5 Things to Know About Air Circulation in Indoor Venues

lone_star_college_seatingAs venues carefully reopen, all are looking for ways to reduce virus transmission inside to keep guests and staff safe. Over the past year, experts have learned a great deal about how COVID-19 is transmitted indoors and the best ways to help reduce the risks. The CDC and other sources have put together resources and information that venues can use. While air circulation is just one factor in preventing virus transmission, when it is carefully managed, it can be part of making a safer experience in your facility.

Understand Droplet Versus Airborne Transmission

The latest information suggests that COVID-19 can be spread not just through droplets, but through airborne aerosols, as well. Understanding the difference between these two transmission paths can help venues understand how to keep particles down and reduce the risks.

Droplets of moisture, transmitted by coughs and sneezes, can contain larger amounts of the virus. Large droplets tend to fall to the ground quickly, within three to six feet of the person who creates them. Their size tends to be between 60 and 120 microns, smaller than the width of a human hair. They can be largely prevented with the use of masks.

Aerosols, on the other hand, are far smaller particles that can be produced by speaking. They are far smaller than droplets, typically 5 microns or less. They contain less of the virus than droplets, so someone would have to inhale more of them to become infected. However, because of their small size, aerosols can travel long distances and can remain floating in the air for hours. Luckily, there are several things that venue operators can do to reduce the number of aerosol particles in the air.

When Possible, Open Doors to Circulate Air

Increasing the amount of outdoor air coming indoors is one important way to cut down on the risk of COVID-19. Circulating outdoor air inside reduces the concentration of the virus. In general, the greater the number of people indoors, the greater the need to ventilate with outdoor air.

When possible, keep doors and windows open to keep air circulating. This is especially important in high traffic areas.

However, it's not always possible or ideal to have open doors and windows. Loud outdoor noises, inclement weather, and other concerns can make it difficult to keep outdoor ventilation going. The CDC recommends limiting the number of people indoors, or limiting the number of people in specific rooms when you can't provide enough air from outside.

Use Air Cleaners in Poorly Ventilated Spaces

Filtration and air cleaning also have an important role in removing contaminants, like viruses, and improving overall air quality in an indoor space. Portable air cleaners, which are also sometimes known as air purifiers, can be particularly helpful. These tools can help in poorly ventilated areas where it is not practical or possible to introduce outdoor air, or in places where outdoor air pollution is high.

If you plan on using portable air purifiers in poorly ventilated areas of your venue, make sure they’re effective for removing tiny airborne particles, which can be reported differently from each manufacturer. Clean Air Delivery Ratings (CADR), using High Efficiency Particulate Air (HEPA) filters, or reporting particle sizes in tenths of micrometers (μm) are all ways effective air cleaning may be reported by purifier manufacturers.

Review HVAC Efficiency & Implement HVAC Best Practices

While portable air cleaners work on a single room, your facility's HVAC system filters air for the entire building before it is distributed through the rooms inside, so leveraging your HVAC systems is key to managing air cleanliness.

Talk to your facility's HVAC technicians about your venue’s system and its capabilities, and what can be done to make them more efficient. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has put forth some guidelines for HVAC efficiency and use in cleaning and purifying the air in your venue, such as:

  • Maintaining equivalent clean air supply required for design occupancy whenever anyone is present in the space
  • Operating HVAC systems for a minimum of three air changes of equivalent clean air supply to flush a space between occupied periods
  • Limiting re-entry of contaminated air from energy recovery devices, outside air intakes, and other sources

    As much as possible, ensure that the air is not blowing directly on guests. For example, in rooms with heaters and AC vents, make sure that airflow is directed carefully. This can reduce the chance of directing aerosolized particles that have gotten through the filter system at individuals.

Use Fans With Caution

Fans can be a great tool for directing indoor air outside to reduce the concentration of aerosol particles. Exhaust fans in bathrooms and kitchens can remove contaminants while also bringing more outdoor air in.

There is still a lot to learn about the impact of indoor fans, such as portable fans and ceiling fans, when it comes to transmission of the virus. Because of this, experts recommend using those with caution. Any standing or floor fans should be pointed away from people to reduce the risk of particles being directed at them. Instead, use them to increase air circulation throughout the room.

Be aware that fans and more powerful HVAC systems may generate more noise. To ensure that guests can enjoy a music or stage performance without interference from your air circulation system, it’s a good idea to have an acoustician as part of your clean air review team. 

Air circulation alone is not enough to stop the transmission of COVID-19 and other viruses within indoor venues. However, when paired with measures like social distancing, frequent hand washing, hand sanitizer stations, and mask policies, it can cut down the risk considerably. By using all these common sense measures together, we can reopen venues safely and get back to the communal activities we enjoy.


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