to demonstrate optimal performance. 

Kay is Chief Operating Officer, Environmental Health Sciences at NV5, a global engineering and environmental company based in Hollywood, FL.Kolimar is a mechanical engineer with an energy efficiency focus in Energy Efficiency Services at NV5. The company’s industrial hygienists, indoor air quality experts, and mechanical engineers have been helping businesses and communities mitigate risk through COVID-19.

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