Sources of Airborne Infectious Disease

You can be exposed to particles infected by airborne infectious disease from 1) droplets released by the infected on surfaces and 2) small particles that can stay suspended in the air for hours. It is important to note that because droplets are larger and heavier, they settle quickly. This means that ventilation is often not enough for remediation, unless the diameter of the particle is reduced by evaporation. Small infected particles are generally caused by coughing, sneezing, and shouting, and are the main concern for dispersing airborne diseases. Because these particles can remain in the air for hours at a time, HVAC system maintenance can be of vital importance to not spreading these particles.

“Control of seasonal influenza has for decades relied on large-droplet precautions even though there is evidence suggesting a far greater importance for airborne transmission by small particles.”

Top recommendations from our experts:

1. Temperature and Humidity Control

  • COVID-19 survives longer at relative indoor humidity levels <30%.
  • Relative humidity levels between 45 – 60% are recommended right now.

2. Ventilation optimization

  • Increase ventilation rates to exchange possibly contaminated air.
  • Monitor positive and negative pressure areas to limit contamination spread.

3. HEPA Filtration / Air Ionization / Surface cleaning

  • Reduce indoor air pollution to ease stress on your respiratory system and decrease the chance of serious viral inflammation.

Recommendations from governing agencies:

ASHRAE recently updated their “Position Document on Airborne Infectious Disease,” which covers how airborne diseases are spread and how your building’s heating, ventilation and air conditioning efforts can accelerate or control such dispersal. Their findings suggest that although disease control has primarily focused on controlling exposure to large droplets, it is the small, airborne particles that are of true concern to the public. This was illustrated back in 1979, when Influenza transmission occurred from person to 72% of the 54 passengers aboard an airliner on the ground in Alaska while the ventilation system was turned off.

Further, your HVAC plays a large role in disease transmission by:

  • supplying clean air to susceptible occupants,
  • containing contaminated air and/or exhausting it to the outdoors,
  • diluting the air in a space with cleaner air from outdoors and/or by filtering the air, and
  • cleaning the air within the room

HVAC recommendations for disease control:

ASHRAE recommends the following HVAC strategies:

  • Directed supply and/or exhaust ventilation, such as non aspirating diffusers for unidirectional low-velocity airflow.
  • Room pressure differentials for ensuring the separation of the infected and healthy.
  • Personalized ventilation systems that supply 100% outdoor air, highly filtered, or UV disinfected air directly to the occupant’s breathing zone.
  • Highly efficient particle filtration to reduce airborne load of infected particles.
  • Some UVGI strategies for general application.

General air-cleaning strategies from the EPA:

The EPA recommends the follow air-cleaning strategies:

  1. Source Control: This strategy involves eliminating indoor pollutants at their source, as opposed to cleaning the indoor air that becomes polluted. If your facility contains chemicals or pollutant sources like gas stoves or upholstery, it is most effective to remove these from the premise. If this is not feasible, take the necessary precautions to ensure that these sources are tightly sealed or away from human traffic.
  2. Improve Ventilation: Another easy way to improve your indoor air quality is to bring more fresh air into your building. Opening windows and doors, running window air conditioners with the vent control open, and utilizing window or attic fans can drastically increase your ventilation rate. Make sure to take these extra steps when engaging in short-term, pollutant-generating activities like painting or installing equipment.
  3. Use Air Cleaners: There are many air cleaners on the market that claim to clean your indoor air, but be weary. Most table-top devices do not have the same capabilities of particulate removal as higher-end products. In addition, many of these air cleaners are not designed to remove gaseous pollutants, so sensitive groups may find them not effective enough on their own.

Other effective solutions:

  1. Keep Track of Your Filter Schedule: Your filters will eventually fill up and stop doing their job properly. This will not only compromise the quality of your indoor air, but will start to wear on your HVAC system. Make sure you have a schedule in place that is based on data… and stick to it.
  2. Make Sure Your Space is Clean: Carpets, upholstery, and furniture can trap and lock pollutants from your indoor air. Use a vacuum containing a HEPA filter to get the most out of your efforts. Through regular maintenance of your indoor environment, you can significantly decrease your pollutant levels and increase indoor air quality.
  3. Monitor Your Humidity: High temperatures and moisture create a breading ground for biological contaminants and pollutants. Monitor your humidity closely to avoid costly situations like mold growth in your facility.

In conclusion

It is important to note that controlling airborne infectious disease is a complex issue that should be tackled with the help of expert consultation. It is recommended that a combination of both small particles and large droplet precautions are taken to provide the best control possible for occupants. While ventilation and proper air-cleaning can provide great control of these airborne particles, nothing is more effective than keeping the infected away from your indoors.

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